Add lo_truncate() to backend and libpq for large object truncation.

Kris Jurka

src/interfaces/libpq/exports.txt

@@ -1,4 +1,4 @@
-# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.14 2006/08/18 19:52:39 tgl Exp $
+# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.15 2007/03/03 19:52:46 momjian Exp $
 # Functions to be exported by libpq DLLs
 PQconnectdb               1
 PQsetdbLogin              2
@@ -136,3 +136,4 @@ PQdescribePrepared        133
 PQdescribePortal          134
 PQsendDescribePrepared    135
 PQsendDescribePortal      136
+lo_truncate               137

src/interfaces/libpq/fe-lobj.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.61 2007/01/05 22:20:01 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.62 2007/03/03 19:52:46 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -122,6 +122,59 @@ lo_close(PGconn *conn, int fd)
 	}
 }
 
+/*
+ * lo_truncate
+ *    truncates an existing large object to the given size
+ *
+ * returns 0 upon success
+ * returns -1 upon failure
+ */
+int
+lo_truncate(PGconn *conn, int fd, size_t len)
+{
+	PQArgBlock	argv[2];
+	PGresult   *res;
+	int			retval;
+	int			result_len;
+
+	if (conn->lobjfuncs == NULL)
+	{
+		if (lo_initialize(conn) < 0)
+			return -1;
+	}
+
+	/* Must check this on-the-fly because it's not there pre-8.3 */
+	if (conn->lobjfuncs->fn_lo_truncate == 0)
+	{
+		printfPQExpBuffer(&conn->errorMessage,
+			  libpq_gettext("cannot determine OID of function lo_truncate\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 = len;
+
+	res = PQfn(conn, conn->lobjfuncs->fn_lo_truncate,
+			   &retval, &result_len, 1, argv, 2);
+
+	if (PQresultStatus(res) == PGRES_COMMAND_OK)
+	{
+		PQclear(res);
+		return retval;
+	}
+	else
+	{
+		PQclear(res);
+		return -1;
+	}
+}
+
+
 /*
  * lo_read
  *	  read len bytes of the large object into buf
@@ -621,6 +674,7 @@ lo_initialize(PGconn *conn)
 	/*
 	 * Execute the query to get all the functions at once.	In 7.3 and later
 	 * we need to be schema-safe.  lo_create only exists in 8.1 and up.
+	 * lo_truncate only exists in 8.3 and up.
 	 */
 	if (conn->sversion >= 70300)
 		query = "select proname, oid from pg_catalog.pg_proc "
@@ -632,6 +686,7 @@ lo_initialize(PGconn *conn)
 			"'lo_unlink', "
 			"'lo_lseek', "
 			"'lo_tell', "
+			"'lo_truncate', "
 			"'loread', "
 			"'lowrite') "
 			"and pronamespace = (select oid from pg_catalog.pg_namespace "
@@ -684,6 +739,8 @@ lo_initialize(PGconn *conn)
 			lobjfuncs->fn_lo_lseek = foid;
 		else if (!strcmp(fname, "lo_tell"))
 			lobjfuncs->fn_lo_tell = foid;
+		else if (!strcmp(fname, "lo_truncate"))
+			lobjfuncs->fn_lo_truncate = foid;
 		else if (!strcmp(fname, "loread"))
 			lobjfuncs->fn_lo_read = foid;
 		else if (!strcmp(fname, "lowrite"))
@@ -694,7 +751,6 @@ lo_initialize(PGconn *conn)
 
 	/*
 	 * Finally check that we really got all large object interface functions
-	 * --- except lo_create, which may not exist.
 	 */
 	if (lobjfuncs->fn_lo_open == 0)
 	{

src/interfaces/libpq/libpq-fe.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.135 2007/01/05 22:20:01 momjian Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.136 2007/03/03 19:52:46 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -489,6 +489,7 @@ extern int	lo_lseek(PGconn *conn, int fd, int offset, int whence);
 extern Oid	lo_creat(PGconn *conn, int mode);
 extern Oid	lo_create(PGconn *conn, Oid lobjId);
 extern int	lo_tell(PGconn *conn, int fd);
+extern int	lo_truncate(PGconn *conn, int fd, size_t len);
 extern int	lo_unlink(PGconn *conn, Oid lobjId);
 extern Oid	lo_import(PGconn *conn, const char *filename);
 extern int	lo_export(PGconn *conn, Oid lobjId, const char *filename);

src/interfaces/libpq/libpq-int.h

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.118 2007/01/26 17:45:41 neilc Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.119 2007/03/03 19:52:47 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -239,6 +239,7 @@ typedef struct pgLobjfuncs
 	Oid			fn_lo_unlink;	/* OID of backend function lo_unlink	*/
 	Oid			fn_lo_lseek;	/* OID of backend function lo_lseek		*/
 	Oid			fn_lo_tell;		/* OID of backend function lo_tell		*/
+	Oid			fn_lo_truncate;	/* OID of backend function lo_truncate	*/
 	Oid			fn_lo_read;		/* OID of backend function LOread		*/
 	Oid			fn_lo_write;	/* OID of backend function LOwrite		*/
 } PGlobjfuncs;