Add logging functions with selectable log output targets

Currently, our "logging" consists of a mix of printf(), perror(), and
other such calls which print output to stdout/stderr.  In normal usage,
browser-switchboard will be launched by D-Bus, which results in
stdout/stderr pointing to /dev/null and debugging output being lost.

To improve this situation, introduce a new set of logging functions
log_out() and log_perror(), and a log_config() which allows choosing the
log target.  These functions log to stdout by default, but also support
syslog output (to the LOG_USER facility, with priority LOG_DEBUG) and
disabling logging entirely.

Thanks to Faheem Pervez (qwerty12) for the suggestion.

diff --git a/log.c b/log.c
new file mode 100644 (file)
index 0000000..36d0fd5
--- /dev/null
+++ b/log.c
@@ -0,0 +1,96 @@
+/*
+ * log.c -- logging functions for browser-switchboard
+ *
+ * Copyright (C) 2010 Steven Luo
+ * Derived from a Python implementation by Jason Simpson and Steven Luo
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+ * USA.
+ */
+
+#include <stdarg.h>
+#include <string.h>
+#include <stdio.h>
+#include <syslog.h>
+
+#include "log.h"
+
+#define DEFAULT_LOGGER LOGTO_STDOUT
+static enum {
+       LOGTO_NONE,
+       LOGTO_STDOUT,
+       LOGTO_SYSLOG,
+} logger = DEFAULT_LOGGER;
+
+/* Configure the logging target, performing any required setup for that
+   target */
+void log_config(char *logger_name) {
+       if (!logger_name) {
+               /* No logger configured, use the default log target */
+               logger = DEFAULT_LOGGER;
+               return;
+       }
+
+       if (!strcmp(logger_name, "stdout"))
+               logger = LOGTO_STDOUT;
+       else if (!strcmp(logger_name, "syslog")) {
+               /* XXX allow syslog facility to be configured? */
+               openlog("browser-switchboard", LOG_PID, LOG_USER);
+               logger = LOGTO_SYSLOG;
+       }
+       else if (!strcmp(logger_name, "none"))
+               logger = LOGTO_NONE;
+       else
+               /* Invalid logger configured, use the default log target */
+               logger = DEFAULT_LOGGER;
+
+       return;
+}
+
+/* Log output to the chosen log target */
+void log_msg(const char *format, ...) {
+       va_list ap;
+
+       if (!format)
+               return;
+
+       va_start(ap, format);
+       switch (logger) {
+               case LOGTO_NONE:
+                       break;
+               case LOGTO_SYSLOG:
+                       /* XXX allow syslog priority to be set by caller? */
+                       vsyslog(LOG_DEBUG, format, ap);
+                       break;
+               case LOGTO_STDOUT:
+               default:
+                       vprintf(format, ap);
+                       break;
+       }
+       va_end(ap);
+}
+
+/* Log strerror(errnum), with the string in prefix appended
+   Behaves like perror() except that it logs to chosen target, not stderr */
+void log_perror(int errnum, const char *prefix) {
+       char *errmsg;
+
+       if (!prefix)
+               return;
+       if (!(errmsg = strerror(errnum)))
+               return;
+
+       log_msg("%s: %s\n", prefix, errmsg);
+}

diff --git a/log.h b/log.h
new file mode 100644 (file)
index 0000000..350dbcc
--- /dev/null
+++ b/log.h
@@ -0,0 +1,30 @@
+/*
+ * log.h -- definitions for the logging functions
+ *
+ * Copyright (C) 2010 Steven Luo
+ * Derived from a Python implementation by Jason Simpson and Steven Luo
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+ * USA.
+ */
+
+#ifndef _LOG_H
+#define _LOG_H 1
+
+void log_config(char *logger_name);
+void log_msg(const char *format, ...);
+void log_perror(int errnum, const char *prefix);
+
+#endif /* _LOG_H */