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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 mainly for testing.
package iotest
import (
"bytes"
"errors"
"fmt"
"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 changes the way errors are handled by a Reader. Normally, a
// Reader returns an error (typically EOF) from the first Read call after the
// last piece of data is read. DataErrReader wraps a Reader and changes its
// behavior so the final error is returned along with the final data, instead
// of in the first call after the final 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
}
// ErrTimeout is a fake timeout error.
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)
}
// ErrReader returns an [io.Reader] that returns 0, err from all Read calls.
func ErrReader(err error) io.Reader {
return &errReader{err: err}
}
type errReader struct {
err error
}
func (r *errReader) Read(p []byte) (int, error) {
return 0, r.err
}
type smallByteReader struct {
r io.Reader
off int
n int
}
func (r *smallByteReader) Read(p []byte) (int, error) {
if len(p) == 0 {
return 0, nil
}
r.n = r.n%3 + 1
n := r.n
if n > len(p) {
n = len(p)
}
n, err := r.r.Read(p[0:n])
if err != nil && err != io.EOF {
err = fmt.Errorf("Read(%d bytes at offset %d): %v", n, r.off, err)
}
r.off += n
return n, err
}
// TestReader tests that reading from r returns the expected file content.
// It does reads of different sizes, until EOF.
// If r implements [io.ReaderAt] or [io.Seeker], TestReader also checks
// that those operations behave as they should.
//
// If TestReader finds any misbehaviors, it returns an error reporting them.
// The error text may span multiple lines.
func TestReader(r io.Reader, content []byte) error {
if len(content) > 0 {
n, err := r.Read(nil)
if n != 0 || err != nil {
return fmt.Errorf("Read(0) = %d, %v, want 0, nil", n, err)
}
}
data, err := io.ReadAll(&smallByteReader{r: r})
if err != nil {
return err
}
if !bytes.Equal(data, content) {
return fmt.Errorf("ReadAll(small amounts) = %q\n\twant %q", data, content)
}
n, err := r.Read(make([]byte, 10))
if n != 0 || err != io.EOF {
return fmt.Errorf("Read(10) at EOF = %v, %v, want 0, EOF", n, err)
}
if r, ok := r.(io.ReadSeeker); ok {
// Seek(0, 1) should report the current file position (EOF).
if off, err := r.Seek(0, 1); off != int64(len(content)) || err != nil {
return fmt.Errorf("Seek(0, 1) from EOF = %d, %v, want %d, nil", off, err, len(content))
}
// Seek backward partway through file, in two steps.
// If middle == 0, len(content) == 0, can't use the -1 and +1 seeks.
middle := len(content) - len(content)/3
if middle > 0 {
if off, err := r.Seek(-1, 1); off != int64(len(content)-1) || err != nil {
return fmt.Errorf("Seek(-1, 1) from EOF = %d, %v, want %d, nil", -off, err, len(content)-1)
}
if off, err := r.Seek(int64(-len(content)/3), 1); off != int64(middle-1) || err != nil {
return fmt.Errorf("Seek(%d, 1) from %d = %d, %v, want %d, nil", -len(content)/3, len(content)-1, off, err, middle-1)
}
if off, err := r.Seek(+1, 1); off != int64(middle) || err != nil {
return fmt.Errorf("Seek(+1, 1) from %d = %d, %v, want %d, nil", middle-1, off, err, middle)
}
}
// Seek(0, 1) should report the current file position (middle).
if off, err := r.Seek(0, 1); off != int64(middle) || err != nil {
return fmt.Errorf("Seek(0, 1) from %d = %d, %v, want %d, nil", middle, off, err, middle)
}
// Reading forward should return the last part of the file.
data, err := io.ReadAll(&smallByteReader{r: r})
if err != nil {
return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
}
if !bytes.Equal(data, content[middle:]) {
return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
}
// Seek relative to end of file, but start elsewhere.
if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
}
if off, err := r.Seek(int64(-len(content)/3), 2); off != int64(middle) || err != nil {
return fmt.Errorf("Seek(%d, 2) from %d = %d, %v, want %d, nil", -len(content)/3, middle/2, off, err, middle)
}
// Reading forward should return the last part of the file (again).
data, err = io.ReadAll(&smallByteReader{r: r})
if err != nil {
return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
}
if !bytes.Equal(data, content[middle:]) {
return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
}
// Absolute seek & read forward.
if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
}
data, err = io.ReadAll(r)
if err != nil {
return fmt.Errorf("ReadAll from offset %d: %v", middle/2, err)
}
if !bytes.Equal(data, content[middle/2:]) {
return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle/2, data, content[middle/2:])
}
}
if r, ok := r.(io.ReaderAt); ok {
data := make([]byte, len(content), len(content)+1)
for i := range data {
data[i] = 0xfe
}
n, err := r.ReadAt(data, 0)
if n != len(data) || err != nil && err != io.EOF {
return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, nil or EOF", len(data), n, err, len(data))
}
if !bytes.Equal(data, content) {
return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
}
n, err = r.ReadAt(data[:1], int64(len(data)))
if n != 0 || err != io.EOF {
return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 0, EOF", len(data), n, err)
}
for i := range data {
data[i] = 0xfe
}
n, err = r.ReadAt(data[:cap(data)], 0)
if n != len(data) || err != io.EOF {
return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, EOF", cap(data), n, err, len(data))
}
if !bytes.Equal(data, content) {
return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
}
for i := range data {
data[i] = 0xfe
}
for i := range data {
n, err = r.ReadAt(data[i:i+1], int64(i))
if n != 1 || err != nil && (i != len(data)-1 || err != io.EOF) {
want := "nil"
if i == len(data)-1 {
want = "nil or EOF"
}
return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 1, %s", i, n, err, want)
}
if data[i] != content[i] {
return fmt.Errorf("ReadAt(1, %d) = %q want %q", i, data[i:i+1], content[i:i+1])
}
}
}
return nil
}
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