fe-protocol2.c

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/*-------------------------------------------------------------------------
 *
 * fe-protocol2.c
 *    functions that are specific to frontend/backend protocol version 2
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-protocol2.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"

#include <ctype.h>
#include <fcntl.h>

#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif
#endif

#include "libpq-fe.h"
#include "libpq-int.h"
#include "port/pg_bswap.h"

static int  getRowDescriptions(PGconn *conn);
static int  getAnotherTuple(PGconn *conn, bool binary);
static int  pqGetErrorNotice2(PGconn *conn, bool isError);
static void checkXactStatus(PGconn *conn, const char *cmdTag);
static int  getNotify(PGconn *conn);


/*
 *      pqSetenvPoll
 *
 * Polls the process of passing the values of a standard set of environment
 * variables to the backend.
 */
PostgresPollingStatusType
pqSetenvPoll(PGconn *conn)
{
    PGresult   *res;

    if (conn == NULL || conn->status == CONNECTION_BAD)
        return PGRES_POLLING_FAILED;

    /* Check whether there are any data for us */
    switch (conn->setenv_state)
    {
            /* These are reading states */
        case SETENV_STATE_CLIENT_ENCODING_WAIT:
        case SETENV_STATE_OPTION_WAIT:
        case SETENV_STATE_QUERY1_WAIT:
        case SETENV_STATE_QUERY2_WAIT:
            {
                /* Load waiting data */
                int         n = pqReadData(conn);

                if (n < 0)
                    goto error_return;
                if (n == 0)
                    return PGRES_POLLING_READING;

                break;
            }

            /* These are writing states, so we just proceed. */
        case SETENV_STATE_CLIENT_ENCODING_SEND:
        case SETENV_STATE_OPTION_SEND:
        case SETENV_STATE_QUERY1_SEND:
        case SETENV_STATE_QUERY2_SEND:
            break;

            /* Should we raise an error if called when not active? */
        case SETENV_STATE_IDLE:
            return PGRES_POLLING_OK;

        default:
            appendPQExpBuffer(&conn->errorMessage,
                              libpq_gettext("invalid setenv state %c, probably indicative of memory corruption\n"),
                              conn->setenv_state);
            goto error_return;
    }

    /* We will loop here until there is nothing left to do in this call. */
    for (;;)
    {
        switch (conn->setenv_state)
        {
                /*
                 * The _CLIENT_ENCODING_SEND code is slightly different from
                 * _OPTION_SEND below (e.g., no getenv() call), which is why a
                 * different state is used.
                 */
            case SETENV_STATE_CLIENT_ENCODING_SEND:
                {
                    char        setQuery[100];  /* note length limit in
                                                 * sprintf below */
                    const char *val = conn->client_encoding_initial;

                    if (val)
                    {
                        if (pg_strcasecmp(val, "default") == 0)
                            sprintf(setQuery, "SET client_encoding = DEFAULT");
                        else
                            sprintf(setQuery, "SET client_encoding = '%.60s'",
                                    val);
#ifdef CONNECTDEBUG
                        fprintf(stderr,
                                "Sending client_encoding with %s\n",
                                setQuery);
#endif
                        if (!PQsendQuery(conn, setQuery))
                            goto error_return;

                        conn->setenv_state = SETENV_STATE_CLIENT_ENCODING_WAIT;
                    }
                    else
                        conn->setenv_state = SETENV_STATE_OPTION_SEND;
                    break;
                }

            case SETENV_STATE_OPTION_SEND:
                {
                    /*
                     * Send SET commands for stuff directed by Environment
                     * Options.  Note: we assume that SET commands won't start
                     * transaction blocks, even in a 7.3 server with
                     * autocommit off.
                     */
                    char        setQuery[100];  /* note length limit in
                                                 * sprintf below */

                    if (conn->next_eo->envName)
                    {
                        const char *val;

                        if ((val = getenv(conn->next_eo->envName)))
                        {
                            if (pg_strcasecmp(val, "default") == 0)
                                sprintf(setQuery, "SET %s = DEFAULT",
                                        conn->next_eo->pgName);
                            else
                                sprintf(setQuery, "SET %s = '%.60s'",
                                        conn->next_eo->pgName, val);
#ifdef CONNECTDEBUG
                            fprintf(stderr,
                                    "Use environment variable %s to send %s\n",
                                    conn->next_eo->envName, setQuery);
#endif
                            if (!PQsendQuery(conn, setQuery))
                                goto error_return;

                            conn->setenv_state = SETENV_STATE_OPTION_WAIT;
                        }
                        else
                            conn->next_eo++;
                    }
                    else
                    {
                        /* No more options to send, so move on to querying */
                        conn->setenv_state = SETENV_STATE_QUERY1_SEND;
                    }
                    break;
                }

            case SETENV_STATE_CLIENT_ENCODING_WAIT:
                {
                    if (PQisBusy(conn))
                        return PGRES_POLLING_READING;

                    res = PQgetResult(conn);

                    if (res)
                    {
                        if (PQresultStatus(res) != PGRES_COMMAND_OK)
                        {
                            PQclear(res);
                            goto error_return;
                        }
                        PQclear(res);
                        /* Keep reading until PQgetResult returns NULL */
                    }
                    else
                    {
                        /* Query finished, so send the next option */
                        conn->setenv_state = SETENV_STATE_OPTION_SEND;
                    }
                    break;
                }

            case SETENV_STATE_OPTION_WAIT:
                {
                    if (PQisBusy(conn))
                        return PGRES_POLLING_READING;

                    res = PQgetResult(conn);

                    if (res)
                    {
                        if (PQresultStatus(res) != PGRES_COMMAND_OK)
                        {
                            PQclear(res);
                            goto error_return;
                        }
                        PQclear(res);
                        /* Keep reading until PQgetResult returns NULL */
                    }
                    else
                    {
                        /* Query finished, so send the next option */
                        conn->next_eo++;
                        conn->setenv_state = SETENV_STATE_OPTION_SEND;
                    }
                    break;
                }

            case SETENV_STATE_QUERY1_SEND:
                {
                    /*
                     * Issue query to get information we need.  Here we must
                     * use begin/commit in case autocommit is off by default
                     * in a 7.3 server.
                     *
                     * Note: version() exists in all protocol-2.0-supporting
                     * backends.  In 7.3 it would be safer to write
                     * pg_catalog.version(), but we can't do that without
                     * causing problems on older versions.
                     */
                    if (!PQsendQuery(conn, "begin; select version(); end"))
                        goto error_return;

                    conn->setenv_state = SETENV_STATE_QUERY1_WAIT;
                    return PGRES_POLLING_READING;
                }

            case SETENV_STATE_QUERY1_WAIT:
                {
                    if (PQisBusy(conn))
                        return PGRES_POLLING_READING;

                    res = PQgetResult(conn);

                    if (res)
                    {
                        char       *val;

                        if (PQresultStatus(res) == PGRES_COMMAND_OK)
                        {
                            /* ignore begin/commit command results */
                            PQclear(res);
                            continue;
                        }

                        if (PQresultStatus(res) != PGRES_TUPLES_OK ||
                            PQntuples(res) != 1)
                        {
                            PQclear(res);
                            goto error_return;
                        }

                        /*
                         * Extract server version and save as if
                         * ParameterStatus
                         */
                        val = PQgetvalue(res, 0, 0);
                        if (val && strncmp(val, "PostgreSQL ", 11) == 0)
                        {
                            char       *ptr;

                            /* strip off PostgreSQL part */
                            val += 11;

                            /*
                             * strip off platform part (scribbles on result,
                             * naughty naughty)
                             */
                            ptr = strchr(val, ' ');
                            if (ptr)
                                *ptr = '\0';

                            pqSaveParameterStatus(conn, "server_version",
                                                  val);
                        }

                        PQclear(res);
                        /* Keep reading until PQgetResult returns NULL */
                    }
                    else
                    {
                        /* Query finished, move to next */
                        conn->setenv_state = SETENV_STATE_QUERY2_SEND;
                    }
                    break;
                }

            case SETENV_STATE_QUERY2_SEND:
                {
                    const char *query;

                    /*
                     * pg_client_encoding does not exist in pre-7.2 servers.
                     * So we need to be prepared for an error here.  Do *not*
                     * start a transaction block, except in 7.3 servers where
                     * we need to prevent autocommit-off from starting a
                     * transaction anyway.
                     */
                    if (conn->sversion >= 70300 &&
                        conn->sversion < 70400)
                        query = "begin; select pg_catalog.pg_client_encoding(); end";
                    else
                        query = "select pg_client_encoding()";
                    if (!PQsendQuery(conn, query))
                        goto error_return;

                    conn->setenv_state = SETENV_STATE_QUERY2_WAIT;
                    return PGRES_POLLING_READING;
                }

            case SETENV_STATE_QUERY2_WAIT:
                {
                    if (PQisBusy(conn))
                        return PGRES_POLLING_READING;

                    res = PQgetResult(conn);

                    if (res)
                    {
                        const char *val;

                        if (PQresultStatus(res) == PGRES_COMMAND_OK)
                        {
                            /* ignore begin/commit command results */
                            PQclear(res);
                            continue;
                        }

                        if (PQresultStatus(res) == PGRES_TUPLES_OK &&
                            PQntuples(res) == 1)
                        {
                            /* Extract client encoding and save it */
                            val = PQgetvalue(res, 0, 0);
                            if (val && *val)    /* null should not happen, but */
                                pqSaveParameterStatus(conn, "client_encoding",
                                                      val);
                        }
                        else
                        {
                            /*
                             * Error: presumably function not available, so
                             * use PGCLIENTENCODING or SQL_ASCII as the
                             * fallback.
                             */
                            val = getenv("PGCLIENTENCODING");
                            if (val && *val)
                                pqSaveParameterStatus(conn, "client_encoding",
                                                      val);
                            else
                                pqSaveParameterStatus(conn, "client_encoding",
                                                      "SQL_ASCII");
                        }

                        PQclear(res);
                        /* Keep reading until PQgetResult returns NULL */
                    }
                    else
                    {
                        /* Query finished, so we're done */
                        conn->setenv_state = SETENV_STATE_IDLE;
                        return PGRES_POLLING_OK;
                    }
                    break;
                }

            default:
                appendPQExpBuffer(&conn->errorMessage,
                                  libpq_gettext("invalid state %c, "
                                                "probably indicative of memory corruption\n"),
                                  conn->setenv_state);
                goto error_return;
        }
    }

    /* Unreachable */

error_return:
    conn->setenv_state = SETENV_STATE_IDLE;
    return PGRES_POLLING_FAILED;
}


/*
 * 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.
 */
void
pqParseInput2(PGconn *conn)
{
    char        id;

    /*
     * Loop to parse successive complete messages available in the buffer.
     */
    for (;;)
    {
        /*
         * Quit if in COPY_OUT state: we expect raw data from the server until
         * PQendcopy is called.  Don't try to parse it according to the normal
         * protocol.  (This is bogus.  The data lines ought to be part of the
         * protocol and have identifying leading characters.)
         */
        if (conn->asyncStatus == PGASYNC_COPY_OUT)
            return;

        /*
         * OK to try to read a message type code.
         */
        conn->inCursor = conn->inStart;
        if (pqGetc(&id, conn))
            return;

        /*
         * NOTIFY and NOTICE messages can happen in any state besides COPY
         * OUT; always process them right away.
         *
         * Most other messages should only be processed while in BUSY state.
         * (In particular, in READY state we hold off further parsing until
         * the application collects the current PGresult.)
         *
         * However, if the state is IDLE then we got trouble; we need to deal
         * with the unexpected message somehow.
         */
        if (id == 'A')
        {
            if (getNotify(conn))
                return;
        }
        else if (id == 'N')
        {
            if (pqGetErrorNotice2(conn, false))
                return;
        }
        else if (conn->asyncStatus != PGASYNC_BUSY)
        {
            /* If not IDLE state, just wait ... */
            if (conn->asyncStatus != PGASYNC_IDLE)
                return;

            /*
             * Unexpected message in IDLE state; need to recover somehow.
             * ERROR messages are displayed using the notice processor;
             * anything else is just dropped on the floor after displaying a
             * suitable warning notice.  (An ERROR is very possibly the
             * backend telling us why it is about to close the connection, so
             * we don't want to just discard it...)
             */
            if (id == 'E')
            {
                if (pqGetErrorNotice2(conn, false /* treat as notice */ ))
                    return;
            }
            else
            {
                pqInternalNotice(&conn->noticeHooks,
                                 "message type 0x%02x arrived from server while idle",
                                 id);
                /* Discard the unexpected message; good idea?? */
                conn->inStart = conn->inEnd;
                break;
            }
        }
        else
        {
            /*
             * In BUSY state, we can process everything.
             */
            switch (id)
            {
                case 'C':       /* command complete */
                    if (pqGets(&conn->workBuffer, conn))
                        return;
                    if (conn->result == NULL)
                    {
                        conn->result = PQmakeEmptyPGresult(conn,
                                                           PGRES_COMMAND_OK);
                        if (!conn->result)
                        {
                            appendPQExpBufferStr(&conn->errorMessage,
                                                 libpq_gettext("out of memory"));
                            pqSaveErrorResult(conn);
                        }
                    }
                    if (conn->result)
                    {
                        strlcpy(conn->result->cmdStatus, conn->workBuffer.data,
                                CMDSTATUS_LEN);
                    }
                    checkXactStatus(conn, conn->workBuffer.data);
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case 'E':       /* error return */
                    if (pqGetErrorNotice2(conn, true))
                        return;
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case 'Z':       /* backend is ready for new query */
                    conn->asyncStatus = PGASYNC_IDLE;
                    break;
                case 'I':       /* empty query */
                    /* read and throw away the closing '\0' */
                    if (pqGetc(&id, conn))
                        return;
                    if (id != '\0')
                        pqInternalNotice(&conn->noticeHooks,
                                         "unexpected character %c following empty query response (\"I\" message)",
                                         id);
                    if (conn->result == NULL)
                    {
                        conn->result = PQmakeEmptyPGresult(conn,
                                                           PGRES_EMPTY_QUERY);
                        if (!conn->result)
                        {
                            appendPQExpBufferStr(&conn->errorMessage,
                                                 libpq_gettext("out of memory"));
                            pqSaveErrorResult(conn);
                        }
                    }
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case 'K':       /* secret key data from the backend */

                    /*
                     * This is expected only during backend startup, but it's
                     * just as easy to handle it as part of the main loop.
                     * Save the data and continue processing.
                     */
                    if (pqGetInt(&(conn->be_pid), 4, conn))
                        return;
                    if (pqGetInt(&(conn->be_key), 4, conn))
                        return;
                    break;
                case 'P':       /* synchronous (normal) portal */
                    if (pqGets(&conn->workBuffer, conn))
                        return;
                    /* We pretty much ignore this message type... */
                    break;
                case 'T':       /* row descriptions (start of query results) */
                    if (conn->result == NULL)
                    {
                        /* First 'T' in a query sequence */
                        if (getRowDescriptions(conn))
                            return;
                        /* getRowDescriptions() moves inStart itself */
                        continue;
                    }
                    else
                    {
                        /*
                         * A new 'T' message is treated as the start of
                         * another PGresult.  (It is not clear that this is
                         * really possible with the current backend.) We stop
                         * parsing until the application accepts the current
                         * result.
                         */
                        conn->asyncStatus = PGASYNC_READY;
                        return;
                    }
                    break;
                case 'D':       /* ASCII data tuple */
                    if (conn->result != NULL)
                    {
                        /* Read another tuple of a normal query response */
                        if (getAnotherTuple(conn, false))
                            return;
                        /* getAnotherTuple() moves inStart itself */
                        continue;
                    }
                    else
                    {
                        pqInternalNotice(&conn->noticeHooks,
                                         "server sent data (\"D\" message) without prior row description (\"T\" message)");
                        /* Discard the unexpected message; good idea?? */
                        conn->inStart = conn->inEnd;
                        return;
                    }
                    break;
                case 'B':       /* Binary data tuple */
                    if (conn->result != NULL)
                    {
                        /* Read another tuple of a normal query response */
                        if (getAnotherTuple(conn, true))
                            return;
                        /* getAnotherTuple() moves inStart itself */
                        continue;
                    }
                    else
                    {
                        pqInternalNotice(&conn->noticeHooks,
                                         "server sent binary data (\"B\" message) without prior row description (\"T\" message)");
                        /* Discard the unexpected message; good idea?? */
                        conn->inStart = conn->inEnd;
                        return;
                    }
                    break;
                case 'G':       /* Start Copy In */
                    conn->asyncStatus = PGASYNC_COPY_IN;
                    break;
                case 'H':       /* Start Copy Out */
                    conn->asyncStatus = PGASYNC_COPY_OUT;
                    break;

                    /*
                     * Don't need to process CopyBothResponse here because it
                     * never arrives from the server during protocol 2.0.
                     */
                default:
                    appendPQExpBuffer(&conn->errorMessage,
                                      libpq_gettext("unexpected response from server; first received character was \"%c\"\n"),
                                      id);
                    /* build an error result holding the error message */
                    pqSaveErrorResult(conn);
                    /* Discard the unexpected message; good idea?? */
                    conn->inStart = conn->inEnd;
                    conn->asyncStatus = PGASYNC_READY;
                    return;
            }                   /* switch on protocol character */
        }
        /* Successfully consumed this message */
        conn->inStart = conn->inCursor;
    }
}

/*
 * parseInput subroutine to read a 'T' (row descriptions) message.
 * We build a PGresult structure containing the attribute data.
 * Returns: 0 if completed message, EOF if error or not enough data
 * received yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  Otherwise, conn->inStart
 * must get advanced past the processed data.
 */
static int
getRowDescriptions(PGconn *conn)
{
    PGresult   *result;
    int         nfields;
    const char *errmsg;
    int         i;

    result = PQmakeEmptyPGresult(conn, PGRES_TUPLES_OK);
    if (!result)
    {
        errmsg = NULL;          /* means "out of memory", see below */
        goto advance_and_error;
    }

    /* parseInput already read the 'T' label. */
    /* the next two bytes are the number of fields  */
    if (pqGetInt(&(result->numAttributes), 2, conn))
        goto EOFexit;
    nfields = result->numAttributes;

    /* allocate space for the attribute descriptors */
    if (nfields > 0)
    {
        result->attDescs = (PGresAttDesc *)
            pqResultAlloc(result, nfields * sizeof(PGresAttDesc), true);
        if (!result->attDescs)
        {
            errmsg = NULL;      /* means "out of memory", see below */
            goto advance_and_error;
        }
        MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
    }

    /* get type info */
    for (i = 0; i < nfields; i++)
    {
        int         typid;
        int         typlen;
        int         atttypmod;

        if (pqGets(&conn->workBuffer, conn) ||
            pqGetInt(&typid, 4, conn) ||
            pqGetInt(&typlen, 2, conn) ||
            pqGetInt(&atttypmod, 4, conn))
            goto EOFexit;

        /*
         * Since pqGetInt treats 2-byte integers as unsigned, we need to
         * coerce the result to signed form.
         */
        typlen = (int) ((int16) typlen);

        result->attDescs[i].name = pqResultStrdup(result,
                                                  conn->workBuffer.data);
        if (!result->attDescs[i].name)
        {
            errmsg = NULL;      /* means "out of memory", see below */
            goto advance_and_error;
        }
        result->attDescs[i].tableid = 0;
        result->attDescs[i].columnid = 0;
        result->attDescs[i].format = 0;
        result->attDescs[i].typid = typid;
        result->attDescs[i].typlen = typlen;
        result->attDescs[i].atttypmod = atttypmod;
    }

    /* Success! */
    conn->result = result;

    /* Advance inStart to show that the "T" message has been processed. */
    conn->inStart = conn->inCursor;

    /*
     * We could perform additional setup for the new result set here, but for
     * now there's nothing else to do.
     */

    /* And we're done. */
    return 0;

advance_and_error:

    /*
     * Discard the failed message.  Unfortunately we don't know for sure where
     * the end is, so just throw away everything in the input buffer. This is
     * not very desirable but it's the best we can do in protocol v2.
     */
    conn->inStart = conn->inEnd;

    /*
     * Replace partially constructed result with an error result. First
     * discard the old result to try to win back some memory.
     */
    pqClearAsyncResult(conn);

    /*
     * If preceding code didn't provide an error message, assume "out of
     * memory" was meant.  The advantage of having this special case is that
     * freeing the old result first greatly improves the odds that gettext()
     * will succeed in providing a translation.
     */
    if (!errmsg)
        errmsg = libpq_gettext("out of memory for query result");

    appendPQExpBuffer(&conn->errorMessage, "%s\n", errmsg);

    /*
     * XXX: if PQmakeEmptyPGresult() fails, there's probably not much we can
     * do to recover...
     */
    conn->result = PQmakeEmptyPGresult(conn, PGRES_FATAL_ERROR);
    conn->asyncStatus = PGASYNC_READY;

EOFexit:
    if (result && result != conn->result)
        PQclear(result);
    return EOF;
}

/*
 * parseInput subroutine to read a 'B' or 'D' (row data) message.
 * We fill rowbuf with column pointers and then call the row processor.
 * Returns: 0 if completed message, EOF if error or not enough data
 * received yet.
 *
 * Note that if we run out of data, we have to suspend and reprocess
 * the message after more data is received.  Otherwise, conn->inStart
 * must get advanced past the processed data.
 */
static int
getAnotherTuple(PGconn *conn, bool binary)
{
    PGresult   *result = conn->result;
    int         nfields = result->numAttributes;
    const char *errmsg;
    PGdataValue *rowbuf;

    /* the backend sends us a bitmap of which attributes are null */
    char        std_bitmap[64]; /* used unless it doesn't fit */
    char       *bitmap = std_bitmap;
    int         i;
    size_t      nbytes;         /* the number of bytes in bitmap  */
    char        bmap;           /* One byte of the bitmap */
    int         bitmap_index;   /* Its index */
    int         bitcnt;         /* number of bits examined in current byte */
    int         vlen;           /* length of the current field value */

    /* Resize row buffer if needed */
    rowbuf = conn->rowBuf;
    if (nfields > conn->rowBufLen)
    {
        rowbuf = (PGdataValue *) realloc(rowbuf,
                                         nfields * sizeof(PGdataValue));
        if (!rowbuf)
        {
            errmsg = NULL;      /* means "out of memory", see below */
            goto advance_and_error;
        }
        conn->rowBuf = rowbuf;
        conn->rowBufLen = nfields;
    }

    /* Save format specifier */
    result->binary = binary;

    /*
     * If it's binary, fix the column format indicators.  We assume the
     * backend will consistently send either B or D, not a mix.
     */
    if (binary)
    {
        for (i = 0; i < nfields; i++)
            result->attDescs[i].format = 1;
    }

    /* Get the null-value bitmap */
    nbytes = (nfields + BITS_PER_BYTE - 1) / BITS_PER_BYTE;
    /* malloc() only for unusually large field counts... */
    if (nbytes > sizeof(std_bitmap))
    {
        bitmap = (char *) malloc(nbytes);
        if (!bitmap)
        {
            errmsg = NULL;      /* means "out of memory", see below */
            goto advance_and_error;
        }
    }

    if (pqGetnchar(bitmap, nbytes, conn))
        goto EOFexit;

    /* Scan the fields */
    bitmap_index = 0;
    bmap = bitmap[bitmap_index];
    bitcnt = 0;

    for (i = 0; i < nfields; i++)
    {
        /* get the value length */
        if (!(bmap & 0200))
            vlen = NULL_LEN;
        else if (pqGetInt(&vlen, 4, conn))
            goto EOFexit;
        else
        {
            if (!binary)
                vlen = vlen - 4;
            if (vlen < 0)
                vlen = 0;
        }
        rowbuf[i].len = vlen;

        /*
         * rowbuf[i].value always points to the next address in the data
         * buffer even if the value is NULL.  This allows row processors to
         * estimate data sizes more easily.
         */
        rowbuf[i].value = conn->inBuffer + conn->inCursor;

        /* Skip over the data value */
        if (vlen > 0)
        {
            if (pqSkipnchar(vlen, conn))
                goto EOFexit;
        }

        /* advance the bitmap stuff */
        bitcnt++;
        if (bitcnt == BITS_PER_BYTE)
        {
            bitmap_index++;
            bmap = bitmap[bitmap_index];
            bitcnt = 0;
        }
        else
            bmap <<= 1;
    }

    /* Release bitmap now if we allocated it */
    if (bitmap != std_bitmap)
        free(bitmap);
    bitmap = NULL;

    /* Advance inStart to show that the "D" message has been processed. */
    conn->inStart = conn->inCursor;

    /* Process the collected row */
    errmsg = NULL;
    if (pqRowProcessor(conn, &errmsg))
        return 0;               /* normal, successful exit */

    goto set_error_result;      /* pqRowProcessor failed, report it */

advance_and_error:

    /*
     * Discard the failed message.  Unfortunately we don't know for sure where
     * the end is, so just throw away everything in the input buffer. This is
     * not very desirable but it's the best we can do in protocol v2.
     */
    conn->inStart = conn->inEnd;

set_error_result:

    /*
     * Replace partially constructed result with an error result. First
     * discard the old result to try to win back some memory.
     */
    pqClearAsyncResult(conn);

    /*
     * If preceding code didn't provide an error message, assume "out of
     * memory" was meant.  The advantage of having this special case is that
     * freeing the old result first greatly improves the odds that gettext()
     * will succeed in providing a translation.
     */
    if (!errmsg)
        errmsg = libpq_gettext("out of memory for query result");

    appendPQExpBuffer(&conn->errorMessage, "%s\n", errmsg);

    /*
     * XXX: if PQmakeEmptyPGresult() fails, there's probably not much we can
     * do to recover...
     */
    conn->result = PQmakeEmptyPGresult(conn, PGRES_FATAL_ERROR);
    conn->asyncStatus = PGASYNC_READY;

EOFexit:
    if (bitmap != NULL && bitmap != std_bitmap)
        free(bitmap);
    return EOF;
}


/*
 * Attempt to read an Error or Notice response message.
 * This is possible in several places, so we break it out as a subroutine.
 * Entry: 'E' or 'N' message type has already been consumed.
 * Exit: returns 0 if successfully consumed message.
 *       returns EOF if not enough data.
 */
static int
pqGetErrorNotice2(PGconn *conn, bool isError)
{
    PGresult   *res = NULL;
    PQExpBufferData workBuf;
    char       *startp;
    char       *splitp;

    /*
     * If this is an error message, pre-emptively clear any incomplete query
     * result we may have.  We'd just throw it away below anyway, and
     * releasing it before collecting the error might avoid out-of-memory.
     */
    if (isError)
        pqClearAsyncResult(conn);

    /*
     * Since the message might be pretty long, we create a temporary
     * PQExpBuffer rather than using conn->workBuffer.  workBuffer is intended
     * for stuff that is expected to be short.
     */
    initPQExpBuffer(&workBuf);
    if (pqGets(&workBuf, conn))
        goto failure;

    /*
     * Make a PGresult to hold the message.  We temporarily lie about the
     * result status, so that PQmakeEmptyPGresult doesn't uselessly copy
     * conn->errorMessage.
     *
     * NB: This allocation can fail, if you run out of memory. The rest of the
     * function handles that gracefully, and we still try to set the error
     * message as the connection's error message.
     */
    res = PQmakeEmptyPGresult(conn, PGRES_EMPTY_QUERY);
    if (res)
    {
        res->resultStatus = isError ? PGRES_FATAL_ERROR : PGRES_NONFATAL_ERROR;
        res->errMsg = pqResultStrdup(res, workBuf.data);
    }

    /*
     * Break the message into fields.  We can't do very much here, but we can
     * split the severity code off, and remove trailing newlines. Also, we use
     * the heuristic that the primary message extends only to the first
     * newline --- anything after that is detail message.  (In some cases it'd
     * be better classed as hint, but we can hardly be expected to guess that
     * here.)
     */
    while (workBuf.len > 0 && workBuf.data[workBuf.len - 1] == '\n')
        workBuf.data[--workBuf.len] = '\0';
    splitp = strstr(workBuf.data, ":  ");
    if (splitp)
    {
        /* what comes before the colon is severity */
        *splitp = '\0';
        pqSaveMessageField(res, PG_DIAG_SEVERITY, workBuf.data);
        startp = splitp + 3;
    }
    else
    {
        /* can't find a colon?  oh well... */
        startp = workBuf.data;
    }
    splitp = strchr(startp, '\n');
    if (splitp)
    {
        /* what comes before the newline is primary message */
        *splitp++ = '\0';
        pqSaveMessageField(res, PG_DIAG_MESSAGE_PRIMARY, startp);
        /* the rest is detail; strip any leading whitespace */
        while (*splitp && isspace((unsigned char) *splitp))
            splitp++;
        pqSaveMessageField(res, PG_DIAG_MESSAGE_DETAIL, splitp);
    }
    else
    {
        /* single-line message, so all primary */
        pqSaveMessageField(res, PG_DIAG_MESSAGE_PRIMARY, startp);
    }

    /*
     * Either save error as current async result, or just emit the notice.
     * Also, if it's an error and we were in a transaction block, assume the
     * server has now gone to error-in-transaction state.
     */
    if (isError)
    {
        pqClearAsyncResult(conn);   /* redundant, but be safe */
        conn->result = res;
        if (res && !PQExpBufferDataBroken(workBuf) && res->errMsg)
            appendPQExpBufferStr(&conn->errorMessage, res->errMsg);
        else
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("out of memory"));
        if (conn->xactStatus == PQTRANS_INTRANS)
            conn->xactStatus = PQTRANS_INERROR;
    }
    else
    {
        if (res)
        {
            if (res->noticeHooks.noticeRec != NULL)
                res->noticeHooks.noticeRec(res->noticeHooks.noticeRecArg, res);
            PQclear(res);
        }
    }

    termPQExpBuffer(&workBuf);
    return 0;

failure:
    if (res)
        PQclear(res);
    termPQExpBuffer(&workBuf);
    return EOF;
}

/*
 * checkXactStatus - attempt to track transaction-block status of server
 *
 * This is called each time we receive a command-complete message.  By
 * watching for messages from BEGIN/COMMIT/ROLLBACK commands, we can do
 * a passable job of tracking the server's xact status.  BUT: this does
 * not work at all on 7.3 servers with AUTOCOMMIT OFF.  (Man, was that
 * feature ever a mistake.)  Caveat user.
 *
 * The tags known here are all those used as far back as 7.0; is it worth
 * adding those from even-older servers?
 */
static void
checkXactStatus(PGconn *conn, const char *cmdTag)
{
    if (strcmp(cmdTag, "BEGIN") == 0)
        conn->xactStatus = PQTRANS_INTRANS;
    else if (strcmp(cmdTag, "COMMIT") == 0)
        conn->xactStatus = PQTRANS_IDLE;
    else if (strcmp(cmdTag, "ROLLBACK") == 0)
        conn->xactStatus = PQTRANS_IDLE;
    else if (strcmp(cmdTag, "START TRANSACTION") == 0)  /* 7.3 only */
        conn->xactStatus = PQTRANS_INTRANS;

    /*
     * Normally we get into INERROR state by detecting an Error message.
     * However, if we see one of these tags then we know for sure the server
     * is in abort state ...
     */
    else if (strcmp(cmdTag, "*ABORT STATE*") == 0)  /* pre-7.3 only */
        conn->xactStatus = PQTRANS_INERROR;
}

/*
 * Attempt to read a Notify response message.
 * This is possible in several places, so we break it out as a subroutine.
 * Entry: 'A' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed Notify message.
 *       returns EOF if not enough data.
 */
static int
getNotify(PGconn *conn)
{
    int         be_pid;
    int         nmlen;
    PGnotify   *newNotify;

    if (pqGetInt(&be_pid, 4, conn))
        return EOF;
    if (pqGets(&conn->workBuffer, conn))
        return EOF;

    /*
     * Store the relation name right after the PQnotify structure so it can
     * all be freed at once.  We don't use NAMEDATALEN because we don't want
     * to tie this interface to a specific server name length.
     */
    nmlen = strlen(conn->workBuffer.data);
    newNotify = (PGnotify *) malloc(sizeof(PGnotify) + nmlen + 1);
    if (newNotify)
    {
        newNotify->relname = (char *) newNotify + sizeof(PGnotify);
        strcpy(newNotify->relname, conn->workBuffer.data);
        /* fake up an empty-string extra field */
        newNotify->extra = newNotify->relname + nmlen;
        newNotify->be_pid = be_pid;
        newNotify->next = NULL;
        if (conn->notifyTail)
            conn->notifyTail->next = newNotify;
        else
            conn->notifyHead = newNotify;
        conn->notifyTail = newNotify;
    }

    return 0;
}


/*
 * PQgetCopyData - read a row of data from the backend during COPY OUT
 *
 * 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
pqGetCopyData2(PGconn *conn, char **buffer, int async)
{
    bool        found;
    int         msgLength;

    for (;;)
    {
        /*
         * Do we have a complete line of data?
         */
        conn->inCursor = conn->inStart;
        found = false;
        while (conn->inCursor < conn->inEnd)
        {
            char        c = conn->inBuffer[conn->inCursor++];

            if (c == '\n')
            {
                found = true;
                break;
            }
        }
        if (!found)
            goto nodata;
        msgLength = conn->inCursor - conn->inStart;

        /*
         * If it's the end-of-data marker, consume it, exit COPY_OUT mode, and
         * let caller read status with PQgetResult().
         */
        if (msgLength == 3 &&
            strncmp(&conn->inBuffer[conn->inStart], "\\.\n", 3) == 0)
        {
            conn->inStart = conn->inCursor;
            conn->asyncStatus = PGASYNC_BUSY;
            return -1;
        }

        /*
         * Pass the line back to the caller.
         */
        *buffer = (char *) malloc(msgLength + 1);
        if (*buffer == NULL)
        {
            appendPQExpBufferStr(&conn->errorMessage,
                                 libpq_gettext("out of memory\n"));
            return -2;
        }
        memcpy(*buffer, &conn->inBuffer[conn->inStart], msgLength);
        (*buffer)[msgLength] = '\0';    /* Add terminating null */

        /* Mark message consumed */
        conn->inStart = conn->inCursor;

        return msgLength;

nodata:
        /* Don't block if async read requested */
        if (async)
            return 0;
        /* Need to load more data */
        if (pqWait(true, false, conn) ||
            pqReadData(conn) < 0)
            return -2;
    }
}


/*
 * PQgetline - gets a newline-terminated string from the backend.
 *
 * See fe-exec.c for documentation.
 */
int
pqGetline2(PGconn *conn, char *s, int maxlen)
{
    int         result = 1;     /* return value if buffer overflows */

    if (conn->sock == PGINVALID_SOCKET ||
        conn->asyncStatus != PGASYNC_COPY_OUT)
    {
        *s = '\0';
        return EOF;
    }

    /*
     * Since this is a purely synchronous routine, we don't bother to maintain
     * conn->inCursor; there is no need to back up.
     */
    while (maxlen > 1)
    {
        if (conn->inStart < conn->inEnd)
        {
            char        c = conn->inBuffer[conn->inStart++];

            if (c == '\n')
            {
                result = 0;     /* success exit */
                break;
            }
            *s++ = c;
            maxlen--;
        }
        else
        {
            /* need to load more data */
            if (pqWait(true, false, conn) ||
                pqReadData(conn) < 0)
            {
                result = EOF;
                break;
            }
        }
    }
    *s = '\0';

    return result;
}

/*
 * PQgetlineAsync - gets a COPY data row without blocking.
 *
 * See fe-exec.c for documentation.
 */
int
pqGetlineAsync2(PGconn *conn, char *buffer, int bufsize)
{
    int         avail;

    if (conn->asyncStatus != PGASYNC_COPY_OUT)
        return -1;              /* we are not doing a copy... */

    /*
     * Move data from libpq's buffer to the caller's. We want to accept data
     * only in units of whole lines, not partial lines.  This ensures that we
     * can recognize the terminator line "\\.\n".  (Otherwise, if it happened
     * to cross a packet/buffer boundary, we might hand the first one or two
     * characters off to the caller, which we shouldn't.)
     */

    conn->inCursor = conn->inStart;

    avail = bufsize;
    while (avail > 0 && conn->inCursor < conn->inEnd)
    {
        char        c = conn->inBuffer[conn->inCursor++];

        *buffer++ = c;
        --avail;
        if (c == '\n')
        {
            /* Got a complete line; mark the data removed from libpq */
            conn->inStart = conn->inCursor;
            /* Is it the endmarker line? */
            if (bufsize - avail == 3 && buffer[-3] == '\\' && buffer[-2] == '.')
                return -1;
            /* No, return the data line to the caller */
            return bufsize - avail;
        }
    }

    /*
     * We don't have a complete line. We'd prefer to leave it in libpq's
     * buffer until the rest arrives, but there is a special case: what if the
     * line is longer than the buffer the caller is offering us?  In that case
     * we'd better hand over a partial line, else we'd get into an infinite
     * loop. Do this in a way that ensures we can't misrecognize a terminator
     * line later: leave last 3 characters in libpq buffer.
     */
    if (avail == 0 && bufsize > 3)
    {
        conn->inStart = conn->inCursor - 3;
        return bufsize - 3;
    }
    return 0;
}

/*
 * PQendcopy
 *
 * See fe-exec.c for documentation.
 */
int
pqEndcopy2(PGconn *conn)
{
    PGresult   *result;

    if (conn->asyncStatus != PGASYNC_COPY_IN &&
        conn->asyncStatus != PGASYNC_COPY_OUT)
    {
        appendPQExpBufferStr(&conn->errorMessage,
                             libpq_gettext("no COPY in progress\n"));
        return 1;
    }

    /*
     * make sure no data is waiting to be sent, abort if we are non-blocking
     * and the flush fails
     */
    if (pqFlush(conn) && pqIsnonblocking(conn))
        return 1;

    /* non blocking connections may have to abort at this point. */
    if (pqIsnonblocking(conn) && PQisBusy(conn))
        return 1;

    /* Return to active duty */
    conn->asyncStatus = PGASYNC_BUSY;

    /* Wait for the completion response */
    result = PQgetResult(conn);

    /* Expecting a successful result */
    if (result && result->resultStatus == PGRES_COMMAND_OK)
    {
        PQclear(result);
        return 0;
    }

    /*
     * Trouble. For backwards-compatibility reasons, we issue the error
     * message as if it were a notice (would be nice to get rid of this
     * silliness, but too many apps probably don't handle errors from
     * PQendcopy reasonably).  Note that the app can still obtain the error
     * status from the PGconn object.
     */
    if (conn->errorMessage.len > 0)
    {
        /* We have to strip the trailing newline ... pain in neck... */
        char        svLast = conn->errorMessage.data[conn->errorMessage.len - 1];

        if (svLast == '\n')
            conn->errorMessage.data[conn->errorMessage.len - 1] = '\0';
        pqInternalNotice(&conn->noticeHooks, "%s", conn->errorMessage.data);
        conn->errorMessage.data[conn->errorMessage.len - 1] = svLast;
    }

    PQclear(result);

    /*
     * The worst case is that we've lost sync with the backend entirely due to
     * application screwup of the copy in/out protocol. To recover, reset the
     * connection (talk about using a sledgehammer...)
     */
    pqInternalNotice(&conn->noticeHooks,
                     "lost synchronization with server, resetting connection");

    /*
     * Users doing non-blocking connections need to handle the reset
     * themselves, they'll need to check the connection status if we return an
     * error.
     */
    if (pqIsnonblocking(conn))
        PQresetStart(conn);
    else
        PQreset(conn);

    return 1;
}


/*
 * PQfn - Send a function call to the POSTGRES backend.
 *
 * See fe-exec.c for documentation.
 */
PGresult *
pqFunctionCall2(PGconn *conn, Oid fnid,
                int *result_buf, int *actual_result_len,
                int result_is_int,
                const PQArgBlock *args, int nargs)
{
    bool        needInput = false;
    ExecStatusType status = PGRES_FATAL_ERROR;
    char        id;
    int         i;

    /* PQfn already validated connection state */

    if (pqPutMsgStart('F', false, conn) < 0 ||  /* function call msg */
        pqPuts(" ", conn) < 0 ||    /* dummy string */
        pqPutInt(fnid, 4, conn) != 0 || /* function id */
        pqPutInt(nargs, 4, conn) != 0)  /* # of args */
    {
        /* error message should be set up already */
        return NULL;
    }

    for (i = 0; i < nargs; ++i)
    {                           /* len.int4 + contents     */
        if (pqPutInt(args[i].len, 4, conn))
            return NULL;

        if (args[i].isint)
        {
            if (pqPutInt(args[i].u.integer, 4, conn))
                return NULL;
        }
        else
        {
            if (pqPutnchar((char *) args[i].u.ptr, args[i].len, conn))
                return NULL;
        }
    }

    if (pqPutMsgEnd(conn) < 0 ||
        pqFlush(conn))
        return NULL;

    for (;;)
    {
        if (needInput)
        {
            /* Wait for some data to arrive (or for the channel to close) */
            if (pqWait(true, false, conn) ||
                pqReadData(conn) < 0)
                break;
        }

        /*
         * Scan the message. If we run out of data, loop around to try again.
         */
        conn->inCursor = conn->inStart;
        needInput = true;

        if (pqGetc(&id, conn))
            continue;

        /*
         * We should see V or E response to the command, but might get N
         * and/or A notices first. We also need to swallow the final Z before
         * returning.
         */
        switch (id)
        {
            case 'V':           /* function result */
                if (pqGetc(&id, conn))
                    continue;
                if (id == 'G')
                {
                    /* function returned nonempty value */
                    if (pqGetInt(actual_result_len, 4, conn))
                        continue;
                    if (result_is_int)
                    {
                        if (pqGetInt(result_buf, 4, conn))
                            continue;
                    }
                    else
                    {
                        if (pqGetnchar((char *) result_buf,
                                       *actual_result_len,
                                       conn))
                            continue;
                    }
                    if (pqGetc(&id, conn))  /* get the last '0' */
                        continue;
                }
                if (id == '0')
                {
                    /* correctly finished function result message */
                    status = PGRES_COMMAND_OK;
                }
                else
                {
                    /* The backend violates the protocol. */
                    appendPQExpBuffer(&conn->errorMessage,
                                      libpq_gettext("protocol error: id=0x%x\n"),
                                      id);
                    pqSaveErrorResult(conn);
                    conn->inStart = conn->inCursor;
                    return pqPrepareAsyncResult(conn);
                }
                break;
            case 'E':           /* error return */
                if (pqGetErrorNotice2(conn, true))
                    continue;
                status = PGRES_FATAL_ERROR;
                break;
            case 'A':           /* notify message */
                /* handle notify and go back to processing return values */
                if (getNotify(conn))
                    continue;
                break;
            case 'N':           /* notice */
                /* handle notice and go back to processing return values */
                if (pqGetErrorNotice2(conn, false))
                    continue;
                break;
            case 'Z':           /* backend is ready for new query */
                /* consume the message and exit */
                conn->inStart = conn->inCursor;
                /* if we saved a result object (probably an error), use it */
                if (conn->result)
                    return pqPrepareAsyncResult(conn);
                return PQmakeEmptyPGresult(conn, status);
            default:
                /* The backend violates the protocol. */
                appendPQExpBuffer(&conn->errorMessage,
                                  libpq_gettext("protocol error: id=0x%x\n"),
                                  id);
                pqSaveErrorResult(conn);
                conn->inStart = conn->inCursor;
                return pqPrepareAsyncResult(conn);
        }
        /* Completed this message, keep going */
        conn->inStart = conn->inCursor;
        needInput = false;
    }

    /*
     * We fall out of the loop only upon failing to read data.
     * conn->errorMessage has been set by pqWait or pqReadData. We want to
     * append it to any already-received error message.
     */
    pqSaveErrorResult(conn);
    return pqPrepareAsyncResult(conn);
}


/*
 * Construct startup packet
 *
 * Returns a malloc'd packet buffer, or NULL if out of memory
 */
char *
pqBuildStartupPacket2(PGconn *conn, int *packetlen,
                      const PQEnvironmentOption *options)
{
    StartupPacket *startpacket;

    *packetlen = sizeof(StartupPacket);
    startpacket = (StartupPacket *) malloc(sizeof(StartupPacket));
    if (!startpacket)
        return NULL;

    MemSet(startpacket, 0, sizeof(StartupPacket));

    startpacket->protoVersion = pg_hton32(conn->pversion);

    /* strncpy is safe here: postmaster will handle full fields correctly */
    strncpy(startpacket->user, conn->pguser, SM_USER);
    strncpy(startpacket->database, conn->dbName, SM_DATABASE);
    strncpy(startpacket->tty, conn->pgtty, SM_TTY);

    if (conn->pgoptions)
        strncpy(startpacket->options, conn->pgoptions, SM_OPTIONS);

    return (char *) startpacket;
}