logging/backend.go

package logging

import (
	"errors"
	"fmt"
	"io"
	"os"
)

type Backend interface {
	Write(*Record) error
	SetFormatter(*Formatter)
	SetLevel(Level)
	Level() Level
	Reopen() error
}

//
// Backend to write in file-like objects
//

type FileBackend struct {
	l         io.Writer
	formatter *Formatter
	level     Level
	filepath  string
}

// Creates a new backend to write the logs on the standard output
func NewStdoutBackend() (b *FileBackend) {
	b = &FileBackend{
		l:         os.Stdout,
		formatter: &defaultFormatter,
	}
	return
}

// Creates a new backend to write the logs on the error output
func NewStderrBackend() (b *FileBackend) {
	b = &FileBackend{
		l:         os.Stderr,
		formatter: &defaultFormatter,
	}
	return
}

// Creates a new backend to write the logs in a given file
func NewFileBackend(filename string) (b *FileBackend, e error) {
	filename_fd, err := os.OpenFile(filename, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
	if err != nil {
		e = errors.New(fmt.Sprintf("Cannot open log file %s (%s)", filename, err.Error()))
	}
	b = &FileBackend{
		l:         filename_fd,
		formatter: &defaultFormatter,
		filepath:  filename,
	}
	return
}

// Creates a new backend to write the logs in a given io.Writer
func NewIoBackend(buf io.Writer) (b *FileBackend) {
	return &FileBackend{
		l:         buf,
		formatter: &defaultFormatter,
	}
}

func (b FileBackend) Write(r *Record) error {
	text := (*b.formatter)(r)
	_, err := io.WriteString(b.l, text)
	return err
}

func (b *FileBackend) SetLevel(l Level) {
	b.level = l
}

func (b *FileBackend) Level() Level {
	return b.level
}

func (b *FileBackend) SetFormatter(f *Formatter) {
	b.formatter = f
}

func (b *FileBackend) Reopen() error {
	if b.filepath == "" {
		return nil
	}

	if c, ok := b.l.(io.Closer); ok {
		if err := c.Close(); err != nil {
			return err
		}
	}

	fd, err := os.OpenFile(b.filepath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
	if err != nil {
		return fmt.Errorf("Cannot open log file %s: %w", b.filepath, err)
	}

	b.l = fd

	return nil
}

//
// Noop Backend
//

type NoopBackend struct{}

func NewNoopBackend() (Backend, error) {
	return &NoopBackend{}, nil
}

func (nb *NoopBackend) Write(r *Record) error {
	return nil
}

func (nb *NoopBackend) SetFormatter(f *Formatter) {}

func (nb *NoopBackend) SetLevel(level Level) {}

func (nb *NoopBackend) Level() Level {
	return DefaultLevel
}

func (nb *NoopBackend) Reopen() error {
	return nil
}