SEO

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 */


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Hideyuki Kawashima <kawasima@ayu.ics.keio.ac.jp> writes:
> 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.

AFAICS the uses of 8192 in fe-misc.c have no relationship to
PQ_BUFFER_SIZE or indeed much of anything. They are just arbitrary
amounts by which to increase the I/O buffer size.

Of course they are not *completely* arbitrary --- they are essentially
guesses about the buffering behavior of the kernel and TCP stack.
But they have nothing to do with the server-side PQ_BUFFER_SIZE.

> The result is attached to this mail.

In future please submit proposed changes as "diff -c" patches.
A complete file is useless because it cannot be applied without
risking overwriting other people's changes.

regards, tom lane

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Thanks for teaching me about 8192 in fe-misc.c.
I recognized the 8192 in fe-misc.c does not relate to PQ_BUFFER_SIZE
in pqcomm.c, but I am pleased if someone revises the magic number.
And I am sorry for my incorrect format patch.
From next time, I will submit my proposition as "diff -c" patches.

-- Hideyuki Kawashima

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