From a7b10adbe871a2330ddde9e593480171a3ef83f2 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Wed, 6 Oct 2021 14:07:20 +0900
Subject: [PATCH] Fix fallback to stderr when using only csvlog

send_message_to_server_log() would force a redirection of a log entry to
stderr in some cases, like the syslogger not being available yet.  If
this happens, csvlog falls back to stderr to log something.  The code
was organized so as stderr was happening before csvlog, with csvlog
calling checking for the same conditions as the stderr code path for a
second time, with a log handling buggy for Windows.

Instead, move the csvlog handling to be before stderr, tracking down if
it is necessary to log something to stderr after.  The reduces the
handling of stderr to a single code path, and fixes one issue with the
case of a Windows service, where stderr is not available, where we would
lose log entries that should have been redirected from csvlog to
stderr.
---
 src/backend/utils/error/elog.c | 56 ++++++++++++++++------------------
 1 file changed, 26 insertions(+), 30 deletions(-)

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 2af87ee3bd..2a88ef9e3b 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -3008,6 +3008,7 @@ static void
 send_message_to_server_log(ErrorData *edata)
 {
 	StringInfoData buf;
+	bool		fallback_to_stderr = false;
 
 	initStringInfo(&buf);
 
@@ -3159,8 +3160,29 @@ send_message_to_server_log(ErrorData *edata)
 	}
 #endif							/* WIN32 */
 
-	/* Write to stderr, if enabled */
-	if ((Log_destination & LOG_DESTINATION_STDERR) || whereToSendOutput == DestDebug)
+	/* Write to CSV log, if enabled */
+	if ((Log_destination & LOG_DESTINATION_CSVLOG) != 0)
+	{
+		/*
+		 * Send CSV data if it's safe to do so (syslogger doesn't need the
+		 * pipe).  If this is not possible, fallback to an entry written
+		 * to stderr.
+		 */
+		if (redirection_done || MyBackendType == B_LOGGER)
+		{
+			write_csvlog(edata);
+		}
+		else
+			fallback_to_stderr = true;
+	}
+
+	/*
+	 * Write to stderr, if enabled or if required because of a previous
+	 * limitation.
+	 */
+	if ((Log_destination & LOG_DESTINATION_STDERR) ||
+		whereToSendOutput == DestDebug ||
+		fallback_to_stderr)
 	{
 		/*
 		 * Use the chunking protocol if we know the syslogger should be
@@ -3189,34 +3211,8 @@ send_message_to_server_log(ErrorData *edata)
 	if (MyBackendType == B_LOGGER)
 		write_syslogger_file(buf.data, buf.len, LOG_DESTINATION_STDERR);
 
-	/* Write to CSV log if enabled */
-	if (Log_destination & LOG_DESTINATION_CSVLOG)
-	{
-		if (redirection_done || MyBackendType == B_LOGGER)
-		{
-			/*
-			 * send CSV data if it's safe to do so (syslogger doesn't need the
-			 * pipe). First get back the space in the message buffer.
-			 */
-			pfree(buf.data);
-			write_csvlog(edata);
-		}
-		else
-		{
-			/*
-			 * syslogger not up (yet), so just dump the message to stderr,
-			 * unless we already did so above.
-			 */
-			if (!(Log_destination & LOG_DESTINATION_STDERR) &&
-				whereToSendOutput != DestDebug)
-				write_console(buf.data, buf.len);
-			pfree(buf.data);
-		}
-	}
-	else
-	{
-		pfree(buf.data);
-	}
+	/* No more need of the message formatted for stderr */
+	pfree(buf.data);
 }
 
 /*
-- 
2.33.0