Function pqSocketCheck

src/interfaces/libpq/fe-misc.c:1154–1193

* 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. */

 * 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 == PGINVALID_SOCKET)
	{
		appendPQExpBufferStr(&conn->errorMessage,
							 libpq_gettext("invalid socket\n"));
		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(conn->sock, forRead, forWrite, end_time);
	while (result < 0 && SOCK_ERRNO == EINTR);

	if (result < 0)
	{
		char		sebuf[PG_STRERROR_R_BUFLEN];

		appendPQExpBuffer(&conn->errorMessage,
						  libpq_gettext("%s() failed: %s\n"),
						  "select",
						  SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
	}

	return result;
}


/*