From 69fed5b26fa34fc825c7ed0a8d97221ff448e9c5 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 22 Oct 2014 18:41:44 -0400
Subject: [PATCH] Ensure libpq reports a suitable error message on unexpected
 socket EOF.

The EOF-detection logic in pqReadData was a bit confused about who should
set up the error message in case the kernel gives us read-ready-but-no-data
rather than ECONNRESET or some other explicit error condition.  Since the
whole point of this situation is that the lower-level functions don't know
there's anything wrong, pqReadData itself must set up the message.  But
keep the assumption that if an errno was reported, a message was set up at
lower levels.

Per bug #11712 from Marko Tiikkaja.  It's been like this for a very long
time, so back-patch to all supported branches.
---
 src/interfaces/libpq/fe-misc.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 44f7d039784..f58d7987423 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -764,12 +764,8 @@ retry3:
 			/* ready for read */
 			break;
 		default:
-			printfPQExpBuffer(&conn->errorMessage,
-							  libpq_gettext(
-								"server closed the connection unexpectedly\n"
-				   "\tThis probably means the server terminated abnormally\n"
-							 "\tbefore or while processing the request.\n"));
-			goto definitelyFailed;
+			/* we override pqReadReady's message with something more useful */
+			goto definitelyEOF;
 	}
 
 	/*
@@ -808,9 +804,16 @@ retry4:
 
 	/*
 	 * OK, we are getting a zero read even though select() says ready. This
-	 * means the connection has been closed.  Cope.  Note that errorMessage
-	 * has been set already.
+	 * means the connection has been closed.  Cope.
 	 */
+definitelyEOF:
+	printfPQExpBuffer(&conn->errorMessage,
+					  libpq_gettext(
+								"server closed the connection unexpectedly\n"
+				   "\tThis probably means the server terminated abnormally\n"
+							 "\tbefore or while processing the request.\n"));
+
+	/* Come here if lower-level code already set a suitable errorMessage */
 definitelyFailed:
 	pqDropConnection(conn);
 	conn->status = CONNECTION_BAD;		/* No more connection to backend */
-- 
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