From 243ff228a9b4b680c2c405320634f4f72c65191c Mon Sep 17 00:00:00 2001
From: David Lamparter <equinox@diac24.net>
Date: Thu, 8 Apr 2021 14:28:43 +0200
Subject: [PATCH] lib: add RFC3164 logging timestamps

This is old-style syslog, used among other things for /dev/log.

Signed-off-by: David Lamparter <equinox@diac24.net>
---
 lib/zlog.c | 37 ++++++++++++++++++++++++++++++++++++-
 lib/zlog.h |  4 ++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/lib/zlog.c b/lib/zlog.c
index e843c1e475..d88337cb83 100644
--- a/lib/zlog.c
+++ b/lib/zlog.c
@@ -117,8 +117,14 @@ struct zlog_msg {
 	 * Valid if ZLOG_TS_ISO8601 is set.
 	 * (0 if timestamp has not been formatted yet)
 	 */
-	uint32_t ts_flags;
 	char ts_str[32], *ts_dot, ts_zonetail[8];
+	uint32_t ts_flags;
+
+	/* "mmm dd hh:mm:ss" for 3164 legacy syslog - too dissimilar from
+	 * the above, so just kept separately here.
+	 */
+	uint32_t ts_3164_flags;
+	char ts_3164_str[16];
 
 	/* at the time of writing, 16 args was the actual maximum of arguments
 	 * to a single zlog call.  Particularly printing flag bitmasks seems
@@ -746,6 +752,35 @@ size_t zlog_msg_ts(struct zlog_msg *msg, struct fbuf *out, uint32_t flags)
 	}
 }
 
+size_t zlog_msg_ts_3164(struct zlog_msg *msg, struct fbuf *out, uint32_t flags)
+{
+	flags &= ZLOG_TS_UTC;
+
+	if (!msg->ts_3164_str[0] || flags != msg->ts_3164_flags) {
+		/* these are "hardcoded" in RFC3164, so they're here too... */
+		static const char *const months[12] = {
+			"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+			"Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
+		};
+		struct tm tm;
+
+		/* RFC3164 explicitly asks for local time, but common usage
+		 * also includes UTC.
+		 */
+		if (flags & ZLOG_TS_UTC)
+			gmtime_r(&msg->ts.tv_sec, &tm);
+		else
+			localtime_r(&msg->ts.tv_sec, &tm);
+
+		snprintfrr(msg->ts_3164_str, sizeof(msg->ts_3164_str),
+			   "%3s %2d %02d:%02d:%02d", months[tm.tm_mon],
+			   tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);
+
+		msg->ts_3164_flags = flags;
+	}
+	return bputs(out, msg->ts_3164_str);
+}
+
 void zlog_set_prefix_ec(bool enable)
 {
 	atomic_store_explicit(&zlog_ec, enable, memory_order_relaxed);
diff --git a/lib/zlog.h b/lib/zlog.h
index 452dbcbd0f..f71d28c99a 100644
--- a/lib/zlog.h
+++ b/lib/zlog.h
@@ -168,6 +168,10 @@ extern void zlog_msg_args(struct zlog_msg *msg, size_t *hdrlen,
 extern size_t zlog_msg_ts(struct zlog_msg *msg, struct fbuf *out,
 			  uint32_t flags);
 
+/* "mmm dd hh:mm:ss" for RFC3164 syslog.  Only ZLOG_TS_UTC for flags. */
+extern size_t zlog_msg_ts_3164(struct zlog_msg *msg, struct fbuf *out,
+			       uint32_t flags);
+
 /* This list & struct implements the actual logging targets.  It is accessed
  * lock-free from all threads, and thus MUST only be changed atomically, i.e.
  * RCU.