Add Logger.Debugf

Makes it easy to print debugging messages which aren't targeted at
the user. See [1] for motivation.

[1]: https://dave.cheney.net/2015/11/05/lets-talk-about-logging

cmd/soju/main.go

@@ -97,7 +97,6 @@ func loadConfig() (*config.Server, *soju.Config, error) {
 		MaxUserNetworks: raw.MaxUserNetworks,
 		MultiUpstream:   raw.MultiUpstream,
 		UpstreamUserIPs: raw.UpstreamUserIPs,
-		Debug:           debug,
 		MOTD:            motd,
 	}
 	return raw, cfg, nil
@@ -140,6 +139,7 @@ func main() {
 
 	srv := soju.NewServer(db)
 	srv.SetConfig(serverCfg)
+	srv.Logger = soju.NewLogger(log.Writer(), debug)
 
 	for _, listen := range cfg.Listen {
 		listenURI := listen

conn.go

@@ -156,9 +156,7 @@ func newConn(srv *Server, ic ircConn, options *connOptions) *conn {
 				break
 			}
 
-			if c.srv.Config().Debug {
-				c.logger.Printf("sent: %v", msg)
-			}
+			c.logger.Debugf("sent: %v", msg)
 			c.conn.SetWriteDeadline(time.Now().Add(writeTimeout))
 			if err := c.conn.WriteMessage(msg); err != nil {
 				c.logger.Printf("failed to write message: %v", err)
@@ -210,10 +208,7 @@ func (c *conn) ReadMessage() (*irc.Message, error) {
 		return nil, err
 	}
 
-	if c.srv.Config().Debug {
-		c.logger.Printf("received: %v", msg)
-	}
-
+	c.logger.Debugf("received: %v", msg)
 	return msg, nil
 }
 

server.go

@@ -38,6 +38,26 @@ var backlogLimit = 4000
 
 type Logger interface {
 	Printf(format string, v ...interface{})
+	Debugf(format string, v ...interface{})
+}
+
+type logger struct {
+	*log.Logger
+	debug bool
+}
+
+func (l logger) Debugf(format string, v ...interface{}) {
+	if !l.debug {
+		return
+	}
+	l.Logger.Printf(format, v...)
+}
+
+func NewLogger(out io.Writer, debug bool) Logger {
+	return logger{
+		Logger: log.New(log.Writer(), "", log.LstdFlags),
+		debug:  debug,
+	}
 }
 
 type prefixLogger struct {
@@ -52,6 +72,11 @@ func (l *prefixLogger) Printf(format string, v ...interface{}) {
 	l.logger.Printf("%v"+format, v...)
 }
 
+func (l *prefixLogger) Debugf(format string, v ...interface{}) {
+	v = append([]interface{}{l.prefix}, v...)
+	l.logger.Debugf("%v"+format, v...)
+}
+
 type int64Gauge struct {
 	v int64 // atomic
 }
@@ -72,7 +97,6 @@ type Config struct {
 	Hostname        string
 	Title           string
 	LogPath         string
-	Debug           bool
 	HTTPOrigins     []string
 	AcceptProxyIPs  config.IPSet
 	MaxUserNetworks int
@@ -109,7 +133,7 @@ type Server struct {
 
 func NewServer(db Database) *Server {
 	srv := &Server{
-		Logger:    log.New(log.Writer(), "", log.LstdFlags),
+		Logger:    NewLogger(log.Writer(), true),
 		db:        db,
 		listeners: make(map[net.Listener]struct{}),
 		users:     make(map[string]*user),