Function PQexecStart

src/interfaces/libpq/fe-exec.c:2313–2373

* Common code for PQexec and sibling routines: prepare to send command */

 * Common code for PQexec and sibling routines: prepare to send command
 */
static bool
PQexecStart(PGconn *conn)
{
	PGresult   *result;

	if (!conn)
		return false;

	if (conn->pipelineStatus != PQ_PIPELINE_OFF)
	{
		appendPQExpBufferStr(&conn->errorMessage,
							 libpq_gettext("synchronous command execution functions are not allowed in pipeline mode\n"));
		return false;
	}

	/*
	 * Since this is the beginning of a query cycle, reset the error buffer.
	 */
	resetPQExpBuffer(&conn->errorMessage);

	/*
	 * Silently discard any prior query result that application didn't eat.
	 * This is probably poor design, but it's here for backward compatibility.
	 */
	while ((result = PQgetResult(conn)) != NULL)
	{
		ExecStatusType resultStatus = result->resultStatus;

		PQclear(result);		/* only need its status */
		if (resultStatus == PGRES_COPY_IN)
		{
			/* get out of a COPY IN state */
			if (PQputCopyEnd(conn,
							 libpq_gettext("COPY terminated by new PQexec")) < 0)
				return false;
			/* keep waiting to swallow the copy's failure message */
		}
		else if (resultStatus == PGRES_COPY_OUT)
		{
			/*
			 * Get out of a COPY OUT state: we just switch back to BUSY and
			 * allow the remaining COPY data to be dropped on the floor.
			 */
			conn->asyncStatus = PGASYNC_BUSY;
			/* keep waiting to swallow the copy's completion message */
		}
		else if (resultStatus == PGRES_COPY_BOTH)
		{
			/* We don't allow PQexec during COPY BOTH */
			appendPQExpBufferStr(&conn->errorMessage,
								 libpq_gettext("PQexec not allowed during COPY BOTH\n"));
			return false;
		}
		/* check for loss of connection, too */
		if (conn->status == CONNECTION_BAD)
			return false;
	}