Re: [HACKERS] listening addresses - Mailing list pgsql-patches

Andrew Dunstan wrote:

>
>
> 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()?
>>
>>
>>
>

Revised patch attached. I think this is about as much trouble as this
problem is worth ;-)

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    22 Mar 2004 12:47:54 -0000
***************
*** 191,196 ****
--- 191,200 ----
                 *addr,
                  hints;
      int            ret;
+     fd_set      rset;
+     struct timeval tv;
+     char        test_byte;
+     int         sel_res;

      /*
       * Force start of collector daemon if something to collect
***************
*** 307,312 ****
--- 311,365 ----
              pgStatSock = -1;
              continue;
          }
+
+ #define TESTBYTEVAL 99
+
+         /* try to send and receive a test byte on the socket */
+
+         test_byte = TESTBYTEVAL;
+         if (send(pgStatSock,&test_byte,1,0) != 1)
+         {
+             ereport(LOG,
+                     (errcode_for_socket_access(),
+                      errmsg("test byte send failure socket for statistics collector: %m")));
+             closesocket(pgStatSock);
+             pgStatSock = -1;
+             continue;
+         }
+         test_byte++;
+         for(;;)
+         {
+             FD_ZERO(&rset);
+             FD_SET(pgStatSock, &rset);
+             tv.tv_sec = 0;
+             tv.tv_usec = 500000;
+             sel_res = select(pgStatSock+1,&rset,NULL,NULL,&tv);
+             if (sel_res != -1 || errno != EINTR)
+                 break;
+         }
+         if( sel_res > 0 && FD_ISSET(pgStatSock,&rset)
+             && recv(pgStatSock,&test_byte,1,0) == 1)
+         {
+             if(test_byte != TESTBYTEVAL)
+             {
+                 ereport(LOG,
+                         (errcode_for_socket_access(),
+                          errmsg("incorrect test value on send/receive on socket for statistics collector")));
+             closesocket(pgStatSock);
+             pgStatSock = -1;
+             continue;
+             }
+         }
+         else
+         {
+             ereport(LOG,
+                     (errcode_for_socket_access(),
+                      errmsg("could receive test byte on socket for statistics collector: %m")));
+             closesocket(pgStatSock);
+             pgStatSock = -1;
+             continue;
+         }
+

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