Please define PQ_BUFFER_SIZE in interfaces/libpq/fe-misc.c - Mailing list pgsql-patches

Hi,

I am accelerating the transfer of resultset
from backend to client using the zlib library.
While coding, I was surprised that
magic number 8192 (which is defined as PQ_BUFFER_SIZE in
backend/libpq/pqcomm.c) are written into the code
in interfaces/libpq/fe-misc.

I thought the magic number should be eliminated.
So I defined the magic number 8192 as PQ_BUFFER_SIZE in fe-misc.c.
The result is attached to this mail.
# it is just a slight modification

I am very happy if you accept my proposition.

Best regards,

-- Hideyuki Kawashima
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Hideyuki KAWASHIMA <kawasima@ayu.ics.keio.ac.jp> Ph.D.
Research Associate, Keio University
/*-------------------------------------------------------------------------
 *
 *     FILE
 *        fe-misc.c
 *
 *     DESCRIPTION
 *         miscellaneous useful functions
 *
 * The communication routines here are analogous to the ones in
 * backend/libpq/pqcomm.c and backend/libpq/pqcomprim.c, but operate
 * in the considerably different environment of the frontend libpq.
 * In particular, we work with a bare nonblock-mode socket, rather than
 * a stdio stream, so that we can avoid unwanted blocking of the application.
 *
 * XXX: MOVE DEBUG PRINTOUT TO HIGHER LEVEL.  As is, block and restart
 * will cause repeat printouts.
 *
 * We must speak the same transmitted data representations as the backend
 * routines.
 *
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/interfaces/libpq/fe-misc.c,v 1.112 2004/12/31 22:03:50 pgsql Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include <errno.h>
#include <signal.h>
#include <time.h>

#ifndef WIN32_CLIENT_ONLY
#include <netinet/in.h>
#include <arpa/inet.h>
#endif

#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#include <sys/time.h>
#endif

#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#ifdef HAVE_SYS_POLL_H
#include <sys/poll.h>
#endif
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif

#include "libpq-fe.h"
#include "libpq-int.h"
#include "pqsignal.h"
#include "mb/pg_wchar.h"

#define PQ_BUFFER_SIZE 8192

static int    pqPutMsgBytes(const void *buf, size_t len, PGconn *conn);
static int    pqSendSome(PGconn *conn, int len);
static int pqSocketCheck(PGconn *conn, int forRead, int forWrite,
              time_t end_time);
static int    pqSocketPoll(int sock, int forRead, int forWrite, time_t end_time);


/*
 * pqGetc: get 1 character from the connection
 *
 *    All these routines return 0 on success, EOF on error.
 *    Note that for the Get routines, EOF only means there is not enough
 *    data in the buffer, not that there is necessarily a hard error.
 */
int
pqGetc(char *result, PGconn *conn)
{
    if (conn->inCursor >= conn->inEnd)
        return EOF;

    *result = conn->inBuffer[conn->inCursor++];

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "From backend> %c\n", *result);

    return 0;
}


/*
 * pqPutc: write 1 char to the current message
 */
int
pqPutc(char c, PGconn *conn)
{
    if (pqPutMsgBytes(&c, 1, conn))
        return EOF;

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend> %c\n", c);

    return 0;
}


/*
 * pqGets:
 * get a null-terminated string from the connection,
 * and store it in an expansible PQExpBuffer.
 * If we run out of memory, all of the string is still read,
 * but the excess characters are silently discarded.
 */
int
pqGets(PQExpBuffer buf, PGconn *conn)
{
    /* Copy conn data to locals for faster search loop */
    char       *inBuffer = conn->inBuffer;
    int            inCursor = conn->inCursor;
    int            inEnd = conn->inEnd;
    int            slen;

    while (inCursor < inEnd && inBuffer[inCursor])
        inCursor++;

    if (inCursor >= inEnd)
        return EOF;

    slen = inCursor - conn->inCursor;

    resetPQExpBuffer(buf);
    appendBinaryPQExpBuffer(buf, inBuffer + conn->inCursor, slen);

    conn->inCursor = ++inCursor;

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "From backend> \"%s\"\n",
                buf->data);

    return 0;
}


/*
 * pqPuts: write a null-terminated string to the current message
 */
int
pqPuts(const char *s, PGconn *conn)
{
    if (pqPutMsgBytes(s, strlen(s) + 1, conn))
        return EOF;

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend> '%s'\n", s);

    return 0;
}

/*
 * pqGetnchar:
 *    get a string of exactly len bytes in buffer s, no null termination
 */
int
pqGetnchar(char *s, size_t len, PGconn *conn)
{
    if (len < 0 || len > (size_t) (conn->inEnd - conn->inCursor))
        return EOF;

    memcpy(s, conn->inBuffer + conn->inCursor, len);
    /* no terminating null */

    conn->inCursor += len;

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "From backend (%lu)> %.*s\n", (unsigned long) len, (int) len, s);

    return 0;
}

/*
 * pqPutnchar:
 *    write exactly len bytes to the current message
 */
int
pqPutnchar(const char *s, size_t len, PGconn *conn)
{
    if (pqPutMsgBytes(s, len, conn))
        return EOF;

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend> %.*s\n", (int) len, s);

    return 0;
}

/*
 * pqGetInt
 *    read a 2 or 4 byte integer and convert from network byte order
 *    to local byte order
 */
int
pqGetInt(int *result, size_t bytes, PGconn *conn)
{
    uint16        tmp2;
    uint32        tmp4;

    switch (bytes)
    {
        case 2:
            if (conn->inCursor + 2 > conn->inEnd)
                return EOF;
            memcpy(&tmp2, conn->inBuffer + conn->inCursor, 2);
            conn->inCursor += 2;
            *result = (int) ntohs(tmp2);
            break;
        case 4:
            if (conn->inCursor + 4 > conn->inEnd)
                return EOF;
            memcpy(&tmp4, conn->inBuffer + conn->inCursor, 4);
            conn->inCursor += 4;
            *result = (int) ntohl(tmp4);
            break;
        default:
            pqInternalNotice(&conn->noticeHooks,
                         "integer of size %lu not supported by pqGetInt",
                             (unsigned long) bytes);
            return EOF;
    }

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "From backend (#%lu)> %d\n", (unsigned long) bytes, *result);

    return 0;
}

/*
 * pqPutInt
 * write an integer of 2 or 4 bytes, converting from host byte order
 * to network byte order.
 */
int
pqPutInt(int value, size_t bytes, PGconn *conn)
{
    uint16        tmp2;
    uint32        tmp4;

    switch (bytes)
    {
        case 2:
            tmp2 = htons((uint16) value);
            if (pqPutMsgBytes((const char *) &tmp2, 2, conn))
                return EOF;
            break;
        case 4:
            tmp4 = htonl((uint32) value);
            if (pqPutMsgBytes((const char *) &tmp4, 4, conn))
                return EOF;
            break;
        default:
            pqInternalNotice(&conn->noticeHooks,
                         "integer of size %lu not supported by pqPutInt",
                             (unsigned long) bytes);
            return EOF;
    }

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend (%lu#)> %d\n", (unsigned long) bytes, value);

    return 0;
}

/*
 * Make sure conn's output buffer can hold bytes_needed bytes (caller must
 * include already-stored data into the value!)
 *
 * Returns 0 on success, EOF if failed to enlarge buffer
 */
int
pqCheckOutBufferSpace(int bytes_needed, PGconn *conn)
{
    int            newsize = conn->outBufSize;
    char       *newbuf;

    if (bytes_needed <= newsize)
        return 0;

    /*
     * If we need to enlarge the buffer, we first try to double it in
     * size; if that doesn't work, enlarge in multiples of 8K.  This
     * avoids thrashing the malloc pool by repeated small enlargements.
     *
     * Note: tests for newsize > 0 are to catch integer overflow.
     */
    do
    {
        newsize *= 2;
    } while (bytes_needed > newsize && newsize > 0);

    if (bytes_needed <= newsize)
    {
        newbuf = realloc(conn->outBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->outBuffer = newbuf;
            conn->outBufSize = newsize;
            return 0;
        }
    }

    newsize = conn->outBufSize;
    do
    {
        newsize += PQ_BUFFER_SIZE;
    } while (bytes_needed > newsize && newsize > 0);

    if (bytes_needed <= newsize)
    {
        newbuf = realloc(conn->outBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->outBuffer = newbuf;
            conn->outBufSize = newsize;
            return 0;
        }
    }

    /* realloc failed. Probably out of memory */
    printfPQExpBuffer(&conn->errorMessage,
                      "cannot allocate memory for output buffer\n");
    return EOF;
}

/*
 * Make sure conn's input buffer can hold bytes_needed bytes (caller must
 * include already-stored data into the value!)
 *
 * Returns 0 on success, EOF if failed to enlarge buffer
 */
int
pqCheckInBufferSpace(int bytes_needed, PGconn *conn)
{
    int            newsize = conn->inBufSize;
    char       *newbuf;

    if (bytes_needed <= newsize)
        return 0;

    /*
     * If we need to enlarge the buffer, we first try to double it in
     * size; if that doesn't work, enlarge in multiples of 8K.  This
     * avoids thrashing the malloc pool by repeated small enlargements.
     *
     * Note: tests for newsize > 0 are to catch integer overflow.
     */
    do
    {
        newsize *= 2;
    } while (bytes_needed > newsize && newsize > 0);

    if (bytes_needed <= newsize)
    {
        newbuf = realloc(conn->inBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->inBuffer = newbuf;
            conn->inBufSize = newsize;
            return 0;
        }
    }

    newsize = conn->inBufSize;
    do
    {
        newsize += PQ_BUFFER_SIZE;
    } while (bytes_needed > newsize && newsize > 0);

    if (bytes_needed <= newsize)
    {
        newbuf = realloc(conn->inBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->inBuffer = newbuf;
            conn->inBufSize = newsize;
            return 0;
        }
    }

    /* realloc failed. Probably out of memory */
    printfPQExpBuffer(&conn->errorMessage,
                      "cannot allocate memory for input buffer\n");
    return EOF;
}

/*
 * pqPutMsgStart: begin construction of a message to the server
 *
 * msg_type is the message type byte, or 0 for a message without type byte
 * (only startup messages have no type byte)
 *
 * force_len forces the message to have a length word; otherwise, we add
 * a length word if protocol 3.
 *
 * Returns 0 on success, EOF on error
 *
 * The idea here is that we construct the message in conn->outBuffer,
 * beginning just past any data already in outBuffer (ie, at
 * outBuffer+outCount).  We enlarge the buffer as needed to hold the message.
 * When the message is complete, we fill in the length word (if needed) and
 * then advance outCount past the message, making it eligible to send.
 *
 * The state variable conn->outMsgStart points to the incomplete message's
 * length word: it is either outCount or outCount+1 depending on whether
 * there is a type byte.  If we are sending a message without length word
 * (pre protocol 3.0 only), then outMsgStart is -1.  The state variable
 * conn->outMsgEnd is the end of the data collected so far.
 */
int
pqPutMsgStart(char msg_type, bool force_len, PGconn *conn)
{
    int            lenPos;
    int            endPos;

    /* allow room for message type byte */
    if (msg_type)
        endPos = conn->outCount + 1;
    else
        endPos = conn->outCount;

    /* do we want a length word? */
    if (force_len || PG_PROTOCOL_MAJOR(conn->pversion) >= 3)
    {
        lenPos = endPos;
        /* allow room for message length */
        endPos += 4;
    }
    else
        lenPos = -1;

    /* make sure there is room for message header */
    if (pqCheckOutBufferSpace(endPos, conn))
        return EOF;
    /* okay, save the message type byte if any */
    if (msg_type)
        conn->outBuffer[conn->outCount] = msg_type;
    /* set up the message pointers */
    conn->outMsgStart = lenPos;
    conn->outMsgEnd = endPos;
    /* length word, if needed, will be filled in by pqPutMsgEnd */

    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend> Msg %c\n",
                msg_type ? msg_type : ' ');

    return 0;
}

/*
 * pqPutMsgBytes: add bytes to a partially-constructed message
 *
 * Returns 0 on success, EOF on error
 */
static int
pqPutMsgBytes(const void *buf, size_t len, PGconn *conn)
{
    /* make sure there is room for it */
    if (pqCheckOutBufferSpace(conn->outMsgEnd + len, conn))
        return EOF;
    /* okay, save the data */
    memcpy(conn->outBuffer + conn->outMsgEnd, buf, len);
    conn->outMsgEnd += len;
    /* no Pfdebug call here, caller should do it */
    return 0;
}

/*
 * pqPutMsgEnd: finish constructing a message and possibly send it
 *
 * Returns 0 on success, EOF on error
 *
 * We don't actually send anything here unless we've accumulated at least
 * 8K worth of data (the typical size of a pipe buffer on Unix systems).
 * This avoids sending small partial packets.  The caller must use pqFlush
 * when it's important to flush all the data out to the server.
 */
int
pqPutMsgEnd(PGconn *conn)
{
    if (conn->Pfdebug)
        fprintf(conn->Pfdebug, "To backend> Msg complete, length %u\n",
                conn->outMsgEnd - conn->outCount);

    /* Fill in length word if needed */
    if (conn->outMsgStart >= 0)
    {
        uint32        msgLen = conn->outMsgEnd - conn->outMsgStart;

        msgLen = htonl(msgLen);
        memcpy(conn->outBuffer + conn->outMsgStart, &msgLen, 4);
    }

    /* Make message eligible to send */
    conn->outCount = conn->outMsgEnd;

    if (conn->outCount >= PQ_BUFFER_SIZE)
    {
        int            toSend = conn->outCount - (conn->outCount % PQ_BUFFER_SIZE);

        if (pqSendSome(conn, toSend) < 0)
            return EOF;
        /* in nonblock mode, don't complain if unable to send it all */
    }

    return 0;
}

/* ----------
 * pqReadData: read more data, if any is available
 * Possible return values:
 *     1: successfully loaded at least one more byte
 *     0: no data is presently available, but no error detected
 *    -1: error detected (including EOF = connection closure);
 *        conn->errorMessage set
 * NOTE: callers must not assume that pointers or indexes into conn->inBuffer
 * remain valid across this call!
 * ----------
 */
int
pqReadData(PGconn *conn)
{
    int            someread = 0;
    int            nread;
    char        sebuf[256];

    if (conn->sock < 0)
    {
        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("connection not open\n"));
        return -1;
    }

    /* Left-justify any data in the buffer to make room */
    if (conn->inStart < conn->inEnd)
    {
        if (conn->inStart > 0)
        {
            memmove(conn->inBuffer, conn->inBuffer + conn->inStart,
                    conn->inEnd - conn->inStart);
            conn->inEnd -= conn->inStart;
            conn->inCursor -= conn->inStart;
            conn->inStart = 0;
        }
    }
    else
    {
        /* buffer is logically empty, reset it */
        conn->inStart = conn->inCursor = conn->inEnd = 0;
    }

    /*
     * If the buffer is fairly full, enlarge it. We need to be able to
     * enlarge the buffer in case a single message exceeds the initial
     * buffer size.  We enlarge before filling the buffer entirely so as
     * to avoid asking the kernel for a partial packet. The magic constant
     * here should be large enough for a TCP packet or Unix pipe
     * bufferload.    8K is the usual pipe buffer size, so...
     */
    if (conn->inBufSize - conn->inEnd < PQ_BUFFER_SIZE)
    {
        if (pqCheckInBufferSpace(conn->inEnd + PQ_BUFFER_SIZE, conn))
        {
            /*
             * We don't insist that the enlarge worked, but we need some
             * room
             */
            if (conn->inBufSize - conn->inEnd < 100)
                return -1;        /* errorMessage already set */
        }
    }

    /* OK, try to read some data */
retry3:
    nread = pqsecure_read(conn, conn->inBuffer + conn->inEnd,
                          conn->inBufSize - conn->inEnd);
    if (nread < 0)
    {
        if (SOCK_ERRNO == EINTR)
            goto retry3;
        /* Some systems return EAGAIN/EWOULDBLOCK for no data */
#ifdef EAGAIN
        if (SOCK_ERRNO == EAGAIN)
            return someread;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
        if (SOCK_ERRNO == EWOULDBLOCK)
            return someread;
#endif
        /* We might get ECONNRESET here if using TCP and backend died */
#ifdef ECONNRESET
        if (SOCK_ERRNO == ECONNRESET)
            goto definitelyFailed;
#endif
        printfPQExpBuffer(&conn->errorMessage,
               libpq_gettext("could not receive data from server: %s\n"),
                        SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
        return -1;
    }
    if (nread > 0)
    {
        conn->inEnd += nread;

        /*
         * Hack to deal with the fact that some kernels will only give us
         * back 1 packet per recv() call, even if we asked for more and
         * there is more available.  If it looks like we are reading a
         * long message, loop back to recv() again immediately, until we
         * run out of data or buffer space.  Without this, the
         * block-and-restart behavior of libpq's higher levels leads to
         * O(N^2) performance on long messages.
         *
         * Since we left-justified the data above, conn->inEnd gives the
         * amount of data already read in the current message.    We
         * consider the message "long" once we have acquired 32k ...
         */
        if (conn->inEnd > 32768 &&
            (conn->inBufSize - conn->inEnd) >= PQ_BUFFER_SIZE)
        {
            someread = 1;
            goto retry3;
        }
        return 1;
    }

    if (someread)
        return 1;                /* got a zero read after successful tries */

    /*
     * A return value of 0 could mean just that no data is now available,
     * or it could mean EOF --- that is, the server has closed the
     * connection. Since we have the socket in nonblock mode, the only way
     * to tell the difference is to see if select() is saying that the
     * file is ready. Grumble.    Fortunately, we don't expect this path to
     * be taken much, since in normal practice we should not be trying to
     * read data unless the file selected for reading already.
     *
     * In SSL mode it's even worse: SSL_read() could say WANT_READ and then
     * data could arrive before we make the pqReadReady() test.  So we
     * must play dumb and assume there is more data, relying on the SSL
     * layer to detect true EOF.
     */

#ifdef USE_SSL
    if (conn->ssl)
        return 0;
#endif

    switch (pqReadReady(conn))
    {
        case 0:
            /* definitely no data available */
            return 0;
        case 1:
            /* ready for read */
            break;
        default:
            goto definitelyFailed;
    }

    /*
     * Still not sure that it's EOF, because some data could have just
     * arrived.
     */
retry4:
    nread = pqsecure_read(conn, conn->inBuffer + conn->inEnd,
                          conn->inBufSize - conn->inEnd);
    if (nread < 0)
    {
        if (SOCK_ERRNO == EINTR)
            goto retry4;
        /* Some systems return EAGAIN/EWOULDBLOCK for no data */
#ifdef EAGAIN
        if (SOCK_ERRNO == EAGAIN)
            return 0;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
        if (SOCK_ERRNO == EWOULDBLOCK)
            return 0;
#endif
        /* We might get ECONNRESET here if using TCP and backend died */
#ifdef ECONNRESET
        if (SOCK_ERRNO == ECONNRESET)
            goto definitelyFailed;
#endif
        printfPQExpBuffer(&conn->errorMessage,
               libpq_gettext("could not receive data from server: %s\n"),
                        SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
        return -1;
    }
    if (nread > 0)
    {
        conn->inEnd += nread;
        return 1;
    }

    /*
     * OK, we are getting a zero read even though select() says ready.
     * This means the connection has been closed.  Cope.
     */
definitelyFailed:
    printfPQExpBuffer(&conn->errorMessage,
                      libpq_gettext(
                            "server closed the connection unexpectedly\n"
               "\tThis probably means the server terminated abnormally\n"
                         "\tbefore or while processing the request.\n"));
    conn->status = CONNECTION_BAD;        /* No more connection to backend */
    pqsecure_close(conn);
    closesocket(conn->sock);
    conn->sock = -1;

    return -1;
}

/*
 * pqSendSome: send data waiting in the output buffer.
 *
 * len is how much to try to send (typically equal to outCount, but may
 * be less).
 *
 * Return 0 on success, -1 on failure and 1 when not all data could be sent
 * because the socket would block and the connection is non-blocking.
 */
static int
pqSendSome(PGconn *conn, int len)
{
    char       *ptr = conn->outBuffer;
    int            remaining = conn->outCount;
    int            result = 0;

    if (conn->sock < 0)
    {
        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("connection not open\n"));
        return -1;
    }

    /* while there's still data to send */
    while (len > 0)
    {
        int            sent;
        char        sebuf[256];

        sent = pqsecure_write(conn, ptr, len);

        if (sent < 0)
        {
            /*
             * Anything except EAGAIN/EWOULDBLOCK/EINTR is trouble. If
             * it's EPIPE or ECONNRESET, assume we've lost the backend
             * connection permanently.
             */
            switch (SOCK_ERRNO)
            {
#ifdef EAGAIN
                case EAGAIN:
                    break;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
                case EWOULDBLOCK:
                    break;
#endif
                case EINTR:
                    continue;

                case EPIPE:
#ifdef ECONNRESET
                case ECONNRESET:
#endif
                    printfPQExpBuffer(&conn->errorMessage,
                                      libpq_gettext(
                            "server closed the connection unexpectedly\n"
                                                    "\tThis probably means the server terminated abnormally\n"
                         "\tbefore or while processing the request.\n"));

                    /*
                     * We used to close the socket here, but that's a bad
                     * idea since there might be unread data waiting
                     * (typically, a NOTICE message from the backend
                     * telling us it's committing hara-kiri...).  Leave
                     * the socket open until pqReadData finds no more data
                     * can be read.  But abandon attempt to send data.
                     */
                    conn->outCount = 0;
                    return -1;

                default:
                    printfPQExpBuffer(&conn->errorMessage,
                    libpq_gettext("could not send data to server: %s\n"),
                        SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
                    /* We don't assume it's a fatal error... */
                    conn->outCount = 0;
                    return -1;
            }
        }
        else
        {
            ptr += sent;
            len -= sent;
            remaining -= sent;
        }

        if (len > 0)
        {
            /*
             * We didn't send it all, wait till we can send more.
             *
             * If the connection is in non-blocking mode we don't wait, but
             * return 1 to indicate that data is still pending.
             */
            if (pqIsnonblocking(conn))
            {
                result = 1;
                break;
            }

            /*
             * There are scenarios in which we can't send data because the
             * communications channel is full, but we cannot expect the
             * server to clear the channel eventually because it's blocked
             * trying to send data to us.  (This can happen when we are
             * sending a large amount of COPY data, and the server has
             * generated lots of NOTICE responses.)  To avoid a deadlock
             * situation, we must be prepared to accept and buffer
             * incoming data before we try again.  Furthermore, it is
             * possible that such incoming data might not arrive until
             * after we've gone to sleep.  Therefore, we wait for either
             * read ready or write ready.
             */
            if (pqReadData(conn) < 0)
            {
                result = -1;    /* error message already set up */
                break;
            }
            if (pqWait(TRUE, TRUE, conn))
            {
                result = -1;
                break;
            }
        }
    }

    /* shift the remaining contents of the buffer */
    if (remaining > 0)
        memmove(conn->outBuffer, ptr, remaining);
    conn->outCount = remaining;

    return result;
}


/*
 * pqFlush: send any data waiting in the output buffer
 *
 * Return 0 on success, -1 on failure and 1 when not all data could be sent
 * because the socket would block and the connection is non-blocking.
 */
int
pqFlush(PGconn *conn)
{
    if (conn->Pfdebug)
        fflush(conn->Pfdebug);

    if (conn->outCount > 0)
        return pqSendSome(conn, conn->outCount);

    return 0;
}


/*
 * pqWait: wait until we can read or write the connection socket
 *
 * JAB: If SSL enabled and used and forRead, buffered bytes short-circuit the
 * call to select().
 *
 * We also stop waiting and return if the kernel flags an exception condition
 * on the socket.  The actual error condition will be detected and reported
 * when the caller tries to read or write the socket.
 */
int
pqWait(int forRead, int forWrite, PGconn *conn)
{
    return pqWaitTimed(forRead, forWrite, conn, (time_t) -1);
}

/*
 * pqWaitTimed: wait, but not past finish_time.
 *
 * If finish_time is exceeded then we return failure (EOF).  This is like
 * the response for a kernel exception because we don't want the caller
 * to try to read/write in that case.
 *
 * finish_time = ((time_t) -1) disables the wait limit.
 */
int
pqWaitTimed(int forRead, int forWrite, PGconn *conn, time_t finish_time)
{
    int            result;

    result = pqSocketCheck(conn, forRead, forWrite, finish_time);

    if (result < 0)
        return EOF;                /* errorMessage is already set */

    if (result == 0)
    {
        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("timeout expired\n"));
        return EOF;
    }

    return 0;
}

/*
 * pqReadReady: is select() saying the file is ready to read?
 * Returns -1 on failure, 0 if not ready, 1 if ready.
 */
int
pqReadReady(PGconn *conn)
{
    return pqSocketCheck(conn, 1, 0, (time_t) 0);
}

/*
 * pqWriteReady: is select() saying the file is ready to write?
 * Returns -1 on failure, 0 if not ready, 1 if ready.
 */
int
pqWriteReady(PGconn *conn)
{
    return pqSocketCheck(conn, 0, 1, (time_t) 0);
}

/*
 * Checks a socket, using poll or select, for data to be read, written,
 * or both.  Returns >0 if one or more conditions are met, 0 if it timed
 * out, -1 if an error occurred.
 *
 * If SSL is in use, the SSL buffer is checked prior to checking the socket
 * for read data directly.
 */
static int
pqSocketCheck(PGconn *conn, int forRead, int forWrite, time_t end_time)
{
    int            result;

    if (!conn)
        return -1;
    if (conn->sock < 0)
    {
        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("socket not open\n"));
        return -1;
    }

#ifdef USE_SSL
    /* Check for SSL library buffering read bytes */
    if (forRead && conn->ssl && SSL_pending(conn->ssl) > 0)
    {
        /* short-circuit the select */
        return 1;
    }
#endif

    /* We will retry as long as we get EINTR */
    do
        result = pqSocketPoll(conn->sock, forRead, forWrite, end_time);
    while (result < 0 && SOCK_ERRNO == EINTR);

    if (result < 0)
    {
        char        sebuf[256];

        printfPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("select() failed: %s\n"),
                        SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
    }

    return result;
}


/*
 * Check a file descriptor for read and/or write data, possibly waiting.
 * If neither forRead nor forWrite are set, immediately return a timeout
 * condition (without waiting).  Return >0 if condition is met, 0
 * if a timeout occurred, -1 if an error or interrupt occurred.
 *
 * Timeout is infinite if end_time is -1.  Timeout is immediate (no blocking)
 * if end_time is 0 (or indeed, any time before now).
 */
static int
pqSocketPoll(int sock, int forRead, int forWrite, time_t end_time)
{
    /* We use poll(2) if available, otherwise select(2) */
#ifdef HAVE_POLL
    struct pollfd input_fd;
    int            timeout_ms;

    if (!forRead && !forWrite)
        return 0;

    input_fd.fd = sock;
    input_fd.events = POLLERR;
    input_fd.revents = 0;

    if (forRead)
        input_fd.events |= POLLIN;
    if (forWrite)
        input_fd.events |= POLLOUT;

    /* Compute appropriate timeout interval */
    if (end_time == ((time_t) -1))
        timeout_ms = -1;
    else
    {
        time_t        now = time(NULL);

        if (end_time > now)
            timeout_ms = (end_time - now) * 1000;
        else
            timeout_ms = 0;
    }

    return poll(&input_fd, 1, timeout_ms);

#else                            /* !HAVE_POLL */

    fd_set        input_mask;
    fd_set        output_mask;
    fd_set        except_mask;
    struct timeval timeout;
    struct timeval *ptr_timeout;

    if (!forRead && !forWrite)
        return 0;

    FD_ZERO(&input_mask);
    FD_ZERO(&output_mask);
    FD_ZERO(&except_mask);
    if (forRead)
        FD_SET(sock, &input_mask);
    if (forWrite)
        FD_SET(sock, &output_mask);
    FD_SET(sock, &except_mask);

    /* Compute appropriate timeout interval */
    if (end_time == ((time_t) -1))
        ptr_timeout = NULL;
    else
    {
        time_t        now = time(NULL);

        if (end_time > now)
            timeout.tv_sec = end_time - now;
        else
            timeout.tv_sec = 0;
        timeout.tv_usec = 0;
        ptr_timeout = &timeout;
    }

    return select(sock + 1, &input_mask, &output_mask,
                  &except_mask, ptr_timeout);
#endif   /* HAVE_POLL */
}


/*
 * A couple of "miscellaneous" multibyte related functions. They used
 * to be in fe-print.c but that file is doomed.
 */

/*
 * returns the byte length of the word beginning s, using the
 * specified encoding.
 */
int
PQmblen(const unsigned char *s, int encoding)
{
    return (pg_encoding_mblen(encoding, s));
}

/*
 * returns the display length of the word beginning s, using the
 * specified encoding.
 */
int
PQdsplen(const unsigned char *s, int encoding)
{
    return (pg_encoding_dsplen(encoding, s));
}

/*
 * Get encoding id from environment variable PGCLIENTENCODING.
 */
int
PQenv2encoding(void)
{
    char       *str;
    int            encoding = PG_SQL_ASCII;

    str = getenv("PGCLIENTENCODING");
    if (str && *str != '\0')
        encoding = pg_char_to_encoding(str);
    return (encoding);
}


#ifdef ENABLE_NLS

char *
libpq_gettext(const char *msgid)
{
    static int    already_bound = 0;

    if (!already_bound)
    {
        already_bound = 1;
        /* No relocatable lookup here because the binary could be anywhere */
        bindtextdomain("libpq", getenv("PGLOCALEDIR") ? getenv("PGLOCALEDIR") : LOCALEDIR);
    }

    return dgettext("libpq", msgid);
}

#endif   /* ENABLE_NLS */