From c9138c6d7da30e142082b8e9f8d8b6e6bb731609 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Tue, 30 Jul 2019 21:48:14 +0200
Subject: [PATCH] log: log to syslog too

---
 log.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 66 insertions(+), 3 deletions(-)

diff --git a/log.c b/log.c
index 297f7c37..27dd6b42 100644
--- a/log.c
+++ b/log.c
@@ -9,12 +9,22 @@
 #include <assert.h>
 #include <unistd.h>
 
+#include <syslog.h>
+
 static bool colorize = false;
 
 static void __attribute__((constructor))
 init(void)
 {
     colorize = isatty(STDOUT_FILENO);
+    openlog(NULL, /*LOG_PID*/0, LOG_USER);
+    setlogmask(LOG_UPTO(LOG_WARNING));
+}
+
+static void __attribute__((destructor))
+fini(void)
+{
+    closelog();
 }
 
 static void
@@ -52,32 +62,85 @@ _log(enum log_class log_class, const char *module, const char *file, int lineno,
     printf("\n");
 }
 
+static void
+_sys_log(enum log_class log_class, const char *module, const char *file,
+         int lineno, const char *fmt, int sys_errno, va_list va)
+{
+    /* Map our log level to syslog's level */
+    int level = -1;
+    switch (log_class) {
+    case LOG_CLASS_ERROR:    level = LOG_ERR; break;
+    case LOG_CLASS_WARNING:  level = LOG_WARNING; break;
+    case LOG_CLASS_INFO:     level = LOG_INFO; break;
+    case LOG_CLASS_DEBUG:    level = LOG_DEBUG; break;
+    }
+
+    assert(level != -1);
+
+    const char *sys_err = sys_errno != 0 ? strerror(sys_errno) : NULL;
+
+    va_list va2;
+    va_copy(va2, va);
+
+    /* Calculate required size of buffer holding the entire log message */
+    int required_len = 0;
+    required_len += strlen(module) + 2;  /* "%s: " */
+    required_len += vsnprintf(NULL, 0, fmt, va2); va_end(va2);
+
+    if (sys_errno != 0)
+        required_len += strlen(sys_err) + 2; /* ": %s" */
+
+    /* Format the msg */
+    char *msg = malloc(required_len + 1);
+    int idx = 0;
+
+    idx += snprintf(&msg[idx], required_len + 1 - idx, "%s: ", module);
+    idx += vsnprintf(&msg[idx], required_len + 1 - idx, fmt, va);
+
+    if (sys_errno != 0) {
+        idx += snprintf(
+            &msg[idx], required_len + 1 - idx, ": %s", strerror(sys_errno));
+    }
+
+    syslog(level, "%s", msg);
+    free(msg);
+}
+
 void
 log_msg(enum log_class log_class, const char *module,
         const char *file, int lineno, const char *fmt, ...)
 {
-    va_list ap1;
+    va_list ap1, ap2;
     va_start(ap1, fmt);
+    va_copy(ap2, ap1);
     _log(log_class, module, file, lineno, fmt, 0, ap1);
+    _sys_log(log_class, module, file, lineno, fmt, 0, ap2);
     va_end(ap1);
+    va_end(ap2);
 }
 
 void log_errno(enum log_class log_class, const char *module,
                const char *file, int lineno,
                const char *fmt, ...)
 {
-    va_list ap1;
+    va_list ap1, ap2;
     va_start(ap1, fmt);
+    va_copy(ap2, ap1);
     _log(log_class, module, file, lineno, fmt, errno, ap1);
+    _sys_log(log_class, module, file, lineno, fmt, errno, ap2);
     va_end(ap1);
+    va_end(ap2);
 }
 
 void log_errno_provided(enum log_class log_class, const char *module,
                         const char *file, int lineno, int _errno,
                         const char *fmt, ...)
 {
-    va_list ap1;
+    va_list ap1, ap2;
     va_start(ap1, fmt);
+    va_copy(ap2, ap1);
     _log(log_class, module, file, lineno, fmt, _errno, ap1);
+    _sys_log(log_class, module, file, lineno, fmt, _errno, ap2);
     va_end(ap1);
+    va_end(ap2);
 }