The attached patch implements some changes that were discussed a

couple weeks ago on the hackers and interfaces lists:

1. When the backend sends a NOTICE message and closes the connection
   (typically, because it was told to by the postmaster after
   another backend coredumped), libpq will now print the notice
   and close the connection cleanly.  Formerly, the frontend app
   would usually terminate ungracefully due to a SIGPIPE.  (I am
   not sure if 6.3.2 behaved that way, but the current cvs sources
   do...)

2. libpq's various printouts to stderr are now fed through a single
   "notice processor" routine, which can be overridden by the
   application to direct notices someplace else.  This should ease
   porting libpq to Windows.

I also noticed and fixed a problem in PQprint: when sending output
to a pager subprocess, it would disable SIGPIPE in case the pager
terminates early (this is good) --- but afterwards it reset SIGPIPE
to SIG_DFL, rather than restoring the application's prior setting
(bad).

			regards, tom lane

src/interfaces/libpq/libpq-fe.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: libpq-fe.h,v 1.36 1998/07/18 18:34:34 momjian Exp $
+ * $Id: libpq-fe.h,v 1.37 1998/08/09 02:59:31 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -121,6 +121,9 @@ extern		"C"
 		int			be_pid;		/* process id of backend */
 	} PGnotify;
 
+/* PQnoticeProcessor is a typedef for a callback function type */
+	typedef void (*PQnoticeProcessor) (void * arg, const char * message);
+
 /* PGAsyncStatusType is private to libpq, really shouldn't be seen by users */
 	typedef enum
 	{
@@ -165,6 +168,10 @@ extern		"C"
 		/* Optional file to write trace info to */
 		FILE	   *Pfdebug;
 
+		/* Callback procedure for notice/error message processing */
+		PQnoticeProcessor	noticeHook;
+		void	   *noticeArg;
+
 		/* Status indicators */
 		ConnStatusType		status;
 		PGAsyncStatusType	asyncStatus;
@@ -300,6 +307,11 @@ extern		"C"
 	extern void PQtrace(PGconn *conn, FILE *debug_port);
 	extern void PQuntrace(PGconn *conn);
 
+	/* Override default notice processor */
+	extern void PQsetNoticeProcessor (PGconn *conn,
+									  PQnoticeProcessor proc,
+									  void *arg);
+
 /* === in fe-exec.c === */
 	/* Simple synchronous query */
 	extern PGresult *PQexec(PGconn *conn, const char *query);
@@ -390,6 +402,7 @@ extern		"C"
 	extern int	pqGetInt(int *result, int bytes, PGconn *conn);
 	extern int	pqPutInt(int value, int bytes, PGconn *conn);
 	extern int	pqReadData(PGconn *conn);
+	extern int	pqReadReady(PGconn *conn);
 	extern int	pqFlush(PGconn *conn);
 	extern int	pqWait(int forRead, int forWrite, PGconn *conn);