MINOR: logs: add a new per-proxy "log-tag" directive

This is equivalent to what was done in commit 48936af ("[MINOR] log:
ability to override the syslog tag") but this time instead of doing
this globally, it does it per proxy. The purpose is to be able to use
a separate log tag for various proxies (eg: make it easier to route
log messages depending on the customer).

doc/configuration.txt

@@ -629,7 +629,7 @@ log-tag <string>
   Sets the tag field in the syslog header to this string. It defaults to the
   program name as launched from the command line, which usually is "haproxy".
   Sometimes it can be useful to differentiate between multiple processes
-  running on the same host.
+  running on the same host. See also the per-proxy "log-tag" directive.
 
 nbproc <number>
   Creates <number> processes when going daemon. This requires the "daemon"
@@ -1353,6 +1353,7 @@ id                                        -          X         X         X
 ignore-persist                            -          X         X         X
 log                                  (*)  X          X         X         X
 log-format                                X          X         X         -
+log-tag                                   X          X         X         X
 max-keep-alive-queue                      X          -         X         X
 maxconn                                   X          X         X         -
 mode                                      X          X         X         X
@@ -3558,6 +3559,20 @@ log-format <string>
   the same log format. Please see section 8.2.4 which covers the log format
   string in depth.
 
+log-tag <string>
+  Specifies the log tag to use for all outgoing logs
+  May be used in sections:    defaults | frontend | listen | backend
+                                 yes   |    yes   |   yes  |   yes
+
+  Sets the tag field in the syslog header to this string. It defaults to the
+  log-tag set in the global section, otherwise the program name as launched
+  from the command line, which usually is "haproxy". Sometimes it can be useful
+  to differentiate between multiple processes running on the same host, or to
+  differentiate customer instances running in the same process. In the backend,
+  logs about servers up/down will use this tag. As a hint, it can be convenient
+  to set a log-tag related to a hosted customer in a defaults section then put
+  all the frontends and backends for that customer, then start another customer
+  in a new defaults section. See also the global "log-tag" directive.
 
 max-keep-alive-queue <value>
   Set the maximum server queue size for maintaining keep-alive connections

include/types/proxy.h

@@ -320,6 +320,7 @@ struct proxy {
 	unsigned int log_count;			/* number of logs produced by the frontend */
 	struct list logsrvs;
 	struct list logformat; 			/* log_format linked list */
+	char *log_tag;                          /* override default syslog tag */
 	char *header_unique_id; 		/* unique-id header */
 	struct list format_unique_id;		/* unique-id format */
 	int to_log;				/* things to be logged (LW_*) */

src/cfgparse.c

@@ -2184,6 +2184,9 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 		if (curproxy->conf.uniqueid_format_string)
 			curproxy->conf.uniqueid_format_string = strdup(curproxy->conf.uniqueid_format_string);
 
+		if (defproxy.log_tag)
+			curproxy->log_tag = strdup(defproxy.log_tag);
+
 		if (defproxy.conf.uif_file) {
 			curproxy->conf.uif_file = strdup(defproxy.conf.uif_file);
 			curproxy->conf.uif_line = defproxy.conf.uif_line;
@@ -2249,6 +2252,7 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 		free(defproxy.conf.uniqueid_format_string);
 		free(defproxy.conf.lfs_file);
 		free(defproxy.conf.uif_file);
+		free(defproxy.log_tag);
 
 		for (rc = 0; rc < HTTP_ERR_SIZE; rc++)
 			chunk_destroy(&defproxy.errmsg[rc]);
@@ -4911,7 +4915,15 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 			err_code |= ERR_WARN;
 		}
 	}
-
+	else if (!strcmp(args[0], "log-tag")) {  /* tag to report to syslog */
+		if (*(args[1]) == 0) {
+			Alert("parsing [%s:%d] : '%s' expects a tag for use in syslog.\n", file, linenum, args[0]);
+			err_code |= ERR_ALERT | ERR_FATAL;
+			goto out;
+		}
+		free(curproxy->log_tag);
+		curproxy->log_tag = strdup(args[1]);
+	}
 	else if (!strcmp(args[0], "log") && kwm == KWM_NO) {
 		/* delete previous herited or defined syslog servers */
 		struct logsrv *back;

src/log.c

@@ -724,10 +724,11 @@ char *lf_port(char *dst, struct sockaddr *sockaddr, size_t size, struct logforma
 /* Re-generate the syslog header at the beginning of logline once a second and
  * return the pointer to the first character after the header.
  */
-static char *update_log_hdr()
+static char *update_log_hdr(const char *log_tag)
 {
 	static long tvsec;
 	static char *dataptr = NULL; /* backup of last end of header, NULL first time */
+	int tag_len;
 
 	if (unlikely(date.tv_sec != tvsec || dataptr == NULL)) {
 		/* this string is rebuild only once a second */
@@ -738,11 +739,10 @@ static char *update_log_hdr()
 		get_localtime(tvsec, &tm);
 
 		hdr_len = snprintf(logline, global.max_syslog_len,
-				   "<<<<>%s %2d %02d:%02d:%02d %s%s[%d]: ",
+				   "<<<<>%s %2d %02d:%02d:%02d %s",
 				   monthname[tm.tm_mon],
 				   tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec,
-				   global.log_send_hostname ? global.log_send_hostname : "",
+				   global.log_send_hostname ? global.log_send_hostname : "");
-				   global.log_tag, pid);
 		/* WARNING: depending upon implementations, snprintf may return
 		 * either -1 or the number of bytes that would be needed to store
 		 * the total message. In both cases, we must adjust it.
@@ -753,7 +753,13 @@ static char *update_log_hdr()
 		dataptr = logline + hdr_len;
 	}
 
-	return dataptr;
+	dataptr[0] = 0; // ensure we get rid of any previous attempt
+
+	tag_len = snprintf(dataptr, logline + global.max_syslog_len - dataptr, "%s[%d]: ", log_tag, pid);
+	if (tag_len < 0 || tag_len > logline + global.max_syslog_len - dataptr)
+		tag_len = logline + global.max_syslog_len - dataptr;
+
+	return dataptr + tag_len;
 }
 
 /*
@@ -769,7 +775,7 @@ void send_log(struct proxy *p, int level, const char *format, ...)
 	if (level < 0 || format == NULL)
 		return;
 
-	dataptr = update_log_hdr(); /* update log header and skip it */
+	dataptr = update_log_hdr(p->log_tag ? p->log_tag : global.log_tag); /* update log header and skip it */
 	data_len = dataptr - logline;
 
 	va_start(argp, format);
@@ -1633,7 +1639,7 @@ void sess_log(struct session *s)
 			build_logline(s, s->unique_id, UNIQUEID_LEN, &s->fe->format_unique_id);
 	}
 
-	tmplog = update_log_hdr();
+	tmplog = update_log_hdr(s->fe->log_tag ? s->fe->log_tag : global.log_tag);
 	size = tmplog - logline;
 	size += build_logline(s, tmplog, global.max_syslog_len - size, &s->fe->logformat);
 	if (size > 0) {