/*-------------------------------------------------------------------------
 *
 *	 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) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 * Portions Copyright (c) 2010-2012 Postgres-XC Development Group
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-misc.c,v 1.137 2008/12/11 07:34:09 petere Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "gtm/gtm_c.h"

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

#include <netinet/in.h>
#include <arpa/inet.h>

#include <unistd.h>
#include <sys/time.h>

#include <poll.h>
#include <sys/poll.h>
#include <sys/select.h>

#include "gtm/libpq-fe.h"
#include "gtm/libpq-int.h"

static int	gtmpqPutMsgBytes(const void *buf, size_t len, GTM_Conn *conn);
static int	gtmpqSendSome(GTM_Conn *conn, int len);
static int gtmpqSocketCheck(GTM_Conn *conn, int forRead, int forWrite,
			  time_t end_time);
static int	gtmpqSocketPoll(int sock, int forRead, int forWrite, time_t end_time);


/*
 * gtmpqGetc: 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
gtmpqGetc(char *result, GTM_Conn *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;
}


/*
 * gtmpqPutc: write 1 char to the current message
 */
int
gtmpqPutc(char c, GTM_Conn *conn)
{
	if (gtmpqPutMsgBytes(&c, 1, conn))
		return EOF;

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

	return 0;
}


/*
 * gtmpqGets[_append]:
 * 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.
 */
static int
gtmpqGets_internal(PQExpBuffer buf, GTM_Conn *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)
		resetGTMPQExpBuffer(buf);

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

	conn->inCursor = ++inCursor;

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

	return 0;
}

int
gtmpqGets(PQExpBuffer buf, GTM_Conn *conn)
{
	return gtmpqGets_internal(buf, conn, true);
}

int
gtmpqGets_append(PQExpBuffer buf, GTM_Conn *conn)
{
	return gtmpqGets_internal(buf, conn, false);
}


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

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

	return 0;
}

/*
 * gtmpqGetnchar:
 *	get a string of exactly len bytes in buffer s, no null termination
 */
int
gtmpqGetnchar(char *s, size_t len, GTM_Conn *conn)
{
	if (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;
}

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

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

	return 0;
}

/*
 * gtmpqGetInt
 *	read a 2 or 4 byte integer and convert from network byte order
 *	to local byte order
 */
int
gtmpqGetInt(int *result, size_t bytes, GTM_Conn *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:
			fprintf(conn->Pfdebug, "Integer size of (%ld) bytes not supported", bytes);
			return EOF;
	}

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

	return 0;
}

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

	switch (bytes)
	{
		case 2:
			tmp2 = htons((uint16) value);
			if (gtmpqPutMsgBytes((const char *) &tmp2, 2, conn))
				return EOF;
			break;
		case 4:
			tmp4 = htonl((uint32) value);
			if (gtmpqPutMsgBytes((const char *) &tmp4, 4, conn))
				return EOF;
			break;
		default:
			fprintf(conn->Pfdebug, "Integer size of (%ld) bytes not supported", 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
gtmpqCheckOutBufferSpace(size_t bytes_needed, GTM_Conn *conn)
{
	int			newsize = conn->outBufSize;
	char	   *newbuf;

	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 */
	printfGTMPQExpBuffer(&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
gtmpqCheckInBufferSpace(size_t bytes_needed, GTM_Conn *conn)
{
	int			newsize = conn->inBufSize;
	char	   *newbuf;

	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 */
	printfGTMPQExpBuffer(&conn->errorMessage,
					  "cannot allocate memory for input buffer\n");
	return EOF;
}

/*
 * gtmpqPutMsgStart: 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
gtmpqPutMsgStart(char msg_type, bool force_len, GTM_Conn *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)
	{
		lenPos = endPos;
		/* allow room for message length */
		endPos += 4;
	}
	else
		lenPos = -1;

	/* make sure there is room for message header */
	if (gtmpqCheckOutBufferSpace(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 gtmpqPutMsgEnd */

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

	return 0;
}

/*
 * gtmpqPutMsgBytes: add bytes to a partially-constructed message
 *
 * Returns 0 on success, EOF on error
 */
static int
gtmpqPutMsgBytes(const void *buf, size_t len, GTM_Conn *conn)
{
	/* make sure there is room for it */
	if (gtmpqCheckOutBufferSpace(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;
}

/*
 * gtmpqPutMsgEnd: 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 gtmpqFlush
 * when it's important to flush all the data out to the server.
 */
int
gtmpqPutMsgEnd(GTM_Conn *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 >= 8192)
	{
		int			toSend = conn->outCount - (conn->outCount % 8192);

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

	return 0;
}

/* ----------
 * gtmpqReadData: 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
gtmpqReadData(GTM_Conn *conn)
{
	int			someread = 0;
	int			nread;

	if (conn->sock < 0)
	{
		printfGTMPQExpBuffer(&conn->errorMessage,
						  "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 < 8192)
	{
		if (gtmpqCheckInBufferSpace(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 = recv(conn->sock, conn->inBuffer + conn->inEnd,
						  conn->inBufSize - conn->inEnd, 0);
	conn->last_call = GTM_LastCall_RECV;
	if (nread < 0)
	{
		conn->last_errno = SOCK_ERRNO;

		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
		printfGTMPQExpBuffer(&conn->errorMessage,
				   "could not receive data from server:\n");
		return -1;
	}
	else
		conn->last_errno = 0;

	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 ...
		 */
#ifdef NOT_USED
		if (conn->inEnd > 32768 &&
			(conn->inBufSize - conn->inEnd) >= 8192)
		{
			someread = 1;
			goto retry3;
		}
#endif
		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 gtmpqReadReady() test.  So we must
	 * play dumb and assume there is more data, relying on the SSL layer to
	 * detect true EOF.
	 */

	switch (gtmpqReadReady(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 = recv(conn->sock, conn->inBuffer + conn->inEnd,
						  conn->inBufSize - conn->inEnd, 0);
	conn->last_call = GTM_LastCall_RECV;
	if (nread < 0)
	{
		conn->last_errno = SOCK_ERRNO;
		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
		printfGTMPQExpBuffer(&conn->errorMessage,
				   "could not receive data from server: \n");
		return -1;
	}
	else
		conn->last_errno = 0;
	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:
	printfGTMPQExpBuffer(&conn->errorMessage,
								"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 */
	close(conn->sock);
	conn->sock = -1;

	return -1;
}

/*
 * gtmpqSendSome: 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
gtmpqSendSome(GTM_Conn *conn, int len)
{
	char	   *ptr = conn->outBuffer;
	int			remaining = conn->outCount;
	int			result = 0;

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

	/* while there's still data to send */
	while (len > 0)
	{
		int			sent;

		sent = send(conn->sock, ptr, len, 0);
		conn->last_call = GTM_LastCall_SEND;

		if (sent < 0)
		{
			conn->last_errno = SOCK_ERRNO;
			/*
			 * 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
					printfGTMPQExpBuffer(&conn->errorMessage,
								"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
					 * gtmpqReadData finds no more data can be read.  But abandon
					 * attempt to send data.
					 */
					conn->outCount = 0;
					return -1;

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

		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.
			 */
			result = 1;
			break;
		}
	}

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

	return result;
}


/*
 * gtmpqFlush: 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
gtmpqFlush(GTM_Conn *conn)
{
	if (conn->Pfdebug)
		fflush(conn->Pfdebug);

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

	return 0;
}


/*
 * gtmpqWait: 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
gtmpqWait(int forRead, int forWrite, GTM_Conn *conn)
{
	return gtmpqWaitTimed(forRead, forWrite, conn, (time_t) -1);
}

/*
 * gtmpqWaitTimed: 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
gtmpqWaitTimed(int forRead, int forWrite, GTM_Conn *conn, time_t finish_time)
{
	int			result;

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

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

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

	return 0;
}

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

/*
 * gtmpqWriteReady: is select() saying the file is ready to write?
 * Returns -1 on failure, 0 if not ready, 1 if ready.
 */
int
gtmpqWriteReady(GTM_Conn *conn)
{
	return gtmpqSocketCheck(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
gtmpqSocketCheck(GTM_Conn *conn, int forRead, int forWrite, time_t end_time)
{
	int			result;

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

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

	if (result < 0)
		printfGTMPQExpBuffer(&conn->errorMessage,
						  "select() failed: \n");

	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
gtmpqSocketPoll(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 */
}