feat(lwlogger): add merge logger function (#1087)

lwlogger/logger.go

@@ -103,6 +103,16 @@ func NewWithWriter(level string, out io.Writer, options ...zap.Option) *zap.Logg
 	return zap.New(core, options...).WithOptions(localOpts...)
 }
 
+// Merges multiple loggers into one. A call to the merged logger will be
+// forwarded to all the loggers
+func Merge(loggers ...*zap.Logger) *zap.Logger {
+	cores := make([]zapcore.Core, len(loggers))
+	for i, log := range loggers {
+		cores[i] = log.Core()
+	}
+	return zap.New(zapcore.NewTee(cores...))
+}
+
 func ValidLevel(level string) bool {
 	for _, l := range SupportedLogLevels {
 		if l == level {

lwlogger/logger_test.go

@@ -19,6 +19,7 @@
 package lwlogger_test
 
 import (
+	"bytes"
 	"io/ioutil"
 	"os"
 	"syscall"
@@ -219,6 +220,24 @@ func TestLoggerNewWithOptions(t *testing.T) {
 	assert.Contains(t, logOutput, "\"awesome\"")
 }
 
+func TestLoggerMerge(t *testing.T) {
+	var bufOne bytes.Buffer
+	var bufTwo bytes.Buffer
+
+	logOne := lwlogger.NewWithWriter("INFO", &bufOne)
+	logTwo := lwlogger.NewWithWriter("DEBUG", &bufTwo)
+
+	mergedLog := lwlogger.Merge(logOne, logTwo)
+	mergedLog.Info("ABCD")
+	mergedLog.Debug("XYZ")
+	_ = mergedLog.Sync()
+
+	assert.Contains(t, bufOne.String(), "ABCD")
+	assert.NotContains(t, bufOne.String(), "XYZ")
+	assert.Contains(t, bufTwo.String(), "ABCD")
+	assert.Contains(t, bufTwo.String(), "XYZ")
+}
+
 func TestValidLevel(t *testing.T) {
 	assert.True(t, lwlogger.ValidLevel("INFO"))
 	assert.True(t, lwlogger.ValidLevel("DEBUG"))