content/2014/go4gophers/chain.go

// +build ignore,OMIT

package main

import (
	"io"
	"io/ioutil"
	"log"
)

// ByteReader implements an io.Reader that emits a stream of its byte value.
type ByteReader byte

func (b ByteReader) Read(buf []byte) (int, error) {
	for i := range buf {
		buf[i] = byte(b)
	}
	return len(buf), nil
}

type LogReader struct {
	io.Reader
}

func (r LogReader) Read(b []byte) (int, error) {
	n, err := r.Reader.Read(b)
	log.Printf("read %d bytes, error: %v", n, err)
	return n, err
}

func main() {
	// START OMIT
	var r io.Reader = ByteReader('A')
	r = io.LimitReader(r, 1e6)
	r = LogReader{r}
	io.Copy(ioutil.Discard, r)
	// STOP OMIT

	return
	io.Copy(ioutil.Discard, LogReader{io.LimitReader(ByteReader('A'), 1e6)})
}