Re: [Fwd: Re: dblink patches for comment]

Tom Lane wrote:
> Joe Conway <mail@joeconway.com> writes:
>> Tom Lane wrote:
>>> you will need to whip up a special-purpose quoting subroutine.
>
>> OK, I see that. I assume I need to care for encoding issues? If so, do I
>> assume server encoding or client encoding?
>
> Hoo, good point.  You can assume the database (server) encoding, because
> that's what the local encoding is from the point of view of libpq ---
> and the code in conninfo_parse knows nothing of encodings anyway.  So
> that's a no-op as far as the quoting itself goes.

OK, got it. I think the attached is what you're looking for, although I
have not yet tested beyond "it compiles" and "it passes make installcheck".

> But that reminds me, weren't you going to add something to force libpq to set client_encoding
> to the database encoding?

Yes, I was going to work that next. I assume it is pretty
straightforward, but I've never been particularly strong on the nuances
of encodings...

Joe
Index: dblink.c
===================================================================
RCS file: /opt/src/cvs/pgsql/contrib/dblink/dblink.c,v
retrieving revision 1.78
diff -c -r1.78 dblink.c
*** dblink.c    2 Jun 2009 03:21:56 -0000    1.78
--- dblink.c    6 Jun 2009 18:24:46 -0000
***************
*** 46,52 ****
--- 46,54 ----
  #include "catalog/pg_type.h"
  #include "executor/executor.h"
  #include "executor/spi.h"
+ #include "foreign/foreign.h"
  #include "lib/stringinfo.h"
+ #include "mb/pg_wchar.h"
  #include "miscadmin.h"
  #include "nodes/execnodes.h"
  #include "nodes/nodes.h"
***************
*** 96,101 ****
--- 98,105 ----
  static void dblink_connstr_check(const char *connstr);
  static void dblink_security_check(PGconn *conn, remoteConn *rconn);
  static void dblink_res_error(const char *conname, PGresult *res, const char *dblink_context_msg, bool fail);
+ static char *get_connect_string(const char *servername);
+ static char *escape_param_str(const char *from, size_t length, int encoding, size_t *result_len);

  /* Global */
  static remoteConn *pconn = NULL;
***************
*** 165,171 ****
              } \
              else \
              { \
!                 connstr = conname_or_str; \
                  dblink_connstr_check(connstr); \
                  conn = PQconnectdb(connstr); \
                  if (PQstatus(conn) == CONNECTION_BAD) \
--- 169,179 ----
              } \
              else \
              { \
!                 connstr = get_connect_string(conname_or_str); \
!                 if (connstr == NULL) \
!                 { \
!                     connstr = conname_or_str; \
!                 } \
                  dblink_connstr_check(connstr); \
                  conn = PQconnectdb(connstr); \
                  if (PQstatus(conn) == CONNECTION_BAD) \
***************
*** 210,215 ****
--- 218,224 ----
  Datum
  dblink_connect(PG_FUNCTION_ARGS)
  {
+     char       *conname_or_str = NULL;
      char       *connstr = NULL;
      char       *connname = NULL;
      char       *msg;
***************
*** 220,235 ****

      if (PG_NARGS() == 2)
      {
!         connstr = text_to_cstring(PG_GETARG_TEXT_PP(1));
          connname = text_to_cstring(PG_GETARG_TEXT_PP(0));
      }
      else if (PG_NARGS() == 1)
!         connstr = text_to_cstring(PG_GETARG_TEXT_PP(0));

      if (connname)
          rconn = (remoteConn *) MemoryContextAlloc(TopMemoryContext,
                                                    sizeof(remoteConn));

      /* check password in connection string if not superuser */
      dblink_connstr_check(connstr);
      conn = PQconnectdb(connstr);
--- 229,249 ----

      if (PG_NARGS() == 2)
      {
!         conname_or_str = text_to_cstring(PG_GETARG_TEXT_PP(1));
          connname = text_to_cstring(PG_GETARG_TEXT_PP(0));
      }
      else if (PG_NARGS() == 1)
!         conname_or_str = text_to_cstring(PG_GETARG_TEXT_PP(0));

      if (connname)
          rconn = (remoteConn *) MemoryContextAlloc(TopMemoryContext,
                                                    sizeof(remoteConn));

+     /* first check for valid foreign data server */
+     connstr = get_connect_string(conname_or_str);
+     if (connstr == NULL)
+         connstr = conname_or_str;
+
      /* check password in connection string if not superuser */
      dblink_connstr_check(connstr);
      conn = PQconnectdb(connstr);
***************
*** 2353,2355 ****
--- 2367,2516 ----
           errcontext("Error occurred on dblink connection named \"%s\": %s.",
                      dblink_context_conname, dblink_context_msg)));
  }
+
+ /*
+  * Obtain connection string for a foreign server
+  */
+ static char *
+ get_connect_string(const char *servername)
+ {
+     ForeignServer       *foreign_server = NULL;
+     UserMapping           *user_mapping;
+     ListCell           *cell;
+     StringInfo            buf = makeStringInfo();
+     ForeignDataWrapper *fdw;
+     AclResult            aclresult;
+
+     /* first gather the server connstr options */
+     if (strlen(servername) < NAMEDATALEN)
+         foreign_server = GetForeignServerByName(servername, true);
+
+     if (foreign_server)
+     {
+         Oid        serverid = foreign_server->serverid;
+         Oid        fdwid = foreign_server->fdwid;
+         Oid        userid = GetUserId();
+         int        encoding = GetDatabaseEncoding();
+
+         user_mapping = GetUserMapping(userid, serverid);
+         fdw    = GetForeignDataWrapper(fdwid);
+
+         /* Check permissions, user must have usage on the server. */
+         aclresult = pg_foreign_server_aclcheck(serverid, userid, ACL_USAGE);
+         if (aclresult != ACLCHECK_OK)
+             aclcheck_error(aclresult, ACL_KIND_FOREIGN_SERVER, foreign_server->servername);
+
+         foreach (cell, fdw->options)
+         {
+             DefElem           *def = lfirst(cell);
+
+             appendStringInfo(buf, "%s='%s' ", def->defname,
+                              escape_param_str(strVal(def->arg), strlen(strVal(def->arg)), encoding, NULL));
+         }
+
+         foreach (cell, foreign_server->options)
+         {
+             DefElem           *def = lfirst(cell);
+
+             appendStringInfo(buf, "%s='%s' ", def->defname,
+                              escape_param_str(strVal(def->arg), strlen(strVal(def->arg)), encoding, NULL));
+         }
+
+         foreach (cell, user_mapping->options)
+         {
+
+             DefElem           *def = lfirst(cell);
+
+             appendStringInfo(buf, "%s='%s' ", def->defname,
+                              escape_param_str(strVal(def->arg), strlen(strVal(def->arg)), encoding, NULL));
+         }
+
+         return buf->data;
+     }
+     else
+         return NULL;
+ }
+
+ /*
+  * Escaping libpq connect parameter strings.
+  *
+  * Replaces "'" with "\'" and "\" with "\\".
+  *
+  * length is the length of the source string.  (Note: if a terminating NUL
+  * is encountered sooner, stops short of "length"; the behavior
+  * is thus rather like strncpy.)
+  *
+  * For safety the target must be 2*length + 1 bytes long.
+  * A terminating NUL character is added to the output string, whether the
+  * input is NUL-terminated or not.
+  *
+  * Returns the target string.
+  * Optionally returns target length if result_len is non NULL
+  * (not counting the terminating NUL).
+  */
+ static char *
+ escape_param_str(const char *from, size_t length, int encoding, size_t *result_len)
+ {
+     const char *source = from;
+     char       *target = (char *) palloc(2*length + 1);
+     char       *to = target;
+     size_t        remaining = length;
+
+     while (remaining > 0 && *source != '\0')
+     {
+         char        c = *source;
+         int            len;
+         int            i;
+
+         /* Fast path for plain ASCII */
+         if (!IS_HIGHBIT_SET(c))
+         {
+             /* Apply escaping if needed */
+             if (c == '\'' || c == '\\')
+                 *target++ = '\\';
+             /* Copy the character */
+             *target++ = c;
+             source++;
+             remaining--;
+             continue;
+         }
+
+         /* Slow path for possible multibyte characters */
+         len = pg_encoding_mblen(encoding, source);
+
+         /* Copy the character */
+         for (i = 0; i < len; i++)
+         {
+             if (remaining == 0 || *source == '\0')
+                 break;
+             *target++ = *source++;
+             remaining--;
+         }
+
+         /*
+          * If we hit premature end of string (ie, incomplete multibyte
+          * character), try to pad out to the correct length with spaces. We
+          * may not be able to pad completely, but we will always be able to
+          * insert at least one pad space (since we'd not have quoted a
+          * multibyte character).  This should be enough to make a string that
+          * the server will error out on.
+          */
+         if (i < len)
+         {
+             for (; i < len; i++)
+             {
+                 if (((size_t) (target - to)) / 2 >= length)
+                     break;
+                 *target++ = ' ';
+             }
+             break;
+         }
+     }
+
+     /* Write the terminating NUL character. */
+     *target = '\0';
+
+     if (result_len)
+         *result_len = target - to;
+     return to;
+ }
Index: expected/dblink.out
===================================================================
RCS file: /opt/src/cvs/pgsql/contrib/dblink/expected/dblink.out,v
retrieving revision 1.24
diff -c -r1.24 dblink.out
*** expected/dblink.out    3 Jul 2008 03:56:57 -0000    1.24
--- expected/dblink.out    2 Jun 2009 16:54:37 -0000
***************
*** 784,786 ****
--- 784,829 ----
   OK
  (1 row)

+ -- test foreign data wrapper functionality
+ CREATE USER dblink_regression_test;
+ CREATE FOREIGN DATA WRAPPER postgresql;
+ CREATE SERVER fdtest FOREIGN DATA WRAPPER postgresql OPTIONS (dbname 'contrib_regression');
+ CREATE USER MAPPING FOR public SERVER fdtest;
+ GRANT USAGE ON FOREIGN SERVER fdtest TO dblink_regression_test;
+ GRANT EXECUTE ON FUNCTION dblink_connect_u(text, text) TO dblink_regression_test;
+ \set ORIGINAL_USER :USER
+ \c - dblink_regression_test
+ -- should fail
+ SELECT dblink_connect('myconn', 'fdtest');
+ ERROR:  password is required
+ DETAIL:  Non-superusers must provide a password in the connection string.
+ -- should succeed
+ SELECT dblink_connect_u('myconn', 'fdtest');
+  dblink_connect_u
+ ------------------
+  OK
+ (1 row)
+
+ SELECT * FROM dblink('myconn','SELECT * FROM foo') AS t(a int, b text, c text[]);
+  a  | b |       c
+ ----+---+---------------
+   0 | a | {a0,b0,c0}
+   1 | b | {a1,b1,c1}
+   2 | c | {a2,b2,c2}
+   3 | d | {a3,b3,c3}
+   4 | e | {a4,b4,c4}
+   5 | f | {a5,b5,c5}
+   6 | g | {a6,b6,c6}
+   7 | h | {a7,b7,c7}
+   8 | i | {a8,b8,c8}
+   9 | j | {a9,b9,c9}
+  10 | k | {a10,b10,c10}
+ (11 rows)
+
+ \c - :ORIGINAL_USER
+ REVOKE USAGE ON FOREIGN SERVER fdtest FROM dblink_regression_test;
+ REVOKE EXECUTE ON FUNCTION dblink_connect_u(text, text) FROM dblink_regression_test;
+ DROP USER dblink_regression_test;
+ DROP USER MAPPING FOR public SERVER fdtest;
+ DROP SERVER fdtest;
+ DROP FOREIGN DATA WRAPPER postgresql;
Index: sql/dblink.sql
===================================================================
RCS file: /opt/src/cvs/pgsql/contrib/dblink/sql/dblink.sql,v
retrieving revision 1.20
diff -c -r1.20 dblink.sql
*** sql/dblink.sql    6 Apr 2008 16:54:48 -0000    1.20
--- sql/dblink.sql    2 Jun 2009 16:54:37 -0000
***************
*** 364,366 ****
--- 364,391 ----
  SELECT dblink_cancel_query('dtest1');
  SELECT dblink_error_message('dtest1');
  SELECT dblink_disconnect('dtest1');
+
+ -- test foreign data wrapper functionality
+ CREATE USER dblink_regression_test;
+
+ CREATE FOREIGN DATA WRAPPER postgresql;
+ CREATE SERVER fdtest FOREIGN DATA WRAPPER postgresql OPTIONS (dbname 'contrib_regression');
+ CREATE USER MAPPING FOR public SERVER fdtest;
+ GRANT USAGE ON FOREIGN SERVER fdtest TO dblink_regression_test;
+ GRANT EXECUTE ON FUNCTION dblink_connect_u(text, text) TO dblink_regression_test;
+
+ \set ORIGINAL_USER :USER
+ \c - dblink_regression_test
+ -- should fail
+ SELECT dblink_connect('myconn', 'fdtest');
+ -- should succeed
+ SELECT dblink_connect_u('myconn', 'fdtest');
+ SELECT * FROM dblink('myconn','SELECT * FROM foo') AS t(a int, b text, c text[]);
+
+ \c - :ORIGINAL_USER
+ REVOKE USAGE ON FOREIGN SERVER fdtest FROM dblink_regression_test;
+ REVOKE EXECUTE ON FUNCTION dblink_connect_u(text, text) FROM dblink_regression_test;
+ DROP USER dblink_regression_test;
+ DROP USER MAPPING FOR public SERVER fdtest;
+ DROP SERVER fdtest;
+ DROP FOREIGN DATA WRAPPER postgresql;