Derive channel logger from session logger (#141)

- This way, each log entry created by channel logger also includes
the fields registered on session logger such as session-id.

Closes #134

Signed-off-by: Anagha Sukumaran <sukumaran.anaghak@in.bosch.com>

log/logger.go

@@ -76,8 +76,18 @@ func NewLoggerWithField(key string, value interface{}) Logger {
 	if logger == nil {
 		InitLogger("debug", "") // nolint: errcheck, gosec	// err will always be nil in this case.
 	}
-	l := logger.WithField(key, value)
-	return l
+	return logger.WithField(key, value)
+}
+
+// NewDerivedLoggerWithField returns a logger that inherits all properties of the parent logger,
+// and add the given fields for each log entry.
+//
+// Panics if parent logger is nil.
+func NewDerivedLoggerWithField(parentLogger Logger, key string, value interface{}) Logger {
+	if parentLogger == nil {
+		panic("parent logger should not be nil")
+	}
+	return parentLogger.WithField(key, value)
 }
 
 // customTextFormatter is defined to override default formating options for log entry.

session/session.go

@@ -394,9 +394,8 @@ func makeAllocation(balInfo perun.BalInfo, chAsset pchannel.Asset) (*pchannel.Al
 
 // addCh adds the channel to session. It locks the session mutex during the operation.
 func (s *session) addCh(ch *channel) {
-	ch.Logger = log.NewLoggerWithField("channel-id", ch.id)
+	ch.Logger = log.NewDerivedLoggerWithField(s.Logger, "channel-id", ch.id)
 	s.Lock()
-	// TODO: (mano) use logger with multiple fields and use session-id, channel-id.
 	s.chs[ch.id] = ch
 	s.Unlock()
 }