Daily bump.

[official-gcc.git] / libgo / go / bufio / bufio_test.go

// 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 bufio_test

import (
        . "bufio"
        "bytes"
        "errors"
        "fmt"
        "io"
        "math/rand"
        "strconv"
        "strings"
        "testing"
        "testing/iotest"
        "time"
        "unicode/utf8"
)

// Reads from a reader and rot13s the result.
type rot13Reader struct {
        r io.Reader
}

func newRot13Reader(r io.Reader) *rot13Reader {
        r13 := new(rot13Reader)
        r13.r = r
        return r13
}

func (r13 *rot13Reader) Read(p []byte) (int, error) {
        n, err := r13.r.Read(p)
        for i := 0; i < n; i++ {
                c := p[i] | 0x20 // lowercase byte
                if 'a' <= c && c <= 'm' {
                        p[i] += 13
                } else if 'n' <= c && c <= 'z' {
                        p[i] -= 13
                }
        }
        return n, err
}

// Call ReadByte to accumulate the text of a file
func readBytes(buf *Reader) string {
        var b [1000]byte
        nb := 0
        for {
                c, err := buf.ReadByte()
                if err == io.EOF {
                        break
                }
                if err == nil {
                        b[nb] = c
                        nb++
                } else if err != iotest.ErrTimeout {
                        panic("Data: " + err.Error())
                }
        }
        return string(b[0:nb])
}

func TestReaderSimple(t *testing.T) {
        data := "hello world"
        b := NewReader(strings.NewReader(data))
        if s := readBytes(b); s != "hello world" {
                t.Errorf("simple hello world test failed: got %q", s)
        }

        b = NewReader(newRot13Reader(strings.NewReader(data)))
        if s := readBytes(b); s != "uryyb jbeyq" {
                t.Errorf("rot13 hello world test failed: got %q", s)
        }
}

type readMaker struct {
        name string
        fn   func(io.Reader) io.Reader
}

var readMakers = []readMaker{
        {"full", func(r io.Reader) io.Reader { return r }},
        {"byte", iotest.OneByteReader},
        {"half", iotest.HalfReader},
        {"data+err", iotest.DataErrReader},
        {"timeout", iotest.TimeoutReader},
}

// Call ReadString (which ends up calling everything else)
// to accumulate the text of a file.
func readLines(b *Reader) string {
        s := ""
        for {
                s1, err := b.ReadString('\n')
                if err == io.EOF {
                        break
                }
                if err != nil && err != iotest.ErrTimeout {
                        panic("GetLines: " + err.Error())
                }
                s += s1
        }
        return s
}

// Call Read to accumulate the text of a file
func reads(buf *Reader, m int) string {
        var b [1000]byte
        nb := 0
        for {
                n, err := buf.Read(b[nb : nb+m])
                nb += n
                if err == io.EOF {
                        break
                }
        }
        return string(b[0:nb])
}

type bufReader struct {
        name string
        fn   func(*Reader) string
}

var bufreaders = []bufReader{
        {"1", func(b *Reader) string { return reads(b, 1) }},
        {"2", func(b *Reader) string { return reads(b, 2) }},
        {"3", func(b *Reader) string { return reads(b, 3) }},
        {"4", func(b *Reader) string { return reads(b, 4) }},
        {"5", func(b *Reader) string { return reads(b, 5) }},
        {"7", func(b *Reader) string { return reads(b, 7) }},
        {"bytes", readBytes},
        {"lines", readLines},
}

const minReadBufferSize = 16

var bufsizes = []int{
        0, minReadBufferSize, 23, 32, 46, 64, 93, 128, 1024, 4096,
}

func TestReader(t *testing.T) {
        var texts [31]string
        str := ""
        all := ""
        for i := 0; i < len(texts)-1; i++ {
                texts[i] = str + "\n"
                all += texts[i]
                str += string(rune(i%26 + 'a'))
        }
        texts[len(texts)-1] = all

        for h := 0; h < len(texts); h++ {
                text := texts[h]
                for i := 0; i < len(readMakers); i++ {
                        for j := 0; j < len(bufreaders); j++ {
                                for k := 0; k < len(bufsizes); k++ {
                                        readmaker := readMakers[i]
                                        bufreader := bufreaders[j]
                                        bufsize := bufsizes[k]
                                        read := readmaker.fn(strings.NewReader(text))
                                        buf := NewReaderSize(read, bufsize)
                                        s := bufreader.fn(buf)
                                        if s != text {
                                                t.Errorf("reader=%s fn=%s bufsize=%d want=%q got=%q",
                                                        readmaker.name, bufreader.name, bufsize, text, s)
                                        }
                                }
                        }
                }
        }
}

type zeroReader struct{}

func (zeroReader) Read(p []byte) (int, error) {
        return 0, nil
}

func TestZeroReader(t *testing.T) {
        var z zeroReader
        r := NewReader(z)

        c := make(chan error)
        go func() {
                _, err := r.ReadByte()
                c <- err
        }()

        select {
        case err := <-c:
                if err == nil {
                        t.Error("error expected")
                } else if err != io.ErrNoProgress {
                        t.Error("unexpected error:", err)
                }
        case <-time.After(time.Second):
                t.Error("test timed out (endless loop in ReadByte?)")
        }
}

// A StringReader delivers its data one string segment at a time via Read.
type StringReader struct {
        data []string
        step int
}

func (r *StringReader) Read(p []byte) (n int, err error) {
        if r.step < len(r.data) {
                s := r.data[r.step]
                n = copy(p, s)
                r.step++
        } else {
                err = io.EOF
        }
        return
}

func readRuneSegments(t *testing.T, segments []string) {
        got := ""
        want := strings.Join(segments, "")
        r := NewReader(&StringReader{data: segments})
        for {
                r, _, err := r.ReadRune()
                if err != nil {
                        if err != io.EOF {
                                return
                        }
                        break
                }
                got += string(r)
        }
        if got != want {
                t.Errorf("segments=%v got=%s want=%s", segments, got, want)
        }
}

var segmentList = [][]string{
        {},
        {""},
        {"日", "本語"},
        {"\u65e5", "\u672c", "\u8a9e"},
        {"\U000065e5", "\U0000672c", "\U00008a9e"},
        {"\xe6", "\x97\xa5\xe6", "\x9c\xac\xe8\xaa\x9e"},
        {"Hello", ", ", "World", "!"},
        {"Hello", ", ", "", "World", "!"},
}

func TestReadRune(t *testing.T) {
        for _, s := range segmentList {
                readRuneSegments(t, s)
        }
}

func TestUnreadRune(t *testing.T) {
        segments := []string{"Hello, world:", "日本語"}
        r := NewReader(&StringReader{data: segments})
        got := ""
        want := strings.Join(segments, "")
        // Normal execution.
        for {
                r1, _, err := r.ReadRune()
                if err != nil {
                        if err != io.EOF {
                                t.Error("unexpected error on ReadRune:", err)
                        }
                        break
                }
                got += string(r1)
                // Put it back and read it again.
                if err = r.UnreadRune(); err != nil {
                        t.Fatal("unexpected error on UnreadRune:", err)
                }
                r2, _, err := r.ReadRune()
                if err != nil {
                        t.Fatal("unexpected error reading after unreading:", err)
                }
                if r1 != r2 {
                        t.Fatalf("incorrect rune after unread: got %c, want %c", r1, r2)
                }
        }
        if got != want {
                t.Errorf("got %q, want %q", got, want)
        }
}

func TestNoUnreadRuneAfterPeek(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.ReadRune()
        br.Peek(1)
        if err := br.UnreadRune(); err == nil {
                t.Error("UnreadRune didn't fail after Peek")
        }
}

func TestNoUnreadByteAfterPeek(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.ReadByte()
        br.Peek(1)
        if err := br.UnreadByte(); err == nil {
                t.Error("UnreadByte didn't fail after Peek")
        }
}

func TestNoUnreadRuneAfterDiscard(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.ReadRune()
        br.Discard(1)
        if err := br.UnreadRune(); err == nil {
                t.Error("UnreadRune didn't fail after Discard")
        }
}

func TestNoUnreadByteAfterDiscard(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.ReadByte()
        br.Discard(1)
        if err := br.UnreadByte(); err == nil {
                t.Error("UnreadByte didn't fail after Discard")
        }
}

func TestNoUnreadRuneAfterWriteTo(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.WriteTo(io.Discard)
        if err := br.UnreadRune(); err == nil {
                t.Error("UnreadRune didn't fail after WriteTo")
        }
}

func TestNoUnreadByteAfterWriteTo(t *testing.T) {
        br := NewReader(strings.NewReader("example"))
        br.WriteTo(io.Discard)
        if err := br.UnreadByte(); err == nil {
                t.Error("UnreadByte didn't fail after WriteTo")
        }
}

func TestUnreadByte(t *testing.T) {
        segments := []string{"Hello, ", "world"}
        r := NewReader(&StringReader{data: segments})
        got := ""
        want := strings.Join(segments, "")
        // Normal execution.
        for {
                b1, err := r.ReadByte()
                if err != nil {
                        if err != io.EOF {
                                t.Error("unexpected error on ReadByte:", err)
                        }
                        break
                }
                got += string(b1)
                // Put it back and read it again.
                if err = r.UnreadByte(); err != nil {
                        t.Fatal("unexpected error on UnreadByte:", err)
                }
                b2, err := r.ReadByte()
                if err != nil {
                        t.Fatal("unexpected error reading after unreading:", err)
                }
                if b1 != b2 {
                        t.Fatalf("incorrect byte after unread: got %q, want %q", b1, b2)
                }
        }
        if got != want {
                t.Errorf("got %q, want %q", got, want)
        }
}

func TestUnreadByteMultiple(t *testing.T) {
        segments := []string{"Hello, ", "world"}
        data := strings.Join(segments, "")
        for n := 0; n <= len(data); n++ {
                r := NewReader(&StringReader{data: segments})
                // Read n bytes.
                for i := 0; i < n; i++ {
                        b, err := r.ReadByte()
                        if err != nil {
                                t.Fatalf("n = %d: unexpected error on ReadByte: %v", n, err)
                        }
                        if b != data[i] {
                                t.Fatalf("n = %d: incorrect byte returned from ReadByte: got %q, want %q", n, b, data[i])
                        }
                }
                // Unread one byte if there is one.
                if n > 0 {
                        if err := r.UnreadByte(); err != nil {
                                t.Errorf("n = %d: unexpected error on UnreadByte: %v", n, err)
                        }
                }
                // Test that we cannot unread any further.
                if err := r.UnreadByte(); err == nil {
                        t.Errorf("n = %d: expected error on UnreadByte", n)
                }
        }
}

func TestUnreadByteOthers(t *testing.T) {
        // A list of readers to use in conjunction with UnreadByte.
        var readers = []func(*Reader, byte) ([]byte, error){
                (*Reader).ReadBytes,
                (*Reader).ReadSlice,
                func(r *Reader, delim byte) ([]byte, error) {
                        data, err := r.ReadString(delim)
                        return []byte(data), err
                },
                // ReadLine doesn't fit the data/pattern easily
                // so we leave it out. It should be covered via
                // the ReadSlice test since ReadLine simply calls
                // ReadSlice, and it's that function that handles
                // the last byte.
        }

        // Try all readers with UnreadByte.
        for rno, read := range readers {
                // Some input data that is longer than the minimum reader buffer size.
                const n = 10
                var buf bytes.Buffer
                for i := 0; i < n; i++ {
                        buf.WriteString("abcdefg")
                }

                r := NewReaderSize(&buf, minReadBufferSize)
                readTo := func(delim byte, want string) {
                        data, err := read(r, delim)
                        if err != nil {
                                t.Fatalf("#%d: unexpected error reading to %c: %v", rno, delim, err)
                        }
                        if got := string(data); got != want {
                                t.Fatalf("#%d: got %q, want %q", rno, got, want)
                        }
                }

                // Read the data with occasional UnreadByte calls.
                for i := 0; i < n; i++ {
                        readTo('d', "abcd")
                        for j := 0; j < 3; j++ {
                                if err := r.UnreadByte(); err != nil {
                                        t.Fatalf("#%d: unexpected error on UnreadByte: %v", rno, err)
                                }
                                readTo('d', "d")
                        }
                        readTo('g', "efg")
                }

                // All data should have been read.
                _, err := r.ReadByte()
                if err != io.EOF {
                        t.Errorf("#%d: got error %v; want EOF", rno, err)
                }
        }
}

// Test that UnreadRune fails if the preceding operation was not a ReadRune.
func TestUnreadRuneError(t *testing.T) {
        buf := make([]byte, 3) // All runes in this test are 3 bytes long
        r := NewReader(&StringReader{data: []string{"日本語日本語日本語"}})
        if r.UnreadRune() == nil {
                t.Error("expected error on UnreadRune from fresh buffer")
        }
        _, _, err := r.ReadRune()
        if err != nil {
                t.Error("unexpected error on ReadRune (1):", err)
        }
        if err = r.UnreadRune(); err != nil {
                t.Error("unexpected error on UnreadRune (1):", err)
        }
        if r.UnreadRune() == nil {
                t.Error("expected error after UnreadRune (1)")
        }
        // Test error after Read.
        _, _, err = r.ReadRune() // reset state
        if err != nil {
                t.Error("unexpected error on ReadRune (2):", err)
        }
        _, err = r.Read(buf)
        if err != nil {
                t.Error("unexpected error on Read (2):", err)
        }
        if r.UnreadRune() == nil {
                t.Error("expected error after Read (2)")
        }
        // Test error after ReadByte.
        _, _, err = r.ReadRune() // reset state
        if err != nil {
                t.Error("unexpected error on ReadRune (2):", err)
        }
        for range buf {
                _, err = r.ReadByte()
                if err != nil {
                        t.Error("unexpected error on ReadByte (2):", err)
                }
        }
        if r.UnreadRune() == nil {
                t.Error("expected error after ReadByte")
        }
        // Test error after UnreadByte.
        _, _, err = r.ReadRune() // reset state
        if err != nil {
                t.Error("unexpected error on ReadRune (3):", err)
        }
        _, err = r.ReadByte()
        if err != nil {
                t.Error("unexpected error on ReadByte (3):", err)
        }
        err = r.UnreadByte()
        if err != nil {
                t.Error("unexpected error on UnreadByte (3):", err)
        }
        if r.UnreadRune() == nil {
                t.Error("expected error after UnreadByte (3)")
        }
        // Test error after ReadSlice.
        _, _, err = r.ReadRune() // reset state
        if err != nil {
                t.Error("unexpected error on ReadRune (4):", err)
        }
        _, err = r.ReadSlice(0)
        if err != io.EOF {
                t.Error("unexpected error on ReadSlice (4):", err)
        }
        if r.UnreadRune() == nil {
                t.Error("expected error after ReadSlice (4)")
        }
}

func TestUnreadRuneAtEOF(t *testing.T) {
        // UnreadRune/ReadRune should error at EOF (was a bug; used to panic)
        r := NewReader(strings.NewReader("x"))
        r.ReadRune()
        r.ReadRune()
        r.UnreadRune()
        _, _, err := r.ReadRune()
        if err == nil {
                t.Error("expected error at EOF")
        } else if err != io.EOF {
                t.Error("expected EOF; got", err)
        }
}

func TestReadWriteRune(t *testing.T) {
        const NRune = 1000
        byteBuf := new(bytes.Buffer)
        w := NewWriter(byteBuf)
        // Write the runes out using WriteRune
        buf := make([]byte, utf8.UTFMax)
        for r := rune(0); r < NRune; r++ {
                size := utf8.EncodeRune(buf, r)
                nbytes, err := w.WriteRune(r)
                if err != nil {
                        t.Fatalf("WriteRune(0x%x) error: %s", r, err)
                }
                if nbytes != size {
                        t.Fatalf("WriteRune(0x%x) expected %d, got %d", r, size, nbytes)
                }
        }
        w.Flush()

        r := NewReader(byteBuf)
        // Read them back with ReadRune
        for r1 := rune(0); r1 < NRune; r1++ {
                size := utf8.EncodeRune(buf, r1)
                nr, nbytes, err := r.ReadRune()
                if nr != r1 || nbytes != size || err != nil {
                        t.Fatalf("ReadRune(0x%x) got 0x%x,%d not 0x%x,%d (err=%s)", r1, nr, nbytes, r1, size, err)
                }
        }
}

func TestWriteInvalidRune(t *testing.T) {
        // Invalid runes, including negative ones, should be written as the
        // replacement character.
        for _, r := range []rune{-1, utf8.MaxRune + 1} {
                var buf bytes.Buffer
                w := NewWriter(&buf)
                w.WriteRune(r)
                w.Flush()
                if s := buf.String(); s != "\uFFFD" {
                        t.Errorf("WriteRune(%d) wrote %q, not replacement character", r, s)
                }
        }
}

func TestReadStringAllocs(t *testing.T) {
        r := strings.NewReader("       foo       foo        42        42        42        42        42        42        42        42       4.2       4.2       4.2       4.2\n")
        buf := NewReader(r)
        allocs := testing.AllocsPerRun(100, func() {
                r.Seek(0, io.SeekStart)
                buf.Reset(r)

                _, err := buf.ReadString('\n')
                if err != nil {
                        t.Fatal(err)
                }
        })
        if allocs != 1 {
                t.Errorf("Unexpected number of allocations, got %f, want 1", allocs)
        }
}

func TestWriter(t *testing.T) {
        var data [8192]byte

        for i := 0; i < len(data); i++ {
                data[i] = byte(' ' + i%('~'-' '))
        }
        w := new(bytes.Buffer)
        for i := 0; i < len(bufsizes); i++ {
                for j := 0; j < len(bufsizes); j++ {
                        nwrite := bufsizes[i]
                        bs := bufsizes[j]

                        // Write nwrite bytes using buffer size bs.
                        // Check that the right amount makes it out
                        // and that the data is correct.

                        w.Reset()
                        buf := NewWriterSize(w, bs)
                        context := fmt.Sprintf("nwrite=%d bufsize=%d", nwrite, bs)
                        n, e1 := buf.Write(data[0:nwrite])
                        if e1 != nil || n != nwrite {
                                t.Errorf("%s: buf.Write %d = %d, %v", context, nwrite, n, e1)
                                continue
                        }
                        if e := buf.Flush(); e != nil {
                                t.Errorf("%s: buf.Flush = %v", context, e)
                        }

                        written := w.Bytes()
                        if len(written) != nwrite {
                                t.Errorf("%s: %d bytes written", context, len(written))
                        }
                        for l := 0; l < len(written); l++ {
                                if written[l] != data[l] {
                                        t.Errorf("wrong bytes written")
                                        t.Errorf("want=%q", data[0:len(written)])
                                        t.Errorf("have=%q", written)
                                }
                        }
                }
        }
}

func TestWriterAppend(t *testing.T) {
        got := new(bytes.Buffer)
        var want []byte
        rn := rand.New(rand.NewSource(0))
        w := NewWriterSize(got, 64)
        for i := 0; i < 100; i++ {
                // Obtain a buffer to append to.
                b := w.AvailableBuffer()
                if w.Available() != cap(b) {
                        t.Fatalf("Available() = %v, want %v", w.Available(), cap(b))
                }

                // While not recommended, it is valid to append to a shifted buffer.
                // This forces Write to copy the input.
                if rn.Intn(8) == 0 && cap(b) > 0 {
                        b = b[1:1:cap(b)]
                }

                // Append a random integer of varying width.
                n := int64(rn.Intn(1 << rn.Intn(30)))
                want = append(strconv.AppendInt(want, n, 10), ' ')
                b = append(strconv.AppendInt(b, n, 10), ' ')
                w.Write(b)
        }
        w.Flush()

        if !bytes.Equal(got.Bytes(), want) {
                t.Errorf("output mismatch:\ngot  %s\nwant %s", got.Bytes(), want)
        }
}

// Check that write errors are returned properly.

type errorWriterTest struct {
        n, m   int
        err    error
        expect error
}

func (w errorWriterTest) Write(p []byte) (int, error) {
        return len(p) * w.n / w.m, w.err
}

var errorWriterTests = []errorWriterTest{
        {0, 1, nil, io.ErrShortWrite},
        {1, 2, nil, io.ErrShortWrite},
        {1, 1, nil, nil},
        {0, 1, io.ErrClosedPipe, io.ErrClosedPipe},
        {1, 2, io.ErrClosedPipe, io.ErrClosedPipe},
        {1, 1, io.ErrClosedPipe, io.ErrClosedPipe},
}

func TestWriteErrors(t *testing.T) {
        for _, w := range errorWriterTests {
                buf := NewWriter(w)
                _, e := buf.Write([]byte("hello world"))
                if e != nil {
                        t.Errorf("Write hello to %v: %v", w, e)
                        continue
                }
                // Two flushes, to verify the error is sticky.
                for i := 0; i < 2; i++ {
                        e = buf.Flush()
                        if e != w.expect {
                                t.Errorf("Flush %d/2 %v: got %v, wanted %v", i+1, w, e, w.expect)
                        }
                }
        }
}

func TestNewReaderSizeIdempotent(t *testing.T) {
        const BufSize = 1000
        b := NewReaderSize(strings.NewReader("hello world"), BufSize)
        // Does it recognize itself?
        b1 := NewReaderSize(b, BufSize)
        if b1 != b {
                t.Error("NewReaderSize did not detect underlying Reader")
        }
        // Does it wrap if existing buffer is too small?
        b2 := NewReaderSize(b, 2*BufSize)
        if b2 == b {
                t.Error("NewReaderSize did not enlarge buffer")
        }
}

func TestNewWriterSizeIdempotent(t *testing.T) {
        const BufSize = 1000
        b := NewWriterSize(new(bytes.Buffer), BufSize)
        // Does it recognize itself?
        b1 := NewWriterSize(b, BufSize)
        if b1 != b {
                t.Error("NewWriterSize did not detect underlying Writer")
        }
        // Does it wrap if existing buffer is too small?
        b2 := NewWriterSize(b, 2*BufSize)
        if b2 == b {
                t.Error("NewWriterSize did not enlarge buffer")
        }
}

func TestWriteString(t *testing.T) {
        const BufSize = 8
        buf := new(bytes.Buffer)
        b := NewWriterSize(buf, BufSize)
        b.WriteString("0")                         // easy
        b.WriteString("123456")                    // still easy
        b.WriteString("7890")                      // easy after flush
        b.WriteString("abcdefghijklmnopqrstuvwxy") // hard
        b.WriteString("z")
        if err := b.Flush(); err != nil {
                t.Error("WriteString", err)
        }
        s := "01234567890abcdefghijklmnopqrstuvwxyz"
        if string(buf.Bytes()) != s {
                t.Errorf("WriteString wants %q gets %q", s, string(buf.Bytes()))
        }
}

func TestBufferFull(t *testing.T) {
        const longString = "And now, hello, world! It is the time for all good men to come to the aid of their party"
        buf := NewReaderSize(strings.NewReader(longString), minReadBufferSize)
        line, err := buf.ReadSlice('!')
        if string(line) != "And now, hello, " || err != ErrBufferFull {
                t.Errorf("first ReadSlice(,) = %q, %v", line, err)
        }
        line, err = buf.ReadSlice('!')
        if string(line) != "world!" || err != nil {
                t.Errorf("second ReadSlice(,) = %q, %v", line, err)
        }
}

func TestPeek(t *testing.T) {
        p := make([]byte, 10)
        // string is 16 (minReadBufferSize) long.
        buf := NewReaderSize(strings.NewReader("abcdefghijklmnop"), minReadBufferSize)
        if s, err := buf.Peek(1); string(s) != "a" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "a", string(s), err)
        }
        if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "abcd", string(s), err)
        }
        if _, err := buf.Peek(-1); err != ErrNegativeCount {
                t.Fatalf("want ErrNegativeCount got %v", err)
        }
        if s, err := buf.Peek(32); string(s) != "abcdefghijklmnop" || err != ErrBufferFull {
                t.Fatalf("want %q, ErrBufFull got %q, err=%v", "abcdefghijklmnop", string(s), err)
        }
        if _, err := buf.Read(p[0:3]); string(p[0:3]) != "abc" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "abc", string(p[0:3]), err)
        }
        if s, err := buf.Peek(1); string(s) != "d" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "d", string(s), err)
        }
        if s, err := buf.Peek(2); string(s) != "de" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "de", string(s), err)
        }
        if _, err := buf.Read(p[0:3]); string(p[0:3]) != "def" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "def", string(p[0:3]), err)
        }
        if s, err := buf.Peek(4); string(s) != "ghij" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "ghij", string(s), err)
        }
        if _, err := buf.Read(p[0:]); string(p[0:]) != "ghijklmnop" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "ghijklmnop", string(p[0:minReadBufferSize]), err)
        }
        if s, err := buf.Peek(0); string(s) != "" || err != nil {
                t.Fatalf("want %q got %q, err=%v", "", string(s), err)
        }
        if _, err := buf.Peek(1); err != io.EOF {
                t.Fatalf("want EOF got %v", err)
        }

        // Test for issue 3022, not exposing a reader's error on a successful Peek.
        buf = NewReaderSize(dataAndEOFReader("abcd"), 32)
        if s, err := buf.Peek(2); string(s) != "ab" || err != nil {
                t.Errorf(`Peek(2) on "abcd", EOF = %q, %v; want "ab", nil`, string(s), err)
        }
        if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
                t.Errorf(`Peek(4) on "abcd", EOF = %q, %v; want "abcd", nil`, string(s), err)
        }
        if n, err := buf.Read(p[0:5]); string(p[0:n]) != "abcd" || err != nil {
                t.Fatalf("Read after peek = %q, %v; want abcd, EOF", p[0:n], err)
        }
        if n, err := buf.Read(p[0:1]); string(p[0:n]) != "" || err != io.EOF {
                t.Fatalf(`second Read after peek = %q, %v; want "", EOF`, p[0:n], err)
        }
}

type dataAndEOFReader string

func (r dataAndEOFReader) Read(p []byte) (int, error) {
        return copy(p, r), io.EOF
}

func TestPeekThenUnreadRune(t *testing.T) {
        // This sequence used to cause a crash.
        r := NewReader(strings.NewReader("x"))
        r.ReadRune()
        r.Peek(1)
        r.UnreadRune()
        r.ReadRune() // Used to panic here
}

var testOutput = []byte("0123456789abcdefghijklmnopqrstuvwxy")
var testInput = []byte("012\n345\n678\n9ab\ncde\nfgh\nijk\nlmn\nopq\nrst\nuvw\nxy")
var testInputrn = []byte("012\r\n345\r\n678\r\n9ab\r\ncde\r\nfgh\r\nijk\r\nlmn\r\nopq\r\nrst\r\nuvw\r\nxy\r\n\n\r\n")

// TestReader wraps a []byte and returns reads of a specific length.
type testReader struct {
        data   []byte
        stride int
}

func (t *testReader) Read(buf []byte) (n int, err error) {
        n = t.stride
        if n > len(t.data) {
                n = len(t.data)
        }
        if n > len(buf) {
                n = len(buf)
        }
        copy(buf, t.data)
        t.data = t.data[n:]
        if len(t.data) == 0 {
                err = io.EOF
        }
        return
}

func testReadLine(t *testing.T, input []byte) {
        //for stride := 1; stride < len(input); stride++ {
        for stride := 1; stride < 2; stride++ {
                done := 0
                reader := testReader{input, stride}
                l := NewReaderSize(&reader, len(input)+1)
                for {
                        line, isPrefix, err := l.ReadLine()
                        if len(line) > 0 && err != nil {
                                t.Errorf("ReadLine returned both data and error: %s", err)
                        }
                        if isPrefix {
                                t.Errorf("ReadLine returned prefix")
                        }
                        if err != nil {
                                if err != io.EOF {
                                        t.Fatalf("Got unknown error: %s", err)
                                }
                                break
                        }
                        if want := testOutput[done : done+len(line)]; !bytes.Equal(want, line) {
                                t.Errorf("Bad line at stride %d: want: %x got: %x", stride, want, line)
                        }
                        done += len(line)
                }
                if done != len(testOutput) {
                        t.Errorf("ReadLine didn't return everything: got: %d, want: %d (stride: %d)", done, len(testOutput), stride)
                }
        }
}

func TestReadLine(t *testing.T) {
        testReadLine(t, testInput)
        testReadLine(t, testInputrn)
}

func TestLineTooLong(t *testing.T) {
        data := make([]byte, 0)
        for i := 0; i < minReadBufferSize*5/2; i++ {
                data = append(data, '0'+byte(i%10))
        }
        buf := bytes.NewReader(data)
        l := NewReaderSize(buf, minReadBufferSize)
        line, isPrefix, err := l.ReadLine()
        if !isPrefix || !bytes.Equal(line, data[:minReadBufferSize]) || err != nil {
                t.Errorf("bad result for first line: got %q want %q %v", line, data[:minReadBufferSize], err)
        }
        data = data[len(line):]
        line, isPrefix, err = l.ReadLine()
        if !isPrefix || !bytes.Equal(line, data[:minReadBufferSize]) || err != nil {
                t.Errorf("bad result for second line: got %q want %q %v", line, data[:minReadBufferSize], err)
        }
        data = data[len(line):]
        line, isPrefix, err = l.ReadLine()
        if isPrefix || !bytes.Equal(line, data[:minReadBufferSize/2]) || err != nil {
                t.Errorf("bad result for third line: got %q want %q %v", line, data[:minReadBufferSize/2], err)
        }
        line, isPrefix, err = l.ReadLine()
        if isPrefix || err == nil {
                t.Errorf("expected no more lines: %x %s", line, err)
        }
}

func TestReadAfterLines(t *testing.T) {
        line1 := "this is line1"
        restData := "this is line2\nthis is line 3\n"
        inbuf := bytes.NewReader([]byte(line1 + "\n" + restData))
        outbuf := new(bytes.Buffer)
        maxLineLength := len(line1) + len(restData)/2
        l := NewReaderSize(inbuf, maxLineLength)
        line, isPrefix, err := l.ReadLine()
        if isPrefix || err != nil || string(line) != line1 {
                t.Errorf("bad result for first line: isPrefix=%v err=%v line=%q", isPrefix, err, string(line))
        }
        n, err := io.Copy(outbuf, l)
        if int(n) != len(restData) || err != nil {
                t.Errorf("bad result for Read: n=%d err=%v", n, err)
        }
        if outbuf.String() != restData {
                t.Errorf("bad result for Read: got %q; expected %q", outbuf.String(), restData)
        }
}

func TestReadEmptyBuffer(t *testing.T) {
        l := NewReaderSize(new(bytes.Buffer), minReadBufferSize)
        line, isPrefix, err := l.ReadLine()
        if err != io.EOF {
                t.Errorf("expected EOF from ReadLine, got '%s' %t %s", line, isPrefix, err)
        }
}

func TestLinesAfterRead(t *testing.T) {
        l := NewReaderSize(bytes.NewReader([]byte("foo")), minReadBufferSize)
        _, err := io.ReadAll(l)
        if err != nil {
                t.Error(err)
                return
        }

        line, isPrefix, err := l.ReadLine()
        if err != io.EOF {
                t.Errorf("expected EOF from ReadLine, got '%s' %t %s", line, isPrefix, err)
        }
}

func TestReadLineNonNilLineOrError(t *testing.T) {
        r := NewReader(strings.NewReader("line 1\n"))
        for i := 0; i < 2; i++ {
                l, _, err := r.ReadLine()
                if l != nil && err != nil {
                        t.Fatalf("on line %d/2; ReadLine=%#v, %v; want non-nil line or Error, but not both",
                                i+1, l, err)
                }
        }
}

type readLineResult struct {
        line     []byte
        isPrefix bool
        err      error
}

var readLineNewlinesTests = []struct {
        input  string
        expect []readLineResult
}{
        {"012345678901234\r\n012345678901234\r\n", []readLineResult{
                {[]byte("012345678901234"), true, nil},
                {nil, false, nil},
                {[]byte("012345678901234"), true, nil},
                {nil, false, nil},
                {nil, false, io.EOF},
        }},
        {"0123456789012345\r012345678901234\r", []readLineResult{
                {[]byte("0123456789012345"), true, nil},
                {[]byte("\r012345678901234"), true, nil},
                {[]byte("\r"), false, nil},
                {nil, false, io.EOF},
        }},
}

func TestReadLineNewlines(t *testing.T) {
        for _, e := range readLineNewlinesTests {
                testReadLineNewlines(t, e.input, e.expect)
        }
}

func testReadLineNewlines(t *testing.T, input string, expect []readLineResult) {
        b := NewReaderSize(strings.NewReader(input), minReadBufferSize)
        for i, e := range expect {
                line, isPrefix, err := b.ReadLine()
                if !bytes.Equal(line, e.line) {
                        t.Errorf("%q call %d, line == %q, want %q", input, i, line, e.line)
                        return
                }
                if isPrefix != e.isPrefix {
                        t.Errorf("%q call %d, isPrefix == %v, want %v", input, i, isPrefix, e.isPrefix)
                        return
                }
                if err != e.err {
                        t.Errorf("%q call %d, err == %v, want %v", input, i, err, e.err)
                        return
                }
        }
}

func createTestInput(n int) []byte {
        input := make([]byte, n)
        for i := range input {
                // 101 and 251 are arbitrary prime numbers.
                // The idea is to create an input sequence
                // which doesn't repeat too frequently.
                input[i] = byte(i % 251)
                if i%101 == 0 {
                        input[i] ^= byte(i / 101)
                }
        }
        return input
}

func TestReaderWriteTo(t *testing.T) {
        input := createTestInput(8192)
        r := NewReader(onlyReader{bytes.NewReader(input)})
        w := new(bytes.Buffer)
        if n, err := r.WriteTo(w); err != nil || n != int64(len(input)) {
                t.Fatalf("r.WriteTo(w) = %d, %v, want %d, nil", n, err, len(input))
        }

        for i, val := range w.Bytes() {
                if val != input[i] {
                        t.Errorf("after write: out[%d] = %#x, want %#x", i, val, input[i])
                }
        }
}

type errorWriterToTest struct {
        rn, wn     int
        rerr, werr error
        expected   error
}

func (r errorWriterToTest) Read(p []byte) (int, error) {
        return len(p) * r.rn, r.rerr
}

func (w errorWriterToTest) Write(p []byte) (int, error) {
        return len(p) * w.wn, w.werr
}

var errorWriterToTests = []errorWriterToTest{
        {1, 0, nil, io.ErrClosedPipe, io.ErrClosedPipe},
        {0, 1, io.ErrClosedPipe, nil, io.ErrClosedPipe},
        {0, 0, io.ErrUnexpectedEOF, io.ErrClosedPipe, io.ErrClosedPipe},
        {0, 1, io.EOF, nil, nil},
}

func TestReaderWriteToErrors(t *testing.T) {
        for i, rw := range errorWriterToTests {
                r := NewReader(rw)
                if _, err := r.WriteTo(rw); err != rw.expected {
                        t.Errorf("r.WriteTo(errorWriterToTests[%d]) = _, %v, want _,%v", i, err, rw.expected)
                }
        }
}

func TestWriterReadFrom(t *testing.T) {
        ws := []func(io.Writer) io.Writer{
                func(w io.Writer) io.Writer { return onlyWriter{w} },
                func(w io.Writer) io.Writer { return w },
        }

        rs := []func(io.Reader) io.Reader{
                iotest.DataErrReader,
                func(r io.Reader) io.Reader { return r },
        }

        for ri, rfunc := range rs {
                for wi, wfunc := range ws {
                        input := createTestInput(8192)
                        b := new(bytes.Buffer)
                        w := NewWriter(wfunc(b))
                        r := rfunc(bytes.NewReader(input))
                        if n, err := w.ReadFrom(r); err != nil || n != int64(len(input)) {
                                t.Errorf("ws[%d],rs[%d]: w.ReadFrom(r) = %d, %v, want %d, nil", wi, ri, n, err, len(input))
                                continue
                        }
                        if err := w.Flush(); err != nil {
                                t.Errorf("Flush returned %v", err)
                                continue
                        }
                        if got, want := b.String(), string(input); got != want {
                                t.Errorf("ws[%d], rs[%d]:\ngot  %q\nwant %q\n", wi, ri, got, want)
                        }
                }
        }
}

type errorReaderFromTest struct {
        rn, wn     int
        rerr, werr error
        expected   error
}

func (r errorReaderFromTest) Read(p []byte) (int, error) {
        return len(p) * r.rn, r.rerr
}

func (w errorReaderFromTest) Write(p []byte) (int, error) {
        return len(p) * w.wn, w.werr
}

var errorReaderFromTests = []errorReaderFromTest{
        {0, 1, io.EOF, nil, nil},
        {1, 1, io.EOF, nil, nil},
        {0, 1, io.ErrClosedPipe, nil, io.ErrClosedPipe},
        {0, 0, io.ErrClosedPipe, io.ErrShortWrite, io.ErrClosedPipe},
        {1, 0, nil, io.ErrShortWrite, io.ErrShortWrite},
}

func TestWriterReadFromErrors(t *testing.T) {
        for i, rw := range errorReaderFromTests {
                w := NewWriter(rw)
                if _, err := w.ReadFrom(rw); err != rw.expected {
                        t.Errorf("w.ReadFrom(errorReaderFromTests[%d]) = _, %v, want _,%v", i, err, rw.expected)
                }
        }
}

// TestWriterReadFromCounts tests that using io.Copy to copy into a
// bufio.Writer does not prematurely flush the buffer. For example, when
// buffering writes to a network socket, excessive network writes should be
// avoided.
func TestWriterReadFromCounts(t *testing.T) {
        var w0 writeCountingDiscard
        b0 := NewWriterSize(&w0, 1234)
        b0.WriteString(strings.Repeat("x", 1000))
        if w0 != 0 {
                t.Fatalf("write 1000 'x's: got %d writes, want 0", w0)
        }
        b0.WriteString(strings.Repeat("x", 200))
        if w0 != 0 {
                t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
        }
        io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 30))})
        if w0 != 0 {
                t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
        }
        io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 9))})
        if w0 != 1 {
                t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
        }

        var w1 writeCountingDiscard
        b1 := NewWriterSize(&w1, 1234)
        b1.WriteString(strings.Repeat("x", 1200))
        b1.Flush()
        if w1 != 1 {
                t.Fatalf("flush 1200 'x's: got %d writes, want 1", w1)
        }
        b1.WriteString(strings.Repeat("x", 89))
        if w1 != 1 {
                t.Fatalf("write 1200 + 89 'x's: got %d writes, want 1", w1)
        }
        io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 700))})
        if w1 != 1 {
                t.Fatalf("write 1200 + 789 'x's: got %d writes, want 1", w1)
        }
        io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 600))})
        if w1 != 2 {
                t.Fatalf("write 1200 + 1389 'x's: got %d writes, want 2", w1)
        }
        b1.Flush()
        if w1 != 3 {
                t.Fatalf("flush 1200 + 1389 'x's: got %d writes, want 3", w1)
        }
}

// A writeCountingDiscard is like io.Discard and counts the number of times
// Write is called on it.
type writeCountingDiscard int

func (w *writeCountingDiscard) Write(p []byte) (int, error) {
        *w++
        return len(p), nil
}

type negativeReader int

func (r *negativeReader) Read([]byte) (int, error) { return -1, nil }

func TestNegativeRead(t *testing.T) {
        // should panic with a description pointing at the reader, not at itself.
        // (should NOT panic with slice index error, for example.)
        b := NewReader(new(negativeReader))
        defer func() {
                switch err := recover().(type) {
                case nil:
                        t.Fatal("read did not panic")
                case error:
                        if !strings.Contains(err.Error(), "reader returned negative count from Read") {
                                t.Fatalf("wrong panic: %v", err)
                        }
                default:
                        t.Fatalf("unexpected panic value: %T(%v)", err, err)
                }
        }()
        b.Read(make([]byte, 100))
}

var errFake = errors.New("fake error")

type errorThenGoodReader struct {
        didErr bool
        nread  int
}

func (r *errorThenGoodReader) Read(p []byte) (int, error) {
        r.nread++
        if !r.didErr {
                r.didErr = true
                return 0, errFake
        }
        return len(p), nil
}

func TestReaderClearError(t *testing.T) {
        r := &errorThenGoodReader{}
        b := NewReader(r)
        buf := make([]byte, 1)
        if _, err := b.Read(nil); err != nil {
                t.Fatalf("1st nil Read = %v; want nil", err)
        }
        if _, err := b.Read(buf); err != errFake {
                t.Fatalf("1st Read = %v; want errFake", err)
        }
        if _, err := b.Read(nil); err != nil {
                t.Fatalf("2nd nil Read = %v; want nil", err)
        }
        if _, err := b.Read(buf); err != nil {
                t.Fatalf("3rd Read with buffer = %v; want nil", err)
        }
        if r.nread != 2 {
                t.Errorf("num reads = %d; want 2", r.nread)
        }
}

// Test for golang.org/issue/5947
func TestWriterReadFromWhileFull(t *testing.T) {
        buf := new(bytes.Buffer)
        w := NewWriterSize(buf, 10)

        // Fill buffer exactly.
        n, err := w.Write([]byte("0123456789"))
        if n != 10 || err != nil {
                t.Fatalf("Write returned (%v, %v), want (10, nil)", n, err)
        }

        // Use ReadFrom to read in some data.
        n2, err := w.ReadFrom(strings.NewReader("abcdef"))
        if n2 != 6 || err != nil {
                t.Fatalf("ReadFrom returned (%v, %v), want (6, nil)", n2, err)
        }
}

type emptyThenNonEmptyReader struct {
        r io.Reader
        n int
}

func (r *emptyThenNonEmptyReader) Read(p []byte) (int, error) {
        if r.n <= 0 {
                return r.r.Read(p)
        }
        r.n--
        return 0, nil
}

// Test for golang.org/issue/7611
func TestWriterReadFromUntilEOF(t *testing.T) {
        buf := new(bytes.Buffer)
        w := NewWriterSize(buf, 5)

        // Partially fill buffer
        n, err := w.Write([]byte("0123"))
        if n != 4 || err != nil {
                t.Fatalf("Write returned (%v, %v), want (4, nil)", n, err)
        }

        // Use ReadFrom to read in some data.
        r := &emptyThenNonEmptyReader{r: strings.NewReader("abcd"), n: 3}
        n2, err := w.ReadFrom(r)
        if n2 != 4 || err != nil {
                t.Fatalf("ReadFrom returned (%v, %v), want (4, nil)", n2, err)
        }
        w.Flush()
        if got, want := string(buf.Bytes()), "0123abcd"; got != want {
                t.Fatalf("buf.Bytes() returned %q, want %q", got, want)
        }
}

func TestWriterReadFromErrNoProgress(t *testing.T) {
        buf := new(bytes.Buffer)
        w := NewWriterSize(buf, 5)

        // Partially fill buffer
        n, err := w.Write([]byte("0123"))
        if n != 4 || err != nil {
                t.Fatalf("Write returned (%v, %v), want (4, nil)", n, err)
        }

        // Use ReadFrom to read in some data.
        r := &emptyThenNonEmptyReader{r: strings.NewReader("abcd"), n: 100}
        n2, err := w.ReadFrom(r)
        if n2 != 0 || err != io.ErrNoProgress {
                t.Fatalf("buf.Bytes() returned (%v, %v), want (0, io.ErrNoProgress)", n2, err)
        }
}

type readFromWriter struct {
        buf           []byte
        writeBytes    int
        readFromBytes int
}

func (w *readFromWriter) Write(p []byte) (int, error) {
        w.buf = append(w.buf, p...)
        w.writeBytes += len(p)
        return len(p), nil
}

func (w *readFromWriter) ReadFrom(r io.Reader) (int64, error) {
        b, err := io.ReadAll(r)
        w.buf = append(w.buf, b...)
        w.readFromBytes += len(b)
        return int64(len(b)), err
}

// Test that calling (*Writer).ReadFrom with a partially-filled buffer
// fills the buffer before switching over to ReadFrom.
func TestWriterReadFromWithBufferedData(t *testing.T) {
        const bufsize = 16

        input := createTestInput(64)
        rfw := &readFromWriter{}
        w := NewWriterSize(rfw, bufsize)

        const writeSize = 8
        if n, err := w.Write(input[:writeSize]); n != writeSize || err != nil {
                t.Errorf("w.Write(%v bytes) = %v, %v; want %v, nil", writeSize, n, err, writeSize)
        }
        n, err := w.ReadFrom(bytes.NewReader(input[writeSize:]))
        if wantn := len(input[writeSize:]); int(n) != wantn || err != nil {
                t.Errorf("io.Copy(w, %v bytes) = %v, %v; want %v, nil", wantn, n, err, wantn)
        }
        if err := w.Flush(); err != nil {
                t.Errorf("w.Flush() = %v, want nil", err)
        }

        if got, want := rfw.writeBytes, bufsize; got != want {
                t.Errorf("wrote %v bytes with Write, want %v", got, want)
        }
        if got, want := rfw.readFromBytes, len(input)-bufsize; got != want {
                t.Errorf("wrote %v bytes with ReadFrom, want %v", got, want)
        }
}

func TestReadZero(t *testing.T) {
        for _, size := range []int{100, 2} {
                t.Run(fmt.Sprintf("bufsize=%d", size), func(t *testing.T) {
                        r := io.MultiReader(strings.NewReader("abc"), &emptyThenNonEmptyReader{r: strings.NewReader("def"), n: 1})
                        br := NewReaderSize(r, size)
                        want := func(s string, wantErr error) {
                                p := make([]byte, 50)
                                n, err := br.Read(p)
                                if err != wantErr || n != len(s) || string(p[:n]) != s {
                                        t.Fatalf("read(%d) = %q, %v, want %q, %v", len(p), string(p[:n]), err, s, wantErr)
                                }
                                t.Logf("read(%d) = %q, %v", len(p), string(p[:n]), err)
                        }
                        want("abc", nil)
                        want("", nil)
                        want("def", nil)
                        want("", io.EOF)
                })
        }
}

func TestReaderReset(t *testing.T) {
        r := NewReader(strings.NewReader("foo foo"))
        buf := make([]byte, 3)
        r.Read(buf)
        if string(buf) != "foo" {
                t.Errorf("buf = %q; want foo", buf)
        }

        r.Reset(strings.NewReader("bar bar"))
        all, err := io.ReadAll(r)
        if err != nil {
                t.Fatal(err)
        }
        if string(all) != "bar bar" {
                t.Errorf("ReadAll = %q; want bar bar", all)
        }

        *r = Reader{} // zero out the Reader
        r.Reset(strings.NewReader("bar bar"))
        all, err = io.ReadAll(r)
        if err != nil {
                t.Fatal(err)
        }
        if string(all) != "bar bar" {
                t.Errorf("ReadAll = %q; want bar bar", all)
        }
}

func TestWriterReset(t *testing.T) {
        var buf1, buf2, buf3 bytes.Buffer
        w := NewWriter(&buf1)
        w.WriteString("foo")

        w.Reset(&buf2) // and not flushed
        w.WriteString("bar")
        w.Flush()
        if buf1.String() != "" {
                t.Errorf("buf1 = %q; want empty", buf1.String())
        }
        if buf2.String() != "bar" {
                t.Errorf("buf2 = %q; want bar", buf2.String())
        }

        *w = Writer{}  // zero out the Writer
        w.Reset(&buf3) // and not flushed
        w.WriteString("bar")
        w.Flush()
        if buf1.String() != "" {
                t.Errorf("buf1 = %q; want empty", buf1.String())
        }
        if buf3.String() != "bar" {
                t.Errorf("buf3 = %q; want bar", buf3.String())
        }
}

func TestReaderDiscard(t *testing.T) {
        tests := []struct {
                name     string
                r        io.Reader
                bufSize  int // 0 means 16
                peekSize int

                n int // input to Discard

                want    int   // from Discard
                wantErr error // from Discard

                wantBuffered int
        }{
                {
                        name:         "normal case",
                        r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
                        peekSize:     16,
                        n:            6,
                        want:         6,
                        wantBuffered: 10,
                },
                {
                        name:         "discard causing read",
                        r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
                        n:            6,
                        want:         6,
                        wantBuffered: 10,
                },
                {
                        name:         "discard all without peek",
                        r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
                        n:            26,
                        want:         26,
                        wantBuffered: 0,
                },
                {
                        name:         "discard more than end",
                        r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
                        n:            27,
                        want:         26,
                        wantErr:      io.EOF,
                        wantBuffered: 0,
                },
                // Any error from filling shouldn't show up until we
                // get past the valid bytes. Here we return 5 valid bytes at the same time
                // as an error, but test that we don't see the error from Discard.
                {
                        name: "fill error, discard less",
                        r: newScriptedReader(func(p []byte) (n int, err error) {
                                if len(p) < 5 {
                                        panic("unexpected small read")
                                }
                                return 5, errors.New("5-then-error")
                        }),
                        n:            4,
                        want:         4,
                        wantErr:      nil,
                        wantBuffered: 1,
                },
                {
                        name: "fill error, discard equal",
                        r: newScriptedReader(func(p []byte) (n int, err error) {
                                if len(p) < 5 {
                                        panic("unexpected small read")
                                }
                                return 5, errors.New("5-then-error")
                        }),
                        n:            5,
                        want:         5,
                        wantErr:      nil,
                        wantBuffered: 0,
                },
                {
                        name: "fill error, discard more",
                        r: newScriptedReader(func(p []byte) (n int, err error) {
                                if len(p) < 5 {
                                        panic("unexpected small read")
                                }
                                return 5, errors.New("5-then-error")
                        }),
                        n:            6,
                        want:         5,
                        wantErr:      errors.New("5-then-error"),
                        wantBuffered: 0,
                },
                // Discard of 0 shouldn't cause a read:
                {
                        name:         "discard zero",
                        r:            newScriptedReader(), // will panic on Read
                        n:            0,
                        want:         0,
                        wantErr:      nil,
                        wantBuffered: 0,
                },
                {
                        name:         "discard negative",
                        r:            newScriptedReader(), // will panic on Read
                        n:            -1,
                        want:         0,
                        wantErr:      ErrNegativeCount,
                        wantBuffered: 0,
                },
        }
        for _, tt := range tests {
                br := NewReaderSize(tt.r, tt.bufSize)
                if tt.peekSize > 0 {
                        peekBuf, err := br.Peek(tt.peekSize)
                        if err != nil {
                                t.Errorf("%s: Peek(%d): %v", tt.name, tt.peekSize, err)
                                continue
                        }
                        if len(peekBuf) != tt.peekSize {
                                t.Errorf("%s: len(Peek(%d)) = %v; want %v", tt.name, tt.peekSize, len(peekBuf), tt.peekSize)
                                continue
                        }
                }
                discarded, err := br.Discard(tt.n)
                if ge, we := fmt.Sprint(err), fmt.Sprint(tt.wantErr); discarded != tt.want || ge != we {
                        t.Errorf("%s: Discard(%d) = (%v, %v); want (%v, %v)", tt.name, tt.n, discarded, ge, tt.want, we)
                        continue
                }
                if bn := br.Buffered(); bn != tt.wantBuffered {
                        t.Errorf("%s: after Discard, Buffered = %d; want %d", tt.name, bn, tt.wantBuffered)
                }
        }

}

func TestReaderSize(t *testing.T) {
        if got, want := NewReader(nil).Size(), DefaultBufSize; got != want {
                t.Errorf("NewReader's Reader.Size = %d; want %d", got, want)
        }
        if got, want := NewReaderSize(nil, 1234).Size(), 1234; got != want {
                t.Errorf("NewReaderSize's Reader.Size = %d; want %d", got, want)
        }
}

func TestWriterSize(t *testing.T) {
        if got, want := NewWriter(nil).Size(), DefaultBufSize; got != want {
                t.Errorf("NewWriter's Writer.Size = %d; want %d", got, want)
        }
        if got, want := NewWriterSize(nil, 1234).Size(), 1234; got != want {
                t.Errorf("NewWriterSize's Writer.Size = %d; want %d", got, want)
        }
}

// An onlyReader only implements io.Reader, no matter what other methods the underlying implementation may have.
type onlyReader struct {
        io.Reader
}

// An onlyWriter only implements io.Writer, no matter what other methods the underlying implementation may have.
type onlyWriter struct {
        io.Writer
}

// A scriptedReader is an io.Reader that executes its steps sequentially.
type scriptedReader []func(p []byte) (n int, err error)

func (sr *scriptedReader) Read(p []byte) (n int, err error) {
        if len(*sr) == 0 {
                panic("too many Read calls on scripted Reader. No steps remain.")
        }
        step := (*sr)[0]
        *sr = (*sr)[1:]
        return step(p)
}

func newScriptedReader(steps ...func(p []byte) (n int, err error)) io.Reader {
        sr := scriptedReader(steps)
        return &sr
}

// eofReader returns the number of bytes read and io.EOF for the read that consumes the last of the content.
type eofReader struct {
        buf []byte
}

func (r *eofReader) Read(p []byte) (int, error) {
        read := copy(p, r.buf)
        r.buf = r.buf[read:]

        switch read {
        case 0, len(r.buf):
                // As allowed in the documentation, this will return io.EOF
                // in the same call that consumes the last of the data.
                // https://godoc.org/io#Reader
                return read, io.EOF
        }

        return read, nil
}

func TestPartialReadEOF(t *testing.T) {
        src := make([]byte, 10)
        eofR := &eofReader{buf: src}
        r := NewReader(eofR)

        // Start by reading 5 of the 10 available bytes.
        dest := make([]byte, 5)
        read, err := r.Read(dest)
        if err != nil {
                t.Fatalf("unexpected error: %v", err)
        }
        if n := len(dest); read != n {
                t.Fatalf("read %d bytes; wanted %d bytes", read, n)
        }

        // The Reader should have buffered all the content from the io.Reader.
        if n := len(eofR.buf); n != 0 {
                t.Fatalf("got %d bytes left in bufio.Reader source; want 0 bytes", n)
        }
        // To prove the point, check that there are still 5 bytes available to read.
        if n := r.Buffered(); n != 5 {
                t.Fatalf("got %d bytes buffered in bufio.Reader; want 5 bytes", n)
        }

        // This is the second read of 0 bytes.
        read, err = r.Read([]byte{})
        if err != nil {
                t.Fatalf("unexpected error: %v", err)
        }
        if read != 0 {
                t.Fatalf("read %d bytes; want 0 bytes", read)
        }
}

type writerWithReadFromError struct{}

func (w writerWithReadFromError) ReadFrom(r io.Reader) (int64, error) {
        return 0, errors.New("writerWithReadFromError error")
}

func (w writerWithReadFromError) Write(b []byte) (n int, err error) {
        return 10, nil
}

func TestWriterReadFromMustSetUnderlyingError(t *testing.T) {
        var wr = NewWriter(writerWithReadFromError{})
        if _, err := wr.ReadFrom(strings.NewReader("test2")); err == nil {
                t.Fatal("expected ReadFrom returns error, got nil")
        }
        if _, err := wr.Write([]byte("123")); err == nil {
                t.Fatal("expected Write returns error, got nil")
        }
}

type writeErrorOnlyWriter struct{}

func (w writeErrorOnlyWriter) Write(p []byte) (n int, err error) {
        return 0, errors.New("writeErrorOnlyWriter error")
}

// Ensure that previous Write errors are immediately returned
// on any ReadFrom. See golang.org/issue/35194.
func TestWriterReadFromMustReturnUnderlyingError(t *testing.T) {
        var wr = NewWriter(writeErrorOnlyWriter{})
        s := "test1"
        wantBuffered := len(s)
        if _, err := wr.WriteString(s); err != nil {
                t.Fatalf("unexpected error: %v", err)
        }
        if err := wr.Flush(); err == nil {
                t.Error("expected flush error, got nil")
        }
        if _, err := wr.ReadFrom(strings.NewReader("test2")); err == nil {
                t.Fatal("expected error, got nil")
        }
        if buffered := wr.Buffered(); buffered != wantBuffered {
                t.Fatalf("Buffered = %v; want %v", buffered, wantBuffered)
        }
}

func BenchmarkReaderCopyOptimal(b *testing.B) {
        // Optimal case is where the underlying reader implements io.WriterTo
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        src := NewReader(srcBuf)
        dstBuf := new(bytes.Buffer)
        dst := onlyWriter{dstBuf}
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                src.Reset(srcBuf)
                dstBuf.Reset()
                io.Copy(dst, src)
        }
}

func BenchmarkReaderCopyUnoptimal(b *testing.B) {
        // Unoptimal case is where the underlying reader doesn't implement io.WriterTo
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        src := NewReader(onlyReader{srcBuf})
        dstBuf := new(bytes.Buffer)
        dst := onlyWriter{dstBuf}
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                src.Reset(onlyReader{srcBuf})
                dstBuf.Reset()
                io.Copy(dst, src)
        }
}

func BenchmarkReaderCopyNoWriteTo(b *testing.B) {
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        srcReader := NewReader(srcBuf)
        src := onlyReader{srcReader}
        dstBuf := new(bytes.Buffer)
        dst := onlyWriter{dstBuf}
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                srcReader.Reset(srcBuf)
                dstBuf.Reset()
                io.Copy(dst, src)
        }
}

func BenchmarkReaderWriteToOptimal(b *testing.B) {
        const bufSize = 16 << 10
        buf := make([]byte, bufSize)
        r := bytes.NewReader(buf)
        srcReader := NewReaderSize(onlyReader{r}, 1<<10)
        if _, ok := io.Discard.(io.ReaderFrom); !ok {
                b.Fatal("io.Discard doesn't support ReaderFrom")
        }
        for i := 0; i < b.N; i++ {
                r.Seek(0, io.SeekStart)
                srcReader.Reset(onlyReader{r})
                n, err := srcReader.WriteTo(io.Discard)
                if err != nil {
                        b.Fatal(err)
                }
                if n != bufSize {
                        b.Fatalf("n = %d; want %d", n, bufSize)
                }
        }
}

func BenchmarkReaderReadString(b *testing.B) {
        r := strings.NewReader("       foo       foo        42        42        42        42        42        42        42        42       4.2       4.2       4.2       4.2\n")
        buf := NewReader(r)
        b.ReportAllocs()
        for i := 0; i < b.N; i++ {
                r.Seek(0, io.SeekStart)
                buf.Reset(r)

                _, err := buf.ReadString('\n')
                if err != nil {
                        b.Fatal(err)
                }
        }
}

func BenchmarkWriterCopyOptimal(b *testing.B) {
        // Optimal case is where the underlying writer implements io.ReaderFrom
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        src := onlyReader{srcBuf}
        dstBuf := new(bytes.Buffer)
        dst := NewWriter(dstBuf)
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                dstBuf.Reset()
                dst.Reset(dstBuf)
                io.Copy(dst, src)
        }
}

func BenchmarkWriterCopyUnoptimal(b *testing.B) {
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        src := onlyReader{srcBuf}
        dstBuf := new(bytes.Buffer)
        dst := NewWriter(onlyWriter{dstBuf})
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                dstBuf.Reset()
                dst.Reset(onlyWriter{dstBuf})
                io.Copy(dst, src)
        }
}

func BenchmarkWriterCopyNoReadFrom(b *testing.B) {
        srcBuf := bytes.NewBuffer(make([]byte, 8192))
        src := onlyReader{srcBuf}
        dstBuf := new(bytes.Buffer)
        dstWriter := NewWriter(dstBuf)
        dst := onlyWriter{dstWriter}
        for i := 0; i < b.N; i++ {
                srcBuf.Reset()
                dstBuf.Reset()
                dstWriter.Reset(dstBuf)
                io.Copy(dst, src)
        }
}

func BenchmarkReaderEmpty(b *testing.B) {
        b.ReportAllocs()
        str := strings.Repeat("x", 16<<10)
        for i := 0; i < b.N; i++ {
                br := NewReader(strings.NewReader(str))
                n, err := io.Copy(io.Discard, br)
                if err != nil {
                        b.Fatal(err)
                }
                if n != int64(len(str)) {
                        b.Fatal("wrong length")
                }
        }
}

func BenchmarkWriterEmpty(b *testing.B) {
        b.ReportAllocs()
        str := strings.Repeat("x", 1<<10)
        bs := []byte(str)
        for i := 0; i < b.N; i++ {
                bw := NewWriter(io.Discard)
                bw.Flush()
                bw.WriteByte('a')
                bw.Flush()
                bw.WriteRune('B')
                bw.Flush()
                bw.Write(bs)
                bw.Flush()
                bw.WriteString(str)
                bw.Flush()
        }
}

func BenchmarkWriterFlush(b *testing.B) {
        b.ReportAllocs()
        bw := NewWriter(io.Discard)
        str := strings.Repeat("x", 50)
        for i := 0; i < b.N; i++ {
                bw.WriteString(str)
                bw.Flush()
        }
}