Add some code to ensure that we don't lose communication sync due to

an oversize message, per suggestion from Oliver Jowett.  I'm a bit
dubious that this is a real problem, since the client likely doesn't
have any more space available than the server, but it's not hard to
make it behave according to the protocol intention.

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 805577bd77471f237ac246e0befbd2aa2b2fe5ad..f9998bbd7fd7ec8e0dd0b4a70425a988b42b8b8a 100644 (file)
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -30,7 +30,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/libpq/pqcomm.c,v 1.172 2004/09/26 00:26:19 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/libpq/pqcomm.c,v 1.173 2004/10/18 23:23:19 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -777,6 +777,36 @@ pq_getbytes(char *s, size_t len)
    return 0;
 }
 
+/* --------------------------------
+ *     pq_discardbytes     - throw away a known number of bytes
+ *
+ *     same as pq_getbytes except we do not copy the data to anyplace.
+ *     this is used for resynchronizing after read errors.
+ *
+ *     returns 0 if OK, EOF if trouble
+ * --------------------------------
+ */
+static int
+pq_discardbytes(size_t len)
+{
+   size_t      amount;
+
+   while (len > 0)
+   {
+       while (PqRecvPointer >= PqRecvLength)
+       {
+           if (pq_recvbuf())   /* If nothing in buffer, then recv some */
+               return EOF;     /* Failed to recv data */
+       }
+       amount = PqRecvLength - PqRecvPointer;
+       if (amount > len)
+           amount = len;
+       PqRecvPointer += amount;
+       len -= amount;
+   }
+   return 0;
+}
+
 /* --------------------------------
  *     pq_getstring    - get a null terminated string from connection
  *
@@ -867,9 +897,8 @@ pq_getmessage(StringInfo s, int maxlen)
    }
 
    len = ntohl(len);
-   len -= 4;                   /* discount length itself */
 
-   if (len < 0 ||
+   if (len < 4 ||
        (maxlen > 0 && len > maxlen))
    {
        ereport(COMMERROR,
@@ -878,10 +907,28 @@ pq_getmessage(StringInfo s, int maxlen)
        return EOF;
    }
 
+   len -= 4;                   /* discount length itself */
+
    if (len > 0)
    {
-       /* Allocate space for message */
-       enlargeStringInfo(s, len);
+       /*
+        * Allocate space for message.  If we run out of room (ridiculously
+        * large message), we will elog(ERROR), but we want to discard the
+        * message body so as not to lose communication sync.
+        */
+       PG_TRY();
+       {
+           enlargeStringInfo(s, len);
+       }
+       PG_CATCH();
+       {
+           if (pq_discardbytes(len) == EOF)
+               ereport(COMMERROR,
+                       (errcode(ERRCODE_PROTOCOL_VIOLATION),
+                        errmsg("incomplete message from client")));
+           PG_RE_THROW();
+       }
+       PG_END_TRY();
 
        /* And grab the message */
        if (pq_getbytes(s->data, len) == EOF)