fe-exec.c

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/*-------------------------------------------------------------------------
 *
 * fe-exec.c
 *    functions related to sending a query down to the backend
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-exec.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <ctype.h>
#include <fcntl.h>
#include <limits.h>
 
#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#endif
 
#include "libpq-fe.h"
#include "libpq-int.h"
#include "mb/pg_wchar.h"
 
/* keep this in same order as ExecStatusType in libpq-fe.h */
char       *const pgresStatus[] = {
    "PGRES_EMPTY_QUERY",
    "PGRES_COMMAND_OK",
    "PGRES_TUPLES_OK",
    "PGRES_COPY_OUT",
    "PGRES_COPY_IN",
    "PGRES_BAD_RESPONSE",
    "PGRES_NONFATAL_ERROR",
    "PGRES_FATAL_ERROR",
    "PGRES_COPY_BOTH",
    "PGRES_SINGLE_TUPLE",
    "PGRES_PIPELINE_SYNC",
    "PGRES_PIPELINE_ABORTED"
};
 
/* We return this if we're unable to make a PGresult at all */
static const PGresult OOM_result = {
    .resultStatus = PGRES_FATAL_ERROR,
    .client_encoding = PG_SQL_ASCII,
    .errMsg = "out of memory\n",
};
 
/*
 * static state needed by PQescapeString and PQescapeBytea; initialize to
 * values that result in backward-compatible behavior
 */
static int  static_client_encoding = PG_SQL_ASCII;
static bool static_std_strings = false;
 
 
static PGEvent *dupEvents(PGEvent *events, int count, size_t *memSize);
static bool pqAddTuple(PGresult *res, PGresAttValue *tup,
                       const char **errmsgp);
static int  PQsendQueryInternal(PGconn *conn, const char *query, bool newQuery);
static bool PQsendQueryStart(PGconn *conn, bool newQuery);
static int  PQsendQueryGuts(PGconn *conn,
                            const char *command,
                            const char *stmtName,
                            int nParams,
                            const Oid *paramTypes,
                            const char *const *paramValues,
                            const int *paramLengths,
                            const int *paramFormats,
                            int resultFormat);
static void parseInput(PGconn *conn);
static PGresult *getCopyResult(PGconn *conn, ExecStatusType copytype);
static bool PQexecStart(PGconn *conn);
static PGresult *PQexecFinish(PGconn *conn);
static int  PQsendTypedCommand(PGconn *conn, char command, char type,
                               const char *target);
static int  check_field_number(const PGresult *res, int field_num);
static void pqPipelineProcessQueue(PGconn *conn);
static int  pqPipelineFlush(PGconn *conn);
 
 
/* ----------------
 * Space management for PGresult.
 *
 * Formerly, libpq did a separate malloc() for each field of each tuple
 * returned by a query.  This was remarkably expensive --- malloc/free
 * consumed a sizable part of the application's runtime.  And there is
 * no real need to keep track of the fields separately, since they will
 * all be freed together when the PGresult is released.  So now, we grab
 * large blocks of storage from malloc and allocate space for query data
 * within these blocks, using a trivially simple allocator.  This reduces
 * the number of malloc/free calls dramatically, and it also avoids
 * fragmentation of the malloc storage arena.
 * The PGresult structure itself is still malloc'd separately.  We could
 * combine it with the first allocation block, but that would waste space
 * for the common case that no extra storage is actually needed (that is,
 * the SQL command did not return tuples).
 *
 * We also malloc the top-level array of tuple pointers separately, because
 * we need to be able to enlarge it via realloc, and our trivial space
 * allocator doesn't handle that effectively.  (Too bad the FE/BE protocol
 * doesn't tell us up front how many tuples will be returned.)
 * All other subsidiary storage for a PGresult is kept in PGresult_data blocks
 * of size PGRESULT_DATA_BLOCKSIZE.  The overhead at the start of each block
 * is just a link to the next one, if any.  Free-space management info is
 * kept in the owning PGresult.
 * A query returning a small amount of data will thus require three malloc
 * calls: one for the PGresult, one for the tuples pointer array, and one
 * PGresult_data block.
 *
 * Only the most recently allocated PGresult_data block is a candidate to
 * have more stuff added to it --- any extra space left over in older blocks
 * is wasted.  We could be smarter and search the whole chain, but the point
 * here is to be simple and fast.  Typical applications do not keep a PGresult
 * around very long anyway, so some wasted space within one is not a problem.
 *
 * Tuning constants for the space allocator are:
 * PGRESULT_DATA_BLOCKSIZE: size of a standard allocation block, in bytes
 * PGRESULT_ALIGN_BOUNDARY: assumed alignment requirement for binary data
 * PGRESULT_SEP_ALLOC_THRESHOLD: objects bigger than this are given separate
 *   blocks, instead of being crammed into a regular allocation block.
 * Requirements for correct function are:
 * PGRESULT_ALIGN_BOUNDARY must be a multiple of the alignment requirements
 *      of all machine data types.  (Currently this is set from configure
 *      tests, so it should be OK automatically.)
 * PGRESULT_SEP_ALLOC_THRESHOLD + PGRESULT_BLOCK_OVERHEAD <=
 *          PGRESULT_DATA_BLOCKSIZE
 *      pqResultAlloc assumes an object smaller than the threshold will fit
 *      in a new block.
 * The amount of space wasted at the end of a block could be as much as
 * PGRESULT_SEP_ALLOC_THRESHOLD, so it doesn't pay to make that too large.
 * ----------------
 */
 
#define PGRESULT_DATA_BLOCKSIZE     2048
#define PGRESULT_ALIGN_BOUNDARY     MAXIMUM_ALIGNOF /* from configure */
#define PGRESULT_BLOCK_OVERHEAD     Max(sizeof(PGresult_data), PGRESULT_ALIGN_BOUNDARY)
#define PGRESULT_SEP_ALLOC_THRESHOLD    (PGRESULT_DATA_BLOCKSIZE / 2)
 
 
/*
 * PQmakeEmptyPGresult
 *   returns a newly allocated, initialized PGresult with given status.
 *   If conn is not NULL and status indicates an error, the conn's
 *   errorMessage is copied.  Also, any PGEvents are copied from the conn.
 *
 * Note: the logic to copy the conn's errorMessage is now vestigial;
 * no internal caller uses it.  However, that behavior is documented for
 * outside callers, so we'd better keep it.
 */
PGresult *
PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
{
    PGresult   *result;
 
    result = (PGresult *) malloc(sizeof(PGresult));
    if (!result)
        return NULL;
 
    result->ntups = 0;
    result->numAttributes = 0;
    result->attDescs = NULL;
    result->tuples = NULL;
    result->tupArrSize = 0;
    result->numParameters = 0;
    result->paramDescs = NULL;
    result->resultStatus = status;
    result->cmdStatus[0] = '\0';
    result->binary = 0;
    result->events = NULL;
    result->nEvents = 0;
    result->errMsg = NULL;
    result->errFields = NULL;
    result->errQuery = NULL;
    result->null_field[0] = '\0';
    result->curBlock = NULL;
    result->curOffset = 0;
    result->spaceLeft = 0;
    result->memorySize = sizeof(PGresult);
 
    if (conn)
    {
        /* copy connection data we might need for operations on PGresult */
        result->noticeHooks = conn->noticeHooks;
        result->client_encoding = conn->client_encoding;
 
        /* consider copying conn's errorMessage */
        switch (status)
        {
            case PGRES_EMPTY_QUERY:
            case PGRES_COMMAND_OK:
            case PGRES_TUPLES_OK:
            case PGRES_COPY_OUT:
            case PGRES_COPY_IN:
            case PGRES_COPY_BOTH:
            case PGRES_SINGLE_TUPLE:
                /* non-error cases */
                break;
            default:
                /* we intentionally do not use or modify errorReported here */
                pqSetResultError(result, &conn->errorMessage, 0);
                break;
        }
 
        /* copy events last; result must be valid if we need to PQclear */
        if (conn->nEvents > 0)
        {
            result->events = dupEvents(conn->events, conn->nEvents,
                                       &result->memorySize);
            if (!result->events)
            {
                PQclear(result);
                return NULL;
            }
            result->nEvents = conn->nEvents;
        }
    }
    else
    {
        /* defaults... */
        result->noticeHooks.noticeRec = NULL;
        result->noticeHooks.noticeRecArg = NULL;
        result->noticeHooks.noticeProc = NULL;
        result->noticeHooks.noticeProcArg = NULL;
        result->client_encoding = PG_SQL_ASCII;
    }
 
    return result;
}
 
/*
 * PQsetResultAttrs
 *
 * Set the attributes for a given result.  This function fails if there are
 * already attributes contained in the provided result.  The call is
 * ignored if numAttributes is zero or attDescs is NULL.  If the
 * function fails, it returns zero.  If the function succeeds, it
 * returns a non-zero value.
 */
int
PQsetResultAttrs(PGresult *res, int numAttributes, PGresAttDesc *attDescs)
{
    int         i;
 
    /* Fail if argument is NULL or OOM_result */
    if (!res || (const PGresult *) res == &OOM_result)
        return false;
 
    /* If attrs already exist, they cannot be overwritten. */
    if (res->numAttributes > 0)
        return false;
 
    /* ignore no-op request */
    if (numAttributes <= 0 || !attDescs)
        return true;
 
    res->attDescs = (PGresAttDesc *)
        PQresultAlloc(res, numAttributes * sizeof(PGresAttDesc));
 
    if (!res->attDescs)
        return false;
 
    res->numAttributes = numAttributes;
    memcpy(res->attDescs, attDescs, numAttributes * sizeof(PGresAttDesc));
 
    /* deep-copy the attribute names, and determine format */
    res->binary = 1;
    for (i = 0; i < res->numAttributes; i++)
    {
        if (res->attDescs[i].name)
            res->attDescs[i].name = pqResultStrdup(res, res->attDescs[i].name);
        else
            res->attDescs[i].name = res->null_field;
 
        if (!res->attDescs[i].name)
            return false;
 
        if (res->attDescs[i].format == 0)
            res->binary = 0;
    }
 
    return true;
}
 
/*
 * PQcopyResult
 *
 * Returns a deep copy of the provided 'src' PGresult, which cannot be NULL.
 * The 'flags' argument controls which portions of the result will or will
 * NOT be copied.  The created result is always put into the
 * PGRES_TUPLES_OK status.  The source result error message is not copied,
 * although cmdStatus is.
 *
 * To set custom attributes, use PQsetResultAttrs.  That function requires
 * that there are no attrs contained in the result, so to use that
 * function you cannot use the PG_COPYRES_ATTRS or PG_COPYRES_TUPLES
 * options with this function.
 *
 * Options:
 *   PG_COPYRES_ATTRS - Copy the source result's attributes
 *
 *   PG_COPYRES_TUPLES - Copy the source result's tuples.  This implies
 *   copying the attrs, seeing how the attrs are needed by the tuples.
 *
 *   PG_COPYRES_EVENTS - Copy the source result's events.
 *
 *   PG_COPYRES_NOTICEHOOKS - Copy the source result's notice hooks.
 */
PGresult *
PQcopyResult(const PGresult *src, int flags)
{
    PGresult   *dest;
    int         i;
 
    if (!src)
        return NULL;
 
    dest = PQmakeEmptyPGresult(NULL, PGRES_TUPLES_OK);
    if (!dest)
        return NULL;
 
    /* Always copy these over.  Is cmdStatus really useful here? */
    dest->client_encoding = src->client_encoding;
    strcpy(dest->cmdStatus, src->cmdStatus);
 
    /* Wants attrs? */
    if (flags & (PG_COPYRES_ATTRS | PG_COPYRES_TUPLES))
    {
        if (!PQsetResultAttrs(dest, src->numAttributes, src->attDescs))
        {
            PQclear(dest);
            return NULL;
        }
    }
 
    /* Wants to copy tuples? */
    if (flags & PG_COPYRES_TUPLES)
    {
        int         tup,
                    field;
 
        for (tup = 0; tup < src->ntups; tup++)
        {
            for (field = 0; field < src->numAttributes; field++)
            {
                if (!PQsetvalue(dest, tup, field,
                                src->tuples[tup][field].value,
                                src->tuples[tup][field].len))
                {
                    PQclear(dest);
                    return NULL;
                }
            }
        }
    }
 
    /* Wants to copy notice hooks? */
    if (flags & PG_COPYRES_NOTICEHOOKS)
        dest->noticeHooks = src->noticeHooks;
 
    /* Wants to copy PGEvents? */
    if ((flags & PG_COPYRES_EVENTS) && src->nEvents > 0)
    {
        dest->events = dupEvents(src->events, src->nEvents,
                                 &dest->memorySize);
        if (!dest->events)
        {
            PQclear(dest);
            return NULL;
        }
        dest->nEvents = src->nEvents;
    }
 
    /* Okay, trigger PGEVT_RESULTCOPY event */
    for (i = 0; i < dest->nEvents; i++)
    {
        /* We don't fire events that had some previous failure */
        if (src->events[i].resultInitialized)
        {
            PGEventResultCopy evt;
 
            evt.src = src;
            evt.dest = dest;
            if (dest->events[i].proc(PGEVT_RESULTCOPY, &evt,
                                     dest->events[i].passThrough))
                dest->events[i].resultInitialized = true;
        }
    }
 
    return dest;
}
 
/*
 * Copy an array of PGEvents (with no extra space for more).
 * Does not duplicate the event instance data, sets this to NULL.
 * Also, the resultInitialized flags are all cleared.
 * The total space allocated is added to *memSize.
 */
static PGEvent *
dupEvents(PGEvent *events, int count, size_t *memSize)
{
    PGEvent    *newEvents;
    size_t      msize;
    int         i;
 
    if (!events || count <= 0)
        return NULL;
 
    msize = count * sizeof(PGEvent);
    newEvents = (PGEvent *) malloc(msize);
    if (!newEvents)
        return NULL;
 
    for (i = 0; i < count; i++)
    {
        newEvents[i].proc = events[i].proc;
        newEvents[i].passThrough = events[i].passThrough;
        newEvents[i].data = NULL;
        newEvents[i].resultInitialized = false;
        newEvents[i].name = strdup(events[i].name);
        if (!newEvents[i].name)
        {
            while (--i >= 0)
                free(newEvents[i].name);
            free(newEvents);
            return NULL;
        }
        msize += strlen(events[i].name) + 1;
    }
 
    *memSize += msize;
    return newEvents;
}
 
 
/*
 * Sets the value for a tuple field.  The tup_num must be less than or
 * equal to PQntuples(res).  If it is equal, a new tuple is created and
 * added to the result.
 * Returns a non-zero value for success and zero for failure.
 * (On failure, we report the specific problem via pqInternalNotice.)
 */
int
PQsetvalue(PGresult *res, int tup_num, int field_num, char *value, int len)
{
    PGresAttValue *attval;
    const char *errmsg = NULL;
 
    /* Fail if argument is NULL or OOM_result */
    if (!res || (const PGresult *) res == &OOM_result)
        return false;
 
    /* Invalid field_num? */
    if (!check_field_number(res, field_num))
        return false;
 
    /* Invalid tup_num, must be <= ntups */
    if (tup_num < 0 || tup_num > res->ntups)
    {
        pqInternalNotice(&res->noticeHooks,
                         "row number %d is out of range 0..%d",
                         tup_num, res->ntups);
        return false;
    }
 
    /* need to allocate a new tuple? */
    if (tup_num == res->ntups)
    {
        PGresAttValue *tup;
        int         i;
 
        tup = (PGresAttValue *)
            pqResultAlloc(res, res->numAttributes * sizeof(PGresAttValue),
                          true);
 
        if (!tup)
            goto fail;
 
        /* initialize each column to NULL */
        for (i = 0; i < res->numAttributes; i++)
        {
            tup[i].len = NULL_LEN;
            tup[i].value = res->null_field;
        }
 
        /* add it to the array */
        if (!pqAddTuple(res, tup, &errmsg))
            goto fail;
    }
 
    attval = &res->tuples[tup_num][field_num];
 
    /* treat either NULL_LEN or NULL value pointer as a NULL field */
    if (len == NULL_LEN || value == NULL)
    {
        attval->len = NULL_LEN;
        attval->value = res->null_field;
    }
    else if (len <= 0)
    {
        attval->len = 0;
        attval->value = res->null_field;
    }
    else
    {
        attval->value = (char *) pqResultAlloc(res, len + 1, true);
        if (!attval->value)
            goto fail;
        attval->len = len;
        memcpy(attval->value, value, len);
        attval->value[len] = '\0';
    }
 
    return true;
 
    /*
     * Report failure via pqInternalNotice.  If preceding code didn't provide
     * an error message, assume "out of memory" was meant.
     */
fail:
    if (!errmsg)
        errmsg = libpq_gettext("out of memory");
    pqInternalNotice(&res->noticeHooks, "%s", errmsg);
 
    return false;
}
 
/*
 * pqResultAlloc - exported routine to allocate local storage in a PGresult.
 *
 * We force all such allocations to be maxaligned, since we don't know
 * whether the value might be binary.
 */
void *
PQresultAlloc(PGresult *res, size_t nBytes)
{
    /* Fail if argument is NULL or OOM_result */
    if (!res || (const PGresult *) res == &OOM_result)
        return NULL;
 
    return pqResultAlloc(res, nBytes, true);
}
 
/*
 * pqResultAlloc -
 *      Allocate subsidiary storage for a PGresult.
 *
 * nBytes is the amount of space needed for the object.
 * If isBinary is true, we assume that we need to align the object on
 * a machine allocation boundary.
 * If isBinary is false, we assume the object is a char string and can
 * be allocated on any byte boundary.
 */
void *
pqResultAlloc(PGresult *res, size_t nBytes, bool isBinary)
{
    char       *space;
    PGresult_data *block;
 
    if (!res)
        return NULL;
 
    if (nBytes <= 0)
        return res->null_field;
 
    /*
     * If alignment is needed, round up the current position to an alignment
     * boundary.
     */
    if (isBinary)
    {
        int         offset = res->curOffset % PGRESULT_ALIGN_BOUNDARY;
 
        if (offset)
        {
            res->curOffset += PGRESULT_ALIGN_BOUNDARY - offset;
            res->spaceLeft -= PGRESULT_ALIGN_BOUNDARY - offset;
        }
    }
 
    /* If there's enough space in the current block, no problem. */
    if (nBytes <= (size_t) res->spaceLeft)
    {
        space = res->curBlock->space + res->curOffset;
        res->curOffset += nBytes;
        res->spaceLeft -= nBytes;
        return space;
    }
 
    /*
     * If the requested object is very large, give it its own block; this
     * avoids wasting what might be most of the current block to start a new
     * block.  (We'd have to special-case requests bigger than the block size
     * anyway.)  The object is always given binary alignment in this case.
     */
    if (nBytes >= PGRESULT_SEP_ALLOC_THRESHOLD)
    {
        size_t      alloc_size = nBytes + PGRESULT_BLOCK_OVERHEAD;
 
        block = (PGresult_data *) malloc(alloc_size);
        if (!block)
            return NULL;
        res->memorySize += alloc_size;
        space = block->space + PGRESULT_BLOCK_OVERHEAD;
        if (res->curBlock)
        {
            /*
             * Tuck special block below the active block, so that we don't
             * have to waste the free space in the active block.
             */
            block->next = res->curBlock->next;
            res->curBlock->next = block;
        }
        else
        {
            /* Must set up the new block as the first active block. */
            block->next = NULL;
            res->curBlock = block;
            res->spaceLeft = 0; /* be sure it's marked full */
        }
        return space;
    }
 
    /* Otherwise, start a new block. */
    block = (PGresult_data *) malloc(PGRESULT_DATA_BLOCKSIZE);
    if (!block)
        return NULL;
    res->memorySize += PGRESULT_DATA_BLOCKSIZE;
    block->next = res->curBlock;
    res->curBlock = block;
    if (isBinary)
    {
        /* object needs full alignment */
        res->curOffset = PGRESULT_BLOCK_OVERHEAD;
        res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - PGRESULT_BLOCK_OVERHEAD;
    }
    else
    {
        /* we can cram it right after the overhead pointer */
        res->curOffset = sizeof(PGresult_data);
        res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - sizeof(PGresult_data);
    }
 
    space = block->space + res->curOffset;
    res->curOffset += nBytes;
    res->spaceLeft -= nBytes;
    return space;
}
 
/*
 * PQresultMemorySize -
 *      Returns total space allocated for the PGresult.
 */
size_t
PQresultMemorySize(const PGresult *res)
{
    if (!res)
        return 0;
    return res->memorySize;
}
 
/*
 * pqResultStrdup -
 *      Like strdup, but the space is subsidiary PGresult space.
 */
char *
pqResultStrdup(PGresult *res, const char *str)
{
    char       *space = (char *) pqResultAlloc(res, strlen(str) + 1, false);
 
    if (space)
        strcpy(space, str);
    return space;
}
 
/*
 * pqSetResultError -
 *      assign a new error message to a PGresult
 *
 * Copy text from errorMessage buffer beginning at given offset
 * (it's caller's responsibility that offset is valid)
 */
void
pqSetResultError(PGresult *res, PQExpBuffer errorMessage, int offset)
{
    char       *msg;
 
    if (!res)
        return;
 
    /*
     * We handle two OOM scenarios here.  The errorMessage buffer might be
     * marked "broken" due to having previously failed to allocate enough
     * memory for the message, or it might be fine but pqResultStrdup fails
     * and returns NULL.  In either case, just make res->errMsg point directly
     * at a constant "out of memory" string.
     */
    if (!PQExpBufferBroken(errorMessage))
        msg = pqResultStrdup(res, errorMessage->data + offset);
    else
        msg = NULL;
    if (msg)
        res->errMsg = msg;
    else
        res->errMsg = libpq_gettext("out of memory\n");
}
 
/*
 * PQclear -
 *    free's the memory associated with a PGresult
 */
void
PQclear(PGresult *res)
{
    PGresult_data *block;
    int         i;
 
    /* As a convenience, do nothing for a NULL pointer */
    if (!res)
        return;
    /* Also, do nothing if the argument is OOM_result */
    if ((const PGresult *) res == &OOM_result)
        return;
 
    /* Close down any events we may have */
    for (i = 0; i < res->nEvents; i++)
    {
        /* only send DESTROY to successfully-initialized event procs */
        if (res->events[i].resultInitialized)
        {
            PGEventResultDestroy evt;
 
            evt.result = res;
            (void) res->events[i].proc(PGEVT_RESULTDESTROY, &evt,
                                       res->events[i].passThrough);
        }
        free(res->events[i].name);
    }
 
    free(res->events);
 
    /* Free all the subsidiary blocks */
    while ((block = res->curBlock) != NULL)
    {
        res->curBlock = block->next;
        free(block);
    }
 
    /* Free the top-level tuple pointer array */
    free(res->tuples);
 
    /* zero out the pointer fields to catch programming errors */
    res->attDescs = NULL;
    res->tuples = NULL;
    res->paramDescs = NULL;
    res->errFields = NULL;
    res->events = NULL;
    res->nEvents = 0;
    /* res->curBlock was zeroed out earlier */
 
    /* Free the PGresult structure itself */
    free(res);
}
 
/*
 * Handy subroutine to deallocate any partially constructed async result.
 *
 * Any "next" result gets cleared too.
 */
void
pqClearAsyncResult(PGconn *conn)
{
    PQclear(conn->result);
    conn->result = NULL;
    conn->error_result = false;
    PQclear(conn->next_result);
    conn->next_result = NULL;
}
 
/*
 * pqSaveErrorResult -
 *    remember that we have an error condition
 *
 * In much of libpq, reporting an error just requires appending text to
 * conn->errorMessage and returning a failure code to one's caller.
 * Where returning a failure code is impractical, instead call this
 * function to remember that an error needs to be reported.
 *
 * (It might seem that appending text to conn->errorMessage should be
 * sufficient, but we can't rely on that working under out-of-memory
 * conditions.  The OOM hazard is also why we don't try to make a new
 * PGresult right here.)
 */
void
pqSaveErrorResult(PGconn *conn)
{
    /* Drop any pending result ... */
    pqClearAsyncResult(conn);
    /* ... and set flag to remember to make an error result later */
    conn->error_result = true;
}
 
/*
 * pqSaveWriteError -
 *    report a write failure
 *
 * As above, after appending conn->write_err_msg to whatever other error we
 * have.  This is used when we've detected a write failure and have exhausted
 * our chances of reporting something else instead.
 */
static void
pqSaveWriteError(PGconn *conn)
{
    /*
     * If write_err_msg is null because of previous strdup failure, do what we
     * can.  (It's likely our machinations here will get OOM failures as well,
     * but might as well try.)
     */
    if (conn->write_err_msg)
    {
        appendPQExpBufferStr(&conn->errorMessage, conn->write_err_msg);
        /* Avoid possibly appending the same message twice */
        conn->write_err_msg[0] = '\0';
    }
    else
        libpq_append_conn_error(conn, "write to server failed");
 
    pqSaveErrorResult(conn);
}
 
/*
 * pqPrepareAsyncResult -
 *    prepare the current async result object for return to the caller
 *
 * If there is not already an async result object, build an error object
 * using whatever is in conn->errorMessage.  In any case, clear the async
 * result storage, and update our notion of how much error text has been
 * returned to the application.
 */
PGresult *
pqPrepareAsyncResult(PGconn *conn)
{
    PGresult   *res;
 
    res = conn->result;
    if (res)
    {
        /*
         * If the pre-existing result is an ERROR (presumably something
         * received from the server), assume that it represents whatever is in
         * conn->errorMessage, and advance errorReported.
         */
        if (res->resultStatus == PGRES_FATAL_ERROR)
            conn->errorReported = conn->errorMessage.len;
    }
    else
    {
        /*
         * We get here after internal-to-libpq errors.  We should probably
         * always have error_result = true, but if we don't, gin up some error
         * text.
         */
        if (!conn->error_result)
            libpq_append_conn_error(conn, "no error text available");
 
        /* Paranoia: be sure errorReported offset is sane */
        if (conn->errorReported < 0 ||
            conn->errorReported >= conn->errorMessage.len)
            conn->errorReported = 0;
 
        /*
         * Make a PGresult struct for the error.  We temporarily lie about the
         * result status, so that PQmakeEmptyPGresult doesn't uselessly copy
         * all of conn->errorMessage.
         */
        res = PQmakeEmptyPGresult(conn, PGRES_EMPTY_QUERY);
        if (res)
        {
            /*
             * Report whatever new error text we have, and advance
             * errorReported.
             */
            res->resultStatus = PGRES_FATAL_ERROR;
            pqSetResultError(res, &conn->errorMessage, conn->errorReported);
            conn->errorReported = conn->errorMessage.len;
        }
        else
        {
            /*
             * Ouch, not enough memory for a PGresult.  Fortunately, we have a
             * card up our sleeve: we can use the static OOM_result.  Casting
             * away const here is a bit ugly, but it seems best to declare
             * OOM_result as const, in hopes it will be allocated in read-only
             * storage.
             */
            res = unconstify(PGresult *, &OOM_result);
 
            /*
             * Don't advance errorReported.  Perhaps we'll be able to report
             * the text later.
             */
        }
    }
 
    /*
     * Replace conn->result with next_result, if any.  In the normal case
     * there isn't a next result and we're just dropping ownership of the
     * current result.  In single-row mode this restores the situation to what
     * it was before we created the current single-row result.
     */
    conn->result = conn->next_result;
    conn->error_result = false; /* next_result is never an error */
    conn->next_result = NULL;
 
    return res;
}
 
/*
 * pqInternalNotice - produce an internally-generated notice message
 *
 * A format string and optional arguments can be passed.  Note that we do
 * libpq_gettext() here, so callers need not.
 *
 * The supplied text is taken as primary message (ie., it should not include
 * a trailing newline, and should not be more than one line).
 */
void
pqInternalNotice(const PGNoticeHooks *hooks, const char *fmt,...)
{
    char        msgBuf[1024];
    va_list     args;
    PGresult   *res;
 
    if (hooks->noticeRec == NULL)
        return;                 /* nobody home to receive notice? */
 
    /* Format the message */
    va_start(args, fmt);
    vsnprintf(msgBuf, sizeof(msgBuf), libpq_gettext(fmt), args);
    va_end(args);
    msgBuf[sizeof(msgBuf) - 1] = '\0';  /* make real sure it's terminated */
 
    /* Make a PGresult to pass to the notice receiver */
    res = PQmakeEmptyPGresult(NULL, PGRES_NONFATAL_ERROR);
    if (!res)
        return;
    res->noticeHooks = *hooks;
 
    /*
     * Set up fields of notice.
     */
    pqSaveMessageField(res, PG_DIAG_MESSAGE_PRIMARY, msgBuf);
    pqSaveMessageField(res, PG_DIAG_SEVERITY, libpq_gettext("NOTICE"));
    pqSaveMessageField(res, PG_DIAG_SEVERITY_NONLOCALIZED, "NOTICE");
    /* XXX should provide a SQLSTATE too? */
 
    /*
     * Result text is always just the primary message + newline.  If we can't
     * allocate it, substitute "out of memory", as in pqSetResultError.
     */
    res->errMsg = (char *) pqResultAlloc(res, strlen(msgBuf) + 2, false);
    if (res->errMsg)
        sprintf(res->errMsg, "%s\n", msgBuf);
    else
        res->errMsg = libpq_gettext("out of memory\n");
 
    /*
     * Pass to receiver, then free it.
     */
    res->noticeHooks.noticeRec(res->noticeHooks.noticeRecArg, res);
    PQclear(res);
}
 
/*
 * pqAddTuple
 *    add a row pointer to the PGresult structure, growing it if necessary
 *    Returns true if OK, false if an error prevented adding the row
 *
 * On error, *errmsgp can be set to an error string to be returned.
 * If it is left NULL, the error is presumed to be "out of memory".
 */
static bool
pqAddTuple(PGresult *res, PGresAttValue *tup, const char **errmsgp)
{
    if (res->ntups >= res->tupArrSize)
    {
        /*
         * Try to grow the array.
         *
         * We can use realloc because shallow copying of the structure is
         * okay. Note that the first time through, res->tuples is NULL. While
         * ANSI says that realloc() should act like malloc() in that case,
         * some old C libraries (like SunOS 4.1.x) coredump instead. On
         * failure realloc is supposed to return NULL without damaging the
         * existing allocation. Note that the positions beyond res->ntups are
         * garbage, not necessarily NULL.
         */
        int         newSize;
        PGresAttValue **newTuples;
 
        /*
         * Since we use integers for row numbers, we can't support more than
         * INT_MAX rows.  Make sure we allow that many, though.
         */
        if (res->tupArrSize <= INT_MAX / 2)
            newSize = (res->tupArrSize > 0) ? res->tupArrSize * 2 : 128;
        else if (res->tupArrSize < INT_MAX)
            newSize = INT_MAX;
        else
        {
            *errmsgp = libpq_gettext("PGresult cannot support more than INT_MAX tuples");
            return false;
        }
 
        /*
         * Also, on 32-bit platforms we could, in theory, overflow size_t even
         * before newSize gets to INT_MAX.  (In practice we'd doubtless hit
         * OOM long before that, but let's check.)
         */
#if INT_MAX >= (SIZE_MAX / 2)
        if (newSize > SIZE_MAX / sizeof(PGresAttValue *))
        {
            *errmsgp = libpq_gettext("size_t overflow");
            return false;
        }
#endif
 
        if (res->tuples == NULL)
            newTuples = (PGresAttValue **)
                malloc(newSize * sizeof(PGresAttValue *));
        else
            newTuples = (PGresAttValue **)
                realloc(res->tuples, newSize * sizeof(PGresAttValue *));
        if (!newTuples)
            return false;       /* malloc or realloc failed */
        res->memorySize +=
            (newSize - res->tupArrSize) * sizeof(PGresAttValue *);
        res->tupArrSize = newSize;
        res->tuples = newTuples;
    }
    res->tuples[res->ntups] = tup;
    res->ntups++;
    return true;
}
 
/*
 * pqSaveMessageField - save one field of an error or notice message
 */
void
pqSaveMessageField(PGresult *res, char code, const char *value)
{
    PGMessageField *pfield;
 
    pfield = (PGMessageField *)
        pqResultAlloc(res,
                      offsetof(PGMessageField, contents) +
                      strlen(value) + 1,
                      true);
    if (!pfield)
        return;                 /* out of memory? */
    pfield->code = code;
    strcpy(pfield->contents, value);
    pfield->next = res->errFields;
    res->errFields = pfield;
}
 
/*
 * pqSaveParameterStatus - remember parameter status sent by backend
 */
void
pqSaveParameterStatus(PGconn *conn, const char *name, const char *value)
{
    pgParameterStatus *pstatus;
    pgParameterStatus *prev;
 
    /*
     * Forget any old information about the parameter
     */
    for (pstatus = conn->pstatus, prev = NULL;
         pstatus != NULL;
         prev = pstatus, pstatus = pstatus->next)
    {
        if (strcmp(pstatus->name, name) == 0)
        {
            if (prev)
                prev->next = pstatus->next;
            else
                conn->pstatus = pstatus->next;
            free(pstatus);      /* frees name and value strings too */
            break;
        }
    }
 
    /*
     * Store new info as a single malloc block
     */
    pstatus = (pgParameterStatus *) malloc(sizeof(pgParameterStatus) +
                                           strlen(name) + strlen(value) + 2);
    if (pstatus)
    {
        char       *ptr;
 
        ptr = ((char *) pstatus) + sizeof(pgParameterStatus);
        pstatus->name = ptr;
        strcpy(ptr, name);
        ptr += strlen(name) + 1;
        pstatus->value = ptr;
        strcpy(ptr, value);
        pstatus->next = conn->pstatus;
        conn->pstatus = pstatus;
    }
 
    /*
     * Save values of settings that are of interest to libpq in fields of the
     * PGconn object.  We keep client_encoding and standard_conforming_strings
     * in static variables as well, so that PQescapeString and PQescapeBytea
     * can behave somewhat sanely (at least in single-connection-using
     * programs).
     */
    if (strcmp(name, "client_encoding") == 0)
    {
        conn->client_encoding = pg_char_to_encoding(value);
        /* if we don't recognize the encoding name, fall back to SQL_ASCII */
        if (conn->client_encoding < 0)
            conn->client_encoding = PG_SQL_ASCII;
        static_client_encoding = conn->client_encoding;
    }
    else if (strcmp(name, "standard_conforming_strings") == 0)
    {
        conn->std_strings = (strcmp(value, "on") == 0);
        static_std_strings = conn->std_strings;
    }
    else if (strcmp(name, "server_version") == 0)
    {
        /* We convert the server version to numeric form. */
        int         cnt;
        int         vmaj,
                    vmin,
                    vrev;
 
        cnt = sscanf(value, "%d.%d.%d", &vmaj, &vmin, &vrev);
 
        if (cnt == 3)
        {
            /* old style, e.g. 9.6.1 */
            conn->sversion = (100 * vmaj + vmin) * 100 + vrev;
        }
        else if (cnt == 2)
        {
            if (vmaj >= 10)
            {
                /* new style, e.g. 10.1 */
                conn->sversion = 100 * 100 * vmaj + vmin;
            }
            else
            {
                /* old style without minor version, e.g. 9.6devel */
                conn->sversion = (100 * vmaj + vmin) * 100;
            }
        }
        else if (cnt == 1)
        {
            /* new style without minor version, e.g. 10devel */
            conn->sversion = 100 * 100 * vmaj;
        }
        else
            conn->sversion = 0; /* unknown */
    }
    else if (strcmp(name, "default_transaction_read_only") == 0)
    {
        conn->default_transaction_read_only =
            (strcmp(value, "on") == 0) ? PG_BOOL_YES : PG_BOOL_NO;
    }
    else if (strcmp(name, "in_hot_standby") == 0)
    {
        conn->in_hot_standby =
            (strcmp(value, "on") == 0) ? PG_BOOL_YES : PG_BOOL_NO;
    }
    else if (strcmp(name, "scram_iterations") == 0)
    {
        conn->scram_sha_256_iterations = atoi(value);
    }
}
 
 
/*
 * pqRowProcessor
 *    Add the received row to the current async result (conn->result).
 *    Returns 1 if OK, 0 if error occurred.
 *
 * On error, *errmsgp can be set to an error string to be returned.
 * (Such a string should already be translated via libpq_gettext().)
 * If it is left NULL, the error is presumed to be "out of memory".
 *
 * In single-row mode, we create a new result holding just the current row,
 * stashing the previous result in conn->next_result so that it becomes
 * active again after pqPrepareAsyncResult().  This allows the result metadata
 * (column descriptions) to be carried forward to each result row.
 */
int
pqRowProcessor(PGconn *conn, const char **errmsgp)
{
    PGresult   *res = conn->result;
    int         nfields = res->numAttributes;
    const PGdataValue *columns = conn->rowBuf;
    PGresAttValue *tup;
    int         i;
 
    /*
     * In single-row mode, make a new PGresult that will hold just this one
     * row; the original conn->result is left unchanged so that it can be used
     * again as the template for future rows.
     */
    if (conn->singleRowMode)
    {
        /* Copy everything that should be in the result at this point */
        res = PQcopyResult(res,
                           PG_COPYRES_ATTRS | PG_COPYRES_EVENTS |
                           PG_COPYRES_NOTICEHOOKS);
        if (!res)
            return 0;
    }
 
    /*
     * Basically we just allocate space in the PGresult for each field and
     * copy the data over.
     *
     * Note: on malloc failure, we return 0 leaving *errmsgp still NULL, which
     * caller will take to mean "out of memory".  This is preferable to trying
     * to set up such a message here, because evidently there's not enough
     * memory for gettext() to do anything.
     */
    tup = (PGresAttValue *)
        pqResultAlloc(res, nfields * sizeof(PGresAttValue), true);
    if (tup == NULL)
        goto fail;
 
    for (i = 0; i < nfields; i++)
    {
        int         clen = columns[i].len;
 
        if (clen < 0)
        {
            /* null field */
            tup[i].len = NULL_LEN;
            tup[i].value = res->null_field;
        }
        else
        {
            bool        isbinary = (res->attDescs[i].format != 0);
            char       *val;
 
            val = (char *) pqResultAlloc(res, clen + 1, isbinary);
            if (val == NULL)
                goto fail;
 
            /* copy and zero-terminate the data (even if it's binary) */
            memcpy(val, columns[i].value, clen);
            val[clen] = '\0';
 
            tup[i].len = clen;
            tup[i].value = val;
        }
    }
 
    /* And add the tuple to the PGresult's tuple array */
    if (!pqAddTuple(res, tup, errmsgp))
        goto fail;
 
    /*
     * Success.  In single-row mode, make the result available to the client
     * immediately.
     */
    if (conn->singleRowMode)
    {
        /* Change result status to special single-row value */
        res->resultStatus = PGRES_SINGLE_TUPLE;
        /* Stash old result for re-use later */
        conn->next_result = conn->result;
        conn->result = res;
        /* And mark the result ready to return */
        conn->asyncStatus = PGASYNC_READY_MORE;
    }
 
    return 1;
 
fail:
    /* release locally allocated PGresult, if we made one */
    if (res != conn->result)
        PQclear(res);
    return 0;
}
 
 
/*
 * pqAllocCmdQueueEntry
 *      Get a command queue entry for caller to fill.
 *
 * If the recycle queue has a free element, that is returned; if not, a
 * fresh one is allocated.  Caller is responsible for adding it to the
 * command queue (pqAppendCmdQueueEntry) once the struct is filled in, or
 * releasing the memory (pqRecycleCmdQueueEntry) if an error occurs.
 *
 * If allocation fails, sets the error message and returns NULL.
 */
static PGcmdQueueEntry *
pqAllocCmdQueueEntry(PGconn *conn)
{
    PGcmdQueueEntry *entry;
 
    if (conn->cmd_queue_recycle == NULL)
    {
        entry = (PGcmdQueueEntry *) malloc(sizeof(PGcmdQueueEntry));
        if (entry == NULL)
        {
            libpq_append_conn_error(conn, "out of memory");
            return NULL;
        }
    }
    else
    {
        entry = conn->cmd_queue_recycle;
        conn->cmd_queue_recycle = entry->next;
    }
    entry->next = NULL;
    entry->query = NULL;
 
    return entry;
}
 
/*
 * pqAppendCmdQueueEntry
 *      Append a caller-allocated entry to the command queue, and update
 *      conn->asyncStatus to account for it.
 *
 * The query itself must already have been put in the output buffer by the
 * caller.
 */
static void
pqAppendCmdQueueEntry(PGconn *conn, PGcmdQueueEntry *entry)
{
    Assert(entry->next == NULL);
 
    if (conn->cmd_queue_head == NULL)
        conn->cmd_queue_head = entry;
    else
        conn->cmd_queue_tail->next = entry;
 
    conn->cmd_queue_tail = entry;
 
    switch (conn->pipelineStatus)
    {
        case PQ_PIPELINE_OFF:
        case PQ_PIPELINE_ON:
 
            /*
             * When not in pipeline aborted state, if there's a result ready
             * to be consumed, let it be so (that is, don't change away from
             * READY or READY_MORE); otherwise set us busy to wait for
             * something to arrive from the server.
             */
            if (conn->asyncStatus == PGASYNC_IDLE)
                conn->asyncStatus = PGASYNC_BUSY;
            break;
 
        case PQ_PIPELINE_ABORTED:
 
            /*
             * In aborted pipeline state, we don't expect anything from the
             * server (since we don't send any queries that are queued).
             * Therefore, if IDLE then do what PQgetResult would do to let
             * itself consume commands from the queue; if we're in any other
             * state, we don't have to do anything.
             */
            if (conn->asyncStatus == PGASYNC_IDLE ||
                conn->asyncStatus == PGASYNC_PIPELINE_IDLE)
                pqPipelineProcessQueue(conn);
            break;
    }
}
 
/*
 * pqRecycleCmdQueueEntry
 *      Push a command queue entry onto the freelist.
 */
static void
pqRecycleCmdQueueEntry(PGconn *conn, PGcmdQueueEntry *entry)
{
    if (entry == NULL)
        return;
 
    /* recyclable entries should not have a follow-on command */
    Assert(entry->next == NULL);
 
    if (entry->query)
    {
        free(entry->query);
        entry->query = NULL;
    }
 
    entry->next = conn->cmd_queue_recycle;
    conn->cmd_queue_recycle = entry;
}
 
 
/*
 * PQsendQuery
 *   Submit a query, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 *
 * PQsendQueryContinue is a non-exported version that behaves identically
 * except that it doesn't reset conn->errorMessage.
 */
int
PQsendQuery(PGconn *conn, const char *query)
{
    return PQsendQueryInternal(conn, query, true);
}
 
int
PQsendQueryContinue(PGconn *conn, const char *query)
{
    return PQsendQueryInternal(conn, query, false);
}
 
static int
PQsendQueryInternal(PGconn *conn, const char *query, bool newQuery)
{
    PGcmdQueueEntry *entry = NULL;
 
    if (!PQsendQueryStart(conn, newQuery))
        return 0;
 
    /* check the argument */
    if (!query)
    {
        libpq_append_conn_error(conn, "command string is a null pointer");
        return 0;
    }
 
    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "%s not allowed in pipeline mode",
                                "PQsendQuery");
        return 0;
    }
 
    entry = pqAllocCmdQueueEntry(conn);
    if (entry == NULL)
        return 0;               /* error msg already set */
 
    /* Send the query message(s) */
    /* construct the outgoing Query message */
    if (pqPutMsgStart(PqMsg_Query, conn) < 0 ||
        pqPuts(query, conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
    {
        /* error message should be set up already */
        pqRecycleCmdQueueEntry(conn, entry);
        return 0;
    }
 
    /* remember we are using simple query protocol */
    entry->queryclass = PGQUERY_SIMPLE;
    /* and remember the query text too, if possible */
    entry->query = strdup(query);
 
    /*
     * Give the data a push.  In nonblock mode, don't complain if we're unable
     * to send it all; PQgetResult() will do any additional flushing needed.
     */
    if (pqFlush(conn) < 0)
        goto sendFailed;
 
    /* OK, it's launched! */
    pqAppendCmdQueueEntry(conn, entry);
 
    return 1;
 
sendFailed:
    pqRecycleCmdQueueEntry(conn, entry);
    /* error message should be set up already */
    return 0;
}
 
/*
 * PQsendQueryParams
 *      Like PQsendQuery, but use extended query protocol so we can pass parameters
 */
int
PQsendQueryParams(PGconn *conn,
                  const char *command,
                  int nParams,
                  const Oid *paramTypes,
                  const char *const *paramValues,
                  const int *paramLengths,
                  const int *paramFormats,
                  int resultFormat)
{
    if (!PQsendQueryStart(conn, true))
        return 0;
 
    /* check the arguments */
    if (!command)
    {
        libpq_append_conn_error(conn, "command string is a null pointer");
        return 0;
    }
    if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT)
    {
        libpq_append_conn_error(conn, "number of parameters must be between 0 and %d",
                                PQ_QUERY_PARAM_MAX_LIMIT);
        return 0;
    }
 
    return PQsendQueryGuts(conn,
                           command,
                           "",  /* use unnamed statement */
                           nParams,
                           paramTypes,
                           paramValues,
                           paramLengths,
                           paramFormats,
                           resultFormat);
}
 
/*
 * PQsendPrepare
 *   Submit a Parse message, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 */
int
PQsendPrepare(PGconn *conn,
              const char *stmtName, const char *query,
              int nParams, const Oid *paramTypes)
{
    PGcmdQueueEntry *entry = NULL;
 
    if (!PQsendQueryStart(conn, true))
        return 0;
 
    /* check the arguments */
    if (!stmtName)
    {
        libpq_append_conn_error(conn, "statement name is a null pointer");
        return 0;
    }
    if (!query)
    {
        libpq_append_conn_error(conn, "command string is a null pointer");
        return 0;
    }
    if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT)
    {
        libpq_append_conn_error(conn, "number of parameters must be between 0 and %d",
                                PQ_QUERY_PARAM_MAX_LIMIT);
        return 0;
    }
 
    entry = pqAllocCmdQueueEntry(conn);
    if (entry == NULL)
        return 0;               /* error msg already set */
 
    /* construct the Parse message */
    if (pqPutMsgStart(PqMsg_Parse, conn) < 0 ||
        pqPuts(stmtName, conn) < 0 ||
        pqPuts(query, conn) < 0)
        goto sendFailed;
 
    if (nParams > 0 && paramTypes)
    {
        int         i;
 
        if (pqPutInt(nParams, 2, conn) < 0)
            goto sendFailed;
        for (i = 0; i < nParams; i++)
        {
            if (pqPutInt(paramTypes[i], 4, conn) < 0)
                goto sendFailed;
        }
    }
    else
    {
        if (pqPutInt(0, 2, conn) < 0)
            goto sendFailed;
    }
    if (pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /* Add a Sync, unless in pipeline mode. */
    if (conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        if (pqPutMsgStart(PqMsg_Sync, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            goto sendFailed;
    }
 
    /* remember we are doing just a Parse */
    entry->queryclass = PGQUERY_PREPARE;
 
    /* and remember the query text too, if possible */
    /* if insufficient memory, query just winds up NULL */
    entry->query = strdup(query);
 
    /*
     * Give the data a push (in pipeline mode, only if we're past the size
     * threshold).  In nonblock mode, don't complain if we're unable to send
     * it all; PQgetResult() will do any additional flushing needed.
     */
    if (pqPipelineFlush(conn) < 0)
        goto sendFailed;
 
    /* OK, it's launched! */
    pqAppendCmdQueueEntry(conn, entry);
 
    return 1;
 
sendFailed:
    pqRecycleCmdQueueEntry(conn, entry);
    /* error message should be set up already */
    return 0;
}
 
/*
 * PQsendQueryPrepared
 *      Like PQsendQuery, but execute a previously prepared statement,
 *      using extended query protocol so we can pass parameters
 */
int
PQsendQueryPrepared(PGconn *conn,
                    const char *stmtName,
                    int nParams,
                    const char *const *paramValues,
                    const int *paramLengths,
                    const int *paramFormats,
                    int resultFormat)
{
    if (!PQsendQueryStart(conn, true))
        return 0;
 
    /* check the arguments */
    if (!stmtName)
    {
        libpq_append_conn_error(conn, "statement name is a null pointer");
        return 0;
    }
    if (nParams < 0 || nParams > PQ_QUERY_PARAM_MAX_LIMIT)
    {
        libpq_append_conn_error(conn, "number of parameters must be between 0 and %d",
                                PQ_QUERY_PARAM_MAX_LIMIT);
        return 0;
    }
 
    return PQsendQueryGuts(conn,
                           NULL,    /* no command to parse */
                           stmtName,
                           nParams,
                           NULL,    /* no param types */
                           paramValues,
                           paramLengths,
                           paramFormats,
                           resultFormat);
}
 
/*
 * PQsendQueryStart
 *  Common startup code for PQsendQuery and sibling routines
 */
static bool
PQsendQueryStart(PGconn *conn, bool newQuery)
{
    if (!conn)
        return false;
 
    /*
     * If this is the beginning of a query cycle, reset the error state.
     * However, in pipeline mode with something already queued, the error
     * buffer belongs to that command and we shouldn't clear it.
     */
    if (newQuery && conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    /* Don't try to send if we know there's no live connection. */
    if (conn->status != CONNECTION_OK)
    {
        libpq_append_conn_error(conn, "no connection to the server");
        return false;
    }
 
    /* Can't send while already busy, either, unless enqueuing for later */
    if (conn->asyncStatus != PGASYNC_IDLE &&
        conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "another command is already in progress");
        return false;
    }
 
    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
    {
        /*
         * When enqueuing commands we don't change much of the connection
         * state since it's already in use for the current command. The
         * connection state will get updated when pqPipelineProcessQueue()
         * advances to start processing the queued message.
         *
         * Just make sure we can safely enqueue given the current connection
         * state. We can enqueue behind another queue item, or behind a
         * non-queue command (one that sends its own sync), but we can't
         * enqueue if the connection is in a copy state.
         */
        switch (conn->asyncStatus)
        {
            case PGASYNC_IDLE:
            case PGASYNC_PIPELINE_IDLE:
            case PGASYNC_READY:
            case PGASYNC_READY_MORE:
            case PGASYNC_BUSY:
                /* ok to queue */
                break;
 
            case PGASYNC_COPY_IN:
            case PGASYNC_COPY_OUT:
            case PGASYNC_COPY_BOTH:
                libpq_append_conn_error(conn, "cannot queue commands during COPY");
                return false;
        }
    }
    else
    {
        /*
         * This command's results will come in immediately. Initialize async
         * result-accumulation state
         */
        pqClearAsyncResult(conn);
 
        /* reset single-row processing mode */
        conn->singleRowMode = false;
    }
 
    /* ready to send command message */
    return true;
}
 
/*
 * PQsendQueryGuts
 *      Common code for sending a query with extended query protocol
 *      PQsendQueryStart should be done already
 *
 * command may be NULL to indicate we use an already-prepared statement
 */
static int
PQsendQueryGuts(PGconn *conn,
                const char *command,
                const char *stmtName,
                int nParams,
                const Oid *paramTypes,
                const char *const *paramValues,
                const int *paramLengths,
                const int *paramFormats,
                int resultFormat)
{
    int         i;
    PGcmdQueueEntry *entry;
 
    entry = pqAllocCmdQueueEntry(conn);
    if (entry == NULL)
        return 0;               /* error msg already set */
 
    /*
     * We will send Parse (if needed), Bind, Describe Portal, Execute, Sync
     * (if not in pipeline mode), using specified statement name and the
     * unnamed portal.
     */
 
    if (command)
    {
        /* construct the Parse message */
        if (pqPutMsgStart(PqMsg_Parse, conn) < 0 ||
            pqPuts(stmtName, conn) < 0 ||
            pqPuts(command, conn) < 0)
            goto sendFailed;
        if (nParams > 0 && paramTypes)
        {
            if (pqPutInt(nParams, 2, conn) < 0)
                goto sendFailed;
            for (i = 0; i < nParams; i++)
            {
                if (pqPutInt(paramTypes[i], 4, conn) < 0)
                    goto sendFailed;
            }
        }
        else
        {
            if (pqPutInt(0, 2, conn) < 0)
                goto sendFailed;
        }
        if (pqPutMsgEnd(conn) < 0)
            goto sendFailed;
    }
 
    /* Construct the Bind message */
    if (pqPutMsgStart(PqMsg_Bind, conn) < 0 ||
        pqPuts("", conn) < 0 ||
        pqPuts(stmtName, conn) < 0)
        goto sendFailed;
 
    /* Send parameter formats */
    if (nParams > 0 && paramFormats)
    {
        if (pqPutInt(nParams, 2, conn) < 0)
            goto sendFailed;
        for (i = 0; i < nParams; i++)
        {
            if (pqPutInt(paramFormats[i], 2, conn) < 0)
                goto sendFailed;
        }
    }
    else
    {
        if (pqPutInt(0, 2, conn) < 0)
            goto sendFailed;
    }
 
    if (pqPutInt(nParams, 2, conn) < 0)
        goto sendFailed;
 
    /* Send parameters */
    for (i = 0; i < nParams; i++)
    {
        if (paramValues && paramValues[i])
        {
            int         nbytes;
 
            if (paramFormats && paramFormats[i] != 0)
            {
                /* binary parameter */
                if (paramLengths)
                    nbytes = paramLengths[i];
                else
                {
                    libpq_append_conn_error(conn, "length must be given for binary parameter");
                    goto sendFailed;
                }
            }
            else
            {
                /* text parameter, do not use paramLengths */
                nbytes = strlen(paramValues[i]);
            }
            if (pqPutInt(nbytes, 4, conn) < 0 ||
                pqPutnchar(paramValues[i], nbytes, conn) < 0)
                goto sendFailed;
        }
        else
        {
            /* take the param as NULL */
            if (pqPutInt(-1, 4, conn) < 0)
                goto sendFailed;
        }
    }
    if (pqPutInt(1, 2, conn) < 0 ||
        pqPutInt(resultFormat, 2, conn))
        goto sendFailed;
    if (pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /* construct the Describe Portal message */
    if (pqPutMsgStart(PqMsg_Describe, conn) < 0 ||
        pqPutc('P', conn) < 0 ||
        pqPuts("", conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /* construct the Execute message */
    if (pqPutMsgStart(PqMsg_Execute, conn) < 0 ||
        pqPuts("", conn) < 0 ||
        pqPutInt(0, 4, conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /* construct the Sync message if not in pipeline mode */
    if (conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        if (pqPutMsgStart(PqMsg_Sync, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            goto sendFailed;
    }
 
    /* remember we are using extended query protocol */
    entry->queryclass = PGQUERY_EXTENDED;
 
    /* and remember the query text too, if possible */
    /* if insufficient memory, query just winds up NULL */
    if (command)
        entry->query = strdup(command);
 
    /*
     * Give the data a push (in pipeline mode, only if we're past the size
     * threshold).  In nonblock mode, don't complain if we're unable to send
     * it all; PQgetResult() will do any additional flushing needed.
     */
    if (pqPipelineFlush(conn) < 0)
        goto sendFailed;
 
    /* OK, it's launched! */
    pqAppendCmdQueueEntry(conn, entry);
 
    return 1;
 
sendFailed:
    pqRecycleCmdQueueEntry(conn, entry);
    /* error message should be set up already */
    return 0;
}
 
/*
 * Select row-by-row processing mode
 */
int
PQsetSingleRowMode(PGconn *conn)
{
    /*
     * Only allow setting the flag when we have launched a query and not yet
     * received any results.
     */
    if (!conn)
        return 0;
    if (conn->asyncStatus != PGASYNC_BUSY)
        return 0;
    if (!conn->cmd_queue_head ||
        (conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE &&
         conn->cmd_queue_head->queryclass != PGQUERY_EXTENDED))
        return 0;
    if (pgHavePendingResult(conn))
        return 0;
 
    /* OK, set flag */
    conn->singleRowMode = true;
    return 1;
}
 
/*
 * Consume any available input from the backend
 * 0 return: some kind of trouble
 * 1 return: no problem
 */
int
PQconsumeInput(PGconn *conn)
{
    if (!conn)
        return 0;
 
    /*
     * for non-blocking connections try to flush the send-queue, otherwise we
     * may never get a response for something that may not have already been
     * sent because it's in our write buffer!
     */
    if (pqIsnonblocking(conn))
    {
        if (pqFlush(conn) < 0)
            return 0;
    }
 
    /*
     * Load more data, if available. We do this no matter what state we are
     * in, since we are probably getting called because the application wants
     * to get rid of a read-select condition. Note that we will NOT block
     * waiting for more input.
     */
    if (pqReadData(conn) < 0)
        return 0;
 
    /* Parsing of the data waits till later. */
    return 1;
}
 
 
/*
 * parseInput: if appropriate, parse input data from backend
 * until input is exhausted or a stopping state is reached.
 * Note that this function will NOT attempt to read more data from the backend.
 */
static void
parseInput(PGconn *conn)
{
    pqParseInput3(conn);
}
 
/*
 * PQisBusy
 *   Return true if PQgetResult would block waiting for input.
 */
 
int
PQisBusy(PGconn *conn)
{
    if (!conn)
        return false;
 
    /* Parse any available data, if our state permits. */
    parseInput(conn);
 
    /*
     * PQgetResult will return immediately in all states except BUSY.  Also,
     * if we've detected read EOF and dropped the connection, we can expect
     * that PQgetResult will fail immediately.  Note that we do *not* check
     * conn->write_failed here --- once that's become set, we know we have
     * trouble, but we need to keep trying to read until we have a complete
     * server message or detect read EOF.
     */
    return conn->asyncStatus == PGASYNC_BUSY && conn->status != CONNECTION_BAD;
}
 
/*
 * PQgetResult
 *    Get the next PGresult produced by a query.  Returns NULL if no
 *    query work remains or an error has occurred (e.g. out of
 *    memory).
 *
 *    In pipeline mode, once all the result of a query have been returned,
 *    PQgetResult returns NULL to let the user know that the next
 *    query is being processed.  At the end of the pipeline, returns a
 *    result with PQresultStatus(result) == PGRES_PIPELINE_SYNC.
 */
PGresult *
PQgetResult(PGconn *conn)
{
    PGresult   *res;
 
    if (!conn)
        return NULL;
 
    /* Parse any available data, if our state permits. */
    parseInput(conn);
 
    /* If not ready to return something, block until we are. */
    while (conn->asyncStatus == PGASYNC_BUSY)
    {
        int         flushResult;
 
        /*
         * If data remains unsent, send it.  Else we might be waiting for the
         * result of a command the backend hasn't even got yet.
         */
        while ((flushResult = pqFlush(conn)) > 0)
        {
            if (pqWait(false, true, conn))
            {
                flushResult = -1;
                break;
            }
        }
 
        /*
         * Wait for some more data, and load it.  (Note: if the connection has
         * been lost, pqWait should return immediately because the socket
         * should be read-ready, either with the last server data or with an
         * EOF indication.  We expect therefore that this won't result in any
         * undue delay in reporting a previous write failure.)
         */
        if (flushResult ||
            pqWait(true, false, conn) ||
            pqReadData(conn) < 0)
        {
            /* Report the error saved by pqWait or pqReadData */
            pqSaveErrorResult(conn);
            conn->asyncStatus = PGASYNC_IDLE;
            return pqPrepareAsyncResult(conn);
        }
 
        /* Parse it. */
        parseInput(conn);
 
        /*
         * If we had a write error, but nothing above obtained a query result
         * or detected a read error, report the write error.
         */
        if (conn->write_failed && conn->asyncStatus == PGASYNC_BUSY)
        {
            pqSaveWriteError(conn);
            conn->asyncStatus = PGASYNC_IDLE;
            return pqPrepareAsyncResult(conn);
        }
    }
 
    /* Return the appropriate thing. */
    switch (conn->asyncStatus)
    {
        case PGASYNC_IDLE:
            res = NULL;         /* query is complete */
            break;
        case PGASYNC_PIPELINE_IDLE:
            Assert(conn->pipelineStatus != PQ_PIPELINE_OFF);
 
            /*
             * We're about to return the NULL that terminates the round of
             * results from the current query; prepare to send the results of
             * the next query, if any, when we're called next.  If there's no
             * next element in the command queue, this gets us in IDLE state.
             */
            pqPipelineProcessQueue(conn);
            res = NULL;         /* query is complete */
            break;
 
        case PGASYNC_READY:
            res = pqPrepareAsyncResult(conn);
 
            /* Advance the queue as appropriate */
            pqCommandQueueAdvance(conn, false,
                                  res->resultStatus == PGRES_PIPELINE_SYNC);
 
            if (conn->pipelineStatus != PQ_PIPELINE_OFF)
            {
                /*
                 * We're about to send the results of the current query.  Set
                 * us idle now, and ...
                 */
                conn->asyncStatus = PGASYNC_PIPELINE_IDLE;
 
                /*
                 * ... in cases when we're sending a pipeline-sync result,
                 * move queue processing forwards immediately, so that next
                 * time we're called, we're prepared to return the next result
                 * received from the server.  In all other cases, leave the
                 * queue state change for next time, so that a terminating
                 * NULL result is sent.
                 *
                 * (In other words: we don't return a NULL after a pipeline
                 * sync.)
                 */
                if (res && res->resultStatus == PGRES_PIPELINE_SYNC)
                    pqPipelineProcessQueue(conn);
            }
            else
            {
                /* Set the state back to BUSY, allowing parsing to proceed. */
                conn->asyncStatus = PGASYNC_BUSY;
            }
            break;
        case PGASYNC_READY_MORE:
            res = pqPrepareAsyncResult(conn);
            /* Set the state back to BUSY, allowing parsing to proceed. */
            conn->asyncStatus = PGASYNC_BUSY;
            break;
        case PGASYNC_COPY_IN:
            res = getCopyResult(conn, PGRES_COPY_IN);
            break;
        case PGASYNC_COPY_OUT:
            res = getCopyResult(conn, PGRES_COPY_OUT);
            break;
        case PGASYNC_COPY_BOTH:
            res = getCopyResult(conn, PGRES_COPY_BOTH);
            break;
        default:
            libpq_append_conn_error(conn, "unexpected asyncStatus: %d", (int) conn->asyncStatus);
            pqSaveErrorResult(conn);
            conn->asyncStatus = PGASYNC_IDLE;   /* try to restore valid state */
            res = pqPrepareAsyncResult(conn);
            break;
    }
 
    /* Time to fire PGEVT_RESULTCREATE events, if there are any */
    if (res && res->nEvents > 0)
        (void) PQfireResultCreateEvents(conn, res);
 
    return res;
}
 
/*
 * getCopyResult
 *    Helper for PQgetResult: generate result for COPY-in-progress cases
 */
static PGresult *
getCopyResult(PGconn *conn, ExecStatusType copytype)
{
    /*
     * If the server connection has been lost, don't pretend everything is
     * hunky-dory; instead return a PGRES_FATAL_ERROR result, and reset the
     * asyncStatus to idle (corresponding to what we'd do if we'd detected I/O
     * error in the earlier steps in PQgetResult).  The text returned in the
     * result is whatever is in conn->errorMessage; we hope that was filled
     * with something relevant when the lost connection was detected.
     */
    if (conn->status != CONNECTION_OK)
    {
        pqSaveErrorResult(conn);
        conn->asyncStatus = PGASYNC_IDLE;
        return pqPrepareAsyncResult(conn);
    }
 
    /* If we have an async result for the COPY, return that */
    if (conn->result && conn->result->resultStatus == copytype)
        return pqPrepareAsyncResult(conn);
 
    /* Otherwise, invent a suitable PGresult */
    return PQmakeEmptyPGresult(conn, copytype);
}
 
 
/*
 * PQexec
 *    send a query to the backend and package up the result in a PGresult
 *
 * If the query was not even sent, return NULL; conn->errorMessage is set to
 * a relevant message.
 * If the query was sent, a new PGresult is returned (which could indicate
 * either success or failure).
 * The user is responsible for freeing the PGresult via PQclear()
 * when done with it.
 */
PGresult *
PQexec(PGconn *conn, const char *query)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendQuery(conn, query))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQexecParams
 *      Like PQexec, but use extended query protocol so we can pass parameters
 */
PGresult *
PQexecParams(PGconn *conn,
             const char *command,
             int nParams,
             const Oid *paramTypes,
             const char *const *paramValues,
             const int *paramLengths,
             const int *paramFormats,
             int resultFormat)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendQueryParams(conn, command,
                           nParams, paramTypes, paramValues, paramLengths,
                           paramFormats, resultFormat))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQprepare
 *    Creates a prepared statement by issuing a Parse message.
 *
 * If the query was not even sent, return NULL; conn->errorMessage is set to
 * a relevant message.
 * If the query was sent, a new PGresult is returned (which could indicate
 * either success or failure).
 * The user is responsible for freeing the PGresult via PQclear()
 * when done with it.
 */
PGresult *
PQprepare(PGconn *conn,
          const char *stmtName, const char *query,
          int nParams, const Oid *paramTypes)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendPrepare(conn, stmtName, query, nParams, paramTypes))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQexecPrepared
 *      Like PQexec, but execute a previously prepared statement,
 *      using extended query protocol so we can pass parameters
 */
PGresult *
PQexecPrepared(PGconn *conn,
               const char *stmtName,
               int nParams,
               const char *const *paramValues,
               const int *paramLengths,
               const int *paramFormats,
               int resultFormat)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendQueryPrepared(conn, stmtName,
                             nParams, paramValues, paramLengths,
                             paramFormats, resultFormat))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * Common code for PQexec and sibling routines: prepare to send command
 */
static bool
PQexecStart(PGconn *conn)
{
    PGresult   *result;
 
    if (!conn)
        return false;
 
    /*
     * Since this is the beginning of a query cycle, reset the error state.
     * However, in pipeline mode with something already queued, the error
     * buffer belongs to that command and we shouldn't clear it.
     */
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "synchronous command execution functions are not allowed in pipeline mode");
        return false;
    }
 
    /*
     * Silently discard any prior query result that application didn't eat.
     * This is probably poor design, but it's here for backward compatibility.
     */
    while ((result = PQgetResult(conn)) != NULL)
    {
        ExecStatusType resultStatus = result->resultStatus;
 
        PQclear(result);        /* only need its status */
        if (resultStatus == PGRES_COPY_IN)
        {
            /* get out of a COPY IN state */
            if (PQputCopyEnd(conn,
                             libpq_gettext("COPY terminated by new PQexec")) < 0)
                return false;
            /* keep waiting to swallow the copy's failure message */
        }
        else if (resultStatus == PGRES_COPY_OUT)
        {
            /*
             * Get out of a COPY OUT state: we just switch back to BUSY and
             * allow the remaining COPY data to be dropped on the floor.
             */
            conn->asyncStatus = PGASYNC_BUSY;
            /* keep waiting to swallow the copy's completion message */
        }
        else if (resultStatus == PGRES_COPY_BOTH)
        {
            /* We don't allow PQexec during COPY BOTH */
            libpq_append_conn_error(conn, "PQexec not allowed during COPY BOTH");
            return false;
        }
        /* check for loss of connection, too */
        if (conn->status == CONNECTION_BAD)
            return false;
    }
 
    /* OK to send a command */
    return true;
}
 
/*
 * Common code for PQexec and sibling routines: wait for command result
 */
static PGresult *
PQexecFinish(PGconn *conn)
{
    PGresult   *result;
    PGresult   *lastResult;
 
    /*
     * For backwards compatibility, return the last result if there are more
     * than one.  (We used to have logic here to concatenate successive error
     * messages, but now that happens automatically, since conn->errorMessage
     * will continue to accumulate errors throughout this loop.)
     *
     * We have to stop if we see copy in/out/both, however. We will resume
     * parsing after application performs the data transfer.
     *
     * Also stop if the connection is lost (else we'll loop infinitely).
     */
    lastResult = NULL;
    while ((result = PQgetResult(conn)) != NULL)
    {
        PQclear(lastResult);
        lastResult = result;
        if (result->resultStatus == PGRES_COPY_IN ||
            result->resultStatus == PGRES_COPY_OUT ||
            result->resultStatus == PGRES_COPY_BOTH ||
            conn->status == CONNECTION_BAD)
            break;
    }
 
    return lastResult;
}
 
/*
 * PQdescribePrepared
 *    Obtain information about a previously prepared statement
 *
 * If the query was not even sent, return NULL; conn->errorMessage is set to
 * a relevant message.
 * If the query was sent, a new PGresult is returned (which could indicate
 * either success or failure).  On success, the PGresult contains status
 * PGRES_COMMAND_OK, and its parameter and column-heading fields describe
 * the statement's inputs and outputs respectively.
 * The user is responsible for freeing the PGresult via PQclear()
 * when done with it.
 */
PGresult *
PQdescribePrepared(PGconn *conn, const char *stmt)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendTypedCommand(conn, PqMsg_Describe, 'S', stmt))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQdescribePortal
 *    Obtain information about a previously created portal
 *
 * This is much like PQdescribePrepared, except that no parameter info is
 * returned.  Note that at the moment, libpq doesn't really expose portals
 * to the client; but this can be used with a portal created by a SQL
 * DECLARE CURSOR command.
 */
PGresult *
PQdescribePortal(PGconn *conn, const char *portal)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendTypedCommand(conn, PqMsg_Describe, 'P', portal))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQsendDescribePrepared
 *   Submit a Describe Statement command, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 */
int
PQsendDescribePrepared(PGconn *conn, const char *stmt)
{
    return PQsendTypedCommand(conn, PqMsg_Describe, 'S', stmt);
}
 
/*
 * PQsendDescribePortal
 *   Submit a Describe Portal command, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 */
int
PQsendDescribePortal(PGconn *conn, const char *portal)
{
    return PQsendTypedCommand(conn, PqMsg_Describe, 'P', portal);
}
 
/*
 * PQclosePrepared
 *    Close a previously prepared statement
 *
 * If the query was not even sent, return NULL; conn->errorMessage is set to
 * a relevant message.
 * If the query was sent, a new PGresult is returned (which could indicate
 * either success or failure).  On success, the PGresult contains status
 * PGRES_COMMAND_OK. The user is responsible for freeing the PGresult via
 * PQclear() when done with it.
 */
PGresult *
PQclosePrepared(PGconn *conn, const char *stmt)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendTypedCommand(conn, PqMsg_Close, 'S', stmt))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQclosePortal
 *    Close a previously created portal
 *
 * This is exactly like PQclosePrepared, but for portals.  Note that at the
 * moment, libpq doesn't really expose portals to the client; but this can be
 * used with a portal created by a SQL DECLARE CURSOR command.
 */
PGresult *
PQclosePortal(PGconn *conn, const char *portal)
{
    if (!PQexecStart(conn))
        return NULL;
    if (!PQsendTypedCommand(conn, PqMsg_Close, 'P', portal))
        return NULL;
    return PQexecFinish(conn);
}
 
/*
 * PQsendClosePrepared
 *   Submit a Close Statement command, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 */
int
PQsendClosePrepared(PGconn *conn, const char *stmt)
{
    return PQsendTypedCommand(conn, PqMsg_Close, 'S', stmt);
}
 
/*
 * PQsendClosePortal
 *   Submit a Close Portal command, but don't wait for it to finish
 *
 * Returns: 1 if successfully submitted
 *          0 if error (conn->errorMessage is set)
 */
int
PQsendClosePortal(PGconn *conn, const char *portal)
{
    return PQsendTypedCommand(conn, PqMsg_Close, 'P', portal);
}
 
/*
 * PQsendTypedCommand
 *   Common code to send a Describe or Close command
 *
 * Available options for "command" are
 *   PqMsg_Close for Close; or
 *   PqMsg_Describe for Describe.
 *
 * Available options for "type" are
 *   'S' to run a command on a prepared statement; or
 *   'P' to run a command on a portal.
 *
 * Returns 1 on success and 0 on failure.
 */
static int
PQsendTypedCommand(PGconn *conn, char command, char type, const char *target)
{
    PGcmdQueueEntry *entry = NULL;
 
    /* Treat null target as empty string */
    if (!target)
        target = "";
 
    if (!PQsendQueryStart(conn, true))
        return 0;
 
    entry = pqAllocCmdQueueEntry(conn);
    if (entry == NULL)
        return 0;               /* error msg already set */
 
    /* construct the Close message */
    if (pqPutMsgStart(command, conn) < 0 ||
        pqPutc(type, conn) < 0 ||
        pqPuts(target, conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /* construct the Sync message */
    if (conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        if (pqPutMsgStart(PqMsg_Sync, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            goto sendFailed;
    }
 
    /* remember if we are doing a Close or a Describe */
    if (command == PqMsg_Close)
    {
        entry->queryclass = PGQUERY_CLOSE;
    }
    else if (command == PqMsg_Describe)
    {
        entry->queryclass = PGQUERY_DESCRIBE;
    }
    else
    {
        libpq_append_conn_error(conn, "unknown command type provided");
        goto sendFailed;
    }
 
    /*
     * Give the data a push (in pipeline mode, only if we're past the size
     * threshold).  In nonblock mode, don't complain if we're unable to send
     * it all; PQgetResult() will do any additional flushing needed.
     */
    if (pqPipelineFlush(conn) < 0)
        goto sendFailed;
 
    /* OK, it's launched! */
    pqAppendCmdQueueEntry(conn, entry);
 
    return 1;
 
sendFailed:
    pqRecycleCmdQueueEntry(conn, entry);
    /* error message should be set up already */
    return 0;
}
 
/*
 * PQnotifies
 *    returns a PGnotify* structure of the latest async notification
 * that has not yet been handled
 *
 * returns NULL, if there is currently
 * no unhandled async notification from the backend
 *
 * the CALLER is responsible for FREE'ing the structure returned
 *
 * Note that this function does not read any new data from the socket;
 * so usually, caller should call PQconsumeInput() first.
 */
PGnotify *
PQnotifies(PGconn *conn)
{
    PGnotify   *event;
 
    if (!conn)
        return NULL;
 
    /* Parse any available data to see if we can extract NOTIFY messages. */
    parseInput(conn);
 
    event = conn->notifyHead;
    if (event)
    {
        conn->notifyHead = event->next;
        if (!conn->notifyHead)
            conn->notifyTail = NULL;
        event->next = NULL;     /* don't let app see the internal state */
    }
    return event;
}
 
/*
 * PQputCopyData - send some data to the backend during COPY IN or COPY BOTH
 *
 * Returns 1 if successful, 0 if data could not be sent (only possible
 * in nonblock mode), or -1 if an error occurs.
 */
int
PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
{
    if (!conn)
        return -1;
    if (conn->asyncStatus != PGASYNC_COPY_IN &&
        conn->asyncStatus != PGASYNC_COPY_BOTH)
    {
        libpq_append_conn_error(conn, "no COPY in progress");
        return -1;
    }
 
    /*
     * Process any NOTICE or NOTIFY messages that might be pending in the
     * input buffer.  Since the server might generate many notices during the
     * COPY, we want to clean those out reasonably promptly to prevent
     * indefinite expansion of the input buffer.  (Note: the actual read of
     * input data into the input buffer happens down inside pqSendSome, but
     * it's not authorized to get rid of the data again.)
     */
    parseInput(conn);
 
    if (nbytes > 0)
    {
        /*
         * Try to flush any previously sent data in preference to growing the
         * output buffer.  If we can't enlarge the buffer enough to hold the
         * data, return 0 in the nonblock case, else hard error. (For
         * simplicity, always assume 5 bytes of overhead.)
         */
        if ((conn->outBufSize - conn->outCount - 5) < nbytes)
        {
            if (pqFlush(conn) < 0)
                return -1;
            if (pqCheckOutBufferSpace(conn->outCount + 5 + (size_t) nbytes,
                                      conn))
                return pqIsnonblocking(conn) ? 0 : -1;
        }
        /* Send the data (too simple to delegate to fe-protocol files) */
        if (pqPutMsgStart(PqMsg_CopyData, conn) < 0 ||
            pqPutnchar(buffer, nbytes, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            return -1;
    }
    return 1;
}
 
/*
 * PQputCopyEnd - send EOF indication to the backend during COPY IN
 *
 * After calling this, use PQgetResult() to check command completion status.
 *
 * Returns 1 if successful, or -1 if an error occurs.
 */
int
PQputCopyEnd(PGconn *conn, const char *errormsg)
{
    if (!conn)
        return -1;
    if (conn->asyncStatus != PGASYNC_COPY_IN &&
        conn->asyncStatus != PGASYNC_COPY_BOTH)
    {
        libpq_append_conn_error(conn, "no COPY in progress");
        return -1;
    }
 
    /*
     * Send the COPY END indicator.  This is simple enough that we don't
     * bother delegating it to the fe-protocol files.
     */
    if (errormsg)
    {
        /* Send COPY FAIL */
        if (pqPutMsgStart(PqMsg_CopyFail, conn) < 0 ||
            pqPuts(errormsg, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            return -1;
    }
    else
    {
        /* Send COPY DONE */
        if (pqPutMsgStart(PqMsg_CopyDone, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            return -1;
    }
 
    /*
     * If we sent the COPY command in extended-query mode, we must issue a
     * Sync as well.
     */
    if (conn->cmd_queue_head &&
        conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE)
    {
        if (pqPutMsgStart(PqMsg_Sync, conn) < 0 ||
            pqPutMsgEnd(conn) < 0)
            return -1;
    }
 
    /* Return to active duty */
    if (conn->asyncStatus == PGASYNC_COPY_BOTH)
        conn->asyncStatus = PGASYNC_COPY_OUT;
    else
        conn->asyncStatus = PGASYNC_BUSY;
 
    /* Try to flush data */
    if (pqFlush(conn) < 0)
        return -1;
 
    return 1;
}
 
/*
 * PQgetCopyData - read a row of data from the backend during COPY OUT
 * or COPY BOTH
 *
 * If successful, sets *buffer to point to a malloc'd row of data, and
 * returns row length (always > 0) as result.
 * Returns 0 if no row available yet (only possible if async is true),
 * -1 if end of copy (consult PQgetResult), or -2 if error (consult
 * PQerrorMessage).
 */
int
PQgetCopyData(PGconn *conn, char **buffer, int async)
{
    *buffer = NULL;             /* for all failure cases */
    if (!conn)
        return -2;
    if (conn->asyncStatus != PGASYNC_COPY_OUT &&
        conn->asyncStatus != PGASYNC_COPY_BOTH)
    {
        libpq_append_conn_error(conn, "no COPY in progress");
        return -2;
    }
    return pqGetCopyData3(conn, buffer, async);
}
 
/*
 * PQgetline - gets a newline-terminated string from the backend.
 *
 * Chiefly here so that applications can use "COPY <rel> to stdout"
 * and read the output string.  Returns a null-terminated string in `buffer`.
 *
 * XXX this routine is now deprecated, because it can't handle binary data.
 * If called during a COPY BINARY we return EOF.
 *
 * PQgetline reads up to `length`-1 characters (like fgets(3)) but strips
 * the terminating \n (like gets(3)).
 *
 * CAUTION: the caller is responsible for detecting the end-of-copy signal
 * (a line containing just "\.") when using this routine.
 *
 * RETURNS:
 *      EOF if error (eg, invalid arguments are given)
 *      0 if EOL is reached (i.e., \n has been read)
 *              (this is required for backward-compatibility -- this
 *               routine used to always return EOF or 0, assuming that
 *               the line ended within `length` bytes.)
 *      1 in other cases (i.e., the buffer was filled before \n is reached)
 */
int
PQgetline(PGconn *conn, char *buffer, int length)
{
    if (!buffer || length <= 0)
        return EOF;
    *buffer = '\0';
    /* length must be at least 3 to hold the \. terminator! */
    if (length < 3)
        return EOF;
 
    if (!conn)
        return EOF;
 
    return pqGetline3(conn, buffer, length);
}
 
/*
 * PQgetlineAsync - gets a COPY data row without blocking.
 *
 * This routine is for applications that want to do "COPY <rel> to stdout"
 * asynchronously, that is without blocking.  Having issued the COPY command
 * and gotten a PGRES_COPY_OUT response, the app should call PQconsumeInput
 * and this routine until the end-of-data signal is detected.  Unlike
 * PQgetline, this routine takes responsibility for detecting end-of-data.
 *
 * On each call, PQgetlineAsync will return data if a complete data row
 * is available in libpq's input buffer.  Otherwise, no data is returned
 * until the rest of the row arrives.
 *
 * If -1 is returned, the end-of-data signal has been recognized (and removed
 * from libpq's input buffer).  The caller *must* next call PQendcopy and
 * then return to normal processing.
 *
 * RETURNS:
 *   -1    if the end-of-copy-data marker has been recognized
 *   0     if no data is available
 *   >0    the number of bytes returned.
 *
 * The data returned will not extend beyond a data-row boundary.  If possible
 * a whole row will be returned at one time.  But if the buffer offered by
 * the caller is too small to hold a row sent by the backend, then a partial
 * data row will be returned.  In text mode this can be detected by testing
 * whether the last returned byte is '\n' or not.
 *
 * The returned data is *not* null-terminated.
 */
 
int
PQgetlineAsync(PGconn *conn, char *buffer, int bufsize)
{
    if (!conn)
        return -1;
 
    return pqGetlineAsync3(conn, buffer, bufsize);
}
 
/*
 * PQputline -- sends a string to the backend during COPY IN.
 * Returns 0 if OK, EOF if not.
 *
 * This is deprecated primarily because the return convention doesn't allow
 * caller to tell the difference between a hard error and a nonblock-mode
 * send failure.
 */
int
PQputline(PGconn *conn, const char *string)
{
    return PQputnbytes(conn, string, strlen(string));
}
 
/*
 * PQputnbytes -- like PQputline, but buffer need not be null-terminated.
 * Returns 0 if OK, EOF if not.
 */
int
PQputnbytes(PGconn *conn, const char *buffer, int nbytes)
{
    if (PQputCopyData(conn, buffer, nbytes) > 0)
        return 0;
    else
        return EOF;
}
 
/*
 * PQendcopy
 *      After completing the data transfer portion of a copy in/out,
 *      the application must call this routine to finish the command protocol.
 *
 * This is deprecated; it's cleaner to use PQgetResult to get the transfer
 * status.
 *
 * RETURNS:
 *      0 on success
 *      1 on failure
 */
int
PQendcopy(PGconn *conn)
{
    if (!conn)
        return 0;
 
    return pqEndcopy3(conn);
}
 
 
/* ----------------
 *      PQfn -  Send a function call to the POSTGRES backend.
 *
 *      conn            : backend connection
 *      fnid            : OID of function to be called
 *      result_buf      : pointer to result buffer
 *      result_len      : actual length of result is returned here
 *      result_is_int   : If the result is an integer, this must be 1,
 *                        otherwise this should be 0
 *      args            : pointer to an array of function arguments
 *                        (each has length, if integer, and value/pointer)
 *      nargs           : # of arguments in args array.
 *
 * RETURNS
 *      PGresult with status = PGRES_COMMAND_OK if successful.
 *          *result_len is > 0 if there is a return value, 0 if not.
 *      PGresult with status = PGRES_FATAL_ERROR if backend returns an error.
 *      NULL on communications failure.  conn->errorMessage will be set.
 * ----------------
 */
 
PGresult *
PQfn(PGconn *conn,
     int fnid,
     int *result_buf,
     int *result_len,
     int result_is_int,
     const PQArgBlock *args,
     int nargs)
{
    *result_len = 0;
 
    if (!conn)
        return NULL;
 
    /*
     * Since this is the beginning of a query cycle, reset the error state.
     * However, in pipeline mode with something already queued, the error
     * buffer belongs to that command and we shouldn't clear it.
     */
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "%s not allowed in pipeline mode", "PQfn");
        return NULL;
    }
 
    if (conn->sock == PGINVALID_SOCKET || conn->asyncStatus != PGASYNC_IDLE ||
        pgHavePendingResult(conn))
    {
        libpq_append_conn_error(conn, "connection in wrong state");
        return NULL;
    }
 
    return pqFunctionCall3(conn, fnid,
                           result_buf, result_len,
                           result_is_int,
                           args, nargs);
}
 
/* ====== Pipeline mode support ======== */
 
/*
 * PQenterPipelineMode
 *      Put an idle connection in pipeline mode.
 *
 * Returns 1 on success. On failure, errorMessage is set and 0 is returned.
 *
 * Commands submitted after this can be pipelined on the connection;
 * there's no requirement to wait for one to finish before the next is
 * dispatched.
 *
 * Queuing of a new query or syncing during COPY is not allowed.
 *
 * A set of commands is terminated by a PQpipelineSync.  Multiple sync
 * points can be established while in pipeline mode.  Pipeline mode can
 * be exited by calling PQexitPipelineMode() once all results are processed.
 *
 * This doesn't actually send anything on the wire, it just puts libpq
 * into a state where it can pipeline work.
 */
int
PQenterPipelineMode(PGconn *conn)
{
    if (!conn)
        return 0;
 
    /* succeed with no action if already in pipeline mode */
    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
        return 1;
 
    if (conn->asyncStatus != PGASYNC_IDLE)
    {
        libpq_append_conn_error(conn, "cannot enter pipeline mode, connection not idle");
        return 0;
    }
 
    conn->pipelineStatus = PQ_PIPELINE_ON;
 
    return 1;
}
 
/*
 * PQexitPipelineMode
 *      End pipeline mode and return to normal command mode.
 *
 * Returns 1 in success (pipeline mode successfully ended, or not in pipeline
 * mode).
 *
 * Returns 0 if in pipeline mode and cannot be ended yet.  Error message will
 * be set.
 */
int
PQexitPipelineMode(PGconn *conn)
{
    if (!conn)
        return 0;
 
    if (conn->pipelineStatus == PQ_PIPELINE_OFF &&
        (conn->asyncStatus == PGASYNC_IDLE ||
         conn->asyncStatus == PGASYNC_PIPELINE_IDLE) &&
        conn->cmd_queue_head == NULL)
        return 1;
 
    switch (conn->asyncStatus)
    {
        case PGASYNC_READY:
        case PGASYNC_READY_MORE:
            /* there are some uncollected results */
            libpq_append_conn_error(conn, "cannot exit pipeline mode with uncollected results");
            return 0;
 
        case PGASYNC_BUSY:
            libpq_append_conn_error(conn, "cannot exit pipeline mode while busy");
            return 0;
 
        case PGASYNC_IDLE:
        case PGASYNC_PIPELINE_IDLE:
            /* OK */
            break;
 
        case PGASYNC_COPY_IN:
        case PGASYNC_COPY_OUT:
        case PGASYNC_COPY_BOTH:
            libpq_append_conn_error(conn, "cannot exit pipeline mode while in COPY");
    }
 
    /* still work to process */
    if (conn->cmd_queue_head != NULL)
    {
        libpq_append_conn_error(conn, "cannot exit pipeline mode with uncollected results");
        return 0;
    }
 
    conn->pipelineStatus = PQ_PIPELINE_OFF;
    conn->asyncStatus = PGASYNC_IDLE;
 
    /* Flush any pending data in out buffer */
    if (pqFlush(conn) < 0)
        return 0;               /* error message is setup already */
    return 1;
}
 
/*
 * pqCommandQueueAdvance
 *      Remove one query from the command queue, if appropriate.
 *
 * If we have received all results corresponding to the head element
 * in the command queue, remove it.
 *
 * In simple query protocol we must not advance the command queue until the
 * ReadyForQuery message has been received.  This is because in simple mode a
 * command can have multiple queries, and we must process result for all of
 * them before moving on to the next command.
 *
 * Another consideration is synchronization during error processing in
 * extended query protocol: we refuse to advance the queue past a SYNC queue
 * element, unless the result we've received is also a SYNC.  In particular
 * this protects us from advancing when an error is received at an
 * inappropriate moment.
 */
void
pqCommandQueueAdvance(PGconn *conn, bool isReadyForQuery, bool gotSync)
{
    PGcmdQueueEntry *prevquery;
 
    if (conn->cmd_queue_head == NULL)
        return;
 
    /*
     * If processing a query of simple query protocol, we only advance the
     * queue when we receive the ReadyForQuery message for it.
     */
    if (conn->cmd_queue_head->queryclass == PGQUERY_SIMPLE && !isReadyForQuery)
        return;
 
    /*
     * If we're waiting for a SYNC, don't advance the queue until we get one.
     */
    if (conn->cmd_queue_head->queryclass == PGQUERY_SYNC && !gotSync)
        return;
 
    /* delink element from queue */
    prevquery = conn->cmd_queue_head;
    conn->cmd_queue_head = conn->cmd_queue_head->next;
 
    /* If the queue is now empty, reset the tail too */
    if (conn->cmd_queue_head == NULL)
        conn->cmd_queue_tail = NULL;
 
    /* and make the queue element recyclable */
    prevquery->next = NULL;
    pqRecycleCmdQueueEntry(conn, prevquery);
}
 
/*
 * pqPipelineProcessQueue: subroutine for PQgetResult
 *      In pipeline mode, start processing the results of the next query in the queue.
 */
static void
pqPipelineProcessQueue(PGconn *conn)
{
    switch (conn->asyncStatus)
    {
        case PGASYNC_COPY_IN:
        case PGASYNC_COPY_OUT:
        case PGASYNC_COPY_BOTH:
        case PGASYNC_READY:
        case PGASYNC_READY_MORE:
        case PGASYNC_BUSY:
            /* client still has to process current query or results */
            return;
 
        case PGASYNC_IDLE:
 
            /*
             * If we're in IDLE mode and there's some command in the queue,
             * get us into PIPELINE_IDLE mode and process normally.  Otherwise
             * there's nothing for us to do.
             */
            if (conn->cmd_queue_head != NULL)
            {
                conn->asyncStatus = PGASYNC_PIPELINE_IDLE;
                break;
            }
            return;
 
        case PGASYNC_PIPELINE_IDLE:
            Assert(conn->pipelineStatus != PQ_PIPELINE_OFF);
            /* next query please */
            break;
    }
 
    /*
     * Reset single-row processing mode.  (Client has to set it up for each
     * query, if desired.)
     */
    conn->singleRowMode = false;
 
    /*
     * If there are no further commands to process in the queue, get us in
     * "real idle" mode now.
     */
    if (conn->cmd_queue_head == NULL)
    {
        conn->asyncStatus = PGASYNC_IDLE;
        return;
    }
 
    /*
     * Reset the error state.  This and the next couple of steps correspond to
     * what PQsendQueryStart didn't do for this query.
     */
    pqClearConnErrorState(conn);
 
    /* Initialize async result-accumulation state */
    pqClearAsyncResult(conn);
 
    if (conn->pipelineStatus == PQ_PIPELINE_ABORTED &&
        conn->cmd_queue_head->queryclass != PGQUERY_SYNC)
    {
        /*
         * In an aborted pipeline we don't get anything from the server for
         * each result; we're just discarding commands from the queue until we
         * get to the next sync from the server.
         *
         * The PGRES_PIPELINE_ABORTED results tell the client that its queries
         * got aborted.
         */
        conn->result = PQmakeEmptyPGresult(conn, PGRES_PIPELINE_ABORTED);
        if (!conn->result)
        {
            libpq_append_conn_error(conn, "out of memory");
            pqSaveErrorResult(conn);
            return;
        }
        conn->asyncStatus = PGASYNC_READY;
    }
    else
    {
        /* allow parsing to continue */
        conn->asyncStatus = PGASYNC_BUSY;
    }
}
 
/*
 * PQpipelineSync
 *      Send a Sync message as part of a pipeline, and flush to server
 *
 * It's legal to start submitting more commands in the pipeline immediately,
 * without waiting for the results of the current pipeline. There's no need to
 * end pipeline mode and start it again.
 *
 * If a command in a pipeline fails, every subsequent command up to and including
 * the result to the Sync message sent by PQpipelineSync gets set to
 * PGRES_PIPELINE_ABORTED state. If the whole pipeline is processed without
 * error, a PGresult with PGRES_PIPELINE_SYNC is produced.
 *
 * Queries can already have been sent before PQpipelineSync is called, but
 * PQpipelineSync need to be called before retrieving command results.
 *
 * The connection will remain in pipeline mode and unavailable for new
 * synchronous command execution functions until all results from the pipeline
 * are processed by the client.
 */
int
PQpipelineSync(PGconn *conn)
{
    PGcmdQueueEntry *entry;
 
    if (!conn)
        return 0;
 
    if (conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "cannot send pipeline when not in pipeline mode");
        return 0;
    }
 
    switch (conn->asyncStatus)
    {
        case PGASYNC_COPY_IN:
        case PGASYNC_COPY_OUT:
        case PGASYNC_COPY_BOTH:
            /* should be unreachable */
            appendPQExpBufferStr(&conn->errorMessage,
                                 "internal error: cannot send pipeline while in COPY\n");
            return 0;
        case PGASYNC_READY:
        case PGASYNC_READY_MORE:
        case PGASYNC_BUSY:
        case PGASYNC_IDLE:
        case PGASYNC_PIPELINE_IDLE:
            /* OK to send sync */
            break;
    }
 
    entry = pqAllocCmdQueueEntry(conn);
    if (entry == NULL)
        return 0;               /* error msg already set */
 
    entry->queryclass = PGQUERY_SYNC;
    entry->query = NULL;
 
    /* construct the Sync message */
    if (pqPutMsgStart(PqMsg_Sync, conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
        goto sendFailed;
 
    /*
     * Give the data a push.  In nonblock mode, don't complain if we're unable
     * to send it all; PQgetResult() will do any additional flushing needed.
     */
    if (PQflush(conn) < 0)
        goto sendFailed;
 
    /* OK, it's launched! */
    pqAppendCmdQueueEntry(conn, entry);
 
    return 1;
 
sendFailed:
    pqRecycleCmdQueueEntry(conn, entry);
    /* error message should be set up already */
    return 0;
}
 
/*
 * PQsendFlushRequest
 *      Send request for server to flush its buffer.  Useful in pipeline
 *      mode when a sync point is not desired.
 */
int
PQsendFlushRequest(PGconn *conn)
{
    if (!conn)
        return 0;
 
    /* Don't try to send if we know there's no live connection. */
    if (conn->status != CONNECTION_OK)
    {
        libpq_append_conn_error(conn, "no connection to the server");
        return 0;
    }
 
    /* Can't send while already busy, either, unless enqueuing for later */
    if (conn->asyncStatus != PGASYNC_IDLE &&
        conn->pipelineStatus == PQ_PIPELINE_OFF)
    {
        libpq_append_conn_error(conn, "another command is already in progress");
        return 0;
    }
 
    if (pqPutMsgStart(PqMsg_Flush, conn) < 0 ||
        pqPutMsgEnd(conn) < 0)
    {
        return 0;
    }
 
    /*
     * Give the data a push (in pipeline mode, only if we're past the size
     * threshold).  In nonblock mode, don't complain if we're unable to send
     * it all; PQgetResult() will do any additional flushing needed.
     */
    if (pqPipelineFlush(conn) < 0)
        return 0;
 
    return 1;
}
 
/* ====== accessor funcs for PGresult ======== */
 
ExecStatusType
PQresultStatus(const PGresult *res)
{
    if (!res)
        return PGRES_FATAL_ERROR;
    return res->resultStatus;
}
 
char *
PQresStatus(ExecStatusType status)
{
    if ((unsigned int) status >= lengthof(pgresStatus))
        return libpq_gettext("invalid ExecStatusType code");
    return pgresStatus[status];
}
 
char *
PQresultErrorMessage(const PGresult *res)
{
    if (!res || !res->errMsg)
        return "";
    return res->errMsg;
}
 
char *
PQresultVerboseErrorMessage(const PGresult *res,
                            PGVerbosity verbosity,
                            PGContextVisibility show_context)
{
    PQExpBufferData workBuf;
 
    /*
     * Because the caller is expected to free the result string, we must
     * strdup any constant result.  We use plain strdup and document that
     * callers should expect NULL if out-of-memory.
     */
    if (!res ||
        (res->resultStatus != PGRES_FATAL_ERROR &&
         res->resultStatus != PGRES_NONFATAL_ERROR))
        return strdup(libpq_gettext("PGresult is not an error result\n"));
 
    initPQExpBuffer(&workBuf);
 
    pqBuildErrorMessage3(&workBuf, res, verbosity, show_context);
 
    /* If insufficient memory to format the message, fail cleanly */
    if (PQExpBufferDataBroken(workBuf))
    {
        termPQExpBuffer(&workBuf);
        return strdup(libpq_gettext("out of memory\n"));
    }
 
    return workBuf.data;
}
 
char *
PQresultErrorField(const PGresult *res, int fieldcode)
{
    PGMessageField *pfield;
 
    if (!res)
        return NULL;
    for (pfield = res->errFields; pfield != NULL; pfield = pfield->next)
    {
        if (pfield->code == fieldcode)
            return pfield->contents;
    }
    return NULL;
}
 
int
PQntuples(const PGresult *res)
{
    if (!res)
        return 0;
    return res->ntups;
}
 
int
PQnfields(const PGresult *res)
{
    if (!res)
        return 0;
    return res->numAttributes;
}
 
int
PQbinaryTuples(const PGresult *res)
{
    if (!res)
        return 0;
    return res->binary;
}
 
/*
 * Helper routines to range-check field numbers and tuple numbers.
 * Return true if OK, false if not
 */
 
static int
check_field_number(const PGresult *res, int field_num)
{
    if (!res)
        return false;           /* no way to display error message... */
    if (field_num < 0 || field_num >= res->numAttributes)
    {
        pqInternalNotice(&res->noticeHooks,
                         "column number %d is out of range 0..%d",
                         field_num, res->numAttributes - 1);
        return false;
    }
    return true;
}
 
static int
check_tuple_field_number(const PGresult *res,
                         int tup_num, int field_num)
{
    if (!res)
        return false;           /* no way to display error message... */
    if (tup_num < 0 || tup_num >= res->ntups)
    {
        pqInternalNotice(&res->noticeHooks,
                         "row number %d is out of range 0..%d",
                         tup_num, res->ntups - 1);
        return false;
    }
    if (field_num < 0 || field_num >= res->numAttributes)
    {
        pqInternalNotice(&res->noticeHooks,
                         "column number %d is out of range 0..%d",
                         field_num, res->numAttributes - 1);
        return false;
    }
    return true;
}
 
static int
check_param_number(const PGresult *res, int param_num)
{
    if (!res)
        return false;           /* no way to display error message... */
    if (param_num < 0 || param_num >= res->numParameters)
    {
        pqInternalNotice(&res->noticeHooks,
                         "parameter number %d is out of range 0..%d",
                         param_num, res->numParameters - 1);
        return false;
    }
 
    return true;
}
 
/*
 * returns NULL if the field_num is invalid
 */
char *
PQfname(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return NULL;
    if (res->attDescs)
        return res->attDescs[field_num].name;
    else
        return NULL;
}
 
/*
 * PQfnumber: find column number given column name
 *
 * The column name is parsed as if it were in a SQL statement, including
 * case-folding and double-quote processing.  But note a possible gotcha:
 * downcasing in the frontend might follow different locale rules than
 * downcasing in the backend...
 *
 * Returns -1 if no match.  In the present backend it is also possible
 * to have multiple matches, in which case the first one is found.
 */
int
PQfnumber(const PGresult *res, const char *field_name)
{
    char       *field_case;
    bool        in_quotes;
    bool        all_lower = true;
    const char *iptr;
    char       *optr;
    int         i;
 
    if (!res)
        return -1;
 
    /*
     * Note: it is correct to reject a zero-length input string; the proper
     * input to match a zero-length field name would be "".
     */
    if (field_name == NULL ||
        field_name[0] == '\0' ||
        res->attDescs == NULL)
        return -1;
 
    /*
     * Check if we can avoid the strdup() and related work because the
     * passed-in string wouldn't be changed before we do the check anyway.
     */
    for (iptr = field_name; *iptr; iptr++)
    {
        char        c = *iptr;
 
        if (c == '"' || c != pg_tolower((unsigned char) c))
        {
            all_lower = false;
            break;
        }
    }
 
    if (all_lower)
        for (i = 0; i < res->numAttributes; i++)
            if (strcmp(field_name, res->attDescs[i].name) == 0)
                return i;
 
    /* Fall through to the normal check if that didn't work out. */
 
    /*
     * Note: this code will not reject partially quoted strings, eg
     * foo"BAR"foo will become fooBARfoo when it probably ought to be an error
     * condition.
     */
    field_case = strdup(field_name);
    if (field_case == NULL)
        return -1;              /* grotty */
 
    in_quotes = false;
    optr = field_case;
    for (iptr = field_case; *iptr; iptr++)
    {
        char        c = *iptr;
 
        if (in_quotes)
        {
            if (c == '"')
            {
                if (iptr[1] == '"')
                {
                    /* doubled quotes become a single quote */
                    *optr++ = '"';
                    iptr++;
                }
                else
                    in_quotes = false;
            }
            else
                *optr++ = c;
        }
        else if (c == '"')
            in_quotes = true;
        else
        {
            c = pg_tolower((unsigned char) c);
            *optr++ = c;
        }
    }
    *optr = '\0';
 
    for (i = 0; i < res->numAttributes; i++)
    {
        if (strcmp(field_case, res->attDescs[i].name) == 0)
        {
            free(field_case);
            return i;
        }
    }
    free(field_case);
    return -1;
}
 
Oid
PQftable(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return InvalidOid;
    if (res->attDescs)
        return res->attDescs[field_num].tableid;
    else
        return InvalidOid;
}
 
int
PQftablecol(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return 0;
    if (res->attDescs)
        return res->attDescs[field_num].columnid;
    else
        return 0;
}
 
int
PQfformat(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return 0;
    if (res->attDescs)
        return res->attDescs[field_num].format;
    else
        return 0;
}
 
Oid
PQftype(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return InvalidOid;
    if (res->attDescs)
        return res->attDescs[field_num].typid;
    else
        return InvalidOid;
}
 
int
PQfsize(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return 0;
    if (res->attDescs)
        return res->attDescs[field_num].typlen;
    else
        return 0;
}
 
int
PQfmod(const PGresult *res, int field_num)
{
    if (!check_field_number(res, field_num))
        return 0;
    if (res->attDescs)
        return res->attDescs[field_num].atttypmod;
    else
        return 0;
}
 
char *
PQcmdStatus(PGresult *res)
{
    if (!res)
        return NULL;
    return res->cmdStatus;
}
 
/*
 * PQoidStatus -
 *  if the last command was an INSERT, return the oid string
 *  if not, return ""
 */
char *
PQoidStatus(const PGresult *res)
{
    /*
     * This must be enough to hold the result. Don't laugh, this is better
     * than what this function used to do.
     */
    static char buf[24];
 
    size_t      len;
 
    if (!res || strncmp(res->cmdStatus, "INSERT ", 7) != 0)
        return "";
 
    len = strspn(res->cmdStatus + 7, "0123456789");
    if (len > sizeof(buf) - 1)
        len = sizeof(buf) - 1;
    memcpy(buf, res->cmdStatus + 7, len);
    buf[len] = '\0';
 
    return buf;
}
 
/*
 * PQoidValue -
 *  a perhaps preferable form of the above which just returns
 *  an Oid type
 */
Oid
PQoidValue(const PGresult *res)
{
    char       *endptr = NULL;
    unsigned long result;
 
    if (!res ||
        strncmp(res->cmdStatus, "INSERT ", 7) != 0 ||
        res->cmdStatus[7] < '0' ||
        res->cmdStatus[7] > '9')
        return InvalidOid;
 
    result = strtoul(res->cmdStatus + 7, &endptr, 10);
 
    if (!endptr || (*endptr != ' ' && *endptr != '\0'))
        return InvalidOid;
    else
        return (Oid) result;
}
 
 
/*
 * PQcmdTuples -
 *  If the last command was INSERT/UPDATE/DELETE/MERGE/MOVE/FETCH/COPY,
 *  return a string containing the number of inserted/affected tuples.
 *  If not, return "".
 *
 *  XXX: this should probably return an int
 */
char *
PQcmdTuples(PGresult *res)
{
    char       *p,
               *c;
 
    if (!res)
        return "";
 
    if (strncmp(res->cmdStatus, "INSERT ", 7) == 0)
    {
        p = res->cmdStatus + 7;
        /* INSERT: skip oid and space */
        while (*p && *p != ' ')
            p++;
        if (*p == 0)
            goto interpret_error;   /* no space? */
        p++;
    }
    else if (strncmp(res->cmdStatus, "SELECT ", 7) == 0 ||
             strncmp(res->cmdStatus, "DELETE ", 7) == 0 ||
             strncmp(res->cmdStatus, "UPDATE ", 7) == 0)
        p = res->cmdStatus + 7;
    else if (strncmp(res->cmdStatus, "FETCH ", 6) == 0 ||
             strncmp(res->cmdStatus, "MERGE ", 6) == 0)
        p = res->cmdStatus + 6;
    else if (strncmp(res->cmdStatus, "MOVE ", 5) == 0 ||
             strncmp(res->cmdStatus, "COPY ", 5) == 0)
        p = res->cmdStatus + 5;
    else
        return "";
 
    /* check that we have an integer (at least one digit, nothing else) */
    for (c = p; *c; c++)
    {
        if (!isdigit((unsigned char) *c))
            goto interpret_error;
    }
    if (c == p)
        goto interpret_error;
 
    return p;
 
interpret_error:
    pqInternalNotice(&res->noticeHooks,
                     "could not interpret result from server: %s",
                     res->cmdStatus);
    return "";
}
 
/*
 * PQgetvalue:
 *  return the value of field 'field_num' of row 'tup_num'
 */
char *
PQgetvalue(const PGresult *res, int tup_num, int field_num)
{
    if (!check_tuple_field_number(res, tup_num, field_num))
        return NULL;
    return res->tuples[tup_num][field_num].value;
}
 
/* PQgetlength:
 *  returns the actual length of a field value in bytes.
 */
int
PQgetlength(const PGresult *res, int tup_num, int field_num)
{
    if (!check_tuple_field_number(res, tup_num, field_num))
        return 0;
    if (res->tuples[tup_num][field_num].len != NULL_LEN)
        return res->tuples[tup_num][field_num].len;
    else
        return 0;
}
 
/* PQgetisnull:
 *  returns the null status of a field value.
 */
int
PQgetisnull(const PGresult *res, int tup_num, int field_num)
{
    if (!check_tuple_field_number(res, tup_num, field_num))
        return 1;               /* pretend it is null */
    if (res->tuples[tup_num][field_num].len == NULL_LEN)
        return 1;
    else
        return 0;
}
 
/* PQnparams:
 *  returns the number of input parameters of a prepared statement.
 */
int
PQnparams(const PGresult *res)
{
    if (!res)
        return 0;
    return res->numParameters;
}
 
/* PQparamtype:
 *  returns type Oid of the specified statement parameter.
 */
Oid
PQparamtype(const PGresult *res, int param_num)
{
    if (!check_param_number(res, param_num))
        return InvalidOid;
    if (res->paramDescs)
        return res->paramDescs[param_num].typid;
    else
        return InvalidOid;
}
 
 
/* PQsetnonblocking:
 *  sets the PGconn's database connection non-blocking if the arg is true
 *  or makes it blocking if the arg is false, this will not protect
 *  you from PQexec(), you'll only be safe when using the non-blocking API.
 *  Needs to be called only on a connected database connection.
 */
int
PQsetnonblocking(PGconn *conn, int arg)
{
    bool        barg;
 
    if (!conn || conn->status == CONNECTION_BAD)
        return -1;
 
    barg = (arg ? true : false);
 
    /* early out if the socket is already in the state requested */
    if (barg == conn->nonblocking)
        return 0;
 
    /*
     * to guarantee constancy for flushing/query/result-polling behavior we
     * need to flush the send queue at this point in order to guarantee proper
     * behavior. this is ok because either they are making a transition _from_
     * or _to_ blocking mode, either way we can block them.
     *
     * Clear error state in case pqFlush adds to it, unless we're actively
     * pipelining, in which case it seems best not to.
     */
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    /* if we are going from blocking to non-blocking flush here */
    if (pqFlush(conn))
        return -1;
 
    conn->nonblocking = barg;
 
    return 0;
}
 
/*
 * return the blocking status of the database connection
 *      true == nonblocking, false == blocking
 */
int
PQisnonblocking(const PGconn *conn)
{
    if (!conn || conn->status == CONNECTION_BAD)
        return false;
    return pqIsnonblocking(conn);
}
 
/* libpq is thread-safe? */
int
PQisthreadsafe(void)
{
    return true;
}
 
 
/* try to force data out, really only useful for non-blocking users */
int
PQflush(PGconn *conn)
{
    if (!conn || conn->status == CONNECTION_BAD)
        return -1;
    return pqFlush(conn);
}
 
/*
 * pqPipelineFlush
 *
 * In pipeline mode, data will be flushed only when the out buffer reaches the
 * threshold value.  In non-pipeline mode, it behaves as stock pqFlush.
 *
 * Returns 0 on success.
 */
static int
pqPipelineFlush(PGconn *conn)
{
    if ((conn->pipelineStatus != PQ_PIPELINE_ON) ||
        (conn->outCount >= OUTBUFFER_THRESHOLD))
        return pqFlush(conn);
    return 0;
}
 
 
/*
 *      PQfreemem - safely frees memory allocated
 *
 * Needed mostly by Win32, unless multithreaded DLL (/MD in VC6)
 * Used for freeing memory from PQescapeBytea()/PQunescapeBytea()
 */
void
PQfreemem(void *ptr)
{
    free(ptr);
}
 
/*
 * PQfreeNotify - free's the memory associated with a PGnotify
 *
 * This function is here only for binary backward compatibility.
 * New code should use PQfreemem().  A macro will automatically map
 * calls to PQfreemem.  It should be removed in the future.  bjm 2003-03-24
 */
 
#undef PQfreeNotify
void        PQfreeNotify(PGnotify *notify);
 
void
PQfreeNotify(PGnotify *notify)
{
    PQfreemem(notify);
}
 
 
/*
 * Escaping arbitrary strings to get valid SQL literal strings.
 *
 * Replaces "'" with "''", and if not std_strings, replaces "\" with "\\".
 *
 * length is the length of the source string.  (Note: if a terminating NUL
 * is encountered sooner, PQescapeString stops short of "length"; the behavior
 * is thus rather like strncpy.)
 *
 * For safety the buffer at "to" must be at least 2*length + 1 bytes long.
 * A terminating NUL character is added to the output string, whether the
 * input is NUL-terminated or not.
 *
 * Returns the actual length of the output (not counting the terminating NUL).
 */
static size_t
PQescapeStringInternal(PGconn *conn,
                       char *to, const char *from, size_t length,
                       int *error,
                       int encoding, bool std_strings)
{
    const char *source = from;
    char       *target = to;
    size_t      remaining = length;
 
    if (error)
        *error = 0;
 
    while (remaining > 0 && *source != '\0')
    {
        char        c = *source;
        int         len;
        int         i;
 
        /* Fast path for plain ASCII */
        if (!IS_HIGHBIT_SET(c))
        {
            /* Apply quoting if needed */
            if (SQL_STR_DOUBLE(c, !std_strings))
                *target++ = c;
            /* Copy the character */
            *target++ = c;
            source++;
            remaining--;
            continue;
        }
 
        /* Slow path for possible multibyte characters */
        len = pg_encoding_mblen(encoding, source);
 
        /* Copy the character */
        for (i = 0; i < len; i++)
        {
            if (remaining == 0 || *source == '\0')
                break;
            *target++ = *source++;
            remaining--;
        }
 
        /*
         * If we hit premature end of string (ie, incomplete multibyte
         * character), try to pad out to the correct length with spaces. We
         * may not be able to pad completely, but we will always be able to
         * insert at least one pad space (since we'd not have quoted a
         * multibyte character).  This should be enough to make a string that
         * the server will error out on.
         */
        if (i < len)
        {
            if (error)
                *error = 1;
            if (conn)
                libpq_append_conn_error(conn, "incomplete multibyte character");
            for (; i < len; i++)
            {
                if (((size_t) (target - to)) / 2 >= length)
                    break;
                *target++ = ' ';
            }
            break;
        }
    }
 
    /* Write the terminating NUL character. */
    *target = '\0';
 
    return target - to;
}
 
size_t
PQescapeStringConn(PGconn *conn,
                   char *to, const char *from, size_t length,
                   int *error)
{
    if (!conn)
    {
        /* force empty-string result */
        *to = '\0';
        if (error)
            *error = 1;
        return 0;
    }
 
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    return PQescapeStringInternal(conn, to, from, length, error,
                                  conn->client_encoding,
                                  conn->std_strings);
}
 
size_t
PQescapeString(char *to, const char *from, size_t length)
{
    return PQescapeStringInternal(NULL, to, from, length, NULL,
                                  static_client_encoding,
                                  static_std_strings);
}
 
 
/*
 * Escape arbitrary strings.  If as_ident is true, we escape the result
 * as an identifier; if false, as a literal.  The result is returned in
 * a newly allocated buffer.  If we fail due to an encoding violation or out
 * of memory condition, we return NULL, storing an error message into conn.
 */
static char *
PQescapeInternal(PGconn *conn, const char *str, size_t len, bool as_ident)
{
    const char *s;
    char       *result;
    char       *rp;
    int         num_quotes = 0; /* single or double, depending on as_ident */
    int         num_backslashes = 0;
    int         input_len;
    int         result_size;
    char        quote_char = as_ident ? '"' : '\'';
 
    /* We must have a connection, else fail immediately. */
    if (!conn)
        return NULL;
 
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    /* Scan the string for characters that must be escaped. */
    for (s = str; (s - str) < len && *s != '\0'; ++s)
    {
        if (*s == quote_char)
            ++num_quotes;
        else if (*s == '\\')
            ++num_backslashes;
        else if (IS_HIGHBIT_SET(*s))
        {
            int         charlen;
 
            /* Slow path for possible multibyte characters */
            charlen = pg_encoding_mblen(conn->client_encoding, s);
 
            /* Multibyte character overruns allowable length. */
            if ((s - str) + charlen > len || memchr(s, 0, charlen) != NULL)
            {
                libpq_append_conn_error(conn, "incomplete multibyte character");
                return NULL;
            }
 
            /* Adjust s, bearing in mind that for loop will increment it. */
            s += charlen - 1;
        }
    }
 
    /* Allocate output buffer. */
    input_len = s - str;
    result_size = input_len + num_quotes + 3;   /* two quotes, plus a NUL */
    if (!as_ident && num_backslashes > 0)
        result_size += num_backslashes + 2;
    result = rp = (char *) malloc(result_size);
    if (rp == NULL)
    {
        libpq_append_conn_error(conn, "out of memory");
        return NULL;
    }
 
    /*
     * If we are escaping a literal that contains backslashes, we use the
     * escape string syntax so that the result is correct under either value
     * of standard_conforming_strings.  We also emit a leading space in this
     * case, to guard against the possibility that the result might be
     * interpolated immediately following an identifier.
     */
    if (!as_ident && num_backslashes > 0)
    {
        *rp++ = ' ';
        *rp++ = 'E';
    }
 
    /* Opening quote. */
    *rp++ = quote_char;
 
    /*
     * Use fast path if possible.
     *
     * We've already verified that the input string is well-formed in the
     * current encoding.  If it contains no quotes and, in the case of
     * literal-escaping, no backslashes, then we can just copy it directly to
     * the output buffer, adding the necessary quotes.
     *
     * If not, we must rescan the input and process each character
     * individually.
     */
    if (num_quotes == 0 && (num_backslashes == 0 || as_ident))
    {
        memcpy(rp, str, input_len);
        rp += input_len;
    }
    else
    {
        for (s = str; s - str < input_len; ++s)
        {
            if (*s == quote_char || (!as_ident && *s == '\\'))
            {
                *rp++ = *s;
                *rp++ = *s;
            }
            else if (!IS_HIGHBIT_SET(*s))
                *rp++ = *s;
            else
            {
                int         i = pg_encoding_mblen(conn->client_encoding, s);
 
                while (1)
                {
                    *rp++ = *s;
                    if (--i == 0)
                        break;
                    ++s;        /* for loop will provide the final increment */
                }
            }
        }
    }
 
    /* Closing quote and terminating NUL. */
    *rp++ = quote_char;
    *rp = '\0';
 
    return result;
}
 
char *
PQescapeLiteral(PGconn *conn, const char *str, size_t len)
{
    return PQescapeInternal(conn, str, len, false);
}
 
char *
PQescapeIdentifier(PGconn *conn, const char *str, size_t len)
{
    return PQescapeInternal(conn, str, len, true);
}
 
/* HEX encoding support for bytea */
static const char hextbl[] = "0123456789abcdef";
 
static const int8 hexlookup[128] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};
 
static inline char
get_hex(char c)
{
    int         res = -1;
 
    if (c > 0 && c < 127)
        res = hexlookup[(unsigned char) c];
 
    return (char) res;
}
 
 
/*
 *      PQescapeBytea   - converts from binary string to the
 *      minimal encoding necessary to include the string in an SQL
 *      INSERT statement with a bytea type column as the target.
 *
 *      We can use either hex or escape (traditional) encoding.
 *      In escape mode, the following transformations are applied:
 *      '\0' == ASCII  0 == \000
 *      '\'' == ASCII 39 == ''
 *      '\\' == ASCII 92 == \\
 *      anything < 0x20, or > 0x7e ---> \ooo
 *                                      (where ooo is an octal expression)
 *
 *      If not std_strings, all backslashes sent to the output are doubled.
 */
static unsigned char *
PQescapeByteaInternal(PGconn *conn,
                      const unsigned char *from, size_t from_length,
                      size_t *to_length, bool std_strings, bool use_hex)
{
    const unsigned char *vp;
    unsigned char *rp;
    unsigned char *result;
    size_t      i;
    size_t      len;
    size_t      bslash_len = (std_strings ? 1 : 2);
 
    /*
     * empty string has 1 char ('\0')
     */
    len = 1;
 
    if (use_hex)
    {
        len += bslash_len + 1 + 2 * from_length;
    }
    else
    {
        vp = from;
        for (i = from_length; i > 0; i--, vp++)
        {
            if (*vp < 0x20 || *vp > 0x7e)
                len += bslash_len + 3;
            else if (*vp == '\'')
                len += 2;
            else if (*vp == '\\')
                len += bslash_len + bslash_len;
            else
                len++;
        }
    }
 
    *to_length = len;
    rp = result = (unsigned char *) malloc(len);
    if (rp == NULL)
    {
        if (conn)
            libpq_append_conn_error(conn, "out of memory");
        return NULL;
    }
 
    if (use_hex)
    {
        if (!std_strings)
            *rp++ = '\\';
        *rp++ = '\\';
        *rp++ = 'x';
    }
 
    vp = from;
    for (i = from_length; i > 0; i--, vp++)
    {
        unsigned char c = *vp;
 
        if (use_hex)
        {
            *rp++ = hextbl[(c >> 4) & 0xF];
            *rp++ = hextbl[c & 0xF];
        }
        else if (c < 0x20 || c > 0x7e)
        {
            if (!std_strings)
                *rp++ = '\\';
            *rp++ = '\\';
            *rp++ = (c >> 6) + '0';
            *rp++ = ((c >> 3) & 07) + '0';
            *rp++ = (c & 07) + '0';
        }
        else if (c == '\'')
        {
            *rp++ = '\'';
            *rp++ = '\'';
        }
        else if (c == '\\')
        {
            if (!std_strings)
            {
                *rp++ = '\\';
                *rp++ = '\\';
            }
            *rp++ = '\\';
            *rp++ = '\\';
        }
        else
            *rp++ = c;
    }
    *rp = '\0';
 
    return result;
}
 
unsigned char *
PQescapeByteaConn(PGconn *conn,
                  const unsigned char *from, size_t from_length,
                  size_t *to_length)
{
    if (!conn)
        return NULL;
 
    if (conn->cmd_queue_head == NULL)
        pqClearConnErrorState(conn);
 
    return PQescapeByteaInternal(conn, from, from_length, to_length,
                                 conn->std_strings,
                                 (conn->sversion >= 90000));
}
 
unsigned char *
PQescapeBytea(const unsigned char *from, size_t from_length, size_t *to_length)
{
    return PQescapeByteaInternal(NULL, from, from_length, to_length,
                                 static_std_strings,
                                 false /* can't use hex */ );
}
 
 
#define ISFIRSTOCTDIGIT(CH) ((CH) >= '0' && (CH) <= '3')
#define ISOCTDIGIT(CH) ((CH) >= '0' && (CH) <= '7')
#define OCTVAL(CH) ((CH) - '0')
 
/*
 *      PQunescapeBytea - converts the null terminated string representation
 *      of a bytea, strtext, into binary, filling a buffer. It returns a
 *      pointer to the buffer (or NULL on error), and the size of the
 *      buffer in retbuflen. The pointer may subsequently be used as an
 *      argument to the function PQfreemem.
 *
 *      The following transformations are made:
 *      \\   == ASCII 92 == \
 *      \ooo == a byte whose value = ooo (ooo is an octal number)
 *      \x   == x (x is any character not matched by the above transformations)
 */
unsigned char *
PQunescapeBytea(const unsigned char *strtext, size_t *retbuflen)
{
    size_t      strtextlen,
                buflen;
    unsigned char *buffer,
               *tmpbuf;
    size_t      i,
                j;
 
    if (strtext == NULL)
        return NULL;
 
    strtextlen = strlen((const char *) strtext);
 
    if (strtext[0] == '\\' && strtext[1] == 'x')
    {
        const unsigned char *s;
        unsigned char *p;
 
        buflen = (strtextlen - 2) / 2;
        /* Avoid unportable malloc(0) */
        buffer = (unsigned char *) malloc(buflen > 0 ? buflen : 1);
        if (buffer == NULL)
            return NULL;
 
        s = strtext + 2;
        p = buffer;
        while (*s)
        {
            char        v1,
                        v2;
 
            /*
             * Bad input is silently ignored.  Note that this includes
             * whitespace between hex pairs, which is allowed by byteain.
             */
            v1 = get_hex(*s++);
            if (!*s || v1 == (char) -1)
                continue;
            v2 = get_hex(*s++);
            if (v2 != (char) -1)
                *p++ = (v1 << 4) | v2;
        }
 
        buflen = p - buffer;
    }
    else
    {
        /*
         * Length of input is max length of output, but add one to avoid
         * unportable malloc(0) if input is zero-length.
         */
        buffer = (unsigned char *) malloc(strtextlen + 1);
        if (buffer == NULL)
            return NULL;
 
        for (i = j = 0; i < strtextlen;)
        {
            switch (strtext[i])
            {
                case '\\':
                    i++;
                    if (strtext[i] == '\\')
                        buffer[j++] = strtext[i++];
                    else
                    {
                        if ((ISFIRSTOCTDIGIT(strtext[i])) &&
                            (ISOCTDIGIT(strtext[i + 1])) &&
                            (ISOCTDIGIT(strtext[i + 2])))
                        {
                            int         byte;
 
                            byte = OCTVAL(strtext[i++]);
                            byte = (byte << 3) + OCTVAL(strtext[i++]);
                            byte = (byte << 3) + OCTVAL(strtext[i++]);
                            buffer[j++] = byte;
                        }
                    }
 
                    /*
                     * Note: if we see '\' followed by something that isn't a
                     * recognized escape sequence, we loop around having done
                     * nothing except advance i.  Therefore the something will
                     * be emitted as ordinary data on the next cycle. Corner
                     * case: '\' at end of string will just be discarded.
                     */
                    break;
 
                default:
                    buffer[j++] = strtext[i++];
                    break;
            }
        }
        buflen = j;             /* buflen is the length of the dequoted data */
    }
 
    /* Shrink the buffer to be no larger than necessary */
    /* +1 avoids unportable behavior when buflen==0 */
    tmpbuf = realloc(buffer, buflen + 1);
 
    /* It would only be a very brain-dead realloc that could fail, but... */
    if (!tmpbuf)
    {
        free(buffer);
        return NULL;
    }
 
    *retbuflen = buflen;
    return tmpbuf;
}