blocking_buffer.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"time"
)

func main() {
	debug = true
	r := NewBlockingReader("hello\n")
	go func() {
		fmt.Println("Starting copy")
		io.Copy(os.Stdout, r)
		fmt.Println("Finished copy (won't ever get here because the reader blocks)")
	}()

	for {
		time.Sleep(time.Second)
		fmt.Println("Still waiting...")
	}
}

var debug = false

type BlockingBuffer struct {
	Reader io.Reader
}

// NewBlockingReader returns a reader that allows reading the given string, then blocks (doesn't return EOF or return from final Read call)
func NewBlockingReader(s string) io.Reader {
	return &BlockingBuffer{Reader: bytes.NewBufferString(s)}
}

func (b *BlockingBuffer) Read(p []byte) (int, error) {
	n, err := b.Reader.Read(p)
	if debug {
		fmt.Println(n, err)
	}
	switch {
	case err == io.EOF && n > 0:
		return n, nil
	case err == io.EOF && n == 0:
		if debug {
			fmt.Println("Hit EOF with no data, blocking")
		}
		select {}
	default:
		return n, err
	}
}