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 <[EMAIL PROTECTED]> 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 */
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