Logging in Reverse, Nice use of the reader interface in logging From: https://rogpeppe.wordpress.com/2011/03/31/logging-in-reverse/

gistfile1.go

package main

import (
	"io"
	"os"
	"log"
)

type msg struct {
	data []byte
	next *msg
}

// ReverseBuffer is an implementation of io.Writer that stores data such
// that it can later be read with the data from all writes reversed.
type ReverseBuffer struct {
	msgs *msg
}

type reverseReader struct {
	data []byte
	msgs *msg
}

func (w *ReverseBuffer) Write(data []byte) (int, os.Error) {
	if len(data) == 0 {
		return 0, nil
	}
	w.msgs = &msg{append([]byte(nil), data...), w.msgs}
	return len(data), nil
}

// Reader returns a new io.Reader that can be used to read all the data
// written to w.  The data from more recent writes is returned first.
func (w *ReverseBuffer) Reader() io.Reader {
	return &reverseReader{nil, w.msgs}
}

func (r *reverseReader) Read(data []byte) (int, os.Error) {
	if len(r.data) == 0 {
		if r.msgs == nil {
			return 0, os.EOF
		}
		r.data = r.msgs.data
		r.msgs = r.msgs.next
	}
	n := copy(data, r.data)
	r.data = r.data[n:]
	return n, nil
}

func main() {
	w := new(ReverseBuffer)
	out := log.New(w, "", log.Ldate|log.Ltime)
	out.Printf("one")
	out.Printf("two")
	out.Printf("three")
	io.Copy(os.Stdout, w.Reader())
}