gocommon/log/hooks/file/file_hook.go

package file

import (
	"fmt"
	"io"
	"os"
	"sync"
	"time"

	"github.com/sirupsen/logrus"
)

// BufSize is the number of log that can be put in buffer before make it full
// BufSize= <value> _before_ calling NewFileHook
// Once the buffer is full, logging will start blocking, waiting for slots to
// be available in the queue.
var BufSize uint = 8192

// defaultFormater will be use if no formatter is given.
var defaultFormater = &logrus.TextFormatter{
	DisableColors:    true,
	TimestampFormat:  time.RFC3339Nano,
	QuoteEmptyFields: true,
}

// Hook will write logs to a file.
type Hook struct {
	Level       logrus.Level
	buf         chan logrus.Entry
	f           logrus.Formatter
	mu          sync.RWMutex
	synchronous bool
	w           io.Writer
	wg          sync.WaitGroup
}

// NewFileHook creates a hook to be added to an instance of logger.
func NewFileHook(w io.Writer, f logrus.Formatter) *Hook {
	if w == nil {
		logrus.Error("Can't create File Hook with an empty writer")
		return nil
	}

	if f == nil {
		f = defaultFormater
	}

	hook := &Hook{
		Level:       logrus.DebugLevel,
		synchronous: true,
		f:           f,
		w:           w,
	}

	return hook
}

// NewAsyncFileHook creates a hook to be added to an instance of logger.
// The hook created will be asynchronous, and it's the responsibility of the user to call the Flush method
// before exiting to empty the log queue.
func NewAsyncFileHook(w io.Writer, f logrus.Formatter) *Hook {
	if w == nil {
		logrus.Error("Can't create File Hook with an empty writer")
		return nil
	}

	if f == nil {
		f = defaultFormater
	}

	hook := &Hook{
		Level: logrus.DebugLevel,
		buf:   make(chan logrus.Entry, BufSize),
		f:     f,
		w:     w,
	}

	go hook.fire() // Log in background

	return hook
}

// Flush waits for the log queue to be empty.
// This func is meant to be used when the hook was created with NewAsyncFileHook.
func (hook *Hook) Flush() {
	if hook.synchronous {
		logrus.Error("Can't call Flush on a File Hook in synchronous execution")
	}

	hook.mu.Lock() // claim the mutex as a Lock - we want exclusive access to it
	defer hook.mu.Unlock()

	hook.wg.Wait()
}

// Fire is called when a log event is fired.
// We assume the entry will be altered by another hook,
// otherwise we might be logging something wrong to Graylog.
func (hook *Hook) Fire(entry *logrus.Entry) error {
	hook.mu.RLock() // Claim the mutex as a RLock - allowing multiple go routines to log simultaneously
	defer hook.mu.RUnlock()

	if hook.synchronous {
		hook.writeEntry(entry)
	} else {
		hook.wg.Add(1)
		hook.buf <- *entry
	}

	return nil
}

// fire will loop on the 'buf' channel, and write entries to the writer.
func (hook *Hook) fire() {
	for {
		entry := <-hook.buf // receive new entry on channel
		hook.writeEntry(&entry)
		hook.wg.Done()
	}
}

// writeEntry write an entry to a file synchronously.
func (hook *Hook) writeEntry(entry *logrus.Entry) {
	if hook.w == nil {
		fmt.Println("Can't write to a file without a writer")
		return
	}

	message, err := hook.f.Format(entry)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to format log line. Error: %s\n", err)
		return
	}

	_, err = hook.w.Write(message)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to write in log file. Error: %s\nLog Line: %s", err, message)
	}
}

// Levels returns the available logging levels.
func (hook *Hook) Levels() []logrus.Level {
	levels := []logrus.Level{}
	for _, level := range logrus.AllLevels {
		if level <= hook.Level {
			levels = append(levels, level)
		}
	}
	return levels
}