Allow remote query execution (dblink)

Joe Conway

contrib/README

@@ -38,6 +38,10 @@ dbase -
 	Converts from dbase/xbase to PostgreSQL
 	by Ivan Baldo, lubaldo@adinet.com.uy
 
+dblink -
+	Allows remote query execution
+	by  Joe Conway, joe.conway@mail.com
+
 earthdistance -
 	Operator for computing earth distance for two points
 	by Hal Snyder <hal@vailsys.com>

contrib/dblink/Makefile

+subdir = contrib/dblink
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_builddir)/src/Makefile.shlib
+include_srcdir = $(top_builddir)/src/include
+
+
+NAME	:= dblink
+SONAME	:= $(NAME)$(DLSUFFIX)
+
+override CFLAGS += -I$(srcdir)
+override CFLAGS += -I$(include_srcdir)
+override CFLAGS += -I$(libpq_srcdir)
+override CFLAGS += $(CFLAGS_SL)
+
+OBJS	= $(NAME).o
+
+all: $(OBJS) $(SONAME) $(NAME).sql 
+
+$(OBJS):  $(NAME).c
+	$(CC) -o $@ -c $(CFLAGS) $<
+
+$(SONAME):  $(OBJS)
+	$(LD) -o $@ -Bshareable $(libpq) $<
+
+$(NAME).sql: $(NAME).sql.in
+	sed -e 's:MODULE_PATHNAME:$(libdir)/contrib/$(SONAME):g' < $< > $@
+
+install: all installdirs
+	$(INSTALL_DATA) README.$(NAME)	$(docdir)/contrib
+	$(INSTALL_DATA) $(NAME).sql	$(datadir)/contrib
+	$(INSTALL_SHLIB) $(SONAME)	$(libdir)/contrib
+
+installdirs:
+	$(mkinstalldirs) $(docdir)/contrib $(datadir)/contrib $(libdir)/contrib
+
+uninstall:
+	rm -rf $(docdir)/contrib/README.$(NAME) $(datadir)/contrib/$(NAME).sql $(libdir)/contrib/$(SONAME)
+
+clean distclean maintainer-clean:
+	rm -f $(SONAME) *.o *.sql
+
+depend dep:
+	$(CC) -MM -MG $(CFLAGS) *.c > depend
+
+ifeq (depend,$(wildcard depend))
+include depend
+endif

contrib/dblink/README.dblink

+/*
+ * dblink
+ *
+ * Functions returning results from a remote database
+ *
+ * Copyright (c) Joseph Conway <joe.conway@mail.com>, 2001;
+ * 
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+Version 0.2 (29 May, 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 0.2
+    - initial release    
+
+Installation:
+  Place these files in a directory called 'dblink' under 'contrib' in the PostgreSQL source tree. Then run:
+
+    make
+    make install
+
+  You can use dblink.sql to create the functions in your database of choice, e.g.
+
+    psql -U postgres template1 < dblink.sql
+
+  installs following functions into database template1:
+
+     dblink() - returns a pointer to results from remote query
+     dblink_tok() - extracts and returns individual field results
+
+Documentation
+==================================================================
+Name
+
+dblink -- Returns a pointer to a data set from a remote database
+
+Synopsis
+
+dblink(text connstr, text sql)
+
+Inputs
+
+  connstr
+
+    standard libpq format connection srting, 
+    e.g. "hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd"
+
+  sql
+
+    sql statement that you wish to execute on the remote host
+    e.g. "select * from pg_class"
+
+Outputs
+
+  Returns setof int (pointer)
+
+Example usage
+
+  select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd','select f1, f2 from mytable');
+
+
+==================================================================
+
+Name
+
+dblink_tok -- Returns individual select field results from a dblink remote query
+
+Synopsis
+
+dblink_tok(int pointer, int fnumber)
+
+Inputs
+
+  pointer
+
+    a pointer returned by a call to dblink()
+
+  fnumber
+
+    the ordinal position (zero based) of the field to be returned from the dblink result set
+
+Outputs
+
+  Returns text
+
+Example usage
+
+  select dblink_tok(t1.dblink_p,0) as f1, dblink_tok(t1.dblink_p,1) as f2
+  from (select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
+                     ,'select f1, f2 from mytable') as dblink_p) as t1;
+
+
+==================================================================
+
+NOTE: If you need to provide selection criteria in a WHERE clause, it is necessary
+to 'fake' a UNION, e.g.
+
+  select
+     dblink_tok(t1.dblink_p,0) as f1
+    ,dblink_tok(t1.dblink_p,1) as f2
+  from
+   (
+    select dblink(
+                   '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
+   ) as t1
+  where
+    f1 = '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:
+
+  create view myremotetable as
+  select
+     dblink_tok(t1.dblink_p,0) as f1
+    ,dblink_tok(t1.dblink_p,1) as f2
+  from
+   (
+    select dblink(
+                   '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
+   ) as t1;
+
+Then you can simply write:
+
+   select f1,f2 from myremotetable where f1 = 'mycriteria';
+
+==================================================================
+
+-- Joe Conway
+

contrib/dblink/dblink.c

+/*
+ * dblink.c
+ *
+ * Functions returning results from a remote database
+ *
+ * Copyright (c) Joseph Conway <joe.conway@mail.com>, 2001;
+ * 
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+#include "dblink.h"
+
+PG_FUNCTION_INFO_V1(dblink);
+Datum
+dblink(PG_FUNCTION_ARGS)
+{
+	PGconn			*conn = NULL;
+	PGresult		*res = NULL;
+	dblink_results	*results;
+	char			*optstr;
+	char			*sqlstatement;
+	char			*curstr = "DECLARE mycursor CURSOR FOR ";
+	char			*execstatement;
+	char			*msg;
+	int				ntuples = 0;
+	ReturnSetInfo 	*rsi;
+
+	if (PG_ARGISNULL(0) || PG_ARGISNULL(1)) {
+		elog(ERROR, "dblink: NULL arguments are not permitted");
+	}
+
+	if (fcinfo->resultinfo == NULL || ! IsA(fcinfo->resultinfo, ReturnSetInfo)) {
+		elog(ERROR, "dblink: function called in context that does not accept a set result");
+	}
+
+	optstr = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
+	sqlstatement = DatumGetCString(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(1))));
+
+	if (fcinfo->flinfo->fn_extra == NULL) {
+
+		conn = PQconnectdb(optstr);
+		if (PQstatus(conn) == CONNECTION_BAD)
+		{
+			msg = PQerrorMessage(conn);
+			PQfinish(conn);
+			elog(ERROR, "dblink: connection error: %s", msg);
+		}
+
+		res = PQexec(conn, "BEGIN");
+		if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		{
+			msg = PQerrorMessage(conn);
+			PQclear(res);
+			PQfinish(conn);
+			elog(ERROR, "dblink: begin error: %s", msg);
+		}
+		PQclear(res);
+
+		execstatement = (char *) palloc(strlen(curstr) + strlen(sqlstatement) + 1);
+		if (execstatement != NULL) {
+			strcpy(execstatement, curstr);
+			strcat(execstatement, sqlstatement);
+			strcat(execstatement, "\0");
+		} else {
+			elog(ERROR, "dblink: insufficient memory" );
+		}
+
+		res = PQexec(conn, execstatement);
+		if (!res || (PQresultStatus(res) != PGRES_COMMAND_OK && PQresultStatus(res) != PGRES_TUPLES_OK))
+		{
+			msg = PQerrorMessage(conn);
+			PQclear(res);
+			PQfinish(conn);
+			elog(ERROR, "dblink: sql error: %s", msg);
+		} else {
+			/*
+			 * got results, start fetching them
+			 */
+		    PQclear(res);
+
+		    res = PQexec(conn, "FETCH ALL in mycursor");
+		    if (!res || PQresultStatus(res) != PGRES_TUPLES_OK) {
+				msg = PQerrorMessage(conn);
+				PQclear(res);
+				PQfinish(conn);
+				elog(ERROR, "dblink: sql error: %s", msg);
+		    }
+
+			ntuples = PQntuples(res);
+
+			if (ntuples > 0) {
+
+				results = init_dblink_results(fcinfo->flinfo->fn_mcxt);
+				results->tup_num = 0;
+				results->res = res;
+				res = NULL;
+
+				(dblink_results *) fcinfo->flinfo->fn_extra = results;
+
+				results = NULL;
+				results = fcinfo->flinfo->fn_extra;
+
+			    /* close the cursor */
+			    res = PQexec(conn, "CLOSE mycursor");
+			    PQclear(res);
+
+			    /* commit the transaction */
+			    res = PQexec(conn, "COMMIT");
+			    PQclear(res);
+
+			    /* close the connection to the database and cleanup */
+			    PQfinish(conn);
+
+				rsi = (ReturnSetInfo *)fcinfo->resultinfo;
+				rsi->isDone = ExprMultipleResult;
+
+				PG_RETURN_POINTER(results);
+
+			} else {
+
+			    PQclear(res);
+
+			    /* close the cursor */
+			    res = PQexec(conn, "CLOSE mycursor");
+			    PQclear(res);
+
+			    /* commit the transaction */
+			    res = PQexec(conn, "COMMIT");
+			    PQclear(res);
+
+			    /* close the connection to the database and cleanup */
+			    PQfinish(conn);
+
+				rsi = (ReturnSetInfo *)fcinfo->resultinfo;
+				rsi->isDone = ExprEndResult ;
+
+				PG_RETURN_NULL();
+			}
+		}
+	} else {
+		/*
+		 * check for more results
+		 */
+
+		results = fcinfo->flinfo->fn_extra;
+		results->tup_num++;
+		ntuples = PQntuples(results->res);
+
+		if (results->tup_num < ntuples) {
+
+			/*
+			 * fetch them if available
+			 */
+
+			rsi = (ReturnSetInfo *)fcinfo->resultinfo;
+			rsi->isDone = ExprMultipleResult;
+
+			PG_RETURN_POINTER(results);
+
+		} else {
+
+			/*
+			 * or if no more, clean things up
+			 */
+
+			results = fcinfo->flinfo->fn_extra;
+
+		    PQclear(results->res);
+
+			rsi = (ReturnSetInfo *)fcinfo->resultinfo;
+			rsi->isDone = ExprEndResult ;
+
+			PG_RETURN_NULL();
+		}
+	}
+	PG_RETURN_NULL();
+}
+
+
+/*
+ * dblink_tok
+ * parse dblink output string
+ * return fldnum item (0 based)
+ * based on provided field separator
+ */
+
+PG_FUNCTION_INFO_V1(dblink_tok);
+Datum
+dblink_tok(PG_FUNCTION_ARGS)
+{
+	dblink_results	*results;
+	int				fldnum;
+	text			*result_text;
+	char			*result;
+	int				nfields = 0;
+	int				text_len = 0;
+
+	if (PG_ARGISNULL(0) || PG_ARGISNULL(1)) {
+		elog(ERROR, "dblink: NULL arguments are not permitted");
+	}
+
+	results = (dblink_results *) PG_GETARG_POINTER(0);
+	if (results == NULL) {
+		elog(ERROR, "dblink: function called with invalid result pointer");
+	}
+
+	fldnum = PG_GETARG_INT32(1);
+	if (fldnum < 0) {
+		elog(ERROR, "dblink: field number < 0 not permitted");
+	}
+
+	nfields = PQnfields(results->res);
+	if (fldnum > (nfields - 1)) {
+		elog(ERROR, "dblink: field number %d does not exist", fldnum);
+	}
+
+	text_len = PQgetlength(results->res, results->tup_num, fldnum);
+
+	result = (char *) palloc(text_len + 1);
+
+	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);
+}
+
+
+/*
+ * internal functions
+ */
+
+
+/*
+ * init_dblink_results
+ *	 - create an empty dblink_results data structure
+ */
+dblink_results *
+init_dblink_results(MemoryContext fn_mcxt)
+{
+	MemoryContext	oldcontext;
+	dblink_results	*retval;
+
+	oldcontext = MemoryContextSwitchTo(fn_mcxt);
+
+	retval = (dblink_results *) palloc(sizeof(dblink_results));
+	MemSet(retval, 0, sizeof(dblink_results));
+
+	retval->tup_num = -1;
+	retval->res = NULL;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return retval;
+}

contrib/dblink/dblink.h

+/*
+ * dblink.h
+ *
+ * Functions returning results from a remote database
+ *
+ * Copyright (c) Joseph Conway <joe.conway@mail.com>, 2001;
+ * 
+ * Permission to use, copy, modify, and distribute this software and its
+ * documentation for any purpose, without fee, and without a written agreement
+ * is hereby granted, provided that the above copyright notice and this
+ * paragraph and the following two paragraphs appear in all copies.
+ * 
+ * IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
+ * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+ * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * 
+ * THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ */
+
+#ifndef DBLINK_H
+#define DBLINK_H
+
+#include <string.h>
+#include "postgres.h"
+#include "libpq-fe.h"
+#include "libpq-int.h"
+#include "fmgr.h"
+#include "access/tupdesc.h"
+#include "executor/executor.h"
+#include "nodes/nodes.h"
+#include "nodes/execnodes.h"
+#include "utils/builtins.h"
+
+/*
+ * This struct holds the results of the remote query.
+ * Use fn_extra to hold a pointer to it across calls
+ */
+typedef struct
+{
+	/*
+	 * last tuple number accessed
+	 */
+	int			tup_num;
+
+	/*
+	 * the actual query results
+	 */
+	PGresult	*res;
+
+} dblink_results;
+
+/*
+ * External declarations
+ */
+extern Datum dblink(PG_FUNCTION_ARGS);
+extern Datum dblink_tok(PG_FUNCTION_ARGS);
+
+/*
+ * Internal declarations
+ */
+dblink_results *init_dblink_results(MemoryContext fn_mcxt);
+
+#endif	 /* DBLINK_H */

contrib/dblink/dblink.sql.in

+CREATE FUNCTION dblink (text,text) RETURNS setof int
+  AS 'MODULE_PATHNAME','dblink' LANGUAGE 'c';
+
+CREATE FUNCTION dblink_tok (int,int) RETURNS text
+  AS 'MODULE_PATHNAME','dblink_tok' LANGUAGE 'c';