Function pqReadData

src/interfaces/libpq/fe-misc.c:617–815

---------- * 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)
	{
		appendPQExpBufferStr(&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 < 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)