Add option to redirect stdout and stderr to a file

When using a daemon, stdout and stderr are redirected to /dev/null.
If the program generates an exception and crashes, we can't get the
message. This option allows to get everything from stdout and stderr in
a file.

lib/smsd/cli.rb

@@ -13,6 +13,7 @@ module SMSd
       self.machine = yield block if block_given?
 
       init_logger
+      redirect_output
       @modem = Biju::Hayes.new(options[:modem], pin: options[:pin])
     rescue Errno::ENOENT => e
       logger.warn e.message
@@ -23,7 +24,7 @@ module SMSd
       @running_since = DateTime.now
 
       catch_signals
-      Process.daemon if options[:daemonize]
+      Process.daemon(false, !@options[:output].nil?) if options[:daemonize]
 
       loop do
         pong if options[:alive]
@@ -60,6 +61,14 @@ module SMSd
       end
     end
 
+    def redirect_output
+      if @options[:output]
+        output_file = File.new(@options[:output], 'a')
+        $stdout.reopen(output_file)
+        $stderr.reopen(output_file)
+      end
+    end
+
     def catch_signals
       signal_term =  proc { @terminate = true }
       Signal.trap('SIGTERM', signal_term)

lib/smsd/cli/options.rb

@@ -34,6 +34,11 @@ module SMSd
             options[:pin] = pin
           end
 
+          opts.on('-r', '--redirect-output FILE',
+                  'Redirect stdout and stderr to a file') do |output|
+            options[:output] = output
+          end
+
           opts.separator ''
           opts.separator 'Common options:'