Here's a small patch for dblink:

   - fixed dblink invalid pointer causing corrupt elog message
   - fixed dblink_tok improper handling of null results
   - fixed examples in README.dblink

Joe Conway

Author: bmomjian

contrib/dblink/README.dblink

@@ -24,12 +24,18 @@
  *
  */
 
-Version 0.2 (29 May, 2001):
+
+Version 0.3 (14 June, 2001):
   Function to test returning data set from remote database
   Tested under Linux (Red Hat 6.2 and 7.0) and PostgreSQL 7.1 and 7.2devel
 
 Release Notes:
 
+  Version 0.3
+    - fixed dblink invalid pointer causing corrupt elog message
+    - fixed dblink_tok improper handling of null results
+    - fixed examples in README.dblink
+
   Version 0.2
     - initial release    
 
@@ -124,11 +130,11 @@ to 'fake' a UNION, e.g.
                    'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
                   ,'select f1, f2 from mytable'
                  ) as dblink_p
-    union
-    select null,null where false
+    union all
+    select null where false
    ) as t1
   where
-    f1 = 'mycriteria';
+    dblink_tok(t1.dblink_p,0) = 'mycriteria';
 
 in order to work around an issue with the query optimizer. A more convenient way to approach
 this problem is to create a view:
@@ -143,8 +149,8 @@ this problem is to create a view:
                    'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
                   ,'select f1, f2 from mytable'
                  ) as dblink_p
-    union
-    select null,null where false
+    union all
+    select null where false
    ) as t1;
 
 Then you can simply write:

contrib/dblink/dblink.c

@@ -57,15 +57,15 @@ dblink(PG_FUNCTION_ARGS)
 		conn = PQconnectdb(optstr);
 		if (PQstatus(conn) == CONNECTION_BAD)
 		{
-			msg = PQerrorMessage(conn);
+			msg = pstrdup(PQerrorMessage(conn));
 			PQfinish(conn);
 			elog(ERROR, "dblink: connection error: %s", msg);
 		}
 
 		res = PQexec(conn, "BEGIN");
 		if (PQresultStatus(res) != PGRES_COMMAND_OK)
 		{
-			msg = PQerrorMessage(conn);
+			msg = pstrdup(PQerrorMessage(conn));
 			PQclear(res);
 			PQfinish(conn);
 			elog(ERROR, "dblink: begin error: %s", msg);
@@ -84,7 +84,7 @@ dblink(PG_FUNCTION_ARGS)
 		res = PQexec(conn, execstatement);
 		if (!res || (PQresultStatus(res) != PGRES_COMMAND_OK && PQresultStatus(res) != PGRES_TUPLES_OK))
 		{
-			msg = PQerrorMessage(conn);
+			msg = pstrdup(PQerrorMessage(conn));
 			PQclear(res);
 			PQfinish(conn);
 			elog(ERROR, "dblink: sql error: %s", msg);
@@ -96,7 +96,7 @@ dblink(PG_FUNCTION_ARGS)
 
 		    res = PQexec(conn, "FETCH ALL in mycursor");
 		    if (!res || PQresultStatus(res) != PGRES_TUPLES_OK) {
-				msg = PQerrorMessage(conn);
+				msg = pstrdup(PQerrorMessage(conn));
 				PQclear(res);
 				PQfinish(conn);
 				elog(ERROR, "dblink: sql error: %s", msg);
@@ -230,20 +230,28 @@ dblink_tok(PG_FUNCTION_ARGS)
 		elog(ERROR, "dblink: field number %d does not exist", fldnum);
 	}
 
-	text_len = PQgetlength(results->res, results->tup_num, fldnum);
+	if (PQgetisnull(results->res, results->tup_num, fldnum) == 1) {
 
-	result = (char *) palloc(text_len + 1);
+		PG_RETURN_NULL();
 
-	if (result != NULL) {
-		strcpy(result, PQgetvalue(results->res, results->tup_num, fldnum));
-		strcat(result, "\0");
 	} else {
-		elog(ERROR, "dblink: insufficient memory" );
-	}
 
-	result_text = DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(result)));
+		text_len = PQgetlength(results->res, results->tup_num, fldnum);
+
+		result = (char *) palloc(text_len + 1);
 
-	PG_RETURN_TEXT_P(result_text);
+		if (result != NULL) {
+			strcpy(result, PQgetvalue(results->res, results->tup_num, fldnum));
+			strcat(result, "\0");
+		} else {
+			elog(ERROR, "dblink: insufficient memory" );
+		}
+
+		result_text = DatumGetTextP(DirectFunctionCall1(textin, CStringGetDatum(result)));
+
+		PG_RETURN_TEXT_P(result_text);
+
+	}
 }