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// Copyright 2009 The Go 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 iotest implements Readers and Writers useful only for testing.
package iotest

import (
        "errors"
        "io"
)

// OneByteReader returns a Reader that implements
// each non-empty Read by reading one byte from r.
func OneByteReader(r io.Reader) io.Reader { return &oneByteReader{r} }

type oneByteReader struct {
        r io.Reader
}

func (r *oneByteReader) Read(p []byte) (int, error) {
        if len(p) == 0 {
                return 0, nil
        }
        return r.r.Read(p[0:1])
}

// HalfReader returns a Reader that implements Read
// by reading half as many requested bytes from r.
func HalfReader(r io.Reader) io.Reader { return &halfReader{r} }

type halfReader struct {
        r io.Reader
}

func (r *halfReader) Read(p []byte) (int, error) {
        return r.r.Read(p[0 : (len(p)+1)/2])
}

// DataErrReader returns a Reader that returns the final
// error with the last data read, instead of by itself with
// zero bytes of data.
func DataErrReader(r io.Reader) io.Reader { return &dataErrReader{r, nil, make([]byte, 1024)} }

type dataErrReader struct {
        r      io.Reader
        unread []byte
        data   []byte
}

func (r *dataErrReader) Read(p []byte) (n int, err error) {
        // loop because first call needs two reads:
        // one to get data and a second to look for an error.
        for {
                if len(r.unread) == 0 {
                        n1, err1 := r.r.Read(r.data)
                        r.unread = r.data[0:n1]
                        err = err1
                }
                if n > 0 || err != nil {
                        break
                }
                n = copy(p, r.unread)
                r.unread = r.unread[n:]
        }
        return
}

var ErrTimeout = errors.New("timeout")

// TimeoutReader returns ErrTimeout on the second read
// with no data.  Subsequent calls to read succeed.
func TimeoutReader(r io.Reader) io.Reader { return &timeoutReader{r, 0} }

type timeoutReader struct {
        r     io.Reader
        count int
}

func (r *timeoutReader) Read(p []byte) (int, error) {
        r.count++
        if r.count == 2 {
                return 0, ErrTimeout
        }
        return r.r.Read(p)
}