fe-protocol3.c

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/*-------------------------------------------------------------------------
 *
 * fe-protocol3.c
 *    functions that are specific to frontend/backend protocol version 3
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-protocol3.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <ctype.h>
#include <fcntl.h>
#include <limits.h>
 
#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#include <netinet/tcp.h>
#endif
 
#include "common/int.h"
#include "libpq-fe.h"
#include "libpq-int.h"
#include "mb/pg_wchar.h"
#include "port/pg_bswap.h"
 
/*
 * This macro lists the backend message types that could be "long" (more
 * than a couple of kilobytes).
 */
#define VALID_LONG_MESSAGE_TYPE(id) \
    ((id) == PqMsg_CopyData || \
     (id) == PqMsg_DataRow || \
     (id) == PqMsg_ErrorResponse || \
     (id) == PqMsg_FunctionCallResponse || \
     (id) == PqMsg_NoticeResponse || \
     (id) == PqMsg_NotificationResponse || \
     (id) == PqMsg_RowDescription)
 
 
static void handleFatalError(PGconn *conn);
static void handleSyncLoss(PGconn *conn, char id, int msgLength);
static int  getRowDescriptions(PGconn *conn, int msgLength);
static int  getParamDescriptions(PGconn *conn, int msgLength);
static int  getAnotherTuple(PGconn *conn, int msgLength);
static int  getParameterStatus(PGconn *conn);
static int  getBackendKeyData(PGconn *conn, int msgLength);
static int  getNotify(PGconn *conn);
static int  getCopyStart(PGconn *conn, ExecStatusType copytype);
static int  getReadyForQuery(PGconn *conn);
static void reportErrorPosition(PQExpBuffer msg, const char *query,
                                int loc, int encoding);
static size_t build_startup_packet(const PGconn *conn, char *packet,
                                   const PQEnvironmentOption *options);
 
 
/*
 * 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
pqParseInput3(PGconn *conn)
{
    char        id;
    int         msgLength;
    int         avail;
 
    /*
     * Loop to parse successive complete messages available in the buffer.
     */
    for (;;)
    {
        /*
         * Try to read a message.  First get the type code and length. Return
         * if not enough data.
         */
        conn->inCursor = conn->inStart;
        if (pqGetc(&id, conn))
            return;
        if (pqGetInt(&msgLength, 4, conn))
            return;
 
        /*
         * Try to validate message type/length here.  A length less than 4 is
         * definitely broken.  Large lengths should only be believed for a few
         * message types.
         */
        if (msgLength < 4)
        {
            handleSyncLoss(conn, id, msgLength);
            return;
        }
        if (msgLength > 30000 && !VALID_LONG_MESSAGE_TYPE(id))
        {
            handleSyncLoss(conn, id, msgLength);
            return;
        }
 
        /*
         * Can't process if message body isn't all here yet.
         */
        msgLength -= 4;
        avail = conn->inEnd - conn->inCursor;
        if (avail < msgLength)
        {
            /*
             * Before returning, enlarge the input buffer if needed to hold
             * the whole message.  This is better than leaving it to
             * pqReadData because we can avoid multiple cycles of realloc()
             * when the message is large; also, we can implement a reasonable
             * recovery strategy if we are unable to make the buffer big
             * enough.
             */
            if (pqCheckInBufferSpace(conn->inCursor + (size_t) msgLength,
                                     conn))
            {
                /*
                 * Abandon the connection.  There's not much else we can
                 * safely do; we can't just ignore the message or we could
                 * miss important changes to the connection state.
                 * pqCheckInBufferSpace() already reported the error.
                 */
                handleFatalError(conn);
            }
            return;
        }
 
        /*
         * NOTIFY and NOTICE messages can happen in any state; 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.
         *
         * ParameterStatus ('S') messages are a special case: in IDLE state we
         * must process 'em (this case could happen if a new value was adopted
         * from config file due to SIGHUP), but otherwise we hold off until
         * BUSY state.
         */
        if (id == PqMsg_NotificationResponse)
        {
            if (getNotify(conn))
                return;
        }
        else if (id == PqMsg_NoticeResponse)
        {
            if (pqGetErrorNotice3(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 handled using the notice processor;
             * ParameterStatus is handled normally; 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 == PqMsg_ErrorResponse)
            {
                if (pqGetErrorNotice3(conn, false /* treat as notice */ ))
                    return;
            }
            else if (id == PqMsg_ParameterStatus)
            {
                if (getParameterStatus(conn))
                    return;
            }
            else
            {
                /* Any other case is unexpected and we summarily skip it */
                pqInternalNotice(&conn->noticeHooks,
                                 "message type 0x%02x arrived from server while idle",
                                 id);
                /* Discard the unexpected message */
                conn->inCursor += msgLength;
            }
        }
        else
        {
            /*
             * In BUSY state, we can process everything.
             */
            switch (id)
            {
                case PqMsg_CommandComplete:
                    if (pqGets(&conn->workBuffer, conn))
                        return;
                    if (!pgHavePendingResult(conn))
                    {
                        conn->result = PQmakeEmptyPGresult(conn,
                                                           PGRES_COMMAND_OK);
                        if (!conn->result)
                        {
                            libpq_append_conn_error(conn, "out of memory");
                            pqSaveErrorResult(conn);
                        }
                    }
                    if (conn->result)
                        strlcpy(conn->result->cmdStatus, conn->workBuffer.data,
                                CMDSTATUS_LEN);
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case PqMsg_ErrorResponse:
                    if (pqGetErrorNotice3(conn, true))
                        return;
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case PqMsg_ReadyForQuery:
                    if (getReadyForQuery(conn))
                        return;
                    if (conn->pipelineStatus != PQ_PIPELINE_OFF)
                    {
                        conn->result = PQmakeEmptyPGresult(conn,
                                                           PGRES_PIPELINE_SYNC);
                        if (!conn->result)
                        {
                            libpq_append_conn_error(conn, "out of memory");
                            pqSaveErrorResult(conn);
                        }
                        else
                        {
                            conn->pipelineStatus = PQ_PIPELINE_ON;
                            conn->asyncStatus = PGASYNC_READY;
                        }
                    }
                    else
                    {
                        /* Advance the command queue and set us idle */
                        pqCommandQueueAdvance(conn, true, false);
                        conn->asyncStatus = PGASYNC_IDLE;
                    }
                    break;
                case PqMsg_EmptyQueryResponse:
                    if (!pgHavePendingResult(conn))
                    {
                        conn->result = PQmakeEmptyPGresult(conn,
                                                           PGRES_EMPTY_QUERY);
                        if (!conn->result)
                        {
                            libpq_append_conn_error(conn, "out of memory");
                            pqSaveErrorResult(conn);
                        }
                    }
                    conn->asyncStatus = PGASYNC_READY;
                    break;
                case PqMsg_ParseComplete:
                    /* If we're doing PQprepare, we're done; else ignore */
                    if (conn->cmd_queue_head &&
                        conn->cmd_queue_head->queryclass == PGQUERY_PREPARE)
                    {
                        if (!pgHavePendingResult(conn))
                        {
                            conn->result = PQmakeEmptyPGresult(conn,
                                                               PGRES_COMMAND_OK);
                            if (!conn->result)
                            {
                                libpq_append_conn_error(conn, "out of memory");
                                pqSaveErrorResult(conn);
                            }
                        }
                        conn->asyncStatus = PGASYNC_READY;
                    }
                    break;
                case PqMsg_BindComplete:
                    /* Nothing to do for this message type */
                    break;
                case PqMsg_CloseComplete:
                    /* If we're doing PQsendClose, we're done; else ignore */
                    if (conn->cmd_queue_head &&
                        conn->cmd_queue_head->queryclass == PGQUERY_CLOSE)
                    {
                        if (!pgHavePendingResult(conn))
                        {
                            conn->result = PQmakeEmptyPGresult(conn,
                                                               PGRES_COMMAND_OK);
                            if (!conn->result)
                            {
                                libpq_append_conn_error(conn, "out of memory");
                                pqSaveErrorResult(conn);
                            }
                        }
                        conn->asyncStatus = PGASYNC_READY;
                    }
                    break;
                case PqMsg_ParameterStatus:
                    if (getParameterStatus(conn))
                        return;
                    break;
                case PqMsg_BackendKeyData:
 
                    /*
                     * 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 (getBackendKeyData(conn, msgLength))
                        return;
                    break;
                case PqMsg_RowDescription:
                    if (conn->error_result ||
                        (conn->result != NULL &&
                         conn->result->resultStatus == PGRES_FATAL_ERROR))
                    {
                        /*
                         * We've already choked for some reason.  Just discard
                         * the data till we get to the end of the query.
                         */
                        conn->inCursor += msgLength;
                    }
                    else if (conn->result == NULL ||
                             (conn->cmd_queue_head &&
                              conn->cmd_queue_head->queryclass == PGQUERY_DESCRIBE))
                    {
                        /* First 'T' in a query sequence */
                        if (getRowDescriptions(conn, msgLength))
                            return;
                    }
                    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 PqMsg_NoData:
 
                    /*
                     * NoData indicates that we will not be seeing a
                     * RowDescription message because the statement or portal
                     * inquired about doesn't return rows.
                     *
                     * If we're doing a Describe, we have to pass something
                     * back to the client, so set up a COMMAND_OK result,
                     * instead of PGRES_TUPLES_OK.  Otherwise we can just
                     * ignore this message.
                     */
                    if (conn->cmd_queue_head &&
                        conn->cmd_queue_head->queryclass == PGQUERY_DESCRIBE)
                    {
                        if (!pgHavePendingResult(conn))
                        {
                            conn->result = PQmakeEmptyPGresult(conn,
                                                               PGRES_COMMAND_OK);
                            if (!conn->result)
                            {
                                libpq_append_conn_error(conn, "out of memory");
                                pqSaveErrorResult(conn);
                            }
                        }
                        conn->asyncStatus = PGASYNC_READY;
                    }
                    break;
                case PqMsg_ParameterDescription:
                    if (getParamDescriptions(conn, msgLength))
                        return;
                    break;
                case PqMsg_DataRow:
                    if (conn->result != NULL &&
                        (conn->result->resultStatus == PGRES_TUPLES_OK ||
                         conn->result->resultStatus == PGRES_TUPLES_CHUNK))
                    {
                        /* Read another tuple of a normal query response */
                        if (getAnotherTuple(conn, msgLength))
                            return;
                    }
                    else if (conn->error_result ||
                             (conn->result != NULL &&
                              conn->result->resultStatus == PGRES_FATAL_ERROR))
                    {
                        /*
                         * We've already choked for some reason.  Just discard
                         * tuples till we get to the end of the query.
                         */
                        conn->inCursor += msgLength;
                    }
                    else
                    {
                        /* Set up to report error at end of query */
                        libpq_append_conn_error(conn, "server sent data (\"D\" message) without prior row description (\"T\" message)");
                        pqSaveErrorResult(conn);
                        /* Discard the unexpected message */
                        conn->inCursor += msgLength;
                    }
                    break;
                case PqMsg_CopyInResponse:
                    if (getCopyStart(conn, PGRES_COPY_IN))
                        return;
                    conn->asyncStatus = PGASYNC_COPY_IN;
                    break;
                case PqMsg_CopyOutResponse:
                    if (getCopyStart(conn, PGRES_COPY_OUT))
                        return;
                    conn->asyncStatus = PGASYNC_COPY_OUT;
                    conn->copy_already_done = 0;
                    break;
                case PqMsg_CopyBothResponse:
                    if (getCopyStart(conn, PGRES_COPY_BOTH))
                        return;
                    conn->asyncStatus = PGASYNC_COPY_BOTH;
                    conn->copy_already_done = 0;
                    break;
                case PqMsg_CopyData:
 
                    /*
                     * If we see Copy Data, just silently drop it.  This would
                     * only occur if application exits COPY OUT mode too
                     * early.
                     */
                    conn->inCursor += msgLength;
                    break;
                case PqMsg_CopyDone:
 
                    /*
                     * If we see Copy Done, just silently drop it.  This is
                     * the normal case during PQendcopy.  We will keep
                     * swallowing data, expecting to see command-complete for
                     * the COPY command.
                     */
                    break;
                default:
                    libpq_append_conn_error(conn, "unexpected response from server; first received character was \"%c\"", id);
                    /* build an error result holding the error message */
                    pqSaveErrorResult(conn);
                    /* not sure if we will see more, so go to ready state */
                    conn->asyncStatus = PGASYNC_READY;
                    /* Discard the unexpected message */
                    conn->inCursor += msgLength;
                    break;
            }                   /* switch on protocol character */
        }
        /* Successfully consumed this message */
        if (conn->inCursor == conn->inStart + 5 + msgLength)
        {
            /* Normal case: parsing agrees with specified length */
            pqParseDone(conn, conn->inCursor);
        }
        else if (conn->error_result && conn->status == CONNECTION_BAD)
        {
            /* The connection was abandoned and we already reported it */
            return;
        }
        else
        {
            /* Trouble --- report it */
            libpq_append_conn_error(conn, "message contents do not agree with length in message type \"%c\"", id);
            /* build an error result holding the error message */
            pqSaveErrorResult(conn);
            conn->asyncStatus = PGASYNC_READY;
            /* trust the specified message length as what to skip */
            conn->inStart += 5 + msgLength;
        }
    }
}
 
/*
 * handleFatalError: clean up after a nonrecoverable error
 *
 * This is for errors where we need to abandon the connection.  The caller has
 * already saved the error message in conn->errorMessage.
 */
static void
handleFatalError(PGconn *conn)
{
    /* build an error result holding the error message */
    pqSaveErrorResult(conn);
    conn->asyncStatus = PGASYNC_READY;  /* drop out of PQgetResult wait loop */
    /* flush input data since we're giving up on processing it */
    pqDropConnection(conn, true);
    conn->status = CONNECTION_BAD;  /* No more connection to backend */
}
 
/*
 * handleSyncLoss: clean up after loss of message-boundary sync
 *
 * There isn't really a lot we can do here except abandon the connection.
 */
static void
handleSyncLoss(PGconn *conn, char id, int msgLength)
{
    libpq_append_conn_error(conn, "lost synchronization with server: got message type \"%c\", length %d",
                            id, msgLength);
    handleFatalError(conn);
}
 
/*
 * parseInput subroutine to read a 'T' (row descriptions) message.
 * We'll build a new PGresult structure (unless called for a Describe
 * command for a prepared statement) containing the attribute data.
 * Returns: 0 if processed message successfully, EOF to suspend parsing
 * (the latter case is not actually used currently).
 */
static int
getRowDescriptions(PGconn *conn, int msgLength)
{
    PGresult   *result;
    int         nfields;
    const char *errmsg;
    int         i;
 
    /*
     * When doing Describe for a prepared statement, there'll already be a
     * PGresult created by getParamDescriptions, and we should fill data into
     * that.  Otherwise, create a new, empty PGresult.
     */
    if (!conn->cmd_queue_head ||
        (conn->cmd_queue_head &&
         conn->cmd_queue_head->queryclass == PGQUERY_DESCRIBE))
    {
        if (conn->result)
            result = conn->result;
        else
            result = PQmakeEmptyPGresult(conn, PGRES_COMMAND_OK);
    }
    else
        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 and message length. */
    /* the next two bytes are the number of fields */
    if (pqGetInt(&(result->numAttributes), 2, conn))
    {
        /* We should not run out of data here, so complain */
        errmsg = libpq_gettext("insufficient data in \"T\" message");
        goto advance_and_error;
    }
    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));
    }
 
    /* result->binary is true only if ALL columns are binary */
    result->binary = (nfields > 0) ? 1 : 0;
 
    /* get type info */
    for (i = 0; i < nfields; i++)
    {
        int         tableid;
        int         columnid;
        int         typid;
        int         typlen;
        int         atttypmod;
        int         format;
 
        if (pqGets(&conn->workBuffer, conn) ||
            pqGetInt(&tableid, 4, conn) ||
            pqGetInt(&columnid, 2, conn) ||
            pqGetInt(&typid, 4, conn) ||
            pqGetInt(&typlen, 2, conn) ||
            pqGetInt(&atttypmod, 4, conn) ||
            pqGetInt(&format, 2, conn))
        {
            /* We should not run out of data here, so complain */
            errmsg = libpq_gettext("insufficient data in \"T\" message");
            goto advance_and_error;
        }
 
        /*
         * Since pqGetInt treats 2-byte integers as unsigned, we need to
         * coerce these results to signed form.
         */
        columnid = (int) ((int16) columnid);
        typlen = (int) ((int16) typlen);
        format = (int) ((int16) format);
 
        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 = tableid;
        result->attDescs[i].columnid = columnid;
        result->attDescs[i].format = format;
        result->attDescs[i].typid = typid;
        result->attDescs[i].typlen = typlen;
        result->attDescs[i].atttypmod = atttypmod;
 
        if (format != 1)
            result->binary = 0;
    }
 
    /* Success! */
    conn->result = result;
 
    /*
     * If we're doing a Describe, we're done, and ready to pass the result
     * back to the client.
     */
    if ((!conn->cmd_queue_head) ||
        (conn->cmd_queue_head &&
         conn->cmd_queue_head->queryclass == PGQUERY_DESCRIBE))
    {
        conn->asyncStatus = PGASYNC_READY;
        return 0;
    }
 
    /*
     * 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 unsaved result, if any */
    if (result && result != conn->result)
        PQclear(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);
    pqSaveErrorResult(conn);
 
    /*
     * Show the message as fully consumed, else pqParseInput3 will overwrite
     * our error with a complaint about that.
     */
    conn->inCursor = conn->inStart + 5 + msgLength;
 
    /*
     * Return zero to allow input parsing to continue.  Subsequent "D"
     * messages will be ignored until we get to end of data, since an error
     * result is already set up.
     */
    return 0;
}
 
/*
 * parseInput subroutine to read a 't' (ParameterDescription) message.
 * We'll build a new PGresult structure containing the parameter data.
 * Returns: 0 if processed message successfully, EOF to suspend parsing
 * (the latter case is not actually used currently).
 */
static int
getParamDescriptions(PGconn *conn, int msgLength)
{
    PGresult   *result;
    const char *errmsg = NULL;  /* means "out of memory", see below */
    int         nparams;
    int         i;
 
    result = PQmakeEmptyPGresult(conn, PGRES_COMMAND_OK);
    if (!result)
        goto advance_and_error;
 
    /* parseInput already read the 't' label and message length. */
    /* the next two bytes are the number of parameters */
    if (pqGetInt(&(result->numParameters), 2, conn))
        goto not_enough_data;
    nparams = result->numParameters;
 
    /* allocate space for the parameter descriptors */
    if (nparams > 0)
    {
        result->paramDescs = (PGresParamDesc *)
            pqResultAlloc(result, nparams * sizeof(PGresParamDesc), true);
        if (!result->paramDescs)
            goto advance_and_error;
        MemSet(result->paramDescs, 0, nparams * sizeof(PGresParamDesc));
    }
 
    /* get parameter info */
    for (i = 0; i < nparams; i++)
    {
        int         typid;
 
        if (pqGetInt(&typid, 4, conn))
            goto not_enough_data;
        result->paramDescs[i].typid = typid;
    }
 
    /* Success! */
    conn->result = result;
 
    return 0;
 
not_enough_data:
    errmsg = libpq_gettext("insufficient data in \"t\" message");
 
advance_and_error:
    /* Discard unsaved result, if any */
    if (result && result != conn->result)
        PQclear(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");
    appendPQExpBuffer(&conn->errorMessage, "%s\n", errmsg);
    pqSaveErrorResult(conn);
 
    /*
     * Show the message as fully consumed, else pqParseInput3 will overwrite
     * our error with a complaint about that.
     */
    conn->inCursor = conn->inStart + 5 + msgLength;
 
    /*
     * Return zero to allow input parsing to continue.  Essentially, we've
     * replaced the COMMAND_OK result with an error result, but since this
     * doesn't affect the protocol state, it's fine.
     */
    return 0;
}
 
/*
 * parseInput subroutine to read a 'D' (row data) message.
 * We fill rowbuf with column pointers and then call the row processor.
 * Returns: 0 if processed message successfully, EOF to suspend parsing
 * (the latter case is not actually used currently).
 */
static int
getAnotherTuple(PGconn *conn, int msgLength)
{
    PGresult   *result = conn->result;
    int         nfields = result->numAttributes;
    const char *errmsg;
    PGdataValue *rowbuf;
    int         tupnfields;     /* # fields from tuple */
    int         vlen;           /* length of the current field value */
    int         i;
 
    /* Get the field count and make sure it's what we expect */
    if (pqGetInt(&tupnfields, 2, conn))
    {
        /* We should not run out of data here, so complain */
        errmsg = libpq_gettext("insufficient data in \"D\" message");
        goto advance_and_error;
    }
 
    if (tupnfields != nfields)
    {
        errmsg = libpq_gettext("unexpected field count in \"D\" message");
        goto advance_and_error;
    }
 
    /* 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;
    }
 
    /* Scan the fields */
    for (i = 0; i < nfields; i++)
    {
        /* get the value length */
        if (pqGetInt(&vlen, 4, conn))
        {
            /* We should not run out of data here, so complain */
            errmsg = libpq_gettext("insufficient data in \"D\" message");
            goto advance_and_error;
        }
        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))
            {
                /* We should not run out of data here, so complain */
                errmsg = libpq_gettext("insufficient data in \"D\" message");
                goto advance_and_error;
            }
        }
    }
 
    /* Process the collected row */
    errmsg = NULL;
    if (pqRowProcessor(conn, &errmsg))
        return 0;               /* normal, successful exit */
 
    /* pqRowProcessor failed, fall through to report it */
 
advance_and_error:
 
    /*
     * 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);
    pqSaveErrorResult(conn);
 
    /*
     * Show the message as fully consumed, else pqParseInput3 will overwrite
     * our error with a complaint about that.
     */
    conn->inCursor = conn->inStart + 5 + msgLength;
 
    /*
     * Return zero to allow input parsing to continue.  Subsequent "D"
     * messages will be ignored until we get to end of data, since an error
     * result is already set up.
     */
    return 0;
}
 
 
/*
 * 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 and length have already been consumed.
 * Exit: returns 0 if successfully consumed message.
 *       returns EOF if not enough data.
 */
int
pqGetErrorNotice3(PGconn *conn, bool isError)
{
    PGresult   *res = NULL;
    bool        have_position = false;
    PQExpBufferData workBuf;
    char        id;
 
    /* If in pipeline mode, set error indicator for it */
    if (isError && conn->pipelineStatus != PQ_PIPELINE_OFF)
        conn->pipelineStatus = PQ_PIPELINE_ABORTED;
 
    /*
     * 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 fields 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.  We shouldn't use
     * conn->errorMessage either, since this might be only a notice.
     */
    initPQExpBuffer(&workBuf);
 
    /*
     * Make a PGresult to hold the accumulated fields.  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;
 
    /*
     * Read the fields and save into res.
     *
     * While at it, save the SQLSTATE in conn->last_sqlstate, and note whether
     * we saw a PG_DIAG_STATEMENT_POSITION field.
     */
    for (;;)
    {
        if (pqGetc(&id, conn))
            goto fail;
        if (id == '\0')
            break;              /* terminator found */
        if (pqGets(&workBuf, conn))
            goto fail;
        pqSaveMessageField(res, id, workBuf.data);
        if (id == PG_DIAG_SQLSTATE)
            strlcpy(conn->last_sqlstate, workBuf.data,
                    sizeof(conn->last_sqlstate));
        else if (id == PG_DIAG_STATEMENT_POSITION)
            have_position = true;
    }
 
    /*
     * Save the active query text, if any, into res as well; but only if we
     * might need it for an error cursor display, which is only true if there
     * is a PG_DIAG_STATEMENT_POSITION field.
     */
    if (have_position && res && conn->cmd_queue_head && conn->cmd_queue_head->query)
        res->errQuery = pqResultStrdup(res, conn->cmd_queue_head->query);
 
    /*
     * Now build the "overall" error message for PQresultErrorMessage.
     */
    resetPQExpBuffer(&workBuf);
    pqBuildErrorMessage3(&workBuf, res, conn->verbosity, conn->show_context);
 
    /*
     * Either save error as current async result, or just emit the notice.
     */
    if (isError)
    {
        pqClearAsyncResult(conn);   /* redundant, but be safe */
        if (res)
        {
            pqSetResultError(res, &workBuf, 0);
            conn->result = res;
        }
        else
        {
            /* Fall back to using the internal-error processing paths */
            conn->error_result = true;
        }
 
        if (PQExpBufferDataBroken(workBuf))
            libpq_append_conn_error(conn, "out of memory");
        else
            appendPQExpBufferStr(&conn->errorMessage, workBuf.data);
    }
    else
    {
        /* if we couldn't allocate the result set, just discard the NOTICE */
        if (res)
        {
            /*
             * We can cheat a little here and not copy the message.  But if we
             * were unlucky enough to run out of memory while filling workBuf,
             * insert "out of memory", as in pqSetResultError.
             */
            if (PQExpBufferDataBroken(workBuf))
                res->errMsg = libpq_gettext("out of memory\n");
            else
                res->errMsg = workBuf.data;
            if (res->noticeHooks.noticeRec != NULL)
                res->noticeHooks.noticeRec(res->noticeHooks.noticeRecArg, res);
            PQclear(res);
        }
    }
 
    termPQExpBuffer(&workBuf);
    return 0;
 
fail:
    PQclear(res);
    termPQExpBuffer(&workBuf);
    return EOF;
}
 
/*
 * Construct an error message from the fields in the given PGresult,
 * appending it to the contents of "msg".
 */
void
pqBuildErrorMessage3(PQExpBuffer msg, const PGresult *res,
                     PGVerbosity verbosity, PGContextVisibility show_context)
{
    const char *val;
    const char *querytext = NULL;
    int         querypos = 0;
 
    /* If we couldn't allocate a PGresult, just say "out of memory" */
    if (res == NULL)
    {
        appendPQExpBufferStr(msg, libpq_gettext("out of memory\n"));
        return;
    }
 
    /*
     * If we don't have any broken-down fields, just return the base message.
     * This mainly applies if we're given a libpq-generated error result.
     */
    if (res->errFields == NULL)
    {
        if (res->errMsg && res->errMsg[0])
            appendPQExpBufferStr(msg, res->errMsg);
        else
            appendPQExpBufferStr(msg, libpq_gettext("no error message available\n"));
        return;
    }
 
    /* Else build error message from relevant fields */
    val = PQresultErrorField(res, PG_DIAG_SEVERITY);
    if (val)
        appendPQExpBuffer(msg, "%s:  ", val);
 
    if (verbosity == PQERRORS_SQLSTATE)
    {
        /*
         * If we have a SQLSTATE, print that and nothing else.  If not (which
         * shouldn't happen for server-generated errors, but might possibly
         * happen for libpq-generated ones), fall back to TERSE format, as
         * that seems better than printing nothing at all.
         */
        val = PQresultErrorField(res, PG_DIAG_SQLSTATE);
        if (val)
        {
            appendPQExpBuffer(msg, "%s\n", val);
            return;
        }
        verbosity = PQERRORS_TERSE;
    }
 
    if (verbosity == PQERRORS_VERBOSE)
    {
        val = PQresultErrorField(res, PG_DIAG_SQLSTATE);
        if (val)
            appendPQExpBuffer(msg, "%s: ", val);
    }
    val = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
    if (val)
        appendPQExpBufferStr(msg, val);
    val = PQresultErrorField(res, PG_DIAG_STATEMENT_POSITION);
    if (val)
    {
        if (verbosity != PQERRORS_TERSE && res->errQuery != NULL)
        {
            /* emit position as a syntax cursor display */
            querytext = res->errQuery;
            querypos = atoi(val);
        }
        else
        {
            /* emit position as text addition to primary message */
            /* translator: %s represents a digit string */
            appendPQExpBuffer(msg, libpq_gettext(" at character %s"),
                              val);
        }
    }
    else
    {
        val = PQresultErrorField(res, PG_DIAG_INTERNAL_POSITION);
        if (val)
        {
            querytext = PQresultErrorField(res, PG_DIAG_INTERNAL_QUERY);
            if (verbosity != PQERRORS_TERSE && querytext != NULL)
            {
                /* emit position as a syntax cursor display */
                querypos = atoi(val);
            }
            else
            {
                /* emit position as text addition to primary message */
                /* translator: %s represents a digit string */
                appendPQExpBuffer(msg, libpq_gettext(" at character %s"),
                                  val);
            }
        }
    }
    appendPQExpBufferChar(msg, '\n');
    if (verbosity != PQERRORS_TERSE)
    {
        if (querytext && querypos > 0)
            reportErrorPosition(msg, querytext, querypos,
                                res->client_encoding);
        val = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
        if (val)
            appendPQExpBuffer(msg, libpq_gettext("DETAIL:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
        if (val)
            appendPQExpBuffer(msg, libpq_gettext("HINT:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_INTERNAL_QUERY);
        if (val)
            appendPQExpBuffer(msg, libpq_gettext("QUERY:  %s\n"), val);
        if (show_context == PQSHOW_CONTEXT_ALWAYS ||
            (show_context == PQSHOW_CONTEXT_ERRORS &&
             res->resultStatus == PGRES_FATAL_ERROR))
        {
            val = PQresultErrorField(res, PG_DIAG_CONTEXT);
            if (val)
                appendPQExpBuffer(msg, libpq_gettext("CONTEXT:  %s\n"),
                                  val);
        }
    }
    if (verbosity == PQERRORS_VERBOSE)
    {
        val = PQresultErrorField(res, PG_DIAG_SCHEMA_NAME);
        if (val)
            appendPQExpBuffer(msg,
                              libpq_gettext("SCHEMA NAME:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_TABLE_NAME);
        if (val)
            appendPQExpBuffer(msg,
                              libpq_gettext("TABLE NAME:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_COLUMN_NAME);
        if (val)
            appendPQExpBuffer(msg,
                              libpq_gettext("COLUMN NAME:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_DATATYPE_NAME);
        if (val)
            appendPQExpBuffer(msg,
                              libpq_gettext("DATATYPE NAME:  %s\n"), val);
        val = PQresultErrorField(res, PG_DIAG_CONSTRAINT_NAME);
        if (val)
            appendPQExpBuffer(msg,
                              libpq_gettext("CONSTRAINT NAME:  %s\n"), val);
    }
    if (verbosity == PQERRORS_VERBOSE)
    {
        const char *valf;
        const char *vall;
 
        valf = PQresultErrorField(res, PG_DIAG_SOURCE_FILE);
        vall = PQresultErrorField(res, PG_DIAG_SOURCE_LINE);
        val = PQresultErrorField(res, PG_DIAG_SOURCE_FUNCTION);
        if (val || valf || vall)
        {
            appendPQExpBufferStr(msg, libpq_gettext("LOCATION:  "));
            if (val)
                appendPQExpBuffer(msg, libpq_gettext("%s, "), val);
            if (valf && vall)   /* unlikely we'd have just one */
                appendPQExpBuffer(msg, libpq_gettext("%s:%s"),
                                  valf, vall);
            appendPQExpBufferChar(msg, '\n');
        }
    }
}
 
/*
 * Add an error-location display to the error message under construction.
 *
 * The cursor location is measured in logical characters; the query string
 * is presumed to be in the specified encoding.
 */
static void
reportErrorPosition(PQExpBuffer msg, const char *query, int loc, int encoding)
{
#define DISPLAY_SIZE    60      /* screen width limit, in screen cols */
#define MIN_RIGHT_CUT   10      /* try to keep this far away from EOL */
 
    char       *wquery;
    int         slen,
                cno,
                i,
               *qidx,
               *scridx,
                qoffset,
                scroffset,
                ibeg,
                iend,
                loc_line;
    bool        mb_encoding,
                beg_trunc,
                end_trunc;
 
    /* Convert loc from 1-based to 0-based; no-op if out of range */
    loc--;
    if (loc < 0)
        return;
 
    /* Need a writable copy of the query */
    wquery = strdup(query);
    if (wquery == NULL)
        return;                 /* fail silently if out of memory */
 
    /*
     * Each character might occupy multiple physical bytes in the string, and
     * in some Far Eastern character sets it might take more than one screen
     * column as well.  We compute the starting byte offset and starting
     * screen column of each logical character, and store these in qidx[] and
     * scridx[] respectively.
     */
 
    /*
     * We need a safe allocation size.
     *
     * The only caller of reportErrorPosition() is pqBuildErrorMessage3(); it
     * gets its query from either a PQresultErrorField() or a PGcmdQueueEntry,
     * both of which must have fit into conn->inBuffer/outBuffer. So slen fits
     * inside an int, but we can't assume that (slen * sizeof(int)) fits
     * inside a size_t.
     */
    slen = strlen(wquery) + 1;
    if (slen > SIZE_MAX / sizeof(int))
    {
        free(wquery);
        return;
    }
 
    qidx = (int *) malloc(slen * sizeof(int));
    if (qidx == NULL)
    {
        free(wquery);
        return;
    }
    scridx = (int *) malloc(slen * sizeof(int));
    if (scridx == NULL)
    {
        free(qidx);
        free(wquery);
        return;
    }
 
    /* We can optimize a bit if it's a single-byte encoding */
    mb_encoding = (pg_encoding_max_length(encoding) != 1);
 
    /*
     * Within the scanning loop, cno is the current character's logical
     * number, qoffset is its offset in wquery, and scroffset is its starting
     * logical screen column (all indexed from 0).  "loc" is the logical
     * character number of the error location.  We scan to determine loc_line
     * (the 1-based line number containing loc) and ibeg/iend (first character
     * number and last+1 character number of the line containing loc). Note
     * that qidx[] and scridx[] are filled only as far as iend.
     */
    qoffset = 0;
    scroffset = 0;
    loc_line = 1;
    ibeg = 0;
    iend = -1;                  /* -1 means not set yet */
 
    for (cno = 0; wquery[qoffset] != '\0'; cno++)
    {
        char        ch = wquery[qoffset];
 
        qidx[cno] = qoffset;
        scridx[cno] = scroffset;
 
        /*
         * Replace tabs with spaces in the writable copy.  (Later we might
         * want to think about coping with their variable screen width, but
         * not today.)
         */
        if (ch == '\t')
            wquery[qoffset] = ' ';
 
        /*
         * If end-of-line, count lines and mark positions. Each \r or \n
         * counts as a line except when \r \n appear together.
         */
        else if (ch == '\r' || ch == '\n')
        {
            if (cno < loc)
            {
                if (ch == '\r' ||
                    cno == 0 ||
                    wquery[qidx[cno - 1]] != '\r')
                    loc_line++;
                /* extract beginning = last line start before loc. */
                ibeg = cno + 1;
            }
            else
            {
                /* set extract end. */
                iend = cno;
                /* done scanning. */
                break;
            }
        }
 
        /* Advance */
        if (mb_encoding)
        {
            int         w;
 
            w = pg_encoding_dsplen(encoding, &wquery[qoffset]);
            /* treat any non-tab control chars as width 1 */
            if (w <= 0)
                w = 1;
            scroffset += w;
            qoffset += PQmblenBounded(&wquery[qoffset], encoding);
        }
        else
        {
            /* We assume wide chars only exist in multibyte encodings */
            scroffset++;
            qoffset++;
        }
    }
    /* Fix up if we didn't find an end-of-line after loc */
    if (iend < 0)
    {
        iend = cno;             /* query length in chars, +1 */
        qidx[iend] = qoffset;
        scridx[iend] = scroffset;
    }
 
    /* Print only if loc is within computed query length */
    if (loc <= cno)
    {
        /* If the line extracted is too long, we truncate it. */
        beg_trunc = false;
        end_trunc = false;
        if (scridx[iend] - scridx[ibeg] > DISPLAY_SIZE)
        {
            /*
             * We first truncate right if it is enough.  This code might be
             * off a space or so on enforcing MIN_RIGHT_CUT if there's a wide
             * character right there, but that should be okay.
             */
            if (scridx[ibeg] + DISPLAY_SIZE >= scridx[loc] + MIN_RIGHT_CUT)
            {
                while (scridx[iend] - scridx[ibeg] > DISPLAY_SIZE)
                    iend--;
                end_trunc = true;
            }
            else
            {
                /* Truncate right if not too close to loc. */
                while (scridx[loc] + MIN_RIGHT_CUT < scridx[iend])
                {
                    iend--;
                    end_trunc = true;
                }
 
                /* Truncate left if still too long. */
                while (scridx[iend] - scridx[ibeg] > DISPLAY_SIZE)
                {
                    ibeg++;
                    beg_trunc = true;
                }
            }
        }
 
        /* truncate working copy at desired endpoint */
        wquery[qidx[iend]] = '\0';
 
        /* Begin building the finished message. */
        i = msg->len;
        appendPQExpBuffer(msg, libpq_gettext("LINE %d: "), loc_line);
        if (beg_trunc)
            appendPQExpBufferStr(msg, "...");
 
        /*
         * While we have the prefix in the msg buffer, compute its screen
         * width.
         */
        scroffset = 0;
        for (; i < msg->len; i += PQmblenBounded(&msg->data[i], encoding))
        {
            int         w = pg_encoding_dsplen(encoding, &msg->data[i]);
 
            if (w <= 0)
                w = 1;
            scroffset += w;
        }
 
        /* Finish up the LINE message line. */
        appendPQExpBufferStr(msg, &wquery[qidx[ibeg]]);
        if (end_trunc)
            appendPQExpBufferStr(msg, "...");
        appendPQExpBufferChar(msg, '\n');
 
        /* Now emit the cursor marker line. */
        scroffset += scridx[loc] - scridx[ibeg];
        for (i = 0; i < scroffset; i++)
            appendPQExpBufferChar(msg, ' ');
        appendPQExpBufferChar(msg, '^');
        appendPQExpBufferChar(msg, '\n');
    }
 
    /* Clean up. */
    free(scridx);
    free(qidx);
    free(wquery);
}
 
 
/*
 * Attempt to read a NegotiateProtocolVersion message.  Sets conn->pversion
 * to the version that's negotiated by the server.
 *
 * Entry: 'v' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed message.
 *       returns 1 on failure. The error message is filled in.
 */
int
pqGetNegotiateProtocolVersion3(PGconn *conn)
{
    int         their_version;
    int         num;
    bool        found_test_protocol_negotiation;
    bool        expect_test_protocol_negotiation;
 
    /*
     * During 19beta only, if protocol grease is in use, assume that it's the
     * cause of any invalid messages encountered below. We'll print extra
     * information for the end user in that case.
     */
    bool        need_grease_info = (conn->max_pversion == PG_PROTOCOL_GREASE);
 
    if (pqGetInt(&their_version, 4, conn) != 0)
        goto eof;
 
    if (pqGetInt(&num, 4, conn) != 0)
        goto eof;
 
    /*
     * Check the protocol version.
     *
     * PG_PROTOCOL_GREASE is intentionally unsupported and reserved. It's
     * higher than any real version, so check for that first, to get the most
     * specific error message. Then check the upper and lower bounds.
     */
    if (their_version == PG_PROTOCOL_GREASE)
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requested \"grease\" protocol version 3.9999");
        goto failure;
    }
 
    if (their_version > conn->pversion)
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requested downgrade to a higher-numbered version");
        goto failure;
    }
 
    if (their_version < PG_PROTOCOL(3, 0))
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requested downgrade to pre-3.0 protocol version");
        goto failure;
    }
 
    /* 3.1 never existed, we went straight from 3.0 to 3.2 */
    if (their_version == PG_PROTOCOL_RESERVED_31)
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requested downgrade to non-existent 3.1 protocol version");
        goto failure;
    }
 
    if (num < 0)
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server reported negative number of unsupported parameters");
        goto failure;
    }
 
    if (their_version == conn->pversion && num == 0)
    {
        libpq_append_conn_error(conn, "received invalid protocol negotiation message: server negotiated but asks for no changes");
        goto failure;
    }
 
    if (their_version < conn->min_pversion)
    {
        libpq_append_conn_error(conn, "server only supports protocol version %d.%d, but \"%s\" was set to %d.%d",
                                PG_PROTOCOL_MAJOR(their_version),
                                PG_PROTOCOL_MINOR(their_version),
                                "min_protocol_version",
                                PG_PROTOCOL_MAJOR(conn->min_pversion),
                                PG_PROTOCOL_MINOR(conn->min_pversion));
 
        need_grease_info = false;   /* this is valid server behavior */
        goto failure;
    }
 
    /* the version is acceptable */
    conn->pversion = their_version;
 
    /*
     * Check that all expected unsupported parameters are reported by the
     * server.
     */
    found_test_protocol_negotiation = false;
    expect_test_protocol_negotiation = (conn->max_pversion == PG_PROTOCOL_GREASE);
 
    for (int i = 0; i < num; i++)
    {
        if (pqGets(&conn->workBuffer, conn))
        {
            goto eof;
        }
        if (strncmp(conn->workBuffer.data, "_pq_.", 5) != 0)
        {
            libpq_append_conn_error(conn, "received invalid protocol negotiation message: server reported unsupported parameter name without a \"%s\" prefix (\"%s\")", "_pq_.", conn->workBuffer.data);
            goto failure;
        }
 
        /* Check if this is the expected test parameter */
        if (expect_test_protocol_negotiation &&
            strcmp(conn->workBuffer.data, "_pq_.test_protocol_negotiation") == 0)
        {
            found_test_protocol_negotiation = true;
        }
        else
        {
            libpq_append_conn_error(conn, "received invalid protocol negotiation message: server reported an unsupported parameter that was not requested (\"%s\")",
                                    conn->workBuffer.data);
            goto failure;
        }
    }
 
    /*
     * If we requested protocol grease, the server must report
     * _pq_.test_protocol_negotiation as unsupported. This ensures
     * comprehensive NegotiateProtocolVersion implementation.
     */
    if (expect_test_protocol_negotiation && !found_test_protocol_negotiation)
    {
        libpq_append_conn_error(conn, "server did not report the unsupported `_pq_.test_protocol_negotiation` parameter in its protocol negotiation message");
        goto failure;
    }
 
    return 0;
 
eof:
    libpq_append_conn_error(conn, "received invalid protocol negotiation message: message too short");
failure:
    if (need_grease_info)
        libpq_append_grease_info(conn);
    conn->asyncStatus = PGASYNC_READY;
    pqSaveErrorResult(conn);
    return 1;
}
 
 
/*
 * Attempt to read a ParameterStatus message.
 * This is possible in several places, so we break it out as a subroutine.
 *
 * Entry: 'S' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed message.
 *       returns EOF if not enough data.
 */
static int
getParameterStatus(PGconn *conn)
{
    PQExpBufferData valueBuf;
 
    /* Get the parameter name */
    if (pqGets(&conn->workBuffer, conn))
        return EOF;
    /* Get the parameter value (could be large) */
    initPQExpBuffer(&valueBuf);
    if (pqGets(&valueBuf, conn))
    {
        termPQExpBuffer(&valueBuf);
        return EOF;
    }
    /* And save it */
    if (!pqSaveParameterStatus(conn, conn->workBuffer.data, valueBuf.data))
    {
        libpq_append_conn_error(conn, "out of memory");
        handleFatalError(conn);
    }
    termPQExpBuffer(&valueBuf);
    return 0;
}
 
/*
 * parseInput subroutine to read a BackendKeyData message.
 * Entry: 'v' message type and length have already been consumed.
 * Exit: returns 0 if successfully consumed message.
 *       returns EOF if not enough data.
 */
static int
getBackendKeyData(PGconn *conn, int msgLength)
{
    int         cancel_key_len;
 
    if (conn->be_cancel_key)
    {
        free(conn->be_cancel_key);
        conn->be_cancel_key = NULL;
        conn->be_cancel_key_len = 0;
    }
 
    if (pqGetInt(&(conn->be_pid), 4, conn))
        return EOF;
 
    cancel_key_len = 5 + msgLength - (conn->inCursor - conn->inStart);
 
    if (cancel_key_len != 4 && conn->pversion == PG_PROTOCOL(3, 0))
    {
        libpq_append_conn_error(conn, "received invalid BackendKeyData message: cancel key with length %d not allowed in protocol version 3.0 (must be 4 bytes)", cancel_key_len);
        handleFatalError(conn);
        return 0;
    }
 
    if (cancel_key_len < 4)
    {
        libpq_append_conn_error(conn, "received invalid BackendKeyData message: cancel key with length %d is too short (minimum 4 bytes)", cancel_key_len);
        handleFatalError(conn);
        return 0;
    }
 
    if (cancel_key_len > 256)
    {
        libpq_append_conn_error(conn, "received invalid BackendKeyData message: cancel key with length %d is too long (maximum 256 bytes)", cancel_key_len);
        handleFatalError(conn);
        return 0;
    }
 
    conn->be_cancel_key = malloc(cancel_key_len);
    if (conn->be_cancel_key == NULL)
    {
        libpq_append_conn_error(conn, "out of memory");
        handleFatalError(conn);
        return 0;
    }
    if (pqGetnchar(conn->be_cancel_key, cancel_key_len, conn))
    {
        free(conn->be_cancel_key);
        conn->be_cancel_key = NULL;
        return EOF;
    }
    conn->be_cancel_key_len = cancel_key_len;
    return 0;
}
 
 
/*
 * 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;
    char       *svname;
    int         nmlen;
    int         extralen;
    PGnotify   *newNotify;
 
    if (pqGetInt(&be_pid, 4, conn))
        return EOF;
    if (pqGets(&conn->workBuffer, conn))
        return EOF;
    /* must save name while getting extra string */
    svname = strdup(conn->workBuffer.data);
    if (!svname)
    {
        /*
         * Notify messages can arrive at any state, so we cannot associate the
         * error with any particular query.  There's no way to return back an
         * "async error", so the best we can do is drop the connection.  That
         * seems better than silently ignoring the notification.
         */
        libpq_append_conn_error(conn, "out of memory");
        handleFatalError(conn);
        return 0;
    }
    if (pqGets(&conn->workBuffer, conn))
    {
        free(svname);
        return EOF;
    }
 
    /*
     * Store the strings right after the PGnotify 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(svname);
    extralen = strlen(conn->workBuffer.data);
    newNotify = (PGnotify *) malloc(sizeof(PGnotify) + nmlen + extralen + 2);
    if (!newNotify)
    {
        free(svname);
        libpq_append_conn_error(conn, "out of memory");
        handleFatalError(conn);
        return 0;
    }
 
    newNotify->relname = (char *) newNotify + sizeof(PGnotify);
    strcpy(newNotify->relname, svname);
    newNotify->extra = newNotify->relname + nmlen + 1;
    strcpy(newNotify->extra, conn->workBuffer.data);
    newNotify->be_pid = be_pid;
    newNotify->next = NULL;
    if (conn->notifyTail)
        conn->notifyTail->next = newNotify;
    else
        conn->notifyHead = newNotify;
    conn->notifyTail = newNotify;
 
    free(svname);
    return 0;
}
 
/*
 * getCopyStart - process CopyInResponse, CopyOutResponse or
 * CopyBothResponse message
 *
 * parseInput already read the message type and length.
 */
static int
getCopyStart(PGconn *conn, ExecStatusType copytype)
{
    PGresult   *result;
    int         nfields;
    int         i;
 
    result = PQmakeEmptyPGresult(conn, copytype);
    if (!result)
        goto failure;
 
    if (pqGetc(&conn->copy_is_binary, conn))
        goto failure;
    result->binary = conn->copy_is_binary;
    /* the next two bytes are the number of fields  */
    if (pqGetInt(&(result->numAttributes), 2, conn))
        goto failure;
    nfields = result->numAttributes;
 
    /* allocate space for the attribute descriptors */
    if (nfields > 0)
    {
        result->attDescs = (PGresAttDesc *)
            pqResultAlloc(result, nfields * sizeof(PGresAttDesc), true);
        if (!result->attDescs)
            goto failure;
        MemSet(result->attDescs, 0, nfields * sizeof(PGresAttDesc));
    }
 
    for (i = 0; i < nfields; i++)
    {
        int         format;
 
        if (pqGetInt(&format, 2, conn))
            goto failure;
 
        /*
         * Since pqGetInt treats 2-byte integers as unsigned, we need to
         * coerce these results to signed form.
         */
        format = (int) ((int16) format);
        result->attDescs[i].format = format;
    }
 
    /* Success! */
    conn->result = result;
    return 0;
 
failure:
    PQclear(result);
    return EOF;
}
 
/*
 * getReadyForQuery - process ReadyForQuery message
 */
static int
getReadyForQuery(PGconn *conn)
{
    char        xact_status;
 
    if (pqGetc(&xact_status, conn))
        return EOF;
    switch (xact_status)
    {
        case 'I':
            conn->xactStatus = PQTRANS_IDLE;
            break;
        case 'T':
            conn->xactStatus = PQTRANS_INTRANS;
            break;
        case 'E':
            conn->xactStatus = PQTRANS_INERROR;
            break;
        default:
            conn->xactStatus = PQTRANS_UNKNOWN;
            break;
    }
 
    return 0;
}
 
/*
 * getCopyDataMessage - fetch next CopyData message, process async messages
 *
 * Returns length word of CopyData message (> 0), or 0 if no complete
 * message available, -1 if end of copy, -2 if error.
 */
static int
getCopyDataMessage(PGconn *conn)
{
    char        id;
    int         msgLength;
    int         avail;
 
    for (;;)
    {
        /*
         * Do we have the next input message?  To make life simpler for async
         * callers, we keep returning 0 until the next message is fully
         * available, even if it is not Copy Data.
         */
        conn->inCursor = conn->inStart;
        if (pqGetc(&id, conn))
            return 0;
        if (pqGetInt(&msgLength, 4, conn))
            return 0;
        if (msgLength < 4)
        {
            handleSyncLoss(conn, id, msgLength);
            return -2;
        }
        avail = conn->inEnd - conn->inCursor;
        if (avail < msgLength - 4)
        {
            /*
             * Before returning, enlarge the input buffer if needed to hold
             * the whole message.  See notes in parseInput.
             */
            if (pqCheckInBufferSpace(conn->inCursor + (size_t) msgLength - 4,
                                     conn))
            {
                /*
                 * Abandon the connection.  There's not much else we can
                 * safely do; we can't just ignore the message or we could
                 * miss important changes to the connection state.
                 * pqCheckInBufferSpace() already reported the error.
                 */
                handleFatalError(conn);
                return -2;
            }
            return 0;
        }
 
        /*
         * If it's a legitimate async message type, process it.  (NOTIFY
         * messages are not currently possible here, but we handle them for
         * completeness.)  Otherwise, if it's anything except Copy Data,
         * report end-of-copy.
         */
        switch (id)
        {
            case PqMsg_NotificationResponse:
                if (getNotify(conn))
                    return 0;
                break;
            case PqMsg_NoticeResponse:
                if (pqGetErrorNotice3(conn, false))
                    return 0;
                break;
            case PqMsg_ParameterStatus:
                if (getParameterStatus(conn))
                    return 0;
                break;
            case PqMsg_CopyData:
                return msgLength;
            case PqMsg_CopyDone:
 
                /*
                 * If this is a CopyDone message, exit COPY_OUT mode and let
                 * caller read status with PQgetResult().  If we're in
                 * COPY_BOTH mode, return to COPY_IN mode.
                 */
                if (conn->asyncStatus == PGASYNC_COPY_BOTH)
                    conn->asyncStatus = PGASYNC_COPY_IN;
                else
                    conn->asyncStatus = PGASYNC_BUSY;
                return -1;
            default:            /* treat as end of copy */
 
                /*
                 * Any other message terminates either COPY_IN or COPY_BOTH
                 * mode.
                 */
                conn->asyncStatus = PGASYNC_BUSY;
                return -1;
        }
 
        /* Drop the processed message and loop around for another */
        pqParseDone(conn, conn->inCursor);
    }
}
 
/*
 * 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
pqGetCopyData3(PGconn *conn, char **buffer, int async)
{
    int         msgLength;
 
    for (;;)
    {
        /*
         * Collect the next input message.  To make life simpler for async
         * callers, we keep returning 0 until the next message is fully
         * available, even if it is not Copy Data.
         */
        msgLength = getCopyDataMessage(conn);
        if (msgLength < 0)
            return msgLength;   /* end-of-copy or error */
        if (msgLength == 0)
        {
            /* 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;
            continue;
        }
 
        /*
         * Drop zero-length messages (shouldn't happen anyway).  Otherwise
         * pass the data back to the caller.
         */
        msgLength -= 4;
        if (msgLength > 0)
        {
            *buffer = (char *) malloc(msgLength + 1);
            if (*buffer == NULL)
            {
                libpq_append_conn_error(conn, "out of memory");
                return -2;
            }
            memcpy(*buffer, &conn->inBuffer[conn->inCursor], msgLength);
            (*buffer)[msgLength] = '\0';    /* Add terminating null */
 
            /* Mark message consumed */
            pqParseDone(conn, conn->inCursor + msgLength);
 
            return msgLength;
        }
 
        /* Empty, so drop it and loop around for another */
        pqParseDone(conn, conn->inCursor);
    }
}
 
/*
 * PQgetline - gets a newline-terminated string from the backend.
 *
 * See fe-exec.c for documentation.
 */
int
pqGetline3(PGconn *conn, char *s, int maxlen)
{
    int         status;
 
    if (conn->sock == PGINVALID_SOCKET ||
        (conn->asyncStatus != PGASYNC_COPY_OUT &&
         conn->asyncStatus != PGASYNC_COPY_BOTH) ||
        conn->copy_is_binary)
    {
        libpq_append_conn_error(conn, "PQgetline: not doing text COPY OUT");
        *s = '\0';
        return EOF;
    }
 
    while ((status = PQgetlineAsync(conn, s, maxlen - 1)) == 0)
    {
        /* need to load more data */
        if (pqWait(true, false, conn) ||
            pqReadData(conn) < 0)
        {
            *s = '\0';
            return EOF;
        }
    }
 
    if (status < 0)
    {
        /* End of copy detected; gin up old-style terminator */
        strcpy(s, "\\.");
        return 0;
    }
 
    /* Add null terminator, and strip trailing \n if present */
    if (s[status - 1] == '\n')
    {
        s[status - 1] = '\0';
        return 0;
    }
    else
    {
        s[status] = '\0';
        return 1;
    }
}
 
/*
 * PQgetlineAsync - gets a COPY data row without blocking.
 *
 * See fe-exec.c for documentation.
 */
int
pqGetlineAsync3(PGconn *conn, char *buffer, int bufsize)
{
    int         msgLength;
    int         avail;
 
    if (conn->asyncStatus != PGASYNC_COPY_OUT
        && conn->asyncStatus != PGASYNC_COPY_BOTH)
        return -1;              /* we are not doing a copy... */
 
    /*
     * Recognize the next input message.  To make life simpler for async
     * callers, we keep returning 0 until the next message is fully available
     * even if it is not Copy Data.  This should keep PQendcopy from blocking.
     * (Note: unlike pqGetCopyData3, we do not change asyncStatus here.)
     */
    msgLength = getCopyDataMessage(conn);
    if (msgLength < 0)
        return -1;              /* end-of-copy or error */
    if (msgLength == 0)
        return 0;               /* no data yet */
 
    /*
     * Move data from libpq's buffer to the caller's.  In the case where a
     * prior call found the caller's buffer too small, we use
     * conn->copy_already_done to remember how much of the row was already
     * returned to the caller.
     */
    conn->inCursor += conn->copy_already_done;
    avail = msgLength - 4 - conn->copy_already_done;
    if (avail <= bufsize)
    {
        /* Able to consume the whole message */
        memcpy(buffer, &conn->inBuffer[conn->inCursor], avail);
        /* Mark message consumed */
        conn->inStart = conn->inCursor + avail;
        /* Reset state for next time */
        conn->copy_already_done = 0;
        return avail;
    }
    else
    {
        /* We must return a partial message */
        memcpy(buffer, &conn->inBuffer[conn->inCursor], bufsize);
        /* The message is NOT consumed from libpq's buffer */
        conn->copy_already_done += bufsize;
        return bufsize;
    }
}
 
/*
 * PQendcopy
 *
 * See fe-exec.c for documentation.
 */
int
pqEndcopy3(PGconn *conn)
{
    PGresult   *result;
 
    if (conn->asyncStatus != PGASYNC_COPY_IN &&
        conn->asyncStatus != PGASYNC_COPY_OUT &&
        conn->asyncStatus != PGASYNC_COPY_BOTH)
    {
        libpq_append_conn_error(conn, "no COPY in progress");
        return 1;
    }
 
    /* Send the CopyDone message if needed */
    if (conn->asyncStatus == PGASYNC_COPY_IN ||
        conn->asyncStatus == PGASYNC_COPY_BOTH)
    {
        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;
        }
    }
 
    /*
     * 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;
 
    /* Return to active duty */
    conn->asyncStatus = PGASYNC_BUSY;
 
    /*
     * Non blocking connections may have to abort at this point.  If everyone
     * played the game there should be no problem, but in error scenarios the
     * expected messages may not have arrived yet.  (We are assuming that the
     * backend's packetizing will ensure that CommandComplete arrives along
     * with the CopyDone; are there corner cases where that doesn't happen?)
     */
    if (pqIsnonblocking(conn) && PQisBusy(conn))
        return 1;
 
    /* 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);
 
    return 1;
}
 
 
/*
 * PQfn - Send a function call to the POSTGRES backend.
 *
 * See fe-exec.c for documentation.
 */
PGresult *
pqFunctionCall3(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         msgLength;
    int         avail;
    int         i;
 
    /* already validated by PQfn */
    Assert(conn->pipelineStatus == PQ_PIPELINE_OFF);
 
    /* PQfn already validated connection state */
 
    if (pqPutMsgStart(PqMsg_FunctionCall, conn) < 0 ||
        pqPutInt(fnid, 4, conn) < 0 ||  /* function id */
        pqPutInt(1, 2, conn) < 0 || /* # of format codes */
        pqPutInt(1, 2, conn) < 0 || /* format code: BINARY */
        pqPutInt(nargs, 2, 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].len == -1)
            continue;           /* it's NULL */
 
        if (args[i].isint)
        {
            if (pqPutInt(args[i].u.integer, args[i].len, conn))
                return NULL;
        }
        else
        {
            if (pqPutnchar(args[i].u.ptr, args[i].len, conn))
                return NULL;
        }
    }
 
    if (pqPutInt(1, 2, conn) < 0)   /* result format code: BINARY */
        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.
         */
        needInput = true;
 
        conn->inCursor = conn->inStart;
        if (pqGetc(&id, conn))
            continue;
        if (pqGetInt(&msgLength, 4, conn))
            continue;
 
        /*
         * Try to validate message type/length here.  A length less than 4 is
         * definitely broken.  Large lengths should only be believed for a few
         * message types.
         */
        if (msgLength < 4)
        {
            handleSyncLoss(conn, id, msgLength);
            break;
        }
        if (msgLength > 30000 && !VALID_LONG_MESSAGE_TYPE(id))
        {
            handleSyncLoss(conn, id, msgLength);
            break;
        }
 
        /*
         * Can't process if message body isn't all here yet.
         */
        msgLength -= 4;
        avail = conn->inEnd - conn->inCursor;
        if (avail < msgLength)
        {
            /*
             * Before looping, enlarge the input buffer if needed to hold the
             * whole message.  See notes in parseInput.
             */
            if (pqCheckInBufferSpace(conn->inCursor + (size_t) msgLength,
                                     conn))
            {
                /*
                 * Abandon the connection.  There's not much else we can
                 * safely do; we can't just ignore the message or we could
                 * miss important changes to the connection state.
                 * pqCheckInBufferSpace() already reported the error.
                 */
                handleFatalError(conn);
                break;
            }
            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 PqMsg_FunctionCallResponse:
                if (pqGetInt(actual_result_len, 4, conn))
                    continue;
                if (*actual_result_len != -1)
                {
                    if (result_is_int)
                    {
                        if (pqGetInt(result_buf, *actual_result_len, conn))
                            continue;
                    }
                    else
                    {
                        if (pqGetnchar(result_buf,
                                       *actual_result_len,
                                       conn))
                            continue;
                    }
                }
                /* correctly finished function result message */
                status = PGRES_COMMAND_OK;
                break;
            case PqMsg_ErrorResponse:
                if (pqGetErrorNotice3(conn, true))
                    continue;
                status = PGRES_FATAL_ERROR;
                break;
            case PqMsg_NotificationResponse:
                /* handle notify and go back to processing return values */
                if (getNotify(conn))
                    continue;
                break;
            case PqMsg_NoticeResponse:
                /* handle notice and go back to processing return values */
                if (pqGetErrorNotice3(conn, false))
                    continue;
                break;
            case PqMsg_ReadyForQuery:
                if (getReadyForQuery(conn))
                    continue;
 
                /* consume the message */
                pqParseDone(conn, conn->inStart + 5 + msgLength);
 
                /*
                 * If we already have a result object (probably an error), use
                 * that.  Otherwise, if we saw a function result message,
                 * report COMMAND_OK.  Otherwise, the backend violated the
                 * protocol, so complain.
                 */
                if (!pgHavePendingResult(conn))
                {
                    if (status == PGRES_COMMAND_OK)
                    {
                        conn->result = PQmakeEmptyPGresult(conn, status);
                        if (!conn->result)
                        {
                            libpq_append_conn_error(conn, "out of memory");
                            pqSaveErrorResult(conn);
                        }
                    }
                    else
                    {
                        libpq_append_conn_error(conn, "protocol error: no function result");
                        pqSaveErrorResult(conn);
                    }
                }
                /* and we're out */
                return pqPrepareAsyncResult(conn);
            case PqMsg_ParameterStatus:
                if (getParameterStatus(conn))
                    continue;
                break;
            default:
                /* The backend violates the protocol. */
                libpq_append_conn_error(conn, "protocol error: id=0x%x", id);
                pqSaveErrorResult(conn);
 
                /*
                 * We can't call parsing done due to the protocol violation
                 * (so message tracing wouldn't work), but trust the specified
                 * message length as what to skip.
                 */
                conn->inStart += 5 + msgLength;
                return pqPrepareAsyncResult(conn);
        }
 
        /* Completed parsing this message, keep going */
        pqParseDone(conn, conn->inStart + 5 + msgLength);
        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 *
pqBuildStartupPacket3(PGconn *conn, int *packetlen,
                      const PQEnvironmentOption *options)
{
    char       *startpacket;
    size_t      len;
 
    len = build_startup_packet(conn, NULL, options);
    if (len == 0 || len > INT_MAX)
        return NULL;
 
    *packetlen = len;
    startpacket = (char *) malloc(*packetlen);
    if (!startpacket)
        return NULL;
 
    len = build_startup_packet(conn, startpacket, options);
    Assert(*packetlen == len);
 
    return startpacket;
}
 
/*
 * Build a startup packet given a filled-in PGconn structure.
 *
 * We need to figure out how much space is needed, then fill it in.
 * To avoid duplicate logic, this routine is called twice: the first time
 * (with packet == NULL) just counts the space needed, the second time
 * (with packet == allocated space) fills it in.  Return value is the number
 * of bytes used, or zero in the unlikely event of size_t overflow.
 */
static size_t
build_startup_packet(const PGconn *conn, char *packet,
                     const PQEnvironmentOption *options)
{
    size_t      packet_len = 0;
    const PQEnvironmentOption *next_eo;
    const char *val;
 
    /* Protocol version comes first. */
    if (packet)
    {
        ProtocolVersion pv = pg_hton32(conn->pversion);
 
        memcpy(packet + packet_len, &pv, sizeof(ProtocolVersion));
    }
    packet_len += sizeof(ProtocolVersion);
 
    /* Add user name, database name, options */
 
#define ADD_STARTUP_OPTION(optname, optval) \
    do { \
        if (packet) \
            strcpy(packet + packet_len, optname); \
        if (pg_add_size_overflow(packet_len, strlen(optname) + 1, &packet_len)) \
            return 0; \
        if (packet) \
            strcpy(packet + packet_len, optval); \
        if (pg_add_size_overflow(packet_len, strlen(optval) + 1, &packet_len)) \
            return 0; \
    } while(0)
 
    if (conn->pguser && conn->pguser[0])
        ADD_STARTUP_OPTION("user", conn->pguser);
    if (conn->dbName && conn->dbName[0])
        ADD_STARTUP_OPTION("database", conn->dbName);
    if (conn->replication && conn->replication[0])
        ADD_STARTUP_OPTION("replication", conn->replication);
    if (conn->pgoptions && conn->pgoptions[0])
        ADD_STARTUP_OPTION("options", conn->pgoptions);
    if (conn->send_appname)
    {
        /* Use appname if present, otherwise use fallback */
        val = conn->appname ? conn->appname : conn->fbappname;
        if (val && val[0])
            ADD_STARTUP_OPTION("application_name", val);
    }
 
    if (conn->client_encoding_initial && conn->client_encoding_initial[0])
        ADD_STARTUP_OPTION("client_encoding", conn->client_encoding_initial);
 
    /*
     * Add the test_protocol_negotiation option when greasing, to test that
     * servers properly report unsupported protocol options in addition to
     * unsupported minor versions.
     */
    if (conn->pversion == PG_PROTOCOL_GREASE)
        ADD_STARTUP_OPTION("_pq_.test_protocol_negotiation", "");
 
    /* Add any environment-driven GUC settings needed */
    for (next_eo = options; next_eo->envName; next_eo++)
    {
        if ((val = getenv(next_eo->envName)) != NULL)
        {
            if (pg_strcasecmp(val, "default") != 0)
                ADD_STARTUP_OPTION(next_eo->pgName, val);
        }
    }
 
    /* Add trailing terminator */
    if (packet)
        packet[packet_len] = '\0';
    if (pg_add_size_overflow(packet_len, 1, &packet_len))
        return 0;
 
    return packet_len;
}