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/fe-auth.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-auth.c,v 1.20 1998/07/20 16:57:13 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-auth.c,v 1.21 1998/08/09 02:59:25 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -445,8 +445,6 @@ pg_krb5_sendauth(const char *PQerrormsg, int sock,
 			(void) sprintf(PQerrormsg,
 				  "pg_krb5_sendauth: authentication rejected: \"%*s\"\n",
 						   error->text.length, error->text.data);
-			fputs(PQerrormsg, stderr);
-			pqdebug("%s", PQerrormsg);
 		}
 		else
 		{

src/interfaces/libpq/fe-connect.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-connect.c,v 1.77 1998/07/26 04:31:36 scrappy Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-connect.c,v 1.78 1998/08/09 02:59:26 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -29,7 +29,6 @@
 #include <ctype.h>
 #include <string.h>
 #include <errno.h>
-#include <signal.h>
 #include <ctype.h>				/* for isspace() */
 
 #include "postgres.h"
@@ -55,6 +54,7 @@ static void closePGconn(PGconn *conn);
 static int	conninfo_parse(const char *conninfo, char *errorMessage);
 static char *conninfo_getval(char *keyword);
 static void conninfo_free(void);
+static void defaultNoticeProcessor(void * arg, const char * message);
 /* XXX Why is this not static? */
 void		PQsetenv(PGconn *conn);
 
@@ -181,11 +181,7 @@ PQconnectdb(const char *conninfo)
 	 */
 	conn = makeEmptyPGconn();
 	if (conn == NULL)
-	{
-		fprintf(stderr,
-		   "FATAL: PQconnectdb() -- unable to allocate memory for a PGconn");
 		return (PGconn *) NULL;
-	}
 
 	/* ----------
 	 * Parse the conninfo string and save settings in conn structure
@@ -297,11 +293,7 @@ PQsetdbLogin(const char *pghost, const char *pgport, const char *pgoptions, cons
 
 	conn = makeEmptyPGconn();
 	if (conn == NULL)
-	{
-		fprintf(stderr,
-		   "FATAL: PQsetdbLogin() -- unable to allocate memory for a PGconn");
 		return (PGconn *) NULL;
-	}
 
 	if ((pghost == NULL) || pghost[0] == '\0')
 	{
@@ -856,6 +848,7 @@ makeEmptyPGconn(void)
 	/* Zero all pointers */
 	MemSet((char *) conn, 0, sizeof(PGconn));
 
+	conn->noticeHook = defaultNoticeProcessor;
 	conn->status = CONNECTION_BAD;
 	conn->asyncStatus = PGASYNC_IDLE;
 	conn->notifyList = DLNewList();
@@ -925,35 +918,20 @@ closePGconn(PGconn *conn)
 	if (conn->sock >= 0)
 	{
 		/*
-		 * Try to send close message.
-		 * If connection is already gone, that's cool.  No reason for kernel
-		 * to kill us when we try to write to it.  So ignore SIGPIPE signals.
+		 * Try to send "close connection" message to backend.
+		 * BUT: backend might have already closed connection.
+		 * To avoid being killed by SIGPIPE, we need to detect this before
+		 * writing.  Check for "read ready" condition which indicates EOF.
 		 */
-#ifndef WIN32
-#if defined(USE_POSIX_SIGNALS)
-		struct sigaction ignore_action;
-		struct sigaction oldaction;
-
-		ignore_action.sa_handler = SIG_IGN;
-		sigemptyset(&ignore_action.sa_mask);
-		ignore_action.sa_flags = 0;
-		sigaction(SIGPIPE, (struct sigaction *) & ignore_action, &oldaction);
-
-		(void) pqPuts("X", conn);
-		(void) pqFlush(conn);
-
-		sigaction(SIGPIPE, &oldaction, NULL);
-#else
-		void (*oldsignal)(int);
-
-		oldsignal = signal(SIGPIPE, SIG_IGN);
-
-		(void) pqPuts("X", conn);
-		(void) pqFlush(conn);
-
-		signal(SIGPIPE, oldsignal);
-#endif
-#endif /* Win32 uses no signals at all */
+		while (pqReadReady(conn)) {
+			if (pqReadData(conn) < 0)
+				break;
+		}
+		if (conn->sock >= 0) {
+			/* Should be safe now... */
+			(void) pqPuts("X", conn);
+			(void) pqFlush(conn);
+		}
 	}
 
 	/*
@@ -987,9 +965,7 @@ closePGconn(PGconn *conn)
 void
 PQfinish(PGconn *conn)
 {
-	if (!conn)
-		fprintf(stderr, "PQfinish() -- pointer to PGconn is null\n");
-	else
+	if (conn)
 	{
 		closePGconn(conn);
 		freePGconn(conn);
@@ -1003,9 +979,7 @@ PQfinish(PGconn *conn)
 void
 PQreset(PGconn *conn)
 {
-	if (!conn)
-		fprintf(stderr, "PQreset() -- pointer to PGconn is null\n");
-	else
+	if (conn)
 	{
 		closePGconn(conn);
 		conn->status = connectDB(conn);
@@ -1383,10 +1357,7 @@ char *
 PQdb(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQdb() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
 	return conn->dbName;
 }
 
@@ -1394,10 +1365,7 @@ char *
 PQuser(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQuser() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
 	return conn->pguser;
 }
 
@@ -1405,11 +1373,7 @@ char *
 PQhost(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQhost() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
-
 	return conn->pghost;
 }
 
@@ -1417,10 +1381,7 @@ char *
 PQoptions(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQoptions() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
 	return conn->pgoptions;
 }
 
@@ -1428,10 +1389,7 @@ char *
 PQtty(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQtty() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
 	return conn->pgtty;
 }
 
@@ -1439,10 +1397,7 @@ char *
 PQport(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQport() -- pointer to PGconn is null\n");
 		return (char *) NULL;
-	}
 	return conn->pgport;
 }
 
@@ -1450,21 +1405,16 @@ ConnStatusType
 PQstatus(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQstatus() -- pointer to PGconn is null\n");
 		return CONNECTION_BAD;
-	}
 	return conn->status;
 }
 
 char *
 PQerrorMessage(PGconn *conn)
 {
+	static char noConn[] = "PQerrorMessage: conn pointer is NULL\n";
 	if (!conn)
-	{
-		fprintf(stderr, "PQerrorMessage() -- pointer to PGconn is null\n");
-		return (char *) NULL;
-	}
+		return noConn;
 	return conn->errorMessage;
 }
 
@@ -1472,10 +1422,7 @@ int
 PQsocket(PGconn *conn)
 {
 	if (!conn)
-	{
-		fprintf(stderr, "PQsocket() -- pointer to PGconn is null\n");
 		return -1;
-	}
 	return conn->sock;
 }
 
@@ -1501,3 +1448,26 @@ PQuntrace(PGconn *conn)
 		conn->Pfdebug = NULL;
 	}
 }
+
+void
+PQsetNoticeProcessor (PGconn *conn, PQnoticeProcessor proc, void *arg)
+{
+	if (conn == NULL)
+		return;
+	conn->noticeHook = proc;
+	conn->noticeArg = arg;
+}
+
+/*
+ * The default notice/error message processor just prints the
+ * message on stderr.  Applications can override this if they
+ * want the messages to go elsewhere (a window, for example).
+ * Note that simply discarding notices is probably a bad idea.
+ */
+
+static void
+defaultNoticeProcessor(void * arg, const char * message)
+{
+	/* Note: we expect the supplied string to end with a newline already. */
+	fprintf(stderr, "%s", message);
+}

src/interfaces/libpq/fe-misc.c

@@ -24,7 +24,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.16 1998/07/03 04:24:14 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.17 1998/08/09 02:59:29 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -50,6 +50,10 @@
 #include "postgres.h"
 #include "libpq-fe.h"
 
+#define DONOTICE(conn,message) \
+	((*(conn)->noticeHook) ((conn)->noticeArg, (message)))
+
+
 /* --------------------------------------------------------------------- */
 /* pqGetc:
    get a character from the connection
@@ -218,7 +222,9 @@ pqGetInt(int *result, int bytes, PGconn *conn)
 			*result = (int) ntohl(tmp4);
 			break;
 		default:
-			fprintf(stderr, "** int size %d not supported\n", bytes);
+			sprintf(conn->errorMessage,
+					"pqGetInt: int size %d not supported\n", bytes);
+			DONOTICE(conn, conn->errorMessage);
 			return EOF;
 	}
 
@@ -252,7 +258,9 @@ pqPutInt(int value, int bytes, PGconn *conn)
 				return EOF;
 			break;
 		default:
-			fprintf(stderr, "** int size %d not supported\n", bytes);
+			sprintf(conn->errorMessage,
+					"pqPutInt: int size %d not supported\n", bytes);
+			DONOTICE(conn, conn->errorMessage);
 			return EOF;
 	}
 
@@ -265,7 +273,7 @@ pqPutInt(int value, int bytes, PGconn *conn)
 /* --------------------------------------------------------------------- */
 /* pqReadReady: is select() saying the file is ready to read?
  */
-static int
+int
 pqReadReady(PGconn *conn)
 {
 	fd_set			input_mask;

src/interfaces/libpq/fe-print.c

@@ -9,7 +9,7 @@
  * didn't really belong there.
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-print.c,v 1.8 1998/07/26 04:31:36 scrappy Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-print.c,v 1.9 1998/08/09 02:59:30 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -106,6 +106,7 @@ PQprint(FILE *fout,
 		int			fs_len = strlen(po->fieldSep);
 		int			total_line_length = 0;
 		int			usePipe = 0;
+		pqsigfunc	oldsigpipehandler = NULL;
 		char	   *pagerenv;
 		char		buf[8192 * 2 + 1];
 
@@ -193,7 +194,7 @@ PQprint(FILE *fout,
 				{
 					usePipe = 1;
 #ifndef WIN32
-					pqsignal(SIGPIPE, SIG_IGN);
+					oldsigpipehandler = pqsignal(SIGPIPE, SIG_IGN);
 #endif
 				}
 				else
@@ -309,7 +310,7 @@ PQprint(FILE *fout,
 			_pclose(fout);
 #else
 			pclose(fout);
-			pqsignal(SIGPIPE, SIG_DFL);
+			pqsignal(SIGPIPE, oldsigpipehandler);
 #endif
 		}
 		if (po->html3 && !po->expanded)

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);
 

src/man/libpq.3

 .\" This is -*-nroff-*-
 .\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/libpq.3,v 1.22 1998/07/15 17:34:06 momjian Exp $
-.TH LIBPQ INTRO 07/08/98 PostgreSQL PostgreSQL
+.\" $Header: /cvsroot/pgsql/src/man/Attic/libpq.3,v 1.23 1998/08/09 02:59:33 momjian Exp $
+.TH LIBPQ INTRO 08/08/98 PostgreSQL PostgreSQL
 .SH DESCRIPTION
 Libpq is the programmer's interface to Postgres.  Libpq is a set of
 library routines which allows
@@ -823,6 +823,36 @@ Disable tracing started by
 .nf
 void PQuntrace(PGconn *conn)
 .fi
+
+.PP
+.SH "LIBPQ Control Functions"
+.PP
+.B PQsetNoticeProcessor
+.IP
+Control reporting of notice and warning messages generated by libpq.
+.nf
+void PQsetNoticeProcessor (PGconn * conn,
+		void (*noticeProcessor) (void * arg, const char * message),
+		void * arg)
+.fi
+By default, libpq prints "notice" messages from the backend on stderr,
+as well as a few error messages that it generates by itself.
+This behavior can be overridden by supplying a callback function that
+does something else with the messages.  The callback function is passed
+the text of the error message (which includes a trailing newline), plus
+a void pointer that is the same one passed to PQsetNoticeProcessor.
+(This pointer can be used to access application-specific state if needed.)
+The default notice processor is simply
+.nf
+static void
+defaultNoticeProcessor(void * arg, const char * message)
+{
+	fprintf(stderr, "%s", message);
+}
+.fi
+To use a special notice processor, call PQsetNoticeProcessor just after
+any creation of a new PGconn object.
+
 .PP
 .SH "User Authentication Functions"
 .PP