Re: [HACKERS] listening addresses

Tom Lane wrote:

>Andrew Dunstan <andrew@dunslane.net> writes:
>
>
>>A small problem with it was reported to me a couple of days ago - user
>>had firewalled off all IP6 traffic. The stats collector happily bound
>>and connected to the socket, but all the packets fell in the bit bucket.
>>They found it quite hard to diagnose the problem.
>>
>>
>
>
>
>>Possible solutions that occurred to me:
>>. an initial "hello"-"yes i'm here" exchange to validate the address
>>
>>
>
>That one seems reasonable to me.  Seems like it would take just a few
>more lines of code in the loop that tries to find a working socket to
>check that we can send a byte and receive it.  You'd have to be careful
>not to block if the socket is indeed not working ... also, is it safe to
>assume that a byte sent with send() is *immediately* ready to recv()?
>
>
>

This patch attempts to implement the idea, with safety in case the
packet is not immediately available.

comments welcome

cheers

andrew
Index: src/backend/postmaster/pgstat.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/postmaster/pgstat.c,v
retrieving revision 1.61
diff -c -r1.61 pgstat.c
*** src/backend/postmaster/pgstat.c    15 Mar 2004 16:21:37 -0000    1.61
--- src/backend/postmaster/pgstat.c    21 Mar 2004 16:41:23 -0000
***************
*** 191,196 ****
--- 191,199 ----
                 *addr,
                  hints;
      int            ret;
+     fd_set      rset;
+     struct timeval tv;
+     char        test_byte;

      /*
       * Force start of collector daemon if something to collect
***************
*** 307,312 ****
--- 310,351 ----
              pgStatSock = -1;
              continue;
          }
+
+ #define TESTBYTEVAL 99
+
+         /* try to send and receive a test byte on the socket */
+
+         FD_ZERO(&rset);
+         FD_SET(pgStatSock, &rset);
+         tv.tv_sec = 0;
+         tv.tv_usec = 500000;
+         test_byte = TESTBYTEVAL;
+         send(pgStatSock,&test_byte,1,0);
+         test_byte++;
+         if(select(pgStatSock+1,&rset,NULL,NULL,&tv) > 0 &&
+            FD_ISSET(pgStatSock,&rset))
+         {
+             recv(pgStatSock,&test_byte,1,0);
+             if(test_byte != TESTBYTEVAL)
+             {
+                 ereport(LOG,
+                         (errcode_for_socket_access(),
+                          errmsg("incorrect test value on send/receive on socket for statistics collector: %m")));
+             closesocket(pgStatSock);
+             pgStatSock = -1;
+             continue;
+             }
+         }
+         else
+         {
+             ereport(LOG,
+                     (errcode_for_socket_access(),
+                      errmsg("could send/receive on socket for statistics collector: %m")));
+             closesocket(pgStatSock);
+             pgStatSock = -1;
+             continue;
+         }
+

          /* If we get here, we have a working socket */
          break;