TUN-3768: Reuse file loggers

This change is focused on fixing rotating loggers in Windows
where it was failing due to Windows file semantics disallowing
the rotation while that file was still being open (because we
had multiple lumberjacks pointing to the same file).

This is fixed by ensuring the initialization happens only once.

logger/create.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"sync"
 
 	"github.com/mattn/go-colorable"
 	"github.com/rs/zerolog"
@@ -143,7 +144,20 @@ func createConsoleLogger(config ConsoleConfig) io.Writer {
 	}
 }
 
+type fileInitializer struct {
+	once          sync.Once
+	writer        io.Writer
+	creationError error
+}
+
+var (
+	singleFileInit   fileInitializer
+	rotatingFileInit fileInitializer
+)
+
 func createFileWriter(config FileConfig) (io.Writer, error) {
+	singleFileInit.once.Do(func() {
+
 		var logFile io.Writer
 		fullpath := config.Fullpath()
 
@@ -155,11 +169,15 @@ func createFileWriter(config FileConfig) (io.Writer, error) {
 			logFile, err = createDirFile(config)
 			// If creating a new logfile fails, then we have no choice but to error out.
 			if err != nil {
-			return nil, err
+				singleFileInit.creationError = err
+				return
 			}
 		}
 
-	return logFile, nil
+		singleFileInit.writer = logFile
+	})
+
+	return singleFileInit.writer, singleFileInit.creationError
 }
 
 func createDirFile(config FileConfig) (io.Writer, error) {
@@ -183,14 +201,19 @@ func createDirFile(config FileConfig) (io.Writer, error) {
 }
 
 func createRollingLogger(config RollingConfig) (io.Writer, error) {
+	rotatingFileInit.once.Do(func() {
 		if err := os.MkdirAll(config.Dirname, dirPermMode); err != nil {
-		return nil, err
+			rotatingFileInit.creationError = err
+			return
 		}
 
-	return &lumberjack.Logger{
+		rotatingFileInit.writer = &lumberjack.Logger{
 			Filename:   path.Join(config.Dirname, config.Filename),
 			MaxBackups: config.maxBackups,
 			MaxSize:    config.maxSize,
 			MaxAge:     config.maxAge,
-	}, nil
+		}
+	})
+
+	return rotatingFileInit.writer, rotatingFileInit.creationError
 }