src/io/io_test.go - go - Git at Google

 // 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 io_test

 import (
 	"bytes"
 	"errors"
 	"fmt"
 	. "io"
 	"strings"
 	"testing"
 )

 // A version of bytes.Buffer without ReadFrom and WriteTo
 type Buffer struct {
 	bytes.Buffer
 	ReaderFrom // conflicts with and hides bytes.Buffer's ReaderFrom.
 	WriterTo   // conflicts with and hides bytes.Buffer's WriterTo.
 }

 // Simple tests, primarily to verify the ReadFrom and WriteTo callouts inside Copy, CopyBuffer and CopyN.

 func TestCopy(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	Copy(wb, rb)
 	if wb.String() != "hello, world." {
 		t.Errorf("Copy did not work properly")
 	}
 }

 func TestCopyNegative(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(Buffer)
 	rb.WriteString("hello")
 	Copy(wb, &LimitedReader{R: rb, N: -1})
 	if wb.String() != "" {
 		t.Errorf("Copy on LimitedReader with N<0 copied data")
 	}

 	CopyN(wb, rb, -1)
 	if wb.String() != "" {
 		t.Errorf("CopyN with N<0 copied data")
 	}
 }

 func TestCopyBuffer(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	CopyBuffer(wb, rb, make([]byte, 1)) // Tiny buffer to keep it honest.
 	if wb.String() != "hello, world." {
 		t.Errorf("CopyBuffer did not work properly")
 	}
 }

 func TestCopyBufferNil(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	CopyBuffer(wb, rb, nil) // Should allocate a buffer.
 	if wb.String() != "hello, world." {
 		t.Errorf("CopyBuffer did not work properly")
 	}
 }

 func TestCopyReadFrom(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(bytes.Buffer) // implements ReadFrom.
 	rb.WriteString("hello, world.")
 	Copy(wb, rb)
 	if wb.String() != "hello, world." {
 		t.Errorf("Copy did not work properly")
 	}
 }

 func TestCopyWriteTo(t *testing.T) {
 	rb := new(bytes.Buffer) // implements WriteTo.
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	Copy(wb, rb)
 	if wb.String() != "hello, world." {
 		t.Errorf("Copy did not work properly")
 	}
 }

 // Version of bytes.Buffer that checks whether WriteTo was called or not
 type writeToChecker struct {
 	bytes.Buffer
 	writeToCalled bool
 }

 func (wt *writeToChecker) WriteTo(w Writer) (int64, error) {
 	wt.writeToCalled = true
 	return wt.Buffer.WriteTo(w)
 }

 // It's preferable to choose WriterTo over ReaderFrom, since a WriterTo can issue one large write,
 // while the ReaderFrom must read until EOF, potentially allocating when running out of buffer.
 // Make sure that we choose WriterTo when both are implemented.
 func TestCopyPriority(t *testing.T) {
 	rb := new(writeToChecker)
 	wb := new(bytes.Buffer)
 	rb.WriteString("hello, world.")
 	Copy(wb, rb)
 	if wb.String() != "hello, world." {
 		t.Errorf("Copy did not work properly")
 	} else if !rb.writeToCalled {
 		t.Errorf("WriteTo was not prioritized over ReadFrom")
 	}
 }

 type zeroErrReader struct {
 	err error
 }

 func (r zeroErrReader) Read(p []byte) (int, error) {
 	return copy(p, []byte{0}), r.err
 }

 type errWriter struct {
 	err error
 }

 func (w errWriter) Write([]byte) (int, error) {
 	return 0, w.err
 }

 // In case a Read results in an error with non-zero bytes read, and
 // the subsequent Write also results in an error, the error from Write
 // is returned, as it is the one that prevented progressing further.
 func TestCopyReadErrWriteErr(t *testing.T) {
 	er, ew := errors.New("readError"), errors.New("writeError")
 	r, w := zeroErrReader{err: er}, errWriter{err: ew}
 	n, err := Copy(w, r)
 	if n != 0 || err != ew {
 		t.Errorf("Copy(zeroErrReader, errWriter) = %d, %v; want 0, writeError", n, err)
 	}
 }

 func TestCopyN(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	CopyN(wb, rb, 5)
 	if wb.String() != "hello" {
 		t.Errorf("CopyN did not work properly")
 	}
 }

 func TestCopyNReadFrom(t *testing.T) {
 	rb := new(Buffer)
 	wb := new(bytes.Buffer) // implements ReadFrom.
 	rb.WriteString("hello")
 	CopyN(wb, rb, 5)
 	if wb.String() != "hello" {
 		t.Errorf("CopyN did not work properly")
 	}
 }

 func TestCopyNWriteTo(t *testing.T) {
 	rb := new(bytes.Buffer) // implements WriteTo.
 	wb := new(Buffer)
 	rb.WriteString("hello, world.")
 	CopyN(wb, rb, 5)
 	if wb.String() != "hello" {
 		t.Errorf("CopyN did not work properly")
 	}
 }

 func BenchmarkCopyNSmall(b *testing.B) {
 	bs := bytes.Repeat([]byte{0}, 512+1)
 	rd := bytes.NewReader(bs)
 	buf := new(Buffer)
 	b.ResetTimer()

 	for i := 0; i < b.N; i++ {
 		CopyN(buf, rd, 512)
 		rd.Reset(bs)
 	}
 }

 func BenchmarkCopyNLarge(b *testing.B) {
 	bs := bytes.Repeat([]byte{0}, (32*1024)+1)
 	rd := bytes.NewReader(bs)
 	buf := new(Buffer)
 	b.ResetTimer()

 	for i := 0; i < b.N; i++ {
 		CopyN(buf, rd, 32*1024)
 		rd.Reset(bs)
 	}
 }

 type noReadFrom struct {
 	w Writer
 }

 func (w *noReadFrom) Write(p []byte) (n int, err error) {
 	return w.w.Write(p)
 }

 type wantedAndErrReader struct{}

 func (wantedAndErrReader) Read(p []byte) (int, error) {
 	return len(p), errors.New("wantedAndErrReader error")
 }

 func TestCopyNEOF(t *testing.T) {
 	// Test that EOF behavior is the same regardless of whether
 	// argument to CopyN has ReadFrom.

 	b := new(bytes.Buffer)

 	n, err := CopyN(&noReadFrom{b}, strings.NewReader("foo"), 3)
 	if n != 3 || err != nil {
 		t.Errorf("CopyN(noReadFrom, foo, 3) = %d, %v; want 3, nil", n, err)
 	}

 	n, err = CopyN(&noReadFrom{b}, strings.NewReader("foo"), 4)
 	if n != 3 || err != EOF {
 		t.Errorf("CopyN(noReadFrom, foo, 4) = %d, %v; want 3, EOF", n, err)
 	}

 	n, err = CopyN(b, strings.NewReader("foo"), 3) // b has read from
 	if n != 3 || err != nil {
 		t.Errorf("CopyN(bytes.Buffer, foo, 3) = %d, %v; want 3, nil", n, err)
 	}

 	n, err = CopyN(b, strings.NewReader("foo"), 4) // b has read from
 	if n != 3 || err != EOF {
 		t.Errorf("CopyN(bytes.Buffer, foo, 4) = %d, %v; want 3, EOF", n, err)
 	}

 	n, err = CopyN(b, wantedAndErrReader{}, 5)
 	if n != 5 || err != nil {
 		t.Errorf("CopyN(bytes.Buffer, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
 	}

 	n, err = CopyN(&noReadFrom{b}, wantedAndErrReader{}, 5)
 	if n != 5 || err != nil {
 		t.Errorf("CopyN(noReadFrom, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
 	}
 }

 func TestReadAtLeast(t *testing.T) {
 	var rb bytes.Buffer
 	testReadAtLeast(t, &rb)
 }

 // A version of bytes.Buffer that returns n > 0, err on Read
 // when the input is exhausted.
 type dataAndErrorBuffer struct {
 	err error
 	bytes.Buffer
 }

 func (r *dataAndErrorBuffer) Read(p []byte) (n int, err error) {
 	n, err = r.Buffer.Read(p)
 	if n > 0 && r.Buffer.Len() == 0 && err == nil {
 		err = r.err
 	}
 	return
 }

 func TestReadAtLeastWithDataAndEOF(t *testing.T) {
 	var rb dataAndErrorBuffer
 	rb.err = EOF
 	testReadAtLeast(t, &rb)
 }

 func TestReadAtLeastWithDataAndError(t *testing.T) {
 	var rb dataAndErrorBuffer
 	rb.err = fmt.Errorf("fake error")
 	testReadAtLeast(t, &rb)
 }

 func testReadAtLeast(t *testing.T, rb ReadWriter) {
 	rb.Write([]byte("0123"))
 	buf := make([]byte, 2)
 	n, err := ReadAtLeast(rb, buf, 2)
 	if err != nil {
 		t.Error(err)
 	}
 	if n != 2 {
 		t.Errorf("expected to have read 2 bytes, got %v", n)
 	}
 	n, err = ReadAtLeast(rb, buf, 4)
 	if err != ErrShortBuffer {
 		t.Errorf("expected ErrShortBuffer got %v", err)
 	}
 	if n != 0 {
 		t.Errorf("expected to have read 0 bytes, got %v", n)
 	}
 	n, err = ReadAtLeast(rb, buf, 1)
 	if err != nil {
 		t.Error(err)
 	}
 	if n != 2 {
 		t.Errorf("expected to have read 2 bytes, got %v", n)
 	}
 	n, err = ReadAtLeast(rb, buf, 2)
 	if err != EOF {
 		t.Errorf("expected EOF, got %v", err)
 	}
 	if n != 0 {
 		t.Errorf("expected to have read 0 bytes, got %v", n)
 	}
 	rb.Write([]byte("4"))
 	n, err = ReadAtLeast(rb, buf, 2)
 	want := ErrUnexpectedEOF
 	if rb, ok := rb.(*dataAndErrorBuffer); ok && rb.err != EOF {
 		want = rb.err
 	}
 	if err != want {
 		t.Errorf("expected %v, got %v", want, err)
 	}
 	if n != 1 {
 		t.Errorf("expected to have read 1 bytes, got %v", n)
 	}
 }

 func TestTeeReader(t *testing.T) {
 	src := []byte("hello, world")
 	dst := make([]byte, len(src))
 	rb := bytes.NewBuffer(src)
 	wb := new(bytes.Buffer)
 	r := TeeReader(rb, wb)
 	if n, err := ReadFull(r, dst); err != nil || n != len(src) {
 		t.Fatalf("ReadFull(r, dst) = %d, %v; want %d, nil", n, err, len(src))
 	}
 	if !bytes.Equal(dst, src) {
 		t.Errorf("bytes read = %q want %q", dst, src)
 	}
 	if !bytes.Equal(wb.Bytes(), src) {
 		t.Errorf("bytes written = %q want %q", wb.Bytes(), src)
 	}
 	if n, err := r.Read(dst); n != 0 || err != EOF {
 		t.Errorf("r.Read at EOF = %d, %v want 0, EOF", n, err)
 	}
 	rb = bytes.NewBuffer(src)
 	pr, pw := Pipe()
 	pr.Close()
 	r = TeeReader(rb, pw)
 	if n, err := ReadFull(r, dst); n != 0 || err != ErrClosedPipe {
 		t.Errorf("closed tee: ReadFull(r, dst) = %d, %v; want 0, EPIPE", n, err)
 	}
 }

 func TestSectionReader_ReadAt(t *testing.T) {
 	dat := "a long sample data, 1234567890"
 	tests := []struct {
 		data   string
 		off    int
 		n      int
 		bufLen int
 		at     int
 		exp    string
 		err    error
 	}{
 		{data: "", off: 0, n: 10, bufLen: 2, at: 0, exp: "", err: EOF},
 		{data: dat, off: 0, n: len(dat), bufLen: 0, at: 0, exp: "", err: nil},
 		{data: dat, off: len(dat), n: 1, bufLen: 1, at: 0, exp: "", err: EOF},
 		{data: dat, off: 0, n: len(dat) + 2, bufLen: len(dat), at: 0, exp: dat, err: nil},
 		{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 0, exp: dat[:len(dat)/2], err: nil},
 		{data: dat, off: 0, n: len(dat), bufLen: len(dat), at: 0, exp: dat, err: nil},
 		{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[2 : 2+len(dat)/2], err: nil},
 		{data: dat, off: 3, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[5 : 5+len(dat)/2], err: nil},
 		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 - 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: nil},
 		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 + 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: EOF},
 		{data: dat, off: 0, n: 0, bufLen: 0, at: -1, exp: "", err: EOF},
 		{data: dat, off: 0, n: 0, bufLen: 0, at: 1, exp: "", err: EOF},
 	}
 	for i, tt := range tests {
 		r := strings.NewReader(tt.data)
 		s := NewSectionReader(r, int64(tt.off), int64(tt.n))
 		buf := make([]byte, tt.bufLen)
 		if n, err := s.ReadAt(buf, int64(tt.at)); n != len(tt.exp) || string(buf[:n]) != tt.exp || err != tt.err {
 			t.Fatalf("%d: ReadAt(%d) = %q, %v; expected %q, %v", i, tt.at, buf[:n], err, tt.exp, tt.err)
 		}
 	}
 }

 func TestSectionReader_Seek(t *testing.T) {
 	// Verifies that NewSectionReader's Seeker behaves like bytes.NewReader (which is like strings.NewReader)
 	br := bytes.NewReader([]byte("foo"))
 	sr := NewSectionReader(br, 0, int64(len("foo")))

 	for _, whence := range []int{SeekStart, SeekCurrent, SeekEnd} {
 		for offset := int64(-3); offset <= 4; offset++ {
 			brOff, brErr := br.Seek(offset, whence)
 			srOff, srErr := sr.Seek(offset, whence)
 			if (brErr != nil) != (srErr != nil) || brOff != srOff {
 				t.Errorf("For whence %d, offset %d: bytes.Reader.Seek = (%v, %v) != SectionReader.Seek = (%v, %v)",
 					whence, offset, brOff, brErr, srErr, srOff)
 			}
 		}
 	}

 	// And verify we can just seek past the end and get an EOF
 	got, err := sr.Seek(100, SeekStart)
 	if err != nil || got != 100 {
 		t.Errorf("Seek = %v, %v; want 100, nil", got, err)
 	}

 	n, err := sr.Read(make([]byte, 10))
 	if n != 0 || err != EOF {
 		t.Errorf("Read = %v, %v; want 0, EOF", n, err)
 	}
 }

 func TestSectionReader_Size(t *testing.T) {
 	tests := []struct {
 		data string
 		want int64
 	}{
 		{"a long sample data, 1234567890", 30},
 		{"", 0},
 	}

 	for _, tt := range tests {
 		r := strings.NewReader(tt.data)
 		sr := NewSectionReader(r, 0, int64(len(tt.data)))
 		if got := sr.Size(); got != tt.want {
 			t.Errorf("Size = %v; want %v", got, tt.want)
 		}
 	}
 }
	// 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 io_test

	import (
	"bytes"
	"errors"
	"fmt"
	. "io"
	"strings"
	"testing"
	)

	// A version of bytes.Buffer without ReadFrom and WriteTo
	type Buffer struct {
	bytes.Buffer
	ReaderFrom // conflicts with and hides bytes.Buffer's ReaderFrom.
	WriterTo // conflicts with and hides bytes.Buffer's WriterTo.
	}

	// Simple tests, primarily to verify the ReadFrom and WriteTo callouts inside Copy, CopyBuffer and CopyN.

	func TestCopy(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	Copy(wb, rb)
	if wb.String() != "hello, world." {
	t.Errorf("Copy did not work properly")
	}
	}

	func TestCopyNegative(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello")
	Copy(wb, &LimitedReader{R: rb, N: -1})
	if wb.String() != "" {
	t.Errorf("Copy on LimitedReader with N<0 copied data")
	}

	CopyN(wb, rb, -1)
	if wb.String() != "" {
	t.Errorf("CopyN with N<0 copied data")
	}
	}

	func TestCopyBuffer(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyBuffer(wb, rb, make([]byte, 1)) // Tiny buffer to keep it honest.
	if wb.String() != "hello, world." {
	t.Errorf("CopyBuffer did not work properly")
	}
	}

	func TestCopyBufferNil(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyBuffer(wb, rb, nil) // Should allocate a buffer.
	if wb.String() != "hello, world." {
	t.Errorf("CopyBuffer did not work properly")
	}
	}

	func TestCopyReadFrom(t *testing.T) {
	rb := new(Buffer)
	wb := new(bytes.Buffer) // implements ReadFrom.
	rb.WriteString("hello, world.")
	Copy(wb, rb)
	if wb.String() != "hello, world." {
	t.Errorf("Copy did not work properly")
	}
	}

	func TestCopyWriteTo(t *testing.T) {
	rb := new(bytes.Buffer) // implements WriteTo.
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	Copy(wb, rb)
	if wb.String() != "hello, world." {
	t.Errorf("Copy did not work properly")
	}
	}

	// Version of bytes.Buffer that checks whether WriteTo was called or not
	type writeToChecker struct {
	bytes.Buffer
	writeToCalled bool
	}

	func (wt *writeToChecker) WriteTo(w Writer) (int64, error) {
	wt.writeToCalled = true
	return wt.Buffer.WriteTo(w)
	}

	// It's preferable to choose WriterTo over ReaderFrom, since a WriterTo can issue one large write,
	// while the ReaderFrom must read until EOF, potentially allocating when running out of buffer.
	// Make sure that we choose WriterTo when both are implemented.
	func TestCopyPriority(t *testing.T) {
	rb := new(writeToChecker)
	wb := new(bytes.Buffer)
	rb.WriteString("hello, world.")
	Copy(wb, rb)
	if wb.String() != "hello, world." {
	t.Errorf("Copy did not work properly")
	} else if !rb.writeToCalled {
	t.Errorf("WriteTo was not prioritized over ReadFrom")
	}
	}

	type zeroErrReader struct {
	err error
	}

	func (r zeroErrReader) Read(p []byte) (int, error) {
	return copy(p, []byte{0}), r.err
	}

	type errWriter struct {
	err error
	}

	func (w errWriter) Write([]byte) (int, error) {
	return 0, w.err
	}

	// In case a Read results in an error with non-zero bytes read, and
	// the subsequent Write also results in an error, the error from Write
	// is returned, as it is the one that prevented progressing further.
	func TestCopyReadErrWriteErr(t *testing.T) {
	er, ew := errors.New("readError"), errors.New("writeError")
	r, w := zeroErrReader{err: er}, errWriter{err: ew}
	n, err := Copy(w, r)
	if n != 0 \|\| err != ew {
	t.Errorf("Copy(zeroErrReader, errWriter) = %d, %v; want 0, writeError", n, err)
	}
	}

	func TestCopyN(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyN(wb, rb, 5)
	if wb.String() != "hello" {
	t.Errorf("CopyN did not work properly")
	}
	}

	func TestCopyNReadFrom(t *testing.T) {
	rb := new(Buffer)
	wb := new(bytes.Buffer) // implements ReadFrom.
	rb.WriteString("hello")
	CopyN(wb, rb, 5)
	if wb.String() != "hello" {
	t.Errorf("CopyN did not work properly")
	}
	}

	func TestCopyNWriteTo(t *testing.T) {
	rb := new(bytes.Buffer) // implements WriteTo.
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyN(wb, rb, 5)
	if wb.String() != "hello" {
	t.Errorf("CopyN did not work properly")
	}
	}

	func BenchmarkCopyNSmall(b *testing.B) {
	bs := bytes.Repeat([]byte{0}, 512+1)
	rd := bytes.NewReader(bs)
	buf := new(Buffer)
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
	CopyN(buf, rd, 512)
	rd.Reset(bs)
	}
	}

	func BenchmarkCopyNLarge(b *testing.B) {
	bs := bytes.Repeat([]byte{0}, (32*1024)+1)
	rd := bytes.NewReader(bs)
	buf := new(Buffer)
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
	CopyN(buf, rd, 32*1024)
	rd.Reset(bs)
	}
	}

	type noReadFrom struct {
	w Writer
	}

	func (w *noReadFrom) Write(p []byte) (n int, err error) {
	return w.w.Write(p)
	}

	type wantedAndErrReader struct{}

	func (wantedAndErrReader) Read(p []byte) (int, error) {
	return len(p), errors.New("wantedAndErrReader error")
	}

	func TestCopyNEOF(t *testing.T) {
	// Test that EOF behavior is the same regardless of whether
	// argument to CopyN has ReadFrom.

	b := new(bytes.Buffer)

	n, err := CopyN(&noReadFrom{b}, strings.NewReader("foo"), 3)
	if n != 3 \|\| err != nil {
	t.Errorf("CopyN(noReadFrom, foo, 3) = %d, %v; want 3, nil", n, err)
	}

	n, err = CopyN(&noReadFrom{b}, strings.NewReader("foo"), 4)
	if n != 3 \|\| err != EOF {
	t.Errorf("CopyN(noReadFrom, foo, 4) = %d, %v; want 3, EOF", n, err)
	}

	n, err = CopyN(b, strings.NewReader("foo"), 3) // b has read from
	if n != 3 \|\| err != nil {
	t.Errorf("CopyN(bytes.Buffer, foo, 3) = %d, %v; want 3, nil", n, err)
	}

	n, err = CopyN(b, strings.NewReader("foo"), 4) // b has read from
	if n != 3 \|\| err != EOF {
	t.Errorf("CopyN(bytes.Buffer, foo, 4) = %d, %v; want 3, EOF", n, err)
	}

	n, err = CopyN(b, wantedAndErrReader{}, 5)
	if n != 5 \|\| err != nil {
	t.Errorf("CopyN(bytes.Buffer, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
	}

	n, err = CopyN(&noReadFrom{b}, wantedAndErrReader{}, 5)
	if n != 5 \|\| err != nil {
	t.Errorf("CopyN(noReadFrom, wantedAndErrReader, 5) = %d, %v; want 5, nil", n, err)
	}
	}

	func TestReadAtLeast(t *testing.T) {
	var rb bytes.Buffer
	testReadAtLeast(t, &rb)
	}

	// A version of bytes.Buffer that returns n > 0, err on Read
	// when the input is exhausted.
	type dataAndErrorBuffer struct {
	err error
	bytes.Buffer
	}

	func (r *dataAndErrorBuffer) Read(p []byte) (n int, err error) {
	n, err = r.Buffer.Read(p)
	if n > 0 && r.Buffer.Len() == 0 && err == nil {
	err = r.err
	}
	return
	}

	func TestReadAtLeastWithDataAndEOF(t *testing.T) {
	var rb dataAndErrorBuffer
	rb.err = EOF
	testReadAtLeast(t, &rb)
	}

	func TestReadAtLeastWithDataAndError(t *testing.T) {
	var rb dataAndErrorBuffer
	rb.err = fmt.Errorf("fake error")
	testReadAtLeast(t, &rb)
	}

	func testReadAtLeast(t *testing.T, rb ReadWriter) {
	rb.Write([]byte("0123"))
	buf := make([]byte, 2)
	n, err := ReadAtLeast(rb, buf, 2)
	if err != nil {
	t.Error(err)
	}
	if n != 2 {
	t.Errorf("expected to have read 2 bytes, got %v", n)
	}
	n, err = ReadAtLeast(rb, buf, 4)
	if err != ErrShortBuffer {
	t.Errorf("expected ErrShortBuffer got %v", err)
	}
	if n != 0 {
	t.Errorf("expected to have read 0 bytes, got %v", n)
	}
	n, err = ReadAtLeast(rb, buf, 1)
	if err != nil {
	t.Error(err)
	}
	if n != 2 {
	t.Errorf("expected to have read 2 bytes, got %v", n)
	}
	n, err = ReadAtLeast(rb, buf, 2)
	if err != EOF {
	t.Errorf("expected EOF, got %v", err)
	}
	if n != 0 {
	t.Errorf("expected to have read 0 bytes, got %v", n)
	}
	rb.Write([]byte("4"))
	n, err = ReadAtLeast(rb, buf, 2)
	want := ErrUnexpectedEOF
	if rb, ok := rb.(*dataAndErrorBuffer); ok && rb.err != EOF {
	want = rb.err
	}
	if err != want {
	t.Errorf("expected %v, got %v", want, err)
	}
	if n != 1 {
	t.Errorf("expected to have read 1 bytes, got %v", n)
	}
	}

	func TestTeeReader(t *testing.T) {
	src := []byte("hello, world")
	dst := make([]byte, len(src))
	rb := bytes.NewBuffer(src)
	wb := new(bytes.Buffer)
	r := TeeReader(rb, wb)
	if n, err := ReadFull(r, dst); err != nil \|\| n != len(src) {
	t.Fatalf("ReadFull(r, dst) = %d, %v; want %d, nil", n, err, len(src))
	}
	if !bytes.Equal(dst, src) {
	t.Errorf("bytes read = %q want %q", dst, src)
	}
	if !bytes.Equal(wb.Bytes(), src) {
	t.Errorf("bytes written = %q want %q", wb.Bytes(), src)
	}
	if n, err := r.Read(dst); n != 0 \|\| err != EOF {
	t.Errorf("r.Read at EOF = %d, %v want 0, EOF", n, err)
	}
	rb = bytes.NewBuffer(src)
	pr, pw := Pipe()
	pr.Close()
	r = TeeReader(rb, pw)
	if n, err := ReadFull(r, dst); n != 0 \|\| err != ErrClosedPipe {
	t.Errorf("closed tee: ReadFull(r, dst) = %d, %v; want 0, EPIPE", n, err)
	}
	}

	func TestSectionReader_ReadAt(t *testing.T) {
	dat := "a long sample data, 1234567890"
	tests := []struct {
	data string
	off int
	n int
	bufLen int
	at int
	exp string
	err error
	}{
	{data: "", off: 0, n: 10, bufLen: 2, at: 0, exp: "", err: EOF},
	{data: dat, off: 0, n: len(dat), bufLen: 0, at: 0, exp: "", err: nil},
	{data: dat, off: len(dat), n: 1, bufLen: 1, at: 0, exp: "", err: EOF},
	{data: dat, off: 0, n: len(dat) + 2, bufLen: len(dat), at: 0, exp: dat, err: nil},
	{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 0, exp: dat[:len(dat)/2], err: nil},
	{data: dat, off: 0, n: len(dat), bufLen: len(dat), at: 0, exp: dat, err: nil},
	{data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[2 : 2+len(dat)/2], err: nil},
	{data: dat, off: 3, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[5 : 5+len(dat)/2], err: nil},
	{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 - 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: nil},
	{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 + 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: EOF},
	{data: dat, off: 0, n: 0, bufLen: 0, at: -1, exp: "", err: EOF},
	{data: dat, off: 0, n: 0, bufLen: 0, at: 1, exp: "", err: EOF},
	}
	for i, tt := range tests {
	r := strings.NewReader(tt.data)
	s := NewSectionReader(r, int64(tt.off), int64(tt.n))
	buf := make([]byte, tt.bufLen)
	if n, err := s.ReadAt(buf, int64(tt.at)); n != len(tt.exp) \|\| string(buf[:n]) != tt.exp \|\| err != tt.err {
	t.Fatalf("%d: ReadAt(%d) = %q, %v; expected %q, %v", i, tt.at, buf[:n], err, tt.exp, tt.err)
	}
	}
	}

	func TestSectionReader_Seek(t *testing.T) {
	// Verifies that NewSectionReader's Seeker behaves like bytes.NewReader (which is like strings.NewReader)
	br := bytes.NewReader([]byte("foo"))
	sr := NewSectionReader(br, 0, int64(len("foo")))

	for _, whence := range []int{SeekStart, SeekCurrent, SeekEnd} {
	for offset := int64(-3); offset <= 4; offset++ {
	brOff, brErr := br.Seek(offset, whence)
	srOff, srErr := sr.Seek(offset, whence)
	if (brErr != nil) != (srErr != nil) \|\| brOff != srOff {
	t.Errorf("For whence %d, offset %d: bytes.Reader.Seek = (%v, %v) != SectionReader.Seek = (%v, %v)",
	whence, offset, brOff, brErr, srErr, srOff)
	}
	}
	}

	// And verify we can just seek past the end and get an EOF
	got, err := sr.Seek(100, SeekStart)
	if err != nil \|\| got != 100 {
	t.Errorf("Seek = %v, %v; want 100, nil", got, err)
	}

	n, err := sr.Read(make([]byte, 10))
	if n != 0 \|\| err != EOF {
	t.Errorf("Read = %v, %v; want 0, EOF", n, err)
	}
	}

	func TestSectionReader_Size(t *testing.T) {
	tests := []struct {
	data string
	want int64
	}{
	{"a long sample data, 1234567890", 30},
	{"", 0},
	}

	for _, tt := range tests {
	r := strings.NewReader(tt.data)
	sr := NewSectionReader(r, 0, int64(len(tt.data)))
	if got := sr.Size(); got != tt.want {
	t.Errorf("Size = %v; want %v", got, tt.want)
	}
	}
	}