Function lo_read

src/interfaces/libpq/fe-lobj.c:247–290

 */

int
lo_read(PGconn *conn, int fd, char *buf, size_t len)
{
	PQArgBlock	argv[2];
	PGresult   *res;
	int			result_len;

	if (lo_initialize(conn) < 0)
		return -1;

	/*
	 * Long ago, somebody thought it'd be a good idea to declare this function
	 * as taking size_t ... but the underlying backend function only accepts a
	 * signed int32 length.  So throw error if the given value overflows
	 * int32.
	 */
	if (len > (size_t) INT_MAX)
	{
		appendPQExpBufferStr(&conn->errorMessage,
							 libpq_gettext("argument of lo_read exceeds integer range\n"));
		return -1;
	}

	argv[0].isint = 1;
	argv[0].len = 4;
	argv[0].u.integer = fd;

	argv[1].isint = 1;
	argv[1].len = 4;
	argv[1].u.integer = (int) len;

	res = PQfn(conn, conn->lobjfuncs->fn_lo_read,
			   (void *) buf, &result_len, 0, argv, 2);
	if (PQresultStatus(res) == PGRES_COMMAND_OK)
	{
		PQclear(res);
		return result_len;
	}
	else
	{
		PQclear(res);
		return -1;
	}
}

/*
 * lo_write