Merge pull request #126 from hashicorp/f-sublogger-hook

Add ability to wrap new subloggers

intlogger.go

@@ -85,6 +85,8 @@ type intLogger struct {
 
 	// create subloggers with their own level setting
 	independentLevels bool
+
+	subloggerHook func(sub Logger) Logger
 }
 
 // New returns a configured logger.
@@ -151,6 +153,7 @@ func newLogger(opts *LoggerOptions) *intLogger {
 		independentLevels: opts.IndependentLevels,
 		headerColor:       headerColor,
 		fieldColor:        fieldColor,
+		subloggerHook:     opts.SubloggerHook,
 	}
 	if opts.IncludeLocation {
 		l.callerOffset = offsetIntLogger + opts.AdditionalLocationOffset
@@ -166,13 +169,21 @@ func newLogger(opts *LoggerOptions) *intLogger {
 		l.timeFormat = opts.TimeFormat
 	}
 
+	if l.subloggerHook == nil {
+		l.subloggerHook = identityHook
+	}
+
 	l.setColorization(opts)
 
 	atomic.StoreInt32(l.level, int32(level))
 
 	return l
 }
 
+func identityHook(logger Logger) Logger {
+	return logger
+}
+
 // offsetIntLogger is the stack frame offset in the call stack for the caller to
 // one of the Warn, Info, Log, etc methods.
 const offsetIntLogger = 3
@@ -774,7 +785,7 @@ func (l *intLogger) With(args ...interface{}) Logger {
 		sl.implied = append(sl.implied, MissingKey, extra)
 	}
 
-	return sl
+	return l.subloggerHook(sl)
 }
 
 // Create a new sub-Logger that a name decending from the current name.
@@ -788,7 +799,7 @@ func (l *intLogger) Named(name string) Logger {
 		sl.name = name
 	}
 
-	return sl
+	return l.subloggerHook(sl)
 }
 
 // Create a new sub-Logger with an explicit name. This ignores the current
@@ -799,7 +810,7 @@ func (l *intLogger) ResetNamed(name string) Logger {
 
 	sl.name = name
 
-	return sl
+	return l.subloggerHook(sl)
 }
 
 func (l *intLogger) ResetOutput(opts *LoggerOptions) error {

logger.go

@@ -299,6 +299,13 @@ type LoggerOptions struct {
 	// logger will not affect any subloggers, and SetLevel on any subloggers
 	// will not affect the parent or sibling loggers.
 	IndependentLevels bool
+
+	// SubloggerHook registers a function that is called when a sublogger via
+	// Named, With, or ResetNamed is created. If defined, the function is passed
+	// the newly created Logger and the returned Logger is returned from the
+	// original function. This option allows customization via interception and
+	// wrapping of Logger instances.
+	SubloggerHook func(sub Logger) Logger
 }
 
 // InterceptLogger describes the interface for using a logger