Function pqGetCopyData3

src/interfaces/libpq/fe-protocol3.c:1892–1945

* PQgetCopyData - read a row of data from the backend during COPY OUT * or COPY BOTH * * If successful, sets *buffer to point to a malloc'd row of data, and * returns row length (always > 0) as result. * Returns 0 if no row available yet (only possible if async is true), * -1 if end of copy (consult PQgetResult), or -2 if error (consult * PQerrorMessage). */

 * PQerrorMessage).
 */
int
pqGetCopyData3(PGconn *conn, char **buffer, int async)
{
	int			msgLength;

	for (;;)
	{
		/*
		 * Collect the next input message.  To make life simpler for async
		 * callers, we keep returning 0 until the next message is fully
		 * available, even if it is not Copy Data.
		 */
		msgLength = getCopyDataMessage(conn);
		if (msgLength < 0)
			return msgLength;	/* end-of-copy or error */
		if (msgLength == 0)
		{
			/* Don't block if async read requested */
			if (async)
				return 0;
			/* Need to load more data */
			if (pqWait(true, false, conn) ||
				pqReadData(conn) < 0)
				return -2;
			continue;
		}

		/*
		 * Drop zero-length messages (shouldn't happen anyway).  Otherwise
		 * pass the data back to the caller.
		 */
		msgLength -= 4;
		if (msgLength > 0)
		{
			*buffer = (char *) malloc(msgLength + 1);
			if (*buffer == NULL)
			{
				appendPQExpBufferStr(&conn->errorMessage,
									 libpq_gettext("out of memory\n"));
				return -2;
			}
			memcpy(*buffer, &conn->inBuffer[conn->inCursor], msgLength);
			(*buffer)[msgLength] = '\0';	/* Add terminating null */

			/* Mark message consumed */
			conn->inStart = conn->inCursor + msgLength;

			return msgLength;
		}

		/* Empty, so drop it and loop around for another */
		conn->inStart = conn->inCursor;
	}
}

/*
 * PQgetline - gets a newline-terminated string from the backend.