log: expose output writer interface (#845)

This allows applications that import GCT to define their own
writer on their own terms.

log/logger.go

@@ -19,12 +19,20 @@ func NewSubLogger(name string) (*SubLogger, error) {
 		return nil, errEmptyLoggerName
 	}
 	name = strings.ToUpper(name)
-	if _, ok := subLoggers[name]; ok {
+	if _, ok := SubLoggers[name]; ok {
 		return nil, errSubLoggerAlreadyregistered
 	}
 	return registerNewSubLogger(name), nil
 }
 
+// SetOutput overrides the default output with a new writer
+func (s *SubLogger) SetOutput(o io.Writer) {
+	RWM.Lock()
+	defer RWM.Unlock()
+
+	s.output = o
+}
+
 func newLogger(c *Config) *Logger {
 	return &Logger{
 		Timestamp:         c.AdvancedSettings.TimeStampFormat,
@@ -75,7 +83,7 @@ func CloseLogger() error {
 }
 
 func validSubLogger(s string) (bool, *SubLogger) {
-	if v, found := subLoggers[s]; found {
+	if v, found := SubLoggers[s]; found {
 		return true, v
 	}
 	return false, nil

log/logger_setup.go

@@ -68,7 +68,7 @@ func configureSubLogger(logger, levels string, output io.Writer) error {
 	logPtr.output = output
 
 	logPtr.Levels = splitLevel(levels)
-	subLoggers[logger] = logPtr
+	SubLoggers[logger] = logPtr
 
 	return nil
 }
@@ -95,9 +95,9 @@ func SetupGlobalLogger() {
 		}
 	}
 
-	for x := range subLoggers {
-		subLoggers[x].Levels = splitLevel(GlobalLogConfig.Level)
-		subLoggers[x].output = getWriters(&GlobalLogConfig.SubLoggerConfig)
+	for x := range SubLoggers {
+		SubLoggers[x].Levels = splitLevel(GlobalLogConfig.Level)
+		SubLoggers[x].output = getWriters(&GlobalLogConfig.SubLoggerConfig)
 	}
 
 	logger = newLogger(GlobalLogConfig)
@@ -128,7 +128,7 @@ func registerNewSubLogger(logger string) *SubLogger {
 	}
 
 	temp.Levels = splitLevel("INFO|WARN|DEBUG|ERROR")
-	subLoggers[logger] = &temp
+	SubLoggers[logger] = &temp
 
 	return &temp
 }

log/sublogger_types.go

@@ -4,7 +4,7 @@ import "io"
 
 // Global vars related to the logger package
 var (
-	subLoggers = map[string]*SubLogger{}
+	SubLoggers = map[string]*SubLogger{}
 
 	Global           *SubLogger
 	BackTester       *SubLogger