tailscale/types/logger/logger.go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package logger defines a type for writing to logs. It's just a
// convenience type so that we don't have to pass verbose func(...)
// types around.
package logger

import (
	"io"
	"log"
)

// Logf is the basic Tailscale logger type: a printf-like func.
// Like log.Printf, the format need not end in a newline.
type Logf func(format string, args ...interface{})

// WithPrefix wraps f, prefixing each format with the provided prefix.
func WithPrefix(f Logf, prefix string) Logf {
	return func(format string, args ...interface{}) {
		f(prefix+format, args...)
	}
}

// FuncWriter returns an io.Writer that writes to f.
func FuncWriter(f Logf) io.Writer {
	return funcWriter{f}
}

// StdLogger returns a standard library logger from a Logf.
func StdLogger(f Logf) *log.Logger {
	return log.New(FuncWriter(f), "", 0)
}

type funcWriter struct{ f Logf }

func (w funcWriter) Write(p []byte) (int, error) {
	w.f("%s", p)
	return len(p), nil
}

// Discard is a Logf that throws away the logs given to it.
func Discard(string, ...interface{}) {}