Refactor logger (#3924)

This patch fixes below

* Previously fatalIf() never writes log other than first logging target.
* quiet flag is not honored to show progress messages other than startup messages.
* Removes console package usage for progress messages.

cmd/file-logger.go

@@ -0,0 +1,86 @@
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/Sirupsen/logrus"
+)
+
+// FileLogger - file logger which logs to a file.
+type FileLogger struct {
+	BaseLogTarget
+	Filename string `json:"filename"`
+	file     *os.File
+}
+
+// Fire - log entry handler.
+func (logger FileLogger) Fire(entry *logrus.Entry) (err error) {
+	if !logger.Enable {
+		return nil
+	}
+
+	msgBytes, err := logger.formatter.Format(entry)
+	if err != nil {
+		return err
+	}
+
+	if _, err = logger.file.Write(msgBytes); err != nil {
+		return err
+	}
+
+	err = logger.file.Sync()
+	return err
+}
+
+// String - represents ConsoleLogger as string.
+func (logger FileLogger) String() string {
+	enableStr := "disabled"
+	if logger.Enable {
+		enableStr = "enabled"
+	}
+
+	return fmt.Sprintf("file:%s:%s", enableStr, logger.Filename)
+}
+
+// NewFileLogger - creates new file logger object.
+func NewFileLogger(filename string) (logger FileLogger) {
+	logger.Enable = true
+	logger.formatter = new(logrus.JSONFormatter)
+	logger.Filename = filename
+
+	return logger
+}
+
+// InitFileLogger - initializes file logger.
+func InitFileLogger(logger *FileLogger) (err error) {
+	if !logger.Enable {
+		return err
+	}
+
+	if logger.formatter == nil {
+		logger.formatter = new(logrus.JSONFormatter)
+	}
+
+	if logger.file == nil {
+		logger.file, err = os.OpenFile(logger.Filename, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0664)
+	}
+
+	return err
+}