Source file src/bufio/bufio_test.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package bufio_test
     6  
     7  import (
     8  	. "bufio"
     9  	"bytes"
    10  	"errors"
    11  	"fmt"
    12  	"io"
    13  	"math/rand"
    14  	"strconv"
    15  	"strings"
    16  	"testing"
    17  	"testing/iotest"
    18  	"time"
    19  	"unicode/utf8"
    20  )
    21  
    22  // Reads from a reader and rot13s the result.
    23  type rot13Reader struct {
    24  	r io.Reader
    25  }
    26  
    27  func newRot13Reader(r io.Reader) *rot13Reader {
    28  	r13 := new(rot13Reader)
    29  	r13.r = r
    30  	return r13
    31  }
    32  
    33  func (r13 *rot13Reader) Read(p []byte) (int, error) {
    34  	n, err := r13.r.Read(p)
    35  	for i := 0; i < n; i++ {
    36  		c := p[i] | 0x20 // lowercase byte
    37  		if 'a' <= c && c <= 'm' {
    38  			p[i] += 13
    39  		} else if 'n' <= c && c <= 'z' {
    40  			p[i] -= 13
    41  		}
    42  	}
    43  	return n, err
    44  }
    45  
    46  // Call ReadByte to accumulate the text of a file
    47  func readBytes(buf *Reader) string {
    48  	var b [1000]byte
    49  	nb := 0
    50  	for {
    51  		c, err := buf.ReadByte()
    52  		if err == io.EOF {
    53  			break
    54  		}
    55  		if err == nil {
    56  			b[nb] = c
    57  			nb++
    58  		} else if err != iotest.ErrTimeout {
    59  			panic("Data: " + err.Error())
    60  		}
    61  	}
    62  	return string(b[0:nb])
    63  }
    64  
    65  func TestReaderSimple(t *testing.T) {
    66  	data := "hello world"
    67  	b := NewReader(strings.NewReader(data))
    68  	if s := readBytes(b); s != "hello world" {
    69  		t.Errorf("simple hello world test failed: got %q", s)
    70  	}
    71  
    72  	b = NewReader(newRot13Reader(strings.NewReader(data)))
    73  	if s := readBytes(b); s != "uryyb jbeyq" {
    74  		t.Errorf("rot13 hello world test failed: got %q", s)
    75  	}
    76  }
    77  
    78  type readMaker struct {
    79  	name string
    80  	fn   func(io.Reader) io.Reader
    81  }
    82  
    83  var readMakers = []readMaker{
    84  	{"full", func(r io.Reader) io.Reader { return r }},
    85  	{"byte", iotest.OneByteReader},
    86  	{"half", iotest.HalfReader},
    87  	{"data+err", iotest.DataErrReader},
    88  	{"timeout", iotest.TimeoutReader},
    89  }
    90  
    91  // Call ReadString (which ends up calling everything else)
    92  // to accumulate the text of a file.
    93  func readLines(b *Reader) string {
    94  	s := ""
    95  	for {
    96  		s1, err := b.ReadString('\n')
    97  		if err == io.EOF {
    98  			break
    99  		}
   100  		if err != nil && err != iotest.ErrTimeout {
   101  			panic("GetLines: " + err.Error())
   102  		}
   103  		s += s1
   104  	}
   105  	return s
   106  }
   107  
   108  // Call Read to accumulate the text of a file
   109  func reads(buf *Reader, m int) string {
   110  	var b [1000]byte
   111  	nb := 0
   112  	for {
   113  		n, err := buf.Read(b[nb : nb+m])
   114  		nb += n
   115  		if err == io.EOF {
   116  			break
   117  		}
   118  	}
   119  	return string(b[0:nb])
   120  }
   121  
   122  type bufReader struct {
   123  	name string
   124  	fn   func(*Reader) string
   125  }
   126  
   127  var bufreaders = []bufReader{
   128  	{"1", func(b *Reader) string { return reads(b, 1) }},
   129  	{"2", func(b *Reader) string { return reads(b, 2) }},
   130  	{"3", func(b *Reader) string { return reads(b, 3) }},
   131  	{"4", func(b *Reader) string { return reads(b, 4) }},
   132  	{"5", func(b *Reader) string { return reads(b, 5) }},
   133  	{"7", func(b *Reader) string { return reads(b, 7) }},
   134  	{"bytes", readBytes},
   135  	{"lines", readLines},
   136  }
   137  
   138  const minReadBufferSize = 16
   139  
   140  var bufsizes = []int{
   141  	0, minReadBufferSize, 23, 32, 46, 64, 93, 128, 1024, 4096,
   142  }
   143  
   144  func TestReader(t *testing.T) {
   145  	var texts [31]string
   146  	str := ""
   147  	all := ""
   148  	for i := 0; i < len(texts)-1; i++ {
   149  		texts[i] = str + "\n"
   150  		all += texts[i]
   151  		str += string(rune(i%26 + 'a'))
   152  	}
   153  	texts[len(texts)-1] = all
   154  
   155  	for h := 0; h < len(texts); h++ {
   156  		text := texts[h]
   157  		for i := 0; i < len(readMakers); i++ {
   158  			for j := 0; j < len(bufreaders); j++ {
   159  				for k := 0; k < len(bufsizes); k++ {
   160  					readmaker := readMakers[i]
   161  					bufreader := bufreaders[j]
   162  					bufsize := bufsizes[k]
   163  					read := readmaker.fn(strings.NewReader(text))
   164  					buf := NewReaderSize(read, bufsize)
   165  					s := bufreader.fn(buf)
   166  					if s != text {
   167  						t.Errorf("reader=%s fn=%s bufsize=%d want=%q got=%q",
   168  							readmaker.name, bufreader.name, bufsize, text, s)
   169  					}
   170  				}
   171  			}
   172  		}
   173  	}
   174  }
   175  
   176  type zeroReader struct{}
   177  
   178  func (zeroReader) Read(p []byte) (int, error) {
   179  	return 0, nil
   180  }
   181  
   182  func TestZeroReader(t *testing.T) {
   183  	var z zeroReader
   184  	r := NewReader(z)
   185  
   186  	c := make(chan error)
   187  	go func() {
   188  		_, err := r.ReadByte()
   189  		c <- err
   190  	}()
   191  
   192  	select {
   193  	case err := <-c:
   194  		if err == nil {
   195  			t.Error("error expected")
   196  		} else if err != io.ErrNoProgress {
   197  			t.Error("unexpected error:", err)
   198  		}
   199  	case <-time.After(time.Second):
   200  		t.Error("test timed out (endless loop in ReadByte?)")
   201  	}
   202  }
   203  
   204  // A StringReader delivers its data one string segment at a time via Read.
   205  type StringReader struct {
   206  	data []string
   207  	step int
   208  }
   209  
   210  func (r *StringReader) Read(p []byte) (n int, err error) {
   211  	if r.step < len(r.data) {
   212  		s := r.data[r.step]
   213  		n = copy(p, s)
   214  		r.step++
   215  	} else {
   216  		err = io.EOF
   217  	}
   218  	return
   219  }
   220  
   221  func readRuneSegments(t *testing.T, segments []string) {
   222  	got := ""
   223  	want := strings.Join(segments, "")
   224  	r := NewReader(&StringReader{data: segments})
   225  	for {
   226  		r, _, err := r.ReadRune()
   227  		if err != nil {
   228  			if err != io.EOF {
   229  				return
   230  			}
   231  			break
   232  		}
   233  		got += string(r)
   234  	}
   235  	if got != want {
   236  		t.Errorf("segments=%v got=%s want=%s", segments, got, want)
   237  	}
   238  }
   239  
   240  var segmentList = [][]string{
   241  	{},
   242  	{""},
   243  	{"日", "本語"},
   244  	{"\u65e5", "\u672c", "\u8a9e"},
   245  	{"\U000065e5", "\U0000672c", "\U00008a9e"},
   246  	{"\xe6", "\x97\xa5\xe6", "\x9c\xac\xe8\xaa\x9e"},
   247  	{"Hello", ", ", "World", "!"},
   248  	{"Hello", ", ", "", "World", "!"},
   249  }
   250  
   251  func TestReadRune(t *testing.T) {
   252  	for _, s := range segmentList {
   253  		readRuneSegments(t, s)
   254  	}
   255  }
   256  
   257  func TestUnreadRune(t *testing.T) {
   258  	segments := []string{"Hello, world:", "日本語"}
   259  	r := NewReader(&StringReader{data: segments})
   260  	got := ""
   261  	want := strings.Join(segments, "")
   262  	// Normal execution.
   263  	for {
   264  		r1, _, err := r.ReadRune()
   265  		if err != nil {
   266  			if err != io.EOF {
   267  				t.Error("unexpected error on ReadRune:", err)
   268  			}
   269  			break
   270  		}
   271  		got += string(r1)
   272  		// Put it back and read it again.
   273  		if err = r.UnreadRune(); err != nil {
   274  			t.Fatal("unexpected error on UnreadRune:", err)
   275  		}
   276  		r2, _, err := r.ReadRune()
   277  		if err != nil {
   278  			t.Fatal("unexpected error reading after unreading:", err)
   279  		}
   280  		if r1 != r2 {
   281  			t.Fatalf("incorrect rune after unread: got %c, want %c", r1, r2)
   282  		}
   283  	}
   284  	if got != want {
   285  		t.Errorf("got %q, want %q", got, want)
   286  	}
   287  }
   288  
   289  func TestNoUnreadRuneAfterPeek(t *testing.T) {
   290  	br := NewReader(strings.NewReader("example"))
   291  	br.ReadRune()
   292  	br.Peek(1)
   293  	if err := br.UnreadRune(); err == nil {
   294  		t.Error("UnreadRune didn't fail after Peek")
   295  	}
   296  }
   297  
   298  func TestNoUnreadByteAfterPeek(t *testing.T) {
   299  	br := NewReader(strings.NewReader("example"))
   300  	br.ReadByte()
   301  	br.Peek(1)
   302  	if err := br.UnreadByte(); err == nil {
   303  		t.Error("UnreadByte didn't fail after Peek")
   304  	}
   305  }
   306  
   307  func TestNoUnreadRuneAfterDiscard(t *testing.T) {
   308  	br := NewReader(strings.NewReader("example"))
   309  	br.ReadRune()
   310  	br.Discard(1)
   311  	if err := br.UnreadRune(); err == nil {
   312  		t.Error("UnreadRune didn't fail after Discard")
   313  	}
   314  }
   315  
   316  func TestNoUnreadByteAfterDiscard(t *testing.T) {
   317  	br := NewReader(strings.NewReader("example"))
   318  	br.ReadByte()
   319  	br.Discard(1)
   320  	if err := br.UnreadByte(); err == nil {
   321  		t.Error("UnreadByte didn't fail after Discard")
   322  	}
   323  }
   324  
   325  func TestNoUnreadRuneAfterWriteTo(t *testing.T) {
   326  	br := NewReader(strings.NewReader("example"))
   327  	br.WriteTo(io.Discard)
   328  	if err := br.UnreadRune(); err == nil {
   329  		t.Error("UnreadRune didn't fail after WriteTo")
   330  	}
   331  }
   332  
   333  func TestNoUnreadByteAfterWriteTo(t *testing.T) {
   334  	br := NewReader(strings.NewReader("example"))
   335  	br.WriteTo(io.Discard)
   336  	if err := br.UnreadByte(); err == nil {
   337  		t.Error("UnreadByte didn't fail after WriteTo")
   338  	}
   339  }
   340  
   341  func TestUnreadByte(t *testing.T) {
   342  	segments := []string{"Hello, ", "world"}
   343  	r := NewReader(&StringReader{data: segments})
   344  	got := ""
   345  	want := strings.Join(segments, "")
   346  	// Normal execution.
   347  	for {
   348  		b1, err := r.ReadByte()
   349  		if err != nil {
   350  			if err != io.EOF {
   351  				t.Error("unexpected error on ReadByte:", err)
   352  			}
   353  			break
   354  		}
   355  		got += string(b1)
   356  		// Put it back and read it again.
   357  		if err = r.UnreadByte(); err != nil {
   358  			t.Fatal("unexpected error on UnreadByte:", err)
   359  		}
   360  		b2, err := r.ReadByte()
   361  		if err != nil {
   362  			t.Fatal("unexpected error reading after unreading:", err)
   363  		}
   364  		if b1 != b2 {
   365  			t.Fatalf("incorrect byte after unread: got %q, want %q", b1, b2)
   366  		}
   367  	}
   368  	if got != want {
   369  		t.Errorf("got %q, want %q", got, want)
   370  	}
   371  }
   372  
   373  func TestUnreadByteMultiple(t *testing.T) {
   374  	segments := []string{"Hello, ", "world"}
   375  	data := strings.Join(segments, "")
   376  	for n := 0; n <= len(data); n++ {
   377  		r := NewReader(&StringReader{data: segments})
   378  		// Read n bytes.
   379  		for i := 0; i < n; i++ {
   380  			b, err := r.ReadByte()
   381  			if err != nil {
   382  				t.Fatalf("n = %d: unexpected error on ReadByte: %v", n, err)
   383  			}
   384  			if b != data[i] {
   385  				t.Fatalf("n = %d: incorrect byte returned from ReadByte: got %q, want %q", n, b, data[i])
   386  			}
   387  		}
   388  		// Unread one byte if there is one.
   389  		if n > 0 {
   390  			if err := r.UnreadByte(); err != nil {
   391  				t.Errorf("n = %d: unexpected error on UnreadByte: %v", n, err)
   392  			}
   393  		}
   394  		// Test that we cannot unread any further.
   395  		if err := r.UnreadByte(); err == nil {
   396  			t.Errorf("n = %d: expected error on UnreadByte", n)
   397  		}
   398  	}
   399  }
   400  
   401  func TestUnreadByteOthers(t *testing.T) {
   402  	// A list of readers to use in conjunction with UnreadByte.
   403  	var readers = []func(*Reader, byte) ([]byte, error){
   404  		(*Reader).ReadBytes,
   405  		(*Reader).ReadSlice,
   406  		func(r *Reader, delim byte) ([]byte, error) {
   407  			data, err := r.ReadString(delim)
   408  			return []byte(data), err
   409  		},
   410  		// ReadLine doesn't fit the data/pattern easily
   411  		// so we leave it out. It should be covered via
   412  		// the ReadSlice test since ReadLine simply calls
   413  		// ReadSlice, and it's that function that handles
   414  		// the last byte.
   415  	}
   416  
   417  	// Try all readers with UnreadByte.
   418  	for rno, read := range readers {
   419  		// Some input data that is longer than the minimum reader buffer size.
   420  		const n = 10
   421  		var buf bytes.Buffer
   422  		for i := 0; i < n; i++ {
   423  			buf.WriteString("abcdefg")
   424  		}
   425  
   426  		r := NewReaderSize(&buf, minReadBufferSize)
   427  		readTo := func(delim byte, want string) {
   428  			data, err := read(r, delim)
   429  			if err != nil {
   430  				t.Fatalf("#%d: unexpected error reading to %c: %v", rno, delim, err)
   431  			}
   432  			if got := string(data); got != want {
   433  				t.Fatalf("#%d: got %q, want %q", rno, got, want)
   434  			}
   435  		}
   436  
   437  		// Read the data with occasional UnreadByte calls.
   438  		for i := 0; i < n; i++ {
   439  			readTo('d', "abcd")
   440  			for j := 0; j < 3; j++ {
   441  				if err := r.UnreadByte(); err != nil {
   442  					t.Fatalf("#%d: unexpected error on UnreadByte: %v", rno, err)
   443  				}
   444  				readTo('d', "d")
   445  			}
   446  			readTo('g', "efg")
   447  		}
   448  
   449  		// All data should have been read.
   450  		_, err := r.ReadByte()
   451  		if err != io.EOF {
   452  			t.Errorf("#%d: got error %v; want EOF", rno, err)
   453  		}
   454  	}
   455  }
   456  
   457  // Test that UnreadRune fails if the preceding operation was not a ReadRune.
   458  func TestUnreadRuneError(t *testing.T) {
   459  	buf := make([]byte, 3) // All runes in this test are 3 bytes long
   460  	r := NewReader(&StringReader{data: []string{"日本語日本語日本語"}})
   461  	if r.UnreadRune() == nil {
   462  		t.Error("expected error on UnreadRune from fresh buffer")
   463  	}
   464  	_, _, err := r.ReadRune()
   465  	if err != nil {
   466  		t.Error("unexpected error on ReadRune (1):", err)
   467  	}
   468  	if err = r.UnreadRune(); err != nil {
   469  		t.Error("unexpected error on UnreadRune (1):", err)
   470  	}
   471  	if r.UnreadRune() == nil {
   472  		t.Error("expected error after UnreadRune (1)")
   473  	}
   474  	// Test error after Read.
   475  	_, _, err = r.ReadRune() // reset state
   476  	if err != nil {
   477  		t.Error("unexpected error on ReadRune (2):", err)
   478  	}
   479  	_, err = r.Read(buf)
   480  	if err != nil {
   481  		t.Error("unexpected error on Read (2):", err)
   482  	}
   483  	if r.UnreadRune() == nil {
   484  		t.Error("expected error after Read (2)")
   485  	}
   486  	// Test error after ReadByte.
   487  	_, _, err = r.ReadRune() // reset state
   488  	if err != nil {
   489  		t.Error("unexpected error on ReadRune (2):", err)
   490  	}
   491  	for range buf {
   492  		_, err = r.ReadByte()
   493  		if err != nil {
   494  			t.Error("unexpected error on ReadByte (2):", err)
   495  		}
   496  	}
   497  	if r.UnreadRune() == nil {
   498  		t.Error("expected error after ReadByte")
   499  	}
   500  	// Test error after UnreadByte.
   501  	_, _, err = r.ReadRune() // reset state
   502  	if err != nil {
   503  		t.Error("unexpected error on ReadRune (3):", err)
   504  	}
   505  	_, err = r.ReadByte()
   506  	if err != nil {
   507  		t.Error("unexpected error on ReadByte (3):", err)
   508  	}
   509  	err = r.UnreadByte()
   510  	if err != nil {
   511  		t.Error("unexpected error on UnreadByte (3):", err)
   512  	}
   513  	if r.UnreadRune() == nil {
   514  		t.Error("expected error after UnreadByte (3)")
   515  	}
   516  	// Test error after ReadSlice.
   517  	_, _, err = r.ReadRune() // reset state
   518  	if err != nil {
   519  		t.Error("unexpected error on ReadRune (4):", err)
   520  	}
   521  	_, err = r.ReadSlice(0)
   522  	if err != io.EOF {
   523  		t.Error("unexpected error on ReadSlice (4):", err)
   524  	}
   525  	if r.UnreadRune() == nil {
   526  		t.Error("expected error after ReadSlice (4)")
   527  	}
   528  }
   529  
   530  func TestUnreadRuneAtEOF(t *testing.T) {
   531  	// UnreadRune/ReadRune should error at EOF (was a bug; used to panic)
   532  	r := NewReader(strings.NewReader("x"))
   533  	r.ReadRune()
   534  	r.ReadRune()
   535  	r.UnreadRune()
   536  	_, _, err := r.ReadRune()
   537  	if err == nil {
   538  		t.Error("expected error at EOF")
   539  	} else if err != io.EOF {
   540  		t.Error("expected EOF; got", err)
   541  	}
   542  }
   543  
   544  func TestReadWriteRune(t *testing.T) {
   545  	const NRune = 1000
   546  	byteBuf := new(bytes.Buffer)
   547  	w := NewWriter(byteBuf)
   548  	// Write the runes out using WriteRune
   549  	buf := make([]byte, utf8.UTFMax)
   550  	for r := rune(0); r < NRune; r++ {
   551  		size := utf8.EncodeRune(buf, r)
   552  		nbytes, err := w.WriteRune(r)
   553  		if err != nil {
   554  			t.Fatalf("WriteRune(0x%x) error: %s", r, err)
   555  		}
   556  		if nbytes != size {
   557  			t.Fatalf("WriteRune(0x%x) expected %d, got %d", r, size, nbytes)
   558  		}
   559  	}
   560  	w.Flush()
   561  
   562  	r := NewReader(byteBuf)
   563  	// Read them back with ReadRune
   564  	for r1 := rune(0); r1 < NRune; r1++ {
   565  		size := utf8.EncodeRune(buf, r1)
   566  		nr, nbytes, err := r.ReadRune()
   567  		if nr != r1 || nbytes != size || err != nil {
   568  			t.Fatalf("ReadRune(0x%x) got 0x%x,%d not 0x%x,%d (err=%s)", r1, nr, nbytes, r1, size, err)
   569  		}
   570  	}
   571  }
   572  
   573  func TestWriteInvalidRune(t *testing.T) {
   574  	// Invalid runes, including negative ones, should be written as the
   575  	// replacement character.
   576  	for _, r := range []rune{-1, utf8.MaxRune + 1} {
   577  		var buf strings.Builder
   578  		w := NewWriter(&buf)
   579  		w.WriteRune(r)
   580  		w.Flush()
   581  		if s := buf.String(); s != "\uFFFD" {
   582  			t.Errorf("WriteRune(%d) wrote %q, not replacement character", r, s)
   583  		}
   584  	}
   585  }
   586  
   587  func TestReadStringAllocs(t *testing.T) {
   588  	r := strings.NewReader("       foo       foo        42        42        42        42        42        42        42        42       4.2       4.2       4.2       4.2\n")
   589  	buf := NewReader(r)
   590  	allocs := testing.AllocsPerRun(100, func() {
   591  		r.Seek(0, io.SeekStart)
   592  		buf.Reset(r)
   593  
   594  		_, err := buf.ReadString('\n')
   595  		if err != nil {
   596  			t.Fatal(err)
   597  		}
   598  	})
   599  	if allocs != 1 {
   600  		t.Errorf("Unexpected number of allocations, got %f, want 1", allocs)
   601  	}
   602  }
   603  
   604  func TestWriter(t *testing.T) {
   605  	var data [8192]byte
   606  
   607  	for i := 0; i < len(data); i++ {
   608  		data[i] = byte(' ' + i%('~'-' '))
   609  	}
   610  	w := new(bytes.Buffer)
   611  	for i := 0; i < len(bufsizes); i++ {
   612  		for j := 0; j < len(bufsizes); j++ {
   613  			nwrite := bufsizes[i]
   614  			bs := bufsizes[j]
   615  
   616  			// Write nwrite bytes using buffer size bs.
   617  			// Check that the right amount makes it out
   618  			// and that the data is correct.
   619  
   620  			w.Reset()
   621  			buf := NewWriterSize(w, bs)
   622  			context := fmt.Sprintf("nwrite=%d bufsize=%d", nwrite, bs)
   623  			n, e1 := buf.Write(data[0:nwrite])
   624  			if e1 != nil || n != nwrite {
   625  				t.Errorf("%s: buf.Write %d = %d, %v", context, nwrite, n, e1)
   626  				continue
   627  			}
   628  			if e := buf.Flush(); e != nil {
   629  				t.Errorf("%s: buf.Flush = %v", context, e)
   630  			}
   631  
   632  			written := w.Bytes()
   633  			if len(written) != nwrite {
   634  				t.Errorf("%s: %d bytes written", context, len(written))
   635  			}
   636  			for l := 0; l < len(written); l++ {
   637  				if written[l] != data[l] {
   638  					t.Errorf("wrong bytes written")
   639  					t.Errorf("want=%q", data[0:len(written)])
   640  					t.Errorf("have=%q", written)
   641  				}
   642  			}
   643  		}
   644  	}
   645  }
   646  
   647  func TestWriterAppend(t *testing.T) {
   648  	got := new(bytes.Buffer)
   649  	var want []byte
   650  	rn := rand.New(rand.NewSource(0))
   651  	w := NewWriterSize(got, 64)
   652  	for i := 0; i < 100; i++ {
   653  		// Obtain a buffer to append to.
   654  		b := w.AvailableBuffer()
   655  		if w.Available() != cap(b) {
   656  			t.Fatalf("Available() = %v, want %v", w.Available(), cap(b))
   657  		}
   658  
   659  		// While not recommended, it is valid to append to a shifted buffer.
   660  		// This forces Write to copy the input.
   661  		if rn.Intn(8) == 0 && cap(b) > 0 {
   662  			b = b[1:1:cap(b)]
   663  		}
   664  
   665  		// Append a random integer of varying width.
   666  		n := int64(rn.Intn(1 << rn.Intn(30)))
   667  		want = append(strconv.AppendInt(want, n, 10), ' ')
   668  		b = append(strconv.AppendInt(b, n, 10), ' ')
   669  		w.Write(b)
   670  	}
   671  	w.Flush()
   672  
   673  	if !bytes.Equal(got.Bytes(), want) {
   674  		t.Errorf("output mismatch:\ngot  %s\nwant %s", got.Bytes(), want)
   675  	}
   676  }
   677  
   678  // Check that write errors are returned properly.
   679  
   680  type errorWriterTest struct {
   681  	n, m   int
   682  	err    error
   683  	expect error
   684  }
   685  
   686  func (w errorWriterTest) Write(p []byte) (int, error) {
   687  	return len(p) * w.n / w.m, w.err
   688  }
   689  
   690  var errorWriterTests = []errorWriterTest{
   691  	{0, 1, nil, io.ErrShortWrite},
   692  	{1, 2, nil, io.ErrShortWrite},
   693  	{1, 1, nil, nil},
   694  	{0, 1, io.ErrClosedPipe, io.ErrClosedPipe},
   695  	{1, 2, io.ErrClosedPipe, io.ErrClosedPipe},
   696  	{1, 1, io.ErrClosedPipe, io.ErrClosedPipe},
   697  }
   698  
   699  func TestWriteErrors(t *testing.T) {
   700  	for _, w := range errorWriterTests {
   701  		buf := NewWriter(w)
   702  		_, e := buf.Write([]byte("hello world"))
   703  		if e != nil {
   704  			t.Errorf("Write hello to %v: %v", w, e)
   705  			continue
   706  		}
   707  		// Two flushes, to verify the error is sticky.
   708  		for i := 0; i < 2; i++ {
   709  			e = buf.Flush()
   710  			if e != w.expect {
   711  				t.Errorf("Flush %d/2 %v: got %v, wanted %v", i+1, w, e, w.expect)
   712  			}
   713  		}
   714  	}
   715  }
   716  
   717  func TestNewReaderSizeIdempotent(t *testing.T) {
   718  	const BufSize = 1000
   719  	b := NewReaderSize(strings.NewReader("hello world"), BufSize)
   720  	// Does it recognize itself?
   721  	b1 := NewReaderSize(b, BufSize)
   722  	if b1 != b {
   723  		t.Error("NewReaderSize did not detect underlying Reader")
   724  	}
   725  	// Does it wrap if existing buffer is too small?
   726  	b2 := NewReaderSize(b, 2*BufSize)
   727  	if b2 == b {
   728  		t.Error("NewReaderSize did not enlarge buffer")
   729  	}
   730  }
   731  
   732  func TestNewWriterSizeIdempotent(t *testing.T) {
   733  	const BufSize = 1000
   734  	b := NewWriterSize(new(bytes.Buffer), BufSize)
   735  	// Does it recognize itself?
   736  	b1 := NewWriterSize(b, BufSize)
   737  	if b1 != b {
   738  		t.Error("NewWriterSize did not detect underlying Writer")
   739  	}
   740  	// Does it wrap if existing buffer is too small?
   741  	b2 := NewWriterSize(b, 2*BufSize)
   742  	if b2 == b {
   743  		t.Error("NewWriterSize did not enlarge buffer")
   744  	}
   745  }
   746  
   747  func TestWriteString(t *testing.T) {
   748  	const BufSize = 8
   749  	buf := new(strings.Builder)
   750  	b := NewWriterSize(buf, BufSize)
   751  	b.WriteString("0")                         // easy
   752  	b.WriteString("123456")                    // still easy
   753  	b.WriteString("7890")                      // easy after flush
   754  	b.WriteString("abcdefghijklmnopqrstuvwxy") // hard
   755  	b.WriteString("z")
   756  	if err := b.Flush(); err != nil {
   757  		t.Error("WriteString", err)
   758  	}
   759  	s := "01234567890abcdefghijklmnopqrstuvwxyz"
   760  	if buf.String() != s {
   761  		t.Errorf("WriteString wants %q gets %q", s, buf.String())
   762  	}
   763  }
   764  
   765  func TestWriteStringStringWriter(t *testing.T) {
   766  	const BufSize = 8
   767  	{
   768  		tw := &teststringwriter{}
   769  		b := NewWriterSize(tw, BufSize)
   770  		b.WriteString("1234")
   771  		tw.check(t, "", "")
   772  		b.WriteString("56789012")   // longer than BufSize
   773  		tw.check(t, "12345678", "") // but not enough (after filling the partially-filled buffer)
   774  		b.Flush()
   775  		tw.check(t, "123456789012", "")
   776  	}
   777  	{
   778  		tw := &teststringwriter{}
   779  		b := NewWriterSize(tw, BufSize)
   780  		b.WriteString("123456789")   // long string, empty buffer:
   781  		tw.check(t, "", "123456789") // use WriteString
   782  	}
   783  	{
   784  		tw := &teststringwriter{}
   785  		b := NewWriterSize(tw, BufSize)
   786  		b.WriteString("abc")
   787  		tw.check(t, "", "")
   788  		b.WriteString("123456789012345")      // long string, non-empty buffer
   789  		tw.check(t, "abc12345", "6789012345") // use Write and then WriteString since the remaining part is still longer than BufSize
   790  	}
   791  	{
   792  		tw := &teststringwriter{}
   793  		b := NewWriterSize(tw, BufSize)
   794  		b.Write([]byte("abc")) // same as above, but use Write instead of WriteString
   795  		tw.check(t, "", "")
   796  		b.WriteString("123456789012345")
   797  		tw.check(t, "abc12345", "6789012345") // same as above
   798  	}
   799  }
   800  
   801  type teststringwriter struct {
   802  	write       string
   803  	writeString string
   804  }
   805  
   806  func (w *teststringwriter) Write(b []byte) (int, error) {
   807  	w.write += string(b)
   808  	return len(b), nil
   809  }
   810  
   811  func (w *teststringwriter) WriteString(s string) (int, error) {
   812  	w.writeString += s
   813  	return len(s), nil
   814  }
   815  
   816  func (w *teststringwriter) check(t *testing.T, write, writeString string) {
   817  	t.Helper()
   818  	if w.write != write {
   819  		t.Errorf("write: expected %q, got %q", write, w.write)
   820  	}
   821  	if w.writeString != writeString {
   822  		t.Errorf("writeString: expected %q, got %q", writeString, w.writeString)
   823  	}
   824  }
   825  
   826  func TestBufferFull(t *testing.T) {
   827  	const longString = "And now, hello, world! It is the time for all good men to come to the aid of their party"
   828  	buf := NewReaderSize(strings.NewReader(longString), minReadBufferSize)
   829  	line, err := buf.ReadSlice('!')
   830  	if string(line) != "And now, hello, " || err != ErrBufferFull {
   831  		t.Errorf("first ReadSlice(,) = %q, %v", line, err)
   832  	}
   833  	line, err = buf.ReadSlice('!')
   834  	if string(line) != "world!" || err != nil {
   835  		t.Errorf("second ReadSlice(,) = %q, %v", line, err)
   836  	}
   837  }
   838  
   839  func TestPeek(t *testing.T) {
   840  	p := make([]byte, 10)
   841  	// string is 16 (minReadBufferSize) long.
   842  	buf := NewReaderSize(strings.NewReader("abcdefghijklmnop"), minReadBufferSize)
   843  	if s, err := buf.Peek(1); string(s) != "a" || err != nil {
   844  		t.Fatalf("want %q got %q, err=%v", "a", string(s), err)
   845  	}
   846  	if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
   847  		t.Fatalf("want %q got %q, err=%v", "abcd", string(s), err)
   848  	}
   849  	if _, err := buf.Peek(-1); err != ErrNegativeCount {
   850  		t.Fatalf("want ErrNegativeCount got %v", err)
   851  	}
   852  	if s, err := buf.Peek(32); string(s) != "abcdefghijklmnop" || err != ErrBufferFull {
   853  		t.Fatalf("want %q, ErrBufFull got %q, err=%v", "abcdefghijklmnop", string(s), err)
   854  	}
   855  	if _, err := buf.Read(p[0:3]); string(p[0:3]) != "abc" || err != nil {
   856  		t.Fatalf("want %q got %q, err=%v", "abc", string(p[0:3]), err)
   857  	}
   858  	if s, err := buf.Peek(1); string(s) != "d" || err != nil {
   859  		t.Fatalf("want %q got %q, err=%v", "d", string(s), err)
   860  	}
   861  	if s, err := buf.Peek(2); string(s) != "de" || err != nil {
   862  		t.Fatalf("want %q got %q, err=%v", "de", string(s), err)
   863  	}
   864  	if _, err := buf.Read(p[0:3]); string(p[0:3]) != "def" || err != nil {
   865  		t.Fatalf("want %q got %q, err=%v", "def", string(p[0:3]), err)
   866  	}
   867  	if s, err := buf.Peek(4); string(s) != "ghij" || err != nil {
   868  		t.Fatalf("want %q got %q, err=%v", "ghij", string(s), err)
   869  	}
   870  	if _, err := buf.Read(p[0:]); string(p[0:]) != "ghijklmnop" || err != nil {
   871  		t.Fatalf("want %q got %q, err=%v", "ghijklmnop", string(p[0:minReadBufferSize]), err)
   872  	}
   873  	if s, err := buf.Peek(0); string(s) != "" || err != nil {
   874  		t.Fatalf("want %q got %q, err=%v", "", string(s), err)
   875  	}
   876  	if _, err := buf.Peek(1); err != io.EOF {
   877  		t.Fatalf("want EOF got %v", err)
   878  	}
   879  
   880  	// Test for issue 3022, not exposing a reader's error on a successful Peek.
   881  	buf = NewReaderSize(dataAndEOFReader("abcd"), 32)
   882  	if s, err := buf.Peek(2); string(s) != "ab" || err != nil {
   883  		t.Errorf(`Peek(2) on "abcd", EOF = %q, %v; want "ab", nil`, string(s), err)
   884  	}
   885  	if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
   886  		t.Errorf(`Peek(4) on "abcd", EOF = %q, %v; want "abcd", nil`, string(s), err)
   887  	}
   888  	if n, err := buf.Read(p[0:5]); string(p[0:n]) != "abcd" || err != nil {
   889  		t.Fatalf("Read after peek = %q, %v; want abcd, EOF", p[0:n], err)
   890  	}
   891  	if n, err := buf.Read(p[0:1]); string(p[0:n]) != "" || err != io.EOF {
   892  		t.Fatalf(`second Read after peek = %q, %v; want "", EOF`, p[0:n], err)
   893  	}
   894  }
   895  
   896  type dataAndEOFReader string
   897  
   898  func (r dataAndEOFReader) Read(p []byte) (int, error) {
   899  	return copy(p, r), io.EOF
   900  }
   901  
   902  func TestPeekThenUnreadRune(t *testing.T) {
   903  	// This sequence used to cause a crash.
   904  	r := NewReader(strings.NewReader("x"))
   905  	r.ReadRune()
   906  	r.Peek(1)
   907  	r.UnreadRune()
   908  	r.ReadRune() // Used to panic here
   909  }
   910  
   911  var testOutput = []byte("0123456789abcdefghijklmnopqrstuvwxy")
   912  var testInput = []byte("012\n345\n678\n9ab\ncde\nfgh\nijk\nlmn\nopq\nrst\nuvw\nxy")
   913  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")
   914  
   915  // TestReader wraps a []byte and returns reads of a specific length.
   916  type testReader struct {
   917  	data   []byte
   918  	stride int
   919  }
   920  
   921  func (t *testReader) Read(buf []byte) (n int, err error) {
   922  	n = t.stride
   923  	if n > len(t.data) {
   924  		n = len(t.data)
   925  	}
   926  	if n > len(buf) {
   927  		n = len(buf)
   928  	}
   929  	copy(buf, t.data)
   930  	t.data = t.data[n:]
   931  	if len(t.data) == 0 {
   932  		err = io.EOF
   933  	}
   934  	return
   935  }
   936  
   937  func testReadLine(t *testing.T, input []byte) {
   938  	//for stride := 1; stride < len(input); stride++ {
   939  	for stride := 1; stride < 2; stride++ {
   940  		done := 0
   941  		reader := testReader{input, stride}
   942  		l := NewReaderSize(&reader, len(input)+1)
   943  		for {
   944  			line, isPrefix, err := l.ReadLine()
   945  			if len(line) > 0 && err != nil {
   946  				t.Errorf("ReadLine returned both data and error: %s", err)
   947  			}
   948  			if isPrefix {
   949  				t.Errorf("ReadLine returned prefix")
   950  			}
   951  			if err != nil {
   952  				if err != io.EOF {
   953  					t.Fatalf("Got unknown error: %s", err)
   954  				}
   955  				break
   956  			}
   957  			if want := testOutput[done : done+len(line)]; !bytes.Equal(want, line) {
   958  				t.Errorf("Bad line at stride %d: want: %x got: %x", stride, want, line)
   959  			}
   960  			done += len(line)
   961  		}
   962  		if done != len(testOutput) {
   963  			t.Errorf("ReadLine didn't return everything: got: %d, want: %d (stride: %d)", done, len(testOutput), stride)
   964  		}
   965  	}
   966  }
   967  
   968  func TestReadLine(t *testing.T) {
   969  	testReadLine(t, testInput)
   970  	testReadLine(t, testInputrn)
   971  }
   972  
   973  func TestLineTooLong(t *testing.T) {
   974  	data := make([]byte, 0)
   975  	for i := 0; i < minReadBufferSize*5/2; i++ {
   976  		data = append(data, '0'+byte(i%10))
   977  	}
   978  	buf := bytes.NewReader(data)
   979  	l := NewReaderSize(buf, minReadBufferSize)
   980  	line, isPrefix, err := l.ReadLine()
   981  	if !isPrefix || !bytes.Equal(line, data[:minReadBufferSize]) || err != nil {
   982  		t.Errorf("bad result for first line: got %q want %q %v", line, data[:minReadBufferSize], err)
   983  	}
   984  	data = data[len(line):]
   985  	line, isPrefix, err = l.ReadLine()
   986  	if !isPrefix || !bytes.Equal(line, data[:minReadBufferSize]) || err != nil {
   987  		t.Errorf("bad result for second line: got %q want %q %v", line, data[:minReadBufferSize], err)
   988  	}
   989  	data = data[len(line):]
   990  	line, isPrefix, err = l.ReadLine()
   991  	if isPrefix || !bytes.Equal(line, data[:minReadBufferSize/2]) || err != nil {
   992  		t.Errorf("bad result for third line: got %q want %q %v", line, data[:minReadBufferSize/2], err)
   993  	}
   994  	line, isPrefix, err = l.ReadLine()
   995  	if isPrefix || err == nil {
   996  		t.Errorf("expected no more lines: %x %s", line, err)
   997  	}
   998  }
   999  
  1000  func TestReadAfterLines(t *testing.T) {
  1001  	line1 := "this is line1"
  1002  	restData := "this is line2\nthis is line 3\n"
  1003  	inbuf := bytes.NewReader([]byte(line1 + "\n" + restData))
  1004  	outbuf := new(strings.Builder)
  1005  	maxLineLength := len(line1) + len(restData)/2
  1006  	l := NewReaderSize(inbuf, maxLineLength)
  1007  	line, isPrefix, err := l.ReadLine()
  1008  	if isPrefix || err != nil || string(line) != line1 {
  1009  		t.Errorf("bad result for first line: isPrefix=%v err=%v line=%q", isPrefix, err, string(line))
  1010  	}
  1011  	n, err := io.Copy(outbuf, l)
  1012  	if int(n) != len(restData) || err != nil {
  1013  		t.Errorf("bad result for Read: n=%d err=%v", n, err)
  1014  	}
  1015  	if outbuf.String() != restData {
  1016  		t.Errorf("bad result for Read: got %q; expected %q", outbuf.String(), restData)
  1017  	}
  1018  }
  1019  
  1020  func TestReadEmptyBuffer(t *testing.T) {
  1021  	l := NewReaderSize(new(bytes.Buffer), minReadBufferSize)
  1022  	line, isPrefix, err := l.ReadLine()
  1023  	if err != io.EOF {
  1024  		t.Errorf("expected EOF from ReadLine, got '%s' %t %s", line, isPrefix, err)
  1025  	}
  1026  }
  1027  
  1028  func TestLinesAfterRead(t *testing.T) {
  1029  	l := NewReaderSize(bytes.NewReader([]byte("foo")), minReadBufferSize)
  1030  	_, err := io.ReadAll(l)
  1031  	if err != nil {
  1032  		t.Error(err)
  1033  		return
  1034  	}
  1035  
  1036  	line, isPrefix, err := l.ReadLine()
  1037  	if err != io.EOF {
  1038  		t.Errorf("expected EOF from ReadLine, got '%s' %t %s", line, isPrefix, err)
  1039  	}
  1040  }
  1041  
  1042  func TestReadLineNonNilLineOrError(t *testing.T) {
  1043  	r := NewReader(strings.NewReader("line 1\n"))
  1044  	for i := 0; i < 2; i++ {
  1045  		l, _, err := r.ReadLine()
  1046  		if l != nil && err != nil {
  1047  			t.Fatalf("on line %d/2; ReadLine=%#v, %v; want non-nil line or Error, but not both",
  1048  				i+1, l, err)
  1049  		}
  1050  	}
  1051  }
  1052  
  1053  type readLineResult struct {
  1054  	line     []byte
  1055  	isPrefix bool
  1056  	err      error
  1057  }
  1058  
  1059  var readLineNewlinesTests = []struct {
  1060  	input  string
  1061  	expect []readLineResult
  1062  }{
  1063  	{"012345678901234\r\n012345678901234\r\n", []readLineResult{
  1064  		{[]byte("012345678901234"), true, nil},
  1065  		{nil, false, nil},
  1066  		{[]byte("012345678901234"), true, nil},
  1067  		{nil, false, nil},
  1068  		{nil, false, io.EOF},
  1069  	}},
  1070  	{"0123456789012345\r012345678901234\r", []readLineResult{
  1071  		{[]byte("0123456789012345"), true, nil},
  1072  		{[]byte("\r012345678901234"), true, nil},
  1073  		{[]byte("\r"), false, nil},
  1074  		{nil, false, io.EOF},
  1075  	}},
  1076  }
  1077  
  1078  func TestReadLineNewlines(t *testing.T) {
  1079  	for _, e := range readLineNewlinesTests {
  1080  		testReadLineNewlines(t, e.input, e.expect)
  1081  	}
  1082  }
  1083  
  1084  func testReadLineNewlines(t *testing.T, input string, expect []readLineResult) {
  1085  	b := NewReaderSize(strings.NewReader(input), minReadBufferSize)
  1086  	for i, e := range expect {
  1087  		line, isPrefix, err := b.ReadLine()
  1088  		if !bytes.Equal(line, e.line) {
  1089  			t.Errorf("%q call %d, line == %q, want %q", input, i, line, e.line)
  1090  			return
  1091  		}
  1092  		if isPrefix != e.isPrefix {
  1093  			t.Errorf("%q call %d, isPrefix == %v, want %v", input, i, isPrefix, e.isPrefix)
  1094  			return
  1095  		}
  1096  		if err != e.err {
  1097  			t.Errorf("%q call %d, err == %v, want %v", input, i, err, e.err)
  1098  			return
  1099  		}
  1100  	}
  1101  }
  1102  
  1103  func createTestInput(n int) []byte {
  1104  	input := make([]byte, n)
  1105  	for i := range input {
  1106  		// 101 and 251 are arbitrary prime numbers.
  1107  		// The idea is to create an input sequence
  1108  		// which doesn't repeat too frequently.
  1109  		input[i] = byte(i % 251)
  1110  		if i%101 == 0 {
  1111  			input[i] ^= byte(i / 101)
  1112  		}
  1113  	}
  1114  	return input
  1115  }
  1116  
  1117  func TestReaderWriteTo(t *testing.T) {
  1118  	input := createTestInput(8192)
  1119  	r := NewReader(onlyReader{bytes.NewReader(input)})
  1120  	w := new(bytes.Buffer)
  1121  	if n, err := r.WriteTo(w); err != nil || n != int64(len(input)) {
  1122  		t.Fatalf("r.WriteTo(w) = %d, %v, want %d, nil", n, err, len(input))
  1123  	}
  1124  
  1125  	for i, val := range w.Bytes() {
  1126  		if val != input[i] {
  1127  			t.Errorf("after write: out[%d] = %#x, want %#x", i, val, input[i])
  1128  		}
  1129  	}
  1130  }
  1131  
  1132  type errorWriterToTest struct {
  1133  	rn, wn     int
  1134  	rerr, werr error
  1135  	expected   error
  1136  }
  1137  
  1138  func (r errorWriterToTest) Read(p []byte) (int, error) {
  1139  	return len(p) * r.rn, r.rerr
  1140  }
  1141  
  1142  func (w errorWriterToTest) Write(p []byte) (int, error) {
  1143  	return len(p) * w.wn, w.werr
  1144  }
  1145  
  1146  var errorWriterToTests = []errorWriterToTest{
  1147  	{1, 0, nil, io.ErrClosedPipe, io.ErrClosedPipe},
  1148  	{0, 1, io.ErrClosedPipe, nil, io.ErrClosedPipe},
  1149  	{0, 0, io.ErrUnexpectedEOF, io.ErrClosedPipe, io.ErrClosedPipe},
  1150  	{0, 1, io.EOF, nil, nil},
  1151  }
  1152  
  1153  func TestReaderWriteToErrors(t *testing.T) {
  1154  	for i, rw := range errorWriterToTests {
  1155  		r := NewReader(rw)
  1156  		if _, err := r.WriteTo(rw); err != rw.expected {
  1157  			t.Errorf("r.WriteTo(errorWriterToTests[%d]) = _, %v, want _,%v", i, err, rw.expected)
  1158  		}
  1159  	}
  1160  }
  1161  
  1162  func TestWriterReadFrom(t *testing.T) {
  1163  	ws := []func(io.Writer) io.Writer{
  1164  		func(w io.Writer) io.Writer { return onlyWriter{w} },
  1165  		func(w io.Writer) io.Writer { return w },
  1166  	}
  1167  
  1168  	rs := []func(io.Reader) io.Reader{
  1169  		iotest.DataErrReader,
  1170  		func(r io.Reader) io.Reader { return r },
  1171  	}
  1172  
  1173  	for ri, rfunc := range rs {
  1174  		for wi, wfunc := range ws {
  1175  			input := createTestInput(8192)
  1176  			b := new(strings.Builder)
  1177  			w := NewWriter(wfunc(b))
  1178  			r := rfunc(bytes.NewReader(input))
  1179  			if n, err := w.ReadFrom(r); err != nil || n != int64(len(input)) {
  1180  				t.Errorf("ws[%d],rs[%d]: w.ReadFrom(r) = %d, %v, want %d, nil", wi, ri, n, err, len(input))
  1181  				continue
  1182  			}
  1183  			if err := w.Flush(); err != nil {
  1184  				t.Errorf("Flush returned %v", err)
  1185  				continue
  1186  			}
  1187  			if got, want := b.String(), string(input); got != want {
  1188  				t.Errorf("ws[%d], rs[%d]:\ngot  %q\nwant %q\n", wi, ri, got, want)
  1189  			}
  1190  		}
  1191  	}
  1192  }
  1193  
  1194  type errorReaderFromTest struct {
  1195  	rn, wn     int
  1196  	rerr, werr error
  1197  	expected   error
  1198  }
  1199  
  1200  func (r errorReaderFromTest) Read(p []byte) (int, error) {
  1201  	return len(p) * r.rn, r.rerr
  1202  }
  1203  
  1204  func (w errorReaderFromTest) Write(p []byte) (int, error) {
  1205  	return len(p) * w.wn, w.werr
  1206  }
  1207  
  1208  var errorReaderFromTests = []errorReaderFromTest{
  1209  	{0, 1, io.EOF, nil, nil},
  1210  	{1, 1, io.EOF, nil, nil},
  1211  	{0, 1, io.ErrClosedPipe, nil, io.ErrClosedPipe},
  1212  	{0, 0, io.ErrClosedPipe, io.ErrShortWrite, io.ErrClosedPipe},
  1213  	{1, 0, nil, io.ErrShortWrite, io.ErrShortWrite},
  1214  }
  1215  
  1216  func TestWriterReadFromErrors(t *testing.T) {
  1217  	for i, rw := range errorReaderFromTests {
  1218  		w := NewWriter(rw)
  1219  		if _, err := w.ReadFrom(rw); err != rw.expected {
  1220  			t.Errorf("w.ReadFrom(errorReaderFromTests[%d]) = _, %v, want _,%v", i, err, rw.expected)
  1221  		}
  1222  	}
  1223  }
  1224  
  1225  // TestWriterReadFromCounts tests that using io.Copy to copy into a
  1226  // bufio.Writer does not prematurely flush the buffer. For example, when
  1227  // buffering writes to a network socket, excessive network writes should be
  1228  // avoided.
  1229  func TestWriterReadFromCounts(t *testing.T) {
  1230  	var w0 writeCountingDiscard
  1231  	b0 := NewWriterSize(&w0, 1234)
  1232  	b0.WriteString(strings.Repeat("x", 1000))
  1233  	if w0 != 0 {
  1234  		t.Fatalf("write 1000 'x's: got %d writes, want 0", w0)
  1235  	}
  1236  	b0.WriteString(strings.Repeat("x", 200))
  1237  	if w0 != 0 {
  1238  		t.Fatalf("write 1200 'x's: got %d writes, want 0", w0)
  1239  	}
  1240  	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 30))})
  1241  	if w0 != 0 {
  1242  		t.Fatalf("write 1230 'x's: got %d writes, want 0", w0)
  1243  	}
  1244  	io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 9))})
  1245  	if w0 != 1 {
  1246  		t.Fatalf("write 1239 'x's: got %d writes, want 1", w0)
  1247  	}
  1248  
  1249  	var w1 writeCountingDiscard
  1250  	b1 := NewWriterSize(&w1, 1234)
  1251  	b1.WriteString(strings.Repeat("x", 1200))
  1252  	b1.Flush()
  1253  	if w1 != 1 {
  1254  		t.Fatalf("flush 1200 'x's: got %d writes, want 1", w1)
  1255  	}
  1256  	b1.WriteString(strings.Repeat("x", 89))
  1257  	if w1 != 1 {
  1258  		t.Fatalf("write 1200 + 89 'x's: got %d writes, want 1", w1)
  1259  	}
  1260  	io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 700))})
  1261  	if w1 != 1 {
  1262  		t.Fatalf("write 1200 + 789 'x's: got %d writes, want 1", w1)
  1263  	}
  1264  	io.Copy(b1, onlyReader{strings.NewReader(strings.Repeat("x", 600))})
  1265  	if w1 != 2 {
  1266  		t.Fatalf("write 1200 + 1389 'x's: got %d writes, want 2", w1)
  1267  	}
  1268  	b1.Flush()
  1269  	if w1 != 3 {
  1270  		t.Fatalf("flush 1200 + 1389 'x's: got %d writes, want 3", w1)
  1271  	}
  1272  }
  1273  
  1274  // A writeCountingDiscard is like io.Discard and counts the number of times
  1275  // Write is called on it.
  1276  type writeCountingDiscard int
  1277  
  1278  func (w *writeCountingDiscard) Write(p []byte) (int, error) {
  1279  	*w++
  1280  	return len(p), nil
  1281  }
  1282  
  1283  type negativeReader int
  1284  
  1285  func (r *negativeReader) Read([]byte) (int, error) { return -1, nil }
  1286  
  1287  func TestNegativeRead(t *testing.T) {
  1288  	// should panic with a description pointing at the reader, not at itself.
  1289  	// (should NOT panic with slice index error, for example.)
  1290  	b := NewReader(new(negativeReader))
  1291  	defer func() {
  1292  		switch err := recover().(type) {
  1293  		case nil:
  1294  			t.Fatal("read did not panic")
  1295  		case error:
  1296  			if !strings.Contains(err.Error(), "reader returned negative count from Read") {
  1297  				t.Fatalf("wrong panic: %v", err)
  1298  			}
  1299  		default:
  1300  			t.Fatalf("unexpected panic value: %T(%v)", err, err)
  1301  		}
  1302  	}()
  1303  	b.Read(make([]byte, 100))
  1304  }
  1305  
  1306  var errFake = errors.New("fake error")
  1307  
  1308  type errorThenGoodReader struct {
  1309  	didErr bool
  1310  	nread  int
  1311  }
  1312  
  1313  func (r *errorThenGoodReader) Read(p []byte) (int, error) {
  1314  	r.nread++
  1315  	if !r.didErr {
  1316  		r.didErr = true
  1317  		return 0, errFake
  1318  	}
  1319  	return len(p), nil
  1320  }
  1321  
  1322  func TestReaderClearError(t *testing.T) {
  1323  	r := &errorThenGoodReader{}
  1324  	b := NewReader(r)
  1325  	buf := make([]byte, 1)
  1326  	if _, err := b.Read(nil); err != nil {
  1327  		t.Fatalf("1st nil Read = %v; want nil", err)
  1328  	}
  1329  	if _, err := b.Read(buf); err != errFake {
  1330  		t.Fatalf("1st Read = %v; want errFake", err)
  1331  	}
  1332  	if _, err := b.Read(nil); err != nil {
  1333  		t.Fatalf("2nd nil Read = %v; want nil", err)
  1334  	}
  1335  	if _, err := b.Read(buf); err != nil {
  1336  		t.Fatalf("3rd Read with buffer = %v; want nil", err)
  1337  	}
  1338  	if r.nread != 2 {
  1339  		t.Errorf("num reads = %d; want 2", r.nread)
  1340  	}
  1341  }
  1342  
  1343  // Test for golang.org/issue/5947
  1344  func TestWriterReadFromWhileFull(t *testing.T) {
  1345  	buf := new(bytes.Buffer)
  1346  	w := NewWriterSize(buf, 10)
  1347  
  1348  	// Fill buffer exactly.
  1349  	n, err := w.Write([]byte("0123456789"))
  1350  	if n != 10 || err != nil {
  1351  		t.Fatalf("Write returned (%v, %v), want (10, nil)", n, err)
  1352  	}
  1353  
  1354  	// Use ReadFrom to read in some data.
  1355  	n2, err := w.ReadFrom(strings.NewReader("abcdef"))
  1356  	if n2 != 6 || err != nil {
  1357  		t.Fatalf("ReadFrom returned (%v, %v), want (6, nil)", n2, err)
  1358  	}
  1359  }
  1360  
  1361  type emptyThenNonEmptyReader struct {
  1362  	r io.Reader
  1363  	n int
  1364  }
  1365  
  1366  func (r *emptyThenNonEmptyReader) Read(p []byte) (int, error) {
  1367  	if r.n <= 0 {
  1368  		return r.r.Read(p)
  1369  	}
  1370  	r.n--
  1371  	return 0, nil
  1372  }
  1373  
  1374  // Test for golang.org/issue/7611
  1375  func TestWriterReadFromUntilEOF(t *testing.T) {
  1376  	buf := new(bytes.Buffer)
  1377  	w := NewWriterSize(buf, 5)
  1378  
  1379  	// Partially fill buffer
  1380  	n, err := w.Write([]byte("0123"))
  1381  	if n != 4 || err != nil {
  1382  		t.Fatalf("Write returned (%v, %v), want (4, nil)", n, err)
  1383  	}
  1384  
  1385  	// Use ReadFrom to read in some data.
  1386  	r := &emptyThenNonEmptyReader{r: strings.NewReader("abcd"), n: 3}
  1387  	n2, err := w.ReadFrom(r)
  1388  	if n2 != 4 || err != nil {
  1389  		t.Fatalf("ReadFrom returned (%v, %v), want (4, nil)", n2, err)
  1390  	}
  1391  	w.Flush()
  1392  	if got, want := buf.String(), "0123abcd"; got != want {
  1393  		t.Fatalf("buf.Bytes() returned %q, want %q", got, want)
  1394  	}
  1395  }
  1396  
  1397  func TestWriterReadFromErrNoProgress(t *testing.T) {
  1398  	buf := new(bytes.Buffer)
  1399  	w := NewWriterSize(buf, 5)
  1400  
  1401  	// Partially fill buffer
  1402  	n, err := w.Write([]byte("0123"))
  1403  	if n != 4 || err != nil {
  1404  		t.Fatalf("Write returned (%v, %v), want (4, nil)", n, err)
  1405  	}
  1406  
  1407  	// Use ReadFrom to read in some data.
  1408  	r := &emptyThenNonEmptyReader{r: strings.NewReader("abcd"), n: 100}
  1409  	n2, err := w.ReadFrom(r)
  1410  	if n2 != 0 || err != io.ErrNoProgress {
  1411  		t.Fatalf("buf.Bytes() returned (%v, %v), want (0, io.ErrNoProgress)", n2, err)
  1412  	}
  1413  }
  1414  
  1415  type readFromWriter struct {
  1416  	buf           []byte
  1417  	writeBytes    int
  1418  	readFromBytes int
  1419  }
  1420  
  1421  func (w *readFromWriter) Write(p []byte) (int, error) {
  1422  	w.buf = append(w.buf, p...)
  1423  	w.writeBytes += len(p)
  1424  	return len(p), nil
  1425  }
  1426  
  1427  func (w *readFromWriter) ReadFrom(r io.Reader) (int64, error) {
  1428  	b, err := io.ReadAll(r)
  1429  	w.buf = append(w.buf, b...)
  1430  	w.readFromBytes += len(b)
  1431  	return int64(len(b)), err
  1432  }
  1433  
  1434  // Test that calling (*Writer).ReadFrom with a partially-filled buffer
  1435  // fills the buffer before switching over to ReadFrom.
  1436  func TestWriterReadFromWithBufferedData(t *testing.T) {
  1437  	const bufsize = 16
  1438  
  1439  	input := createTestInput(64)
  1440  	rfw := &readFromWriter{}
  1441  	w := NewWriterSize(rfw, bufsize)
  1442  
  1443  	const writeSize = 8
  1444  	if n, err := w.Write(input[:writeSize]); n != writeSize || err != nil {
  1445  		t.Errorf("w.Write(%v bytes) = %v, %v; want %v, nil", writeSize, n, err, writeSize)
  1446  	}
  1447  	n, err := w.ReadFrom(bytes.NewReader(input[writeSize:]))
  1448  	if wantn := len(input[writeSize:]); int(n) != wantn || err != nil {
  1449  		t.Errorf("io.Copy(w, %v bytes) = %v, %v; want %v, nil", wantn, n, err, wantn)
  1450  	}
  1451  	if err := w.Flush(); err != nil {
  1452  		t.Errorf("w.Flush() = %v, want nil", err)
  1453  	}
  1454  
  1455  	if got, want := rfw.writeBytes, bufsize; got != want {
  1456  		t.Errorf("wrote %v bytes with Write, want %v", got, want)
  1457  	}
  1458  	if got, want := rfw.readFromBytes, len(input)-bufsize; got != want {
  1459  		t.Errorf("wrote %v bytes with ReadFrom, want %v", got, want)
  1460  	}
  1461  }
  1462  
  1463  func TestReadZero(t *testing.T) {
  1464  	for _, size := range []int{100, 2} {
  1465  		t.Run(fmt.Sprintf("bufsize=%d", size), func(t *testing.T) {
  1466  			r := io.MultiReader(strings.NewReader("abc"), &emptyThenNonEmptyReader{r: strings.NewReader("def"), n: 1})
  1467  			br := NewReaderSize(r, size)
  1468  			want := func(s string, wantErr error) {
  1469  				p := make([]byte, 50)
  1470  				n, err := br.Read(p)
  1471  				if err != wantErr || n != len(s) || string(p[:n]) != s {
  1472  					t.Fatalf("read(%d) = %q, %v, want %q, %v", len(p), string(p[:n]), err, s, wantErr)
  1473  				}
  1474  				t.Logf("read(%d) = %q, %v", len(p), string(p[:n]), err)
  1475  			}
  1476  			want("abc", nil)
  1477  			want("", nil)
  1478  			want("def", nil)
  1479  			want("", io.EOF)
  1480  		})
  1481  	}
  1482  }
  1483  
  1484  func TestReaderReset(t *testing.T) {
  1485  	checkAll := func(r *Reader, want string) {
  1486  		t.Helper()
  1487  		all, err := io.ReadAll(r)
  1488  		if err != nil {
  1489  			t.Fatal(err)
  1490  		}
  1491  		if string(all) != want {
  1492  			t.Errorf("ReadAll returned %q, want %q", all, want)
  1493  		}
  1494  	}
  1495  
  1496  	r := NewReader(strings.NewReader("foo foo"))
  1497  	buf := make([]byte, 3)
  1498  	r.Read(buf)
  1499  	if string(buf) != "foo" {
  1500  		t.Errorf("buf = %q; want foo", buf)
  1501  	}
  1502  
  1503  	r.Reset(strings.NewReader("bar bar"))
  1504  	checkAll(r, "bar bar")
  1505  
  1506  	*r = Reader{} // zero out the Reader
  1507  	r.Reset(strings.NewReader("bar bar"))
  1508  	checkAll(r, "bar bar")
  1509  
  1510  	// Wrap a reader and then Reset to that reader.
  1511  	r.Reset(strings.NewReader("recur"))
  1512  	r2 := NewReader(r)
  1513  	checkAll(r2, "recur")
  1514  	r.Reset(strings.NewReader("recur2"))
  1515  	r2.Reset(r)
  1516  	checkAll(r2, "recur2")
  1517  }
  1518  
  1519  func TestWriterReset(t *testing.T) {
  1520  	var buf1, buf2, buf3, buf4, buf5 strings.Builder
  1521  	w := NewWriter(&buf1)
  1522  	w.WriteString("foo")
  1523  
  1524  	w.Reset(&buf2) // and not flushed
  1525  	w.WriteString("bar")
  1526  	w.Flush()
  1527  	if buf1.String() != "" {
  1528  		t.Errorf("buf1 = %q; want empty", buf1.String())
  1529  	}
  1530  	if buf2.String() != "bar" {
  1531  		t.Errorf("buf2 = %q; want bar", buf2.String())
  1532  	}
  1533  
  1534  	*w = Writer{}  // zero out the Writer
  1535  	w.Reset(&buf3) // and not flushed
  1536  	w.WriteString("bar")
  1537  	w.Flush()
  1538  	if buf1.String() != "" {
  1539  		t.Errorf("buf1 = %q; want empty", buf1.String())
  1540  	}
  1541  	if buf3.String() != "bar" {
  1542  		t.Errorf("buf3 = %q; want bar", buf3.String())
  1543  	}
  1544  
  1545  	// Wrap a writer and then Reset to that writer.
  1546  	w.Reset(&buf4)
  1547  	w2 := NewWriter(w)
  1548  	w2.WriteString("recur")
  1549  	w2.Flush()
  1550  	if buf4.String() != "recur" {
  1551  		t.Errorf("buf4 = %q, want %q", buf4.String(), "recur")
  1552  	}
  1553  	w.Reset(&buf5)
  1554  	w2.Reset(w)
  1555  	w2.WriteString("recur2")
  1556  	w2.Flush()
  1557  	if buf5.String() != "recur2" {
  1558  		t.Errorf("buf5 = %q, want %q", buf5.String(), "recur2")
  1559  	}
  1560  }
  1561  
  1562  func TestReaderDiscard(t *testing.T) {
  1563  	tests := []struct {
  1564  		name     string
  1565  		r        io.Reader
  1566  		bufSize  int // 0 means 16
  1567  		peekSize int
  1568  
  1569  		n int // input to Discard
  1570  
  1571  		want    int   // from Discard
  1572  		wantErr error // from Discard
  1573  
  1574  		wantBuffered int
  1575  	}{
  1576  		{
  1577  			name:         "normal case",
  1578  			r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
  1579  			peekSize:     16,
  1580  			n:            6,
  1581  			want:         6,
  1582  			wantBuffered: 10,
  1583  		},
  1584  		{
  1585  			name:         "discard causing read",
  1586  			r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
  1587  			n:            6,
  1588  			want:         6,
  1589  			wantBuffered: 10,
  1590  		},
  1591  		{
  1592  			name:         "discard all without peek",
  1593  			r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
  1594  			n:            26,
  1595  			want:         26,
  1596  			wantBuffered: 0,
  1597  		},
  1598  		{
  1599  			name:         "discard more than end",
  1600  			r:            strings.NewReader("abcdefghijklmnopqrstuvwxyz"),
  1601  			n:            27,
  1602  			want:         26,
  1603  			wantErr:      io.EOF,
  1604  			wantBuffered: 0,
  1605  		},
  1606  		// Any error from filling shouldn't show up until we
  1607  		// get past the valid bytes. Here we return 5 valid bytes at the same time
  1608  		// as an error, but test that we don't see the error from Discard.
  1609  		{
  1610  			name: "fill error, discard less",
  1611  			r: newScriptedReader(func(p []byte) (n int, err error) {
  1612  				if len(p) < 5 {
  1613  					panic("unexpected small read")
  1614  				}
  1615  				return 5, errors.New("5-then-error")
  1616  			}),
  1617  			n:            4,
  1618  			want:         4,
  1619  			wantErr:      nil,
  1620  			wantBuffered: 1,
  1621  		},
  1622  		{
  1623  			name: "fill error, discard equal",
  1624  			r: newScriptedReader(func(p []byte) (n int, err error) {
  1625  				if len(p) < 5 {
  1626  					panic("unexpected small read")
  1627  				}
  1628  				return 5, errors.New("5-then-error")
  1629  			}),
  1630  			n:            5,
  1631  			want:         5,
  1632  			wantErr:      nil,
  1633  			wantBuffered: 0,
  1634  		},
  1635  		{
  1636  			name: "fill error, discard more",
  1637  			r: newScriptedReader(func(p []byte) (n int, err error) {
  1638  				if len(p) < 5 {
  1639  					panic("unexpected small read")
  1640  				}
  1641  				return 5, errors.New("5-then-error")
  1642  			}),
  1643  			n:            6,
  1644  			want:         5,
  1645  			wantErr:      errors.New("5-then-error"),
  1646  			wantBuffered: 0,
  1647  		},
  1648  		// Discard of 0 shouldn't cause a read:
  1649  		{
  1650  			name:         "discard zero",
  1651  			r:            newScriptedReader(), // will panic on Read
  1652  			n:            0,
  1653  			want:         0,
  1654  			wantErr:      nil,
  1655  			wantBuffered: 0,
  1656  		},
  1657  		{
  1658  			name:         "discard negative",
  1659  			r:            newScriptedReader(), // will panic on Read
  1660  			n:            -1,
  1661  			want:         0,
  1662  			wantErr:      ErrNegativeCount,
  1663  			wantBuffered: 0,
  1664  		},
  1665  	}
  1666  	for _, tt := range tests {
  1667  		br := NewReaderSize(tt.r, tt.bufSize)
  1668  		if tt.peekSize > 0 {
  1669  			peekBuf, err := br.Peek(tt.peekSize)
  1670  			if err != nil {
  1671  				t.Errorf("%s: Peek(%d): %v", tt.name, tt.peekSize, err)
  1672  				continue
  1673  			}
  1674  			if len(peekBuf) != tt.peekSize {
  1675  				t.Errorf("%s: len(Peek(%d)) = %v; want %v", tt.name, tt.peekSize, len(peekBuf), tt.peekSize)
  1676  				continue
  1677  			}
  1678  		}
  1679  		discarded, err := br.Discard(tt.n)
  1680  		if ge, we := fmt.Sprint(err), fmt.Sprint(tt.wantErr); discarded != tt.want || ge != we {
  1681  			t.Errorf("%s: Discard(%d) = (%v, %v); want (%v, %v)", tt.name, tt.n, discarded, ge, tt.want, we)
  1682  			continue
  1683  		}
  1684  		if bn := br.Buffered(); bn != tt.wantBuffered {
  1685  			t.Errorf("%s: after Discard, Buffered = %d; want %d", tt.name, bn, tt.wantBuffered)
  1686  		}
  1687  	}
  1688  
  1689  }
  1690  
  1691  func TestReaderSize(t *testing.T) {
  1692  	if got, want := NewReader(nil).Size(), DefaultBufSize; got != want {
  1693  		t.Errorf("NewReader's Reader.Size = %d; want %d", got, want)
  1694  	}
  1695  	if got, want := NewReaderSize(nil, 1234).Size(), 1234; got != want {
  1696  		t.Errorf("NewReaderSize's Reader.Size = %d; want %d", got, want)
  1697  	}
  1698  }
  1699  
  1700  func TestWriterSize(t *testing.T) {
  1701  	if got, want := NewWriter(nil).Size(), DefaultBufSize; got != want {
  1702  		t.Errorf("NewWriter's Writer.Size = %d; want %d", got, want)
  1703  	}
  1704  	if got, want := NewWriterSize(nil, 1234).Size(), 1234; got != want {
  1705  		t.Errorf("NewWriterSize's Writer.Size = %d; want %d", got, want)
  1706  	}
  1707  }
  1708  
  1709  // An onlyReader only implements io.Reader, no matter what other methods the underlying implementation may have.
  1710  type onlyReader struct {
  1711  	io.Reader
  1712  }
  1713  
  1714  // An onlyWriter only implements io.Writer, no matter what other methods the underlying implementation may have.
  1715  type onlyWriter struct {
  1716  	io.Writer
  1717  }
  1718  
  1719  // A scriptedReader is an io.Reader that executes its steps sequentially.
  1720  type scriptedReader []func(p []byte) (n int, err error)
  1721  
  1722  func (sr *scriptedReader) Read(p []byte) (n int, err error) {
  1723  	if len(*sr) == 0 {
  1724  		panic("too many Read calls on scripted Reader. No steps remain.")
  1725  	}
  1726  	step := (*sr)[0]
  1727  	*sr = (*sr)[1:]
  1728  	return step(p)
  1729  }
  1730  
  1731  func newScriptedReader(steps ...func(p []byte) (n int, err error)) io.Reader {
  1732  	sr := scriptedReader(steps)
  1733  	return &sr
  1734  }
  1735  
  1736  // eofReader returns the number of bytes read and io.EOF for the read that consumes the last of the content.
  1737  type eofReader struct {
  1738  	buf []byte
  1739  }
  1740  
  1741  func (r *eofReader) Read(p []byte) (int, error) {
  1742  	read := copy(p, r.buf)
  1743  	r.buf = r.buf[read:]
  1744  
  1745  	switch read {
  1746  	case 0, len(r.buf):
  1747  		// As allowed in the documentation, this will return io.EOF
  1748  		// in the same call that consumes the last of the data.
  1749  		// https://godoc.org/io#Reader
  1750  		return read, io.EOF
  1751  	}
  1752  
  1753  	return read, nil
  1754  }
  1755  
  1756  func TestPartialReadEOF(t *testing.T) {
  1757  	src := make([]byte, 10)
  1758  	eofR := &eofReader{buf: src}
  1759  	r := NewReader(eofR)
  1760  
  1761  	// Start by reading 5 of the 10 available bytes.
  1762  	dest := make([]byte, 5)
  1763  	read, err := r.Read(dest)
  1764  	if err != nil {
  1765  		t.Fatalf("unexpected error: %v", err)
  1766  	}
  1767  	if n := len(dest); read != n {
  1768  		t.Fatalf("read %d bytes; wanted %d bytes", read, n)
  1769  	}
  1770  
  1771  	// The Reader should have buffered all the content from the io.Reader.
  1772  	if n := len(eofR.buf); n != 0 {
  1773  		t.Fatalf("got %d bytes left in bufio.Reader source; want 0 bytes", n)
  1774  	}
  1775  	// To prove the point, check that there are still 5 bytes available to read.
  1776  	if n := r.Buffered(); n != 5 {
  1777  		t.Fatalf("got %d bytes buffered in bufio.Reader; want 5 bytes", n)
  1778  	}
  1779  
  1780  	// This is the second read of 0 bytes.
  1781  	read, err = r.Read([]byte{})
  1782  	if err != nil {
  1783  		t.Fatalf("unexpected error: %v", err)
  1784  	}
  1785  	if read != 0 {
  1786  		t.Fatalf("read %d bytes; want 0 bytes", read)
  1787  	}
  1788  }
  1789  
  1790  type writerWithReadFromError struct{}
  1791  
  1792  func (w writerWithReadFromError) ReadFrom(r io.Reader) (int64, error) {
  1793  	return 0, errors.New("writerWithReadFromError error")
  1794  }
  1795  
  1796  func (w writerWithReadFromError) Write(b []byte) (n int, err error) {
  1797  	return 10, nil
  1798  }
  1799  
  1800  func TestWriterReadFromMustSetUnderlyingError(t *testing.T) {
  1801  	var wr = NewWriter(writerWithReadFromError{})
  1802  	if _, err := wr.ReadFrom(strings.NewReader("test2")); err == nil {
  1803  		t.Fatal("expected ReadFrom returns error, got nil")
  1804  	}
  1805  	if _, err := wr.Write([]byte("123")); err == nil {
  1806  		t.Fatal("expected Write returns error, got nil")
  1807  	}
  1808  }
  1809  
  1810  type writeErrorOnlyWriter struct{}
  1811  
  1812  func (w writeErrorOnlyWriter) Write(p []byte) (n int, err error) {
  1813  	return 0, errors.New("writeErrorOnlyWriter error")
  1814  }
  1815  
  1816  // Ensure that previous Write errors are immediately returned
  1817  // on any ReadFrom. See golang.org/issue/35194.
  1818  func TestWriterReadFromMustReturnUnderlyingError(t *testing.T) {
  1819  	var wr = NewWriter(writeErrorOnlyWriter{})
  1820  	s := "test1"
  1821  	wantBuffered := len(s)
  1822  	if _, err := wr.WriteString(s); err != nil {
  1823  		t.Fatalf("unexpected error: %v", err)
  1824  	}
  1825  	if err := wr.Flush(); err == nil {
  1826  		t.Error("expected flush error, got nil")
  1827  	}
  1828  	if _, err := wr.ReadFrom(strings.NewReader("test2")); err == nil {
  1829  		t.Fatal("expected error, got nil")
  1830  	}
  1831  	if buffered := wr.Buffered(); buffered != wantBuffered {
  1832  		t.Fatalf("Buffered = %v; want %v", buffered, wantBuffered)
  1833  	}
  1834  }
  1835  
  1836  func BenchmarkReaderCopyOptimal(b *testing.B) {
  1837  	// Optimal case is where the underlying reader implements io.WriterTo
  1838  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1839  	src := NewReader(srcBuf)
  1840  	dstBuf := new(bytes.Buffer)
  1841  	dst := onlyWriter{dstBuf}
  1842  	for i := 0; i < b.N; i++ {
  1843  		srcBuf.Reset()
  1844  		src.Reset(srcBuf)
  1845  		dstBuf.Reset()
  1846  		io.Copy(dst, src)
  1847  	}
  1848  }
  1849  
  1850  func BenchmarkReaderCopyUnoptimal(b *testing.B) {
  1851  	// Unoptimal case is where the underlying reader doesn't implement io.WriterTo
  1852  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1853  	src := NewReader(onlyReader{srcBuf})
  1854  	dstBuf := new(bytes.Buffer)
  1855  	dst := onlyWriter{dstBuf}
  1856  	for i := 0; i < b.N; i++ {
  1857  		srcBuf.Reset()
  1858  		src.Reset(onlyReader{srcBuf})
  1859  		dstBuf.Reset()
  1860  		io.Copy(dst, src)
  1861  	}
  1862  }
  1863  
  1864  func BenchmarkReaderCopyNoWriteTo(b *testing.B) {
  1865  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1866  	srcReader := NewReader(srcBuf)
  1867  	src := onlyReader{srcReader}
  1868  	dstBuf := new(bytes.Buffer)
  1869  	dst := onlyWriter{dstBuf}
  1870  	for i := 0; i < b.N; i++ {
  1871  		srcBuf.Reset()
  1872  		srcReader.Reset(srcBuf)
  1873  		dstBuf.Reset()
  1874  		io.Copy(dst, src)
  1875  	}
  1876  }
  1877  
  1878  func BenchmarkReaderWriteToOptimal(b *testing.B) {
  1879  	const bufSize = 16 << 10
  1880  	buf := make([]byte, bufSize)
  1881  	r := bytes.NewReader(buf)
  1882  	srcReader := NewReaderSize(onlyReader{r}, 1<<10)
  1883  	if _, ok := io.Discard.(io.ReaderFrom); !ok {
  1884  		b.Fatal("io.Discard doesn't support ReaderFrom")
  1885  	}
  1886  	for i := 0; i < b.N; i++ {
  1887  		r.Seek(0, io.SeekStart)
  1888  		srcReader.Reset(onlyReader{r})
  1889  		n, err := srcReader.WriteTo(io.Discard)
  1890  		if err != nil {
  1891  			b.Fatal(err)
  1892  		}
  1893  		if n != bufSize {
  1894  			b.Fatalf("n = %d; want %d", n, bufSize)
  1895  		}
  1896  	}
  1897  }
  1898  
  1899  func BenchmarkReaderReadString(b *testing.B) {
  1900  	r := strings.NewReader("       foo       foo        42        42        42        42        42        42        42        42       4.2       4.2       4.2       4.2\n")
  1901  	buf := NewReader(r)
  1902  	b.ReportAllocs()
  1903  	for i := 0; i < b.N; i++ {
  1904  		r.Seek(0, io.SeekStart)
  1905  		buf.Reset(r)
  1906  
  1907  		_, err := buf.ReadString('\n')
  1908  		if err != nil {
  1909  			b.Fatal(err)
  1910  		}
  1911  	}
  1912  }
  1913  
  1914  func BenchmarkWriterCopyOptimal(b *testing.B) {
  1915  	// Optimal case is where the underlying writer implements io.ReaderFrom
  1916  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1917  	src := onlyReader{srcBuf}
  1918  	dstBuf := new(bytes.Buffer)
  1919  	dst := NewWriter(dstBuf)
  1920  	for i := 0; i < b.N; i++ {
  1921  		srcBuf.Reset()
  1922  		dstBuf.Reset()
  1923  		dst.Reset(dstBuf)
  1924  		io.Copy(dst, src)
  1925  	}
  1926  }
  1927  
  1928  func BenchmarkWriterCopyUnoptimal(b *testing.B) {
  1929  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1930  	src := onlyReader{srcBuf}
  1931  	dstBuf := new(bytes.Buffer)
  1932  	dst := NewWriter(onlyWriter{dstBuf})
  1933  	for i := 0; i < b.N; i++ {
  1934  		srcBuf.Reset()
  1935  		dstBuf.Reset()
  1936  		dst.Reset(onlyWriter{dstBuf})
  1937  		io.Copy(dst, src)
  1938  	}
  1939  }
  1940  
  1941  func BenchmarkWriterCopyNoReadFrom(b *testing.B) {
  1942  	srcBuf := bytes.NewBuffer(make([]byte, 8192))
  1943  	src := onlyReader{srcBuf}
  1944  	dstBuf := new(bytes.Buffer)
  1945  	dstWriter := NewWriter(dstBuf)
  1946  	dst := onlyWriter{dstWriter}
  1947  	for i := 0; i < b.N; i++ {
  1948  		srcBuf.Reset()
  1949  		dstBuf.Reset()
  1950  		dstWriter.Reset(dstBuf)
  1951  		io.Copy(dst, src)
  1952  	}
  1953  }
  1954  
  1955  func BenchmarkReaderEmpty(b *testing.B) {
  1956  	b.ReportAllocs()
  1957  	str := strings.Repeat("x", 16<<10)
  1958  	for i := 0; i < b.N; i++ {
  1959  		br := NewReader(strings.NewReader(str))
  1960  		n, err := io.Copy(io.Discard, br)
  1961  		if err != nil {
  1962  			b.Fatal(err)
  1963  		}
  1964  		if n != int64(len(str)) {
  1965  			b.Fatal("wrong length")
  1966  		}
  1967  	}
  1968  }
  1969  
  1970  func BenchmarkWriterEmpty(b *testing.B) {
  1971  	b.ReportAllocs()
  1972  	str := strings.Repeat("x", 1<<10)
  1973  	bs := []byte(str)
  1974  	for i := 0; i < b.N; i++ {
  1975  		bw := NewWriter(io.Discard)
  1976  		bw.Flush()
  1977  		bw.WriteByte('a')
  1978  		bw.Flush()
  1979  		bw.WriteRune('B')
  1980  		bw.Flush()
  1981  		bw.Write(bs)
  1982  		bw.Flush()
  1983  		bw.WriteString(str)
  1984  		bw.Flush()
  1985  	}
  1986  }
  1987  
  1988  func BenchmarkWriterFlush(b *testing.B) {
  1989  	b.ReportAllocs()
  1990  	bw := NewWriter(io.Discard)
  1991  	str := strings.Repeat("x", 50)
  1992  	for i := 0; i < b.N; i++ {
  1993  		bw.WriteString(str)
  1994  		bw.Flush()
  1995  	}
  1996  }
  1997  

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