MEDIUM: connection: Add option to disable legacy error log

In case of connection failure, a dedicated error message is output,
following the format described in section "Error log format" of the
documentation. These messages cannot be configured through a log-format
option.
This patch adds a new option, "dontloglegacyconnerr", that disables
those error logs when set, and "replaces" them by a regular log line
that follows the configured log-format (thanks to a call to sess_log in
session_kill_embryonic).
The new fc_conn_err sample fetch allows to add the legacy error log
information into a regular log format.
This new option is unset by default so the logging logic will remain the
same until this new option is used.

doc/configuration.txt

@@ -9033,6 +9033,23 @@ no option logasap
              logging.
 
 
+option dontloglegacyconnerr
+no option dontloglegacyconnerr
+  Enable or disable dedicated connection error logging.
+  May be used in sections :   defaults | frontend | listen | backend
+                                 yes   |    yes   |   yes  |   no
+  Arguments : none
+
+  In case of connection error, if the option is disabled, a log line following
+  the format described in section 8.2.6, the legacy format, will be emitted.
+  Otherwise, a log line following the configured log-format for the listener
+  will be emitted. The error code and the corresponding message found in the
+  error log can be added to a log-format thanks to the "fc_conn_err" and
+  "fc_conn_err_str" sample fetches.
+
+  See also : "option httpslog" and section 8 about logging.
+
+
 option mysql-check [ user <username> [ { post-41 | pre-41 } ] ]
   Use MySQL health checks for server testing
   May be used in sections :   defaults | frontend | listen | backend
@@ -20984,7 +21001,9 @@ protocol header, HAProxy will log the event using a shorter, fixed line format.
 By default, logs are emitted at the LOG_INFO level, unless the option
 "log-separate-errors" is set in the backend, in which case the LOG_ERR level
 will be used. Connections on which no data are exchanged (e.g. probes) are not
-logged if the "dontlognull" option is set.
+logged if the "dontlognull" option is set. If the "dontloglegacyconnerr" option
+is set, those messages are not emitted and a line following the configured
+log-format is emitted instead.
 
 The format looks like this :
 

include/haproxy/proxy-t.h

@@ -95,7 +95,8 @@ enum PR_SRV_STATE_FILE {
 #define PR_O_FF_ALWAYS  0x00002000      /* always set x-forwarded-for */
 #define PR_O_PERSIST    0x00004000      /* server persistence stays effective even when server is down */
 #define PR_O_LOGASAP    0x00008000      /* log as soon as possible, without waiting for the stream to complete */
-/* unused: 0x00010000 */
+#define PR_O_NOLGCYCONNERR 0x00010000   /* log a dedicated error log message in case of connection failure instead of the legacy connection error message */
+
 #define PR_O_CHK_CACHE  0x00020000      /* require examination of cacheability of the 'set-cookie' field */
 #define PR_O_TCP_CLI_KA 0x00040000      /* enable TCP keep-alive on client-side streams */
 #define PR_O_TCP_SRV_KA 0x00080000      /* enable TCP keep-alive on server-side streams */

src/proxy.c

@@ -72,6 +72,7 @@ const struct cfg_opt cfg_opts[] =
 	{ "http-ignore-probes", PR_O_IGNORE_PRB, PR_CAP_FE, 0, PR_MODE_HTTP },
 	{ "prefer-last-server", PR_O_PREF_LAST,  PR_CAP_BE, 0, PR_MODE_HTTP },
 	{ "logasap",      PR_O_LOGASAP,    PR_CAP_FE, 0, 0 },
+	{ "dontloglegacyconnerr", PR_O_NOLGCYCONNERR, PR_CAP_FE, 0, 0 },
 	{ "nolinger",     PR_O_TCP_NOLING, PR_CAP_FE | PR_CAP_BE, 0, 0 },
 	{ "persist",      PR_O_PERSIST,    PR_CAP_BE, 0, 0 },
 	{ "srvtcpka",     PR_O_TCP_SRV_KA, PR_CAP_BE, 0, 0 },

src/session.c

@@ -357,14 +357,20 @@ static void session_kill_embryonic(struct session *sess, unsigned int state)
 				conn->err_code = CO_ER_SSL_TIMEOUT;
 		}
 
-		session_prepare_log_prefix(sess);
+		if (sess->fe->options & PR_O_NOLGCYCONNERR) {
-		err_msg = conn_err_code_str(conn);
+			/* Display a log line following the configured log-format. */
-		if (err_msg)
+			sess_log(sess);
-			send_log(sess->fe, level, "%s: %s\n", trash.area,
+		}
-				 err_msg);
+		else {
-		else
+			session_prepare_log_prefix(sess);
-			send_log(sess->fe, level, "%s: unknown connection error (code=%d flags=%08x)\n",
+			err_msg = conn_err_code_str(conn);
-				 trash.area, conn->err_code, conn->flags);
+			if (err_msg)
+				send_log(sess->fe, level, "%s: %s\n", trash.area,
+					 err_msg);
+			else
+				send_log(sess->fe, level, "%s: unknown connection error (code=%d flags=%08x)\n",
+					 trash.area, conn->err_code, conn->flags);
+		}
 	}
 
 	/* kill the connection now */