fe-misc.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 *   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/pqformat.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) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-misc.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <signal.h>
#include <time.h>
 
#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#include <sys/select.h>
#include <sys/time.h>
#endif
 
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
 
#include "libpq-fe.h"
#include "libpq-int.h"
#include "mb/pg_wchar.h"
#include "pg_config_paths.h"
#include "port/pg_bswap.h"
 
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,
                          pg_usec_time_t end_time);
 
/*
 * PQlibVersion: return the libpq version number
 */
int
PQlibVersion(void)
{
    return PG_VERSION_NUM;
}
 
 
/*
 * pqGetc: read 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++];
 
    return 0;
}
 
 
/*
 * pqPutc: write 1 char to the current message
 */
int
pqPutc(char c, PGconn *conn)
{
    if (pqPutMsgBytes(&c, 1, conn))
        return EOF;
 
    return 0;
}
 
 
/*
 * pqGets[_append]:
 * read 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.
 */
static int
pqGets_internal(PQExpBuffer buf, PGconn *conn, bool resetbuffer)
{
    /* 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;
 
    if (resetbuffer)
        resetPQExpBuffer(buf);
 
    appendBinaryPQExpBuffer(buf, inBuffer + conn->inCursor, slen);
 
    conn->inCursor = ++inCursor;
 
    return 0;
}
 
int
pqGets(PQExpBuffer buf, PGconn *conn)
{
    return pqGets_internal(buf, conn, true);
}
 
int
pqGets_append(PQExpBuffer buf, PGconn *conn)
{
    return pqGets_internal(buf, conn, false);
}
 
 
/*
 * 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;
 
    return 0;
}
 
/*
 * pqGetnchar:
 *  read exactly len bytes in buffer s, no null termination
 */
int
pqGetnchar(void *s, size_t len, PGconn *conn)
{
    if (len > (size_t) (conn->inEnd - conn->inCursor))
        return EOF;
 
    memcpy(s, conn->inBuffer + conn->inCursor, len);
    /* no terminating null */
 
    conn->inCursor += len;
 
    return 0;
}
 
/*
 * pqSkipnchar:
 *  skip over len bytes in input buffer.
 *
 * Note: this is primarily useful for its debug output, which should
 * be exactly the same as for pqGetnchar.  We assume the data in question
 * will actually be used, but just isn't getting copied anywhere as yet.
 */
int
pqSkipnchar(size_t len, PGconn *conn)
{
    if (len > (size_t) (conn->inEnd - conn->inCursor))
        return EOF;
 
    conn->inCursor += len;
 
    return 0;
}
 
/*
 * pqPutnchar:
 *  write exactly len bytes to the current message
 */
int
pqPutnchar(const void *s, size_t len, PGconn *conn)
{
    if (pqPutMsgBytes(s, len, conn))
        return EOF;
 
    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) pg_ntoh16(tmp2);
            break;
        case 4:
            if (conn->inCursor + 4 > conn->inEnd)
                return EOF;
            memcpy(&tmp4, conn->inBuffer + conn->inCursor, 4);
            conn->inCursor += 4;
            *result = (int) pg_ntoh32(tmp4);
            break;
        default:
            pqInternalNotice(&conn->noticeHooks,
                             "integer of size %zu not supported by pqGetInt",
                             bytes);
            return EOF;
    }
 
    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 = pg_hton16((uint16) value);
            if (pqPutMsgBytes((const char *) &tmp2, 2, conn))
                return EOF;
            break;
        case 4:
            tmp4 = pg_hton32((uint32) value);
            if (pqPutMsgBytes((const char *) &tmp4, 4, conn))
                return EOF;
            break;
        default:
            pqInternalNotice(&conn->noticeHooks,
                             "integer of size %zu not supported by pqPutInt",
                             bytes);
            return EOF;
    }
 
    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(size_t bytes_needed, PGconn *conn)
{
    int         newsize = conn->outBufSize;
    char       *newbuf;
 
    /* Quick exit if we have enough space */
    if (bytes_needed <= (size_t) 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 (newsize > 0 && bytes_needed > (size_t) newsize);
 
    if (newsize > 0 && bytes_needed <= (size_t) newsize)
    {
        newbuf = realloc(conn->outBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->outBuffer = newbuf;
            conn->outBufSize = newsize;
            return 0;
        }
    }
 
    newsize = conn->outBufSize;
    do
    {
        newsize += 8192;
    } while (newsize > 0 && bytes_needed > (size_t) newsize);
 
    if (newsize > 0 && bytes_needed <= (size_t) newsize)
    {
        newbuf = realloc(conn->outBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->outBuffer = newbuf;
            conn->outBufSize = newsize;
            return 0;
        }
    }
 
    /* realloc failed. Probably out of memory */
    appendPQExpBufferStr(&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(size_t bytes_needed, PGconn *conn)
{
    int         newsize = conn->inBufSize;
    char       *newbuf;
 
    /* Quick exit if we have enough space */
    if (bytes_needed <= (size_t) newsize)
        return 0;
 
    /*
     * Before concluding that we need to enlarge the buffer, left-justify
     * whatever is in it and recheck.  The caller's value of bytes_needed
     * includes any data to the left of inStart, but we can delete that in
     * preference to enlarging the buffer.  It's slightly ugly to have this
     * function do this, but it's better than making callers worry about it.
     */
    bytes_needed -= conn->inStart;
 
    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;
    }
 
    /* Recheck whether we have enough space */
    if (bytes_needed <= (size_t) 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 (newsize > 0 && bytes_needed > (size_t) newsize);
 
    if (newsize > 0 && bytes_needed <= (size_t) newsize)
    {
        newbuf = realloc(conn->inBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->inBuffer = newbuf;
            conn->inBufSize = newsize;
            return 0;
        }
    }
 
    newsize = conn->inBufSize;
    do
    {
        newsize += 8192;
    } while (newsize > 0 && bytes_needed > (size_t) newsize);
 
    if (newsize > 0 && bytes_needed <= (size_t) newsize)
    {
        newbuf = realloc(conn->inBuffer, newsize);
        if (newbuf)
        {
            /* realloc succeeded */
            conn->inBuffer = newbuf;
            conn->inBufSize = newsize;
            return 0;
        }
    }
 
    /* realloc failed. Probably out of memory */
    appendPQExpBufferStr(&conn->errorMessage,
                         "cannot allocate memory for input buffer\n");
    return EOF;
}
 
/*
 * pqParseDone: after a server-to-client message has successfully
 * been parsed, advance conn->inStart to account for it.
 */
void
pqParseDone(PGconn *conn, int newInStart)
{
    /* trace server-to-client message */
    if (conn->Pfdebug)
        pqTraceOutputMessage(conn, conn->inBuffer + conn->inStart, false);
 
    /* Mark message as done */
    conn->inStart = newInStart;
}
 
/*
 * 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)
 *
 * 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.  The state variable conn->outMsgEnd is the end of
 * the data collected so far.
 */
int
pqPutMsgStart(char msg_type, 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? */
    lenPos = endPos;
    /* allow room for message length */
    endPos += 4;
 
    /* 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 */
 
    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)
{
    /* Fill in length word if needed */
    if (conn->outMsgStart >= 0)
    {
        uint32      msgLen = conn->outMsgEnd - conn->outMsgStart;
 
        msgLen = pg_hton32(msgLen);
        memcpy(conn->outBuffer + conn->outMsgStart, &msgLen, 4);
    }
 
    /* trace client-to-server message */
    if (conn->Pfdebug)
    {
        if (conn->outCount < conn->outMsgStart)
            pqTraceOutputMessage(conn, conn->outBuffer + conn->outCount, true);
        else
            pqTraceOutputNoTypeByteMessage(conn,
                                           conn->outBuffer + conn->outMsgStart);
    }
 
    /* Make message eligible to send */
    conn->outCount = conn->outMsgEnd;
 
    /* If appropriate, try to push out some data */
    if (conn->outCount >= 8192)
    {
        int         toSend = conn->outCount;
 
        /*
         * On Unix-pipe connections, it seems profitable to prefer sending
         * pipe-buffer-sized packets not randomly-sized ones, so retain the
         * last partial-8K chunk in our buffer for now.  On TCP connections,
         * the advantage of that is far less clear.  Moreover, it flat out
         * isn't safe when using SSL or GSSAPI, because those code paths have
         * API stipulations that if they fail to send all the data that was
         * offered in the previous write attempt, we mustn't offer less data
         * in this write attempt.  The previous write attempt might've been
         * pqFlush attempting to send everything in the buffer, so we mustn't
         * offer less now.  (Presently, we won't try to use SSL or GSSAPI on
         * Unix connections, so those checks are just Asserts.  They'll have
         * to become part of the regular if-test if we ever change that.)
         */
        if (conn->raddr.addr.ss_family == AF_UNIX)
        {
#ifdef USE_SSL
            Assert(!conn->ssl_in_use);
#endif
#ifdef ENABLE_GSS
            Assert(!conn->gssenc);
#endif
            toSend -= toSend % 8192;
        }
 
        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;
 
    if (conn->sock == PGINVALID_SOCKET)
    {
        libpq_append_conn_error(conn, "connection not open");
        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 < 8192)
    {
        if (pqCheckInBufferSpace(conn->inEnd + (size_t) 8192, 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)
    {
        switch (SOCK_ERRNO)
        {
            case EINTR:
                goto retry3;
 
                /* Some systems return EAGAIN/EWOULDBLOCK for no data */
#ifdef EAGAIN
            case EAGAIN:
                return someread;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
            case EWOULDBLOCK:
                return someread;
#endif
 
                /* We might get ECONNRESET etc here if connection failed */
            case ALL_CONNECTION_FAILURE_ERRNOS:
                goto definitelyFailed;
 
            default:
                /* pqsecure_read set the error message for us */
                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) >= 8192)
        {
            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, but the second
     * SSL_read() could still say WANT_READ because the data received was not
     * a complete SSL record.  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_in_use)
        return 0;
#endif
 
    switch (pqReadReady(conn))
    {
        case 0:
            /* definitely no data available */
            return 0;
        case 1:
            /* ready for read */
            break;
        default:
            /* we override pqReadReady's message with something more useful */
            goto definitelyEOF;
    }
 
    /*
     * 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)
    {
        switch (SOCK_ERRNO)
        {
            case EINTR:
                goto retry4;
 
                /* Some systems return EAGAIN/EWOULDBLOCK for no data */
#ifdef EAGAIN
            case EAGAIN:
                return 0;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
            case EWOULDBLOCK:
                return 0;
#endif
 
                /* We might get ECONNRESET etc here if connection failed */
            case ALL_CONNECTION_FAILURE_ERRNOS:
                goto definitelyFailed;
 
            default:
                /* pqsecure_read set the error message for us */
                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.
     */
definitelyEOF:
    libpq_append_conn_error(conn, "server closed the connection unexpectedly\n"
                            "\tThis probably means the server terminated abnormally\n"
                            "\tbefore or while processing the request.");
 
    /* Come here if lower-level code already set a suitable errorMessage */
definitelyFailed:
    /* Do *not* drop any already-read data; caller still wants it */
    pqDropConnection(conn, false);
    conn->status = CONNECTION_BAD;  /* No more connection to backend */
    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.
 *
 * Note that this is also responsible for consuming data from the socket
 * (putting it in conn->inBuffer) in any situation where we can't send
 * all the specified data immediately.
 *
 * If a socket-level write failure occurs, conn->write_failed is set and the
 * error message is saved in conn->write_err_msg, but we clear the output
 * buffer and return zero anyway; this is because callers should soldier on
 * until we have read what we can from the server and checked for an error
 * message.  write_err_msg should be reported only when we are unable to
 * obtain a server error first.  Much of that behavior is implemented at
 * lower levels, but this function deals with some edge cases.
 */
static int
pqSendSome(PGconn *conn, int len)
{
    char       *ptr = conn->outBuffer;
    int         remaining = conn->outCount;
    int         result = 0;
 
    /*
     * If we already had a write failure, we will never again try to send data
     * on that connection.  Even if the kernel would let us, we've probably
     * lost message boundary sync with the server.  conn->write_failed
     * therefore persists until the connection is reset, and we just discard
     * all data presented to be written.  However, as long as we still have a
     * valid socket, we should continue to absorb data from the backend, so
     * that we can collect any final error messages.
     */
    if (conn->write_failed)
    {
        /* conn->write_err_msg should be set up already */
        conn->outCount = 0;
        /* Absorb input data if any, and detect socket closure */
        if (conn->sock != PGINVALID_SOCKET)
        {
            if (pqReadData(conn) < 0)
                return -1;
        }
        return 0;
    }
 
    if (conn->sock == PGINVALID_SOCKET)
    {
        conn->write_failed = true;
        /* Store error message in conn->write_err_msg, if possible */
        /* (strdup failure is OK, we'll cope later) */
        conn->write_err_msg = strdup(libpq_gettext("connection not open\n"));
        /* Discard queued data; no chance it'll ever be sent */
        conn->outCount = 0;
        return 0;
    }
 
    /* while there's still data to send */
    while (len > 0)
    {
        int         sent;
 
#ifndef WIN32
        sent = pqsecure_write(conn, ptr, len);
#else
 
        /*
         * Windows can fail on large sends, per KB article Q201213. The
         * failure-point appears to be different in different versions of
         * Windows, but 64k should always be safe.
         */
        sent = pqsecure_write(conn, ptr, Min(len, 65536));
#endif
 
        if (sent < 0)
        {
            /* Anything except EAGAIN/EWOULDBLOCK/EINTR is trouble */
            switch (SOCK_ERRNO)
            {
#ifdef EAGAIN
                case EAGAIN:
                    break;
#endif
#if defined(EWOULDBLOCK) && (!defined(EAGAIN) || (EWOULDBLOCK != EAGAIN))
                case EWOULDBLOCK:
                    break;
#endif
                case EINTR:
                    continue;
 
                default:
                    /* Discard queued data; no chance it'll ever be sent */
                    conn->outCount = 0;
 
                    /* Absorb input data if any, and detect socket closure */
                    if (conn->sock != PGINVALID_SOCKET)
                    {
                        if (pqReadData(conn) < 0)
                            return -1;
                    }
 
                    /*
                     * Lower-level code should already have filled
                     * conn->write_err_msg (and set conn->write_failed) or
                     * conn->errorMessage.  In the former case, we pretend
                     * there's no problem; the write_failed condition will be
                     * dealt with later.  Otherwise, report the error now.
                     */
                    if (conn->write_failed)
                        return 0;
                    else
                        return -1;
            }
        }
        else
        {
            ptr += sent;
            len -= sent;
            remaining -= sent;
        }
 
        if (len > 0)
        {
            /*
             * We didn't send it all, wait till we can send more.
             *
             * 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.
             *
             * In non-blocking mode, we don't wait here directly, but return 1
             * to indicate that data is still pending.  The caller should wait
             * for both read and write ready conditions, and call
             * PQconsumeInput() on read ready, but just in case it doesn't, we
             * call pqReadData() ourselves before returning.  That's not
             * enough if the data has not arrived yet, but it's the best we
             * can do, and works pretty well in practice.  (The documentation
             * used to say that you only need to wait for write-ready, so
             * there are still plenty of applications like that out there.)
             *
             * Note that errors here don't result in write_failed becoming
             * set.
             */
            if (pqReadData(conn) < 0)
            {
                result = -1;    /* error message already set up */
                break;
            }
 
            if (pqIsnonblocking(conn))
            {
                result = 1;
                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.
 * (See pqSendSome comments about how failure should be handled.)
 */
int
pqFlush(PGconn *conn)
{
    if (conn->outCount > 0)
    {
        if (conn->Pfdebug)
            fflush(conn->Pfdebug);
 
        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, -1);
}
 
/*
 * pqWaitTimed: wait, but not past end_time.
 *
 * Returns -1 on failure, 0 if the socket is readable/writable, 1 if it timed out.
 *
 * The timeout is specified by end_time, which is the int64 number of
 * microseconds since the Unix epoch (that is, time_t times 1 million).
 * Timeout is infinite if end_time is -1.  Timeout is immediate (no blocking)
 * if end_time is 0 (or indeed, any time before now).
 */
int
pqWaitTimed(int forRead, int forWrite, PGconn *conn, pg_usec_time_t end_time)
{
    int         result;
 
    result = pqSocketCheck(conn, forRead, forWrite, end_time);
 
    if (result < 0)
        return -1;              /* errorMessage is already set */
 
    if (result == 0)
    {
        libpq_append_conn_error(conn, "timeout expired");
        return 1;
    }
 
    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, 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, 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 an altsock is set for asynchronous authentication, that will be used in
 * preference to the "server" socket. Otherwise, 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, pg_usec_time_t end_time)
{
    int         result;
    pgsocket    sock;
 
    if (!conn)
        return -1;
 
    if (conn->altsock != PGINVALID_SOCKET)
        sock = conn->altsock;
    else
    {
        sock = conn->sock;
        if (sock == PGINVALID_SOCKET)
        {
            libpq_append_conn_error(conn, "invalid socket");
            return -1;
        }
 
#ifdef USE_SSL
        /* Check for SSL library buffering read bytes */
        if (forRead && conn->ssl_in_use && pgtls_read_pending(conn))
        {
            /* short-circuit the select */
            return 1;
        }
#endif
    }
 
    /* We will retry as long as we get EINTR */
    do
        result = PQsocketPoll(sock, forRead, forWrite, end_time);
    while (result < 0 && SOCK_ERRNO == EINTR);
 
    if (result < 0)
    {
        char        sebuf[PG_STRERROR_R_BUFLEN];
 
        libpq_append_conn_error(conn, "%s() failed: %s", "select",
                                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.
 *
 * The timeout is specified by end_time, which is the int64 number of
 * microseconds since the Unix epoch (that is, time_t times 1 million).
 * Timeout is infinite if end_time is -1.  Timeout is immediate (no blocking)
 * if end_time is 0 (or indeed, any time before now).
 */
int
PQsocketPoll(int sock, int forRead, int forWrite, pg_usec_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 == -1)
        timeout_ms = -1;
    else if (end_time == 0)
        timeout_ms = 0;
    else
    {
        pg_usec_time_t now = PQgetCurrentTimeUSec();
 
        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 == -1)
        ptr_timeout = NULL;
    else if (end_time == 0)
    {
        timeout.tv_sec = 0;
        timeout.tv_usec = 0;
        ptr_timeout = &timeout;
    }
    else
    {
        pg_usec_time_t now = PQgetCurrentTimeUSec();
 
        if (end_time > now)
        {
            timeout.tv_sec = (end_time - now) / 1000000;
            timeout.tv_usec = (end_time - now) % 1000000;
        }
        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 */
}
 
/*
 * PQgetCurrentTimeUSec: get current time with microsecond precision
 *
 * This provides a platform-independent way of producing a reference
 * value for PQsocketPoll's timeout parameter.
 */
pg_usec_time_t
PQgetCurrentTimeUSec(void)
{
    struct timeval tval;
 
    gettimeofday(&tval, NULL);
    return (pg_usec_time_t) tval.tv_sec * 1000000 + tval.tv_usec;
}
 
 
/*
 * A couple of "miscellaneous" multibyte related functions. They used
 * to be in fe-print.c but that file is doomed.
 */
 
/*
 * Like pg_encoding_mblen().  Use this in callers that want the
 * dynamically-linked libpq's stance on encodings, even if that means
 * different behavior in different startups of the executable.
 */
int
PQmblen(const char *s, int encoding)
{
    return pg_encoding_mblen(encoding, s);
}
 
/*
 * Like pg_encoding_mblen_bounded().  Use this in callers that want the
 * dynamically-linked libpq's stance on encodings, even if that means
 * different behavior in different startups of the executable.
 */
int
PQmblenBounded(const char *s, int encoding)
{
    return strnlen(s, pg_encoding_mblen(encoding, s));
}
 
/*
 * Returns the display length of the character beginning at s, using the
 * specified encoding.
 */
int
PQdsplen(const 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);
        if (encoding < 0)
            encoding = PG_SQL_ASCII;
    }
    return encoding;
}
 
 
#ifdef ENABLE_NLS
 
static void
libpq_binddomain(void)
{
    /*
     * At least on Windows, there are gettext implementations that fail if
     * multiple threads call bindtextdomain() concurrently.  Use a mutex and
     * flag variable to ensure that we call it just once per process.  It is
     * not known that similar bugs exist on non-Windows platforms, but we
     * might as well do it the same way everywhere.
     */
    static volatile bool already_bound = false;
    static pthread_mutex_t binddomain_mutex = PTHREAD_MUTEX_INITIALIZER;
 
    if (!already_bound)
    {
        /* bindtextdomain() does not preserve errno */
#ifdef WIN32
        int         save_errno = GetLastError();
#else
        int         save_errno = errno;
#endif
 
        (void) pthread_mutex_lock(&binddomain_mutex);
 
        if (!already_bound)
        {
            const char *ldir;
 
            /*
             * No relocatable lookup here because the calling executable could
             * be anywhere
             */
            ldir = getenv("PGLOCALEDIR");
            if (!ldir)
                ldir = LOCALEDIR;
            bindtextdomain(PG_TEXTDOMAIN("libpq"), ldir);
            already_bound = true;
        }
 
        (void) pthread_mutex_unlock(&binddomain_mutex);
 
#ifdef WIN32
        SetLastError(save_errno);
#else
        errno = save_errno;
#endif
    }
}
 
char *
libpq_gettext(const char *msgid)
{
    libpq_binddomain();
    return dgettext(PG_TEXTDOMAIN("libpq"), msgid);
}
 
char *
libpq_ngettext(const char *msgid, const char *msgid_plural, unsigned long n)
{
    libpq_binddomain();
    return dngettext(PG_TEXTDOMAIN("libpq"), msgid, msgid_plural, n);
}
 
#endif                          /* ENABLE_NLS */
 
 
/*
 * Append a formatted string to the given buffer, after translating it.  A
 * newline is automatically appended; the format should not end with a
 * newline.
 */
void
libpq_append_error(PQExpBuffer errorMessage, const char *fmt,...)
{
    int         save_errno = errno;
    bool        done;
    va_list     args;
 
    Assert(fmt[strlen(fmt) - 1] != '\n');
 
    if (PQExpBufferBroken(errorMessage))
        return;                 /* already failed */
 
    /* Loop in case we have to retry after enlarging the buffer. */
    do
    {
        errno = save_errno;
        va_start(args, fmt);
        done = appendPQExpBufferVA(errorMessage, libpq_gettext(fmt), args);
        va_end(args);
    } while (!done);
 
    appendPQExpBufferChar(errorMessage, '\n');
}
 
/*
 * Append a formatted string to the error message buffer of the given
 * connection, after translating it.  A newline is automatically appended; the
 * format should not end with a newline.
 */
void
libpq_append_conn_error(PGconn *conn, const char *fmt,...)
{
    int         save_errno = errno;
    bool        done;
    va_list     args;
 
    Assert(fmt[strlen(fmt) - 1] != '\n');
 
    if (PQExpBufferBroken(&conn->errorMessage))
        return;                 /* already failed */
 
    /* Loop in case we have to retry after enlarging the buffer. */
    do
    {
        errno = save_errno;
        va_start(args, fmt);
        done = appendPQExpBufferVA(&conn->errorMessage, libpq_gettext(fmt), args);
        va_end(args);
    } while (!done);
 
    appendPQExpBufferChar(&conn->errorMessage, '\n');
}
 
/*
 * For 19beta only, some protocol errors will have additional information
 * appended to help with the "grease" campaign.
 */
void
libpq_append_grease_info(PGconn *conn)
{
    /* translator: %s is a URL */
    libpq_append_conn_error(conn,
                            "\tThis indicates a bug in either the server being contacted\n"
                            "\tor a proxy handling the connection. Please consider\n"
                            "\treporting this to the maintainers of that software.\n"
                            "\tFor more information, including instructions on how to\n"
                            "\twork around this issue for now, visit\n"
                            "\t\t%s",
                            "https://www.postgresql.org/docs/devel/libpq-connect.html#LIBPQ-CONNECT-MAX-PROTOCOL-VERSION");
}