src/bytes/buffer.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package bytes

 // Simple byte buffer for marshaling data.

 import (
 	"errors"
 	"io"
 	"unicode/utf8"
 )

 // A Buffer is a variable-sized buffer of bytes with Read and Write methods.
 // The zero value for Buffer is an empty buffer ready to use.
 type Buffer struct {
 	buf       []byte   // contents are the bytes buf[off : len(buf)]
 	off       int      // read at &buf[off], write at &buf[len(buf)]
 	bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation.
 	lastRead  readOp   // last read operation, so that Unread* can work correctly.

 	// FIXME: it would be advisable to align Buffer to cachelines to avoid false
 	// sharing.
 }

 // The readOp constants describe the last action performed on
 // the buffer, so that UnreadRune and UnreadByte can check for
 // invalid usage. opReadRuneX constants are chosen such that
 // converted to int they correspond to the rune size that was read.
 type readOp int8

 // Don't use iota for these, as the values need to correspond with the
 // names and comments, which is easier to see when being explicit.
 const (
 	opRead      readOp = -1 // Any other read operation.
 	opInvalid   readOp = 0  // Non-read operation.
 	opReadRune1 readOp = 1  // Read rune of size 1.
 	opReadRune2 readOp = 2  // Read rune of size 2.
 	opReadRune3 readOp = 3  // Read rune of size 3.
 	opReadRune4 readOp = 4  // Read rune of size 4.
 )

 // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
 var ErrTooLarge = errors.New("bytes.Buffer: too large")
 var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")

 const maxInt = int(^uint(0) >> 1)

 // Bytes returns a slice of length b.Len() holding the unread portion of the buffer.
 // The slice is valid for use only until the next buffer modification (that is,
 // only until the next call to a method like Read, Write, Reset, or Truncate).
 // The slice aliases the buffer content at least until the next buffer modification,
 // so immediate changes to the slice will affect the result of future reads.
 func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }

 // String returns the contents of the unread portion of the buffer
 // as a string. If the Buffer is a nil pointer, it returns "<nil>".
 //
 // To build strings more efficiently, see the strings.Builder type.
 func (b *Buffer) String() string {
 	if b == nil {
 		// Special case, useful in debugging.
 		return "<nil>"
 	}
 	return string(b.buf[b.off:])
 }

 // empty returns whether the unread portion of the buffer is empty.
 func (b *Buffer) empty() bool { return len(b.buf) <= b.off }

 // Len returns the number of bytes of the unread portion of the buffer;
 // b.Len() == len(b.Bytes()).
 func (b *Buffer) Len() int { return len(b.buf) - b.off }

 // Cap returns the capacity of the buffer's underlying byte slice, that is, the
 // total space allocated for the buffer's data.
 func (b *Buffer) Cap() int { return cap(b.buf) }

 // Truncate discards all but the first n unread bytes from the buffer
 // but continues to use the same allocated storage.
 // It panics if n is negative or greater than the length of the buffer.
 func (b *Buffer) Truncate(n int) {
 	if n == 0 {
 		b.Reset()
 		return
 	}
 	b.lastRead = opInvalid
 	if n < 0 || n > b.Len() {
 		panic("bytes.Buffer: truncation out of range")
 	}
 	b.buf = b.buf[:b.off+n]
 }

 // Reset resets the buffer to be empty,
 // but it retains the underlying storage for use by future writes.
 // Reset is the same as Truncate(0).
 func (b *Buffer) Reset() {
 	b.buf = b.buf[:0]
 	b.off = 0
 	b.lastRead = opInvalid
 }

 // tryGrowByReslice is a inlineable version of grow for the fast-case where the
 // internal buffer only needs to be resliced.
 // It returns the index where bytes should be written and whether it succeeded.
 func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
 	if l := len(b.buf); n <= cap(b.buf)-l {
 		b.buf = b.buf[:l+n]
 		return l, true
 	}
 	return 0, false
 }

 // grow grows the buffer to guarantee space for n more bytes.
 // It returns the index where bytes should be written.
 // If the buffer can't grow it will panic with ErrTooLarge.
 func (b *Buffer) grow(n int) int {
 	m := b.Len()
 	// If buffer is empty, reset to recover space.
 	if m == 0 && b.off != 0 {
 		b.Reset()
 	}
 	// Try to grow by means of a reslice.
 	if i, ok := b.tryGrowByReslice(n); ok {
 		return i
 	}
 	// Check if we can make use of bootstrap array.
 	if b.buf == nil && n <= len(b.bootstrap) {
 		b.buf = b.bootstrap[:n]
 		return 0
 	}
 	c := cap(b.buf)
 	if n <= c/2-m {
 		// We can slide things down instead of allocating a new
 		// slice. We only need m+n <= c to slide, but
 		// we instead let capacity get twice as large so we
 		// don't spend all our time copying.
 		copy(b.buf, b.buf[b.off:])
 	} else if c > maxInt-c-n {
 		panic(ErrTooLarge)
 	} else {
 		// Not enough space anywhere, we need to allocate.
 		buf := makeSlice(2*c + n)
 		copy(buf, b.buf[b.off:])
 		b.buf = buf
 	}
 	// Restore b.off and len(b.buf).
 	b.off = 0
 	b.buf = b.buf[:m+n]
 	return m
 }

 // Grow grows the buffer's capacity, if necessary, to guarantee space for
 // another n bytes. After Grow(n), at least n bytes can be written to the
 // buffer without another allocation.
 // If n is negative, Grow will panic.
 // If the buffer can't grow it will panic with ErrTooLarge.
 func (b *Buffer) Grow(n int) {
 	if n < 0 {
 		panic("bytes.Buffer.Grow: negative count")
 	}
 	m := b.grow(n)
 	b.buf = b.buf[:m]
 }

 // Write appends the contents of p to the buffer, growing the buffer as
 // needed. The return value n is the length of p; err is always nil. If the
 // buffer becomes too large, Write will panic with ErrTooLarge.
 func (b *Buffer) Write(p []byte) (n int, err error) {
 	b.lastRead = opInvalid
 	m, ok := b.tryGrowByReslice(len(p))
 	if !ok {
 		m = b.grow(len(p))
 	}
 	return copy(b.buf[m:], p), nil
 }

 // WriteString appends the contents of s to the buffer, growing the buffer as
 // needed. The return value n is the length of s; err is always nil. If the
 // buffer becomes too large, WriteString will panic with ErrTooLarge.
 func (b *Buffer) WriteString(s string) (n int, err error) {
 	b.lastRead = opInvalid
 	m, ok := b.tryGrowByReslice(len(s))
 	if !ok {
 		m = b.grow(len(s))
 	}
 	return copy(b.buf[m:], s), nil
 }

 // MinRead is the minimum slice size passed to a Read call by
 // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
 // what is required to hold the contents of r, ReadFrom will not grow the
 // underlying buffer.
 const MinRead = 512

 // ReadFrom reads data from r until EOF and appends it to the buffer, growing
 // the buffer as needed. The return value n is the number of bytes read. Any
 // error except io.EOF encountered during the read is also returned. If the
 // buffer becomes too large, ReadFrom will panic with ErrTooLarge.
 func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
 	b.lastRead = opInvalid
 	for {
 		i := b.grow(MinRead)
 		b.buf = b.buf[:i]
 		m, e := r.Read(b.buf[i:cap(b.buf)])
 		if m < 0 {
 			panic(errNegativeRead)
 		}

 		b.buf = b.buf[:i+m]
 		n += int64(m)
 		if e == io.EOF {
 			return n, nil // e is EOF, so return nil explicitly
 		}
 		if e != nil {
 			return n, e
 		}
 	}
 }

 // makeSlice allocates a slice of size n. If the allocation fails, it panics
 // with ErrTooLarge.
 func makeSlice(n int) []byte {
 	// If the make fails, give a known error.
 	defer func() {
 		if recover() != nil {
 			panic(ErrTooLarge)
 		}
 	}()
 	return make([]byte, n)
 }

 // WriteTo writes data to w until the buffer is drained or an error occurs.
 // The return value n is the number of bytes written; it always fits into an
 // int, but it is int64 to match the io.WriterTo interface. Any error
 // encountered during the write is also returned.
 func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
 	b.lastRead = opInvalid
 	if nBytes := b.Len(); nBytes > 0 {
 		m, e := w.Write(b.buf[b.off:])
 		if m > nBytes {
 			panic("bytes.Buffer.WriteTo: invalid Write count")
 		}
 		b.off += m
 		n = int64(m)
 		if e != nil {
 			return n, e
 		}
 		// all bytes should have been written, by definition of
 		// Write method in io.Writer
 		if m != nBytes {
 			return n, io.ErrShortWrite
 		}
 	}
 	// Buffer is now empty; reset.
 	b.Reset()
 	return n, nil
 }

 // WriteByte appends the byte c to the buffer, growing the buffer as needed.
 // The returned error is always nil, but is included to match bufio.Writer's
 // WriteByte. If the buffer becomes too large, WriteByte will panic with
 // ErrTooLarge.
 func (b *Buffer) WriteByte(c byte) error {
 	b.lastRead = opInvalid
 	m, ok := b.tryGrowByReslice(1)
 	if !ok {
 		m = b.grow(1)
 	}
 	b.buf[m] = c
 	return nil
 }

 // WriteRune appends the UTF-8 encoding of Unicode code point r to the
 // buffer, returning its length and an error, which is always nil but is
 // included to match bufio.Writer's WriteRune. The buffer is grown as needed;
 // if it becomes too large, WriteRune will panic with ErrTooLarge.
 func (b *Buffer) WriteRune(r rune) (n int, err error) {
 	if r < utf8.RuneSelf {
 		b.WriteByte(byte(r))
 		return 1, nil
 	}
 	b.lastRead = opInvalid
 	m, ok := b.tryGrowByReslice(utf8.UTFMax)
 	if !ok {
 		m = b.grow(utf8.UTFMax)
 	}
 	n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r)
 	b.buf = b.buf[:m+n]
 	return n, nil
 }

 // Read reads the next len(p) bytes from the buffer or until the buffer
 // is drained. The return value n is the number of bytes read. If the
 // buffer has no data to return, err is io.EOF (unless len(p) is zero);
 // otherwise it is nil.
 func (b *Buffer) Read(p []byte) (n int, err error) {
 	b.lastRead = opInvalid
 	if b.empty() {
 		// Buffer is empty, reset to recover space.
 		b.Reset()
 		if len(p) == 0 {
 			return 0, nil
 		}
 		return 0, io.EOF
 	}
 	n = copy(p, b.buf[b.off:])
 	b.off += n
 	if n > 0 {
 		b.lastRead = opRead
 	}
 	return n, nil
 }

 // Next returns a slice containing the next n bytes from the buffer,
 // advancing the buffer as if the bytes had been returned by Read.
 // If there are fewer than n bytes in the buffer, Next returns the entire buffer.
 // The slice is only valid until the next call to a read or write method.
 func (b *Buffer) Next(n int) []byte {
 	b.lastRead = opInvalid
 	m := b.Len()
 	if n > m {
 		n = m
 	}
 	data := b.buf[b.off : b.off+n]
 	b.off += n
 	if n > 0 {
 		b.lastRead = opRead
 	}
 	return data
 }

 // ReadByte reads and returns the next byte from the buffer.
 // If no byte is available, it returns error io.EOF.
 func (b *Buffer) ReadByte() (byte, error) {
 	if b.empty() {
 		// Buffer is empty, reset to recover space.
 		b.Reset()
 		return 0, io.EOF
 	}
 	c := b.buf[b.off]
 	b.off++
 	b.lastRead = opRead
 	return c, nil
 }

 // ReadRune reads and returns the next UTF-8-encoded
 // Unicode code point from the buffer.
 // If no bytes are available, the error returned is io.EOF.
 // If the bytes are an erroneous UTF-8 encoding, it
 // consumes one byte and returns U+FFFD, 1.
 func (b *Buffer) ReadRune() (r rune, size int, err error) {
 	if b.empty() {
 		// Buffer is empty, reset to recover space.
 		b.Reset()
 		return 0, 0, io.EOF
 	}
 	c := b.buf[b.off]
 	if c < utf8.RuneSelf {
 		b.off++
 		b.lastRead = opReadRune1
 		return rune(c), 1, nil
 	}
 	r, n := utf8.DecodeRune(b.buf[b.off:])
 	b.off += n
 	b.lastRead = readOp(n)
 	return r, n, nil
 }

 // UnreadRune unreads the last rune returned by ReadRune.
 // If the most recent read or write operation on the buffer was
 // not a successful ReadRune, UnreadRune returns an error.  (In this regard
 // it is stricter than UnreadByte, which will unread the last byte
 // from any read operation.)
 func (b *Buffer) UnreadRune() error {
 	if b.lastRead <= opInvalid {
 		return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
 	}
 	if b.off >= int(b.lastRead) {
 		b.off -= int(b.lastRead)
 	}
 	b.lastRead = opInvalid
 	return nil
 }

 // UnreadByte unreads the last byte returned by the most recent successful
 // read operation that read at least one byte. If a write has happened since
 // the last read, if the last read returned an error, or if the read read zero
 // bytes, UnreadByte returns an error.
 func (b *Buffer) UnreadByte() error {
 	if b.lastRead == opInvalid {
 		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
 	}
 	b.lastRead = opInvalid
 	if b.off > 0 {
 		b.off--
 	}
 	return nil
 }

 // ReadBytes reads until the first occurrence of delim in the input,
 // returning a slice containing the data up to and including the delimiter.
 // If ReadBytes encounters an error before finding a delimiter,
 // it returns the data read before the error and the error itself (often io.EOF).
 // ReadBytes returns err != nil if and only if the returned data does not end in
 // delim.
 func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {
 	slice, err := b.readSlice(delim)
 	// return a copy of slice. The buffer's backing array may
 	// be overwritten by later calls.
 	line = append(line, slice...)
 	return line, err
 }

 // readSlice is like ReadBytes but returns a reference to internal buffer data.
 func (b *Buffer) readSlice(delim byte) (line []byte, err error) {
 	i := IndexByte(b.buf[b.off:], delim)
 	end := b.off + i + 1
 	if i < 0 {
 		end = len(b.buf)
 		err = io.EOF
 	}
 	line = b.buf[b.off:end]
 	b.off = end
 	b.lastRead = opRead
 	return line, err
 }

 // ReadString reads until the first occurrence of delim in the input,
 // returning a string containing the data up to and including the delimiter.
 // If ReadString encounters an error before finding a delimiter,
 // it returns the data read before the error and the error itself (often io.EOF).
 // ReadString returns err != nil if and only if the returned data does not end
 // in delim.
 func (b *Buffer) ReadString(delim byte) (line string, err error) {
 	slice, err := b.readSlice(delim)
 	return string(slice), err
 }

 // NewBuffer creates and initializes a new Buffer using buf as its
 // initial contents. The new Buffer takes ownership of buf, and the
 // caller should not use buf after this call. NewBuffer is intended to
 // prepare a Buffer to read existing data. It can also be used to size
 // the internal buffer for writing. To do that, buf should have the
 // desired capacity but a length of zero.
 //
 // In most cases, new(Buffer) (or just declaring a Buffer variable) is
 // sufficient to initialize a Buffer.
 func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }

 // NewBufferString creates and initializes a new Buffer using string s as its
 // initial contents. It is intended to prepare a buffer to read an existing
 // string.
 //
 // In most cases, new(Buffer) (or just declaring a Buffer variable) is
 // sufficient to initialize a Buffer.
 func NewBufferString(s string) *Buffer {
 	return &Buffer{buf: []byte(s)}
 }
	// 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 bytes

	// Simple byte buffer for marshaling data.

	import (
	"errors"
	"io"
	"unicode/utf8"
	)

	// A Buffer is a variable-sized buffer of bytes with Read and Write methods.
	// The zero value for Buffer is an empty buffer ready to use.
	type Buffer struct {
	buf []byte // contents are the bytes buf[off : len(buf)]
	off int // read at &buf[off], write at &buf[len(buf)]
	bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation.
	lastRead readOp // last read operation, so that Unread* can work correctly.

	// FIXME: it would be advisable to align Buffer to cachelines to avoid false
	// sharing.
	}

	// The readOp constants describe the last action performed on
	// the buffer, so that UnreadRune and UnreadByte can check for
	// invalid usage. opReadRuneX constants are chosen such that
	// converted to int they correspond to the rune size that was read.
	type readOp int8

	// Don't use iota for these, as the values need to correspond with the
	// names and comments, which is easier to see when being explicit.
	const (
	opRead readOp = -1 // Any other read operation.
	opInvalid readOp = 0 // Non-read operation.
	opReadRune1 readOp = 1 // Read rune of size 1.
	opReadRune2 readOp = 2 // Read rune of size 2.
	opReadRune3 readOp = 3 // Read rune of size 3.
	opReadRune4 readOp = 4 // Read rune of size 4.
	)

	// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
	var ErrTooLarge = errors.New("bytes.Buffer: too large")
	var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")

	const maxInt = int(^uint(0) >> 1)

	// Bytes returns a slice of length b.Len() holding the unread portion of the buffer.
	// The slice is valid for use only until the next buffer modification (that is,
	// only until the next call to a method like Read, Write, Reset, or Truncate).
	// The slice aliases the buffer content at least until the next buffer modification,
	// so immediate changes to the slice will affect the result of future reads.
	func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }

	// String returns the contents of the unread portion of the buffer
	// as a string. If the Buffer is a nil pointer, it returns "<nil>".
	//
	// To build strings more efficiently, see the strings.Builder type.
	func (b *Buffer) String() string {
	if b == nil {
	// Special case, useful in debugging.
	return "<nil>"
	}
	return string(b.buf[b.off:])
	}

	// empty returns whether the unread portion of the buffer is empty.
	func (b *Buffer) empty() bool { return len(b.buf) <= b.off }

	// Len returns the number of bytes of the unread portion of the buffer;
	// b.Len() == len(b.Bytes()).
	func (b *Buffer) Len() int { return len(b.buf) - b.off }

	// Cap returns the capacity of the buffer's underlying byte slice, that is, the
	// total space allocated for the buffer's data.
	func (b *Buffer) Cap() int { return cap(b.buf) }

	// Truncate discards all but the first n unread bytes from the buffer
	// but continues to use the same allocated storage.
	// It panics if n is negative or greater than the length of the buffer.
	func (b *Buffer) Truncate(n int) {
	if n == 0 {
	b.Reset()
	return
	}
	b.lastRead = opInvalid
	if n < 0 \|\| n > b.Len() {
	panic("bytes.Buffer: truncation out of range")
	}
	b.buf = b.buf[:b.off+n]
	}

	// Reset resets the buffer to be empty,
	// but it retains the underlying storage for use by future writes.
	// Reset is the same as Truncate(0).
	func (b *Buffer) Reset() {
	b.buf = b.buf[:0]
	b.off = 0
	b.lastRead = opInvalid
	}

	// tryGrowByReslice is a inlineable version of grow for the fast-case where the
	// internal buffer only needs to be resliced.
	// It returns the index where bytes should be written and whether it succeeded.
	func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
	if l := len(b.buf); n <= cap(b.buf)-l {
	b.buf = b.buf[:l+n]
	return l, true
	}
	return 0, false
	}

	// grow grows the buffer to guarantee space for n more bytes.
	// It returns the index where bytes should be written.
	// If the buffer can't grow it will panic with ErrTooLarge.
	func (b *Buffer) grow(n int) int {
	m := b.Len()
	// If buffer is empty, reset to recover space.
	if m == 0 && b.off != 0 {
	b.Reset()
	}
	// Try to grow by means of a reslice.
	if i, ok := b.tryGrowByReslice(n); ok {
	return i
	}
	// Check if we can make use of bootstrap array.
	if b.buf == nil && n <= len(b.bootstrap) {
	b.buf = b.bootstrap[:n]
	return 0
	}
	c := cap(b.buf)
	if n <= c/2-m {
	// We can slide things down instead of allocating a new
	// slice. We only need m+n <= c to slide, but
	// we instead let capacity get twice as large so we
	// don't spend all our time copying.
	copy(b.buf, b.buf[b.off:])
	} else if c > maxInt-c-n {
	panic(ErrTooLarge)
	} else {
	// Not enough space anywhere, we need to allocate.
	buf := makeSlice(2*c + n)
	copy(buf, b.buf[b.off:])
	b.buf = buf
	}
	// Restore b.off and len(b.buf).
	b.off = 0
	b.buf = b.buf[:m+n]
	return m
	}

	// Grow grows the buffer's capacity, if necessary, to guarantee space for
	// another n bytes. After Grow(n), at least n bytes can be written to the
	// buffer without another allocation.
	// If n is negative, Grow will panic.
	// If the buffer can't grow it will panic with ErrTooLarge.
	func (b *Buffer) Grow(n int) {
	if n < 0 {
	panic("bytes.Buffer.Grow: negative count")
	}
	m := b.grow(n)
	b.buf = b.buf[:m]
	}

	// Write appends the contents of p to the buffer, growing the buffer as
	// needed. The return value n is the length of p; err is always nil. If the
	// buffer becomes too large, Write will panic with ErrTooLarge.
	func (b *Buffer) Write(p []byte) (n int, err error) {
	b.lastRead = opInvalid
	m, ok := b.tryGrowByReslice(len(p))
	if !ok {
	m = b.grow(len(p))
	}
	return copy(b.buf[m:], p), nil
	}

	// WriteString appends the contents of s to the buffer, growing the buffer as
	// needed. The return value n is the length of s; err is always nil. If the
	// buffer becomes too large, WriteString will panic with ErrTooLarge.
	func (b *Buffer) WriteString(s string) (n int, err error) {
	b.lastRead = opInvalid
	m, ok := b.tryGrowByReslice(len(s))
	if !ok {
	m = b.grow(len(s))
	}
	return copy(b.buf[m:], s), nil
	}

	// MinRead is the minimum slice size passed to a Read call by
	// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
	// what is required to hold the contents of r, ReadFrom will not grow the
	// underlying buffer.
	const MinRead = 512

	// ReadFrom reads data from r until EOF and appends it to the buffer, growing
	// the buffer as needed. The return value n is the number of bytes read. Any
	// error except io.EOF encountered during the read is also returned. If the
	// buffer becomes too large, ReadFrom will panic with ErrTooLarge.
	func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
	b.lastRead = opInvalid
	for {
	i := b.grow(MinRead)
	b.buf = b.buf[:i]
	m, e := r.Read(b.buf[i:cap(b.buf)])
	if m < 0 {
	panic(errNegativeRead)
	}

	b.buf = b.buf[:i+m]
	n += int64(m)
	if e == io.EOF {
	return n, nil // e is EOF, so return nil explicitly
	}
	if e != nil {
	return n, e
	}
	}
	}

	// makeSlice allocates a slice of size n. If the allocation fails, it panics
	// with ErrTooLarge.
	func makeSlice(n int) []byte {
	// If the make fails, give a known error.
	defer func() {
	if recover() != nil {
	panic(ErrTooLarge)
	}
	}()
	return make([]byte, n)
	}

	// WriteTo writes data to w until the buffer is drained or an error occurs.
	// The return value n is the number of bytes written; it always fits into an
	// int, but it is int64 to match the io.WriterTo interface. Any error
	// encountered during the write is also returned.
	func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
	b.lastRead = opInvalid
	if nBytes := b.Len(); nBytes > 0 {
	m, e := w.Write(b.buf[b.off:])
	if m > nBytes {
	panic("bytes.Buffer.WriteTo: invalid Write count")
	}
	b.off += m
	n = int64(m)
	if e != nil {
	return n, e
	}
	// all bytes should have been written, by definition of
	// Write method in io.Writer
	if m != nBytes {
	return n, io.ErrShortWrite
	}
	}
	// Buffer is now empty; reset.
	b.Reset()
	return n, nil
	}

	// WriteByte appends the byte c to the buffer, growing the buffer as needed.
	// The returned error is always nil, but is included to match bufio.Writer's
	// WriteByte. If the buffer becomes too large, WriteByte will panic with
	// ErrTooLarge.
	func (b *Buffer) WriteByte(c byte) error {
	b.lastRead = opInvalid
	m, ok := b.tryGrowByReslice(1)
	if !ok {
	m = b.grow(1)
	}
	b.buf[m] = c
	return nil
	}

	// WriteRune appends the UTF-8 encoding of Unicode code point r to the
	// buffer, returning its length and an error, which is always nil but is
	// included to match bufio.Writer's WriteRune. The buffer is grown as needed;
	// if it becomes too large, WriteRune will panic with ErrTooLarge.
	func (b *Buffer) WriteRune(r rune) (n int, err error) {
	if r < utf8.RuneSelf {
	b.WriteByte(byte(r))
	return 1, nil
	}
	b.lastRead = opInvalid
	m, ok := b.tryGrowByReslice(utf8.UTFMax)
	if !ok {
	m = b.grow(utf8.UTFMax)
	}
	n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r)
	b.buf = b.buf[:m+n]
	return n, nil
	}

	// Read reads the next len(p) bytes from the buffer or until the buffer
	// is drained. The return value n is the number of bytes read. If the
	// buffer has no data to return, err is io.EOF (unless len(p) is zero);
	// otherwise it is nil.
	func (b *Buffer) Read(p []byte) (n int, err error) {
	b.lastRead = opInvalid
	if b.empty() {
	// Buffer is empty, reset to recover space.
	b.Reset()
	if len(p) == 0 {
	return 0, nil
	}
	return 0, io.EOF
	}
	n = copy(p, b.buf[b.off:])
	b.off += n
	if n > 0 {
	b.lastRead = opRead
	}
	return n, nil
	}

	// Next returns a slice containing the next n bytes from the buffer,
	// advancing the buffer as if the bytes had been returned by Read.
	// If there are fewer than n bytes in the buffer, Next returns the entire buffer.
	// The slice is only valid until the next call to a read or write method.
	func (b *Buffer) Next(n int) []byte {
	b.lastRead = opInvalid
	m := b.Len()
	if n > m {
	n = m
	}
	data := b.buf[b.off : b.off+n]
	b.off += n
	if n > 0 {
	b.lastRead = opRead
	}
	return data
	}

	// ReadByte reads and returns the next byte from the buffer.
	// If no byte is available, it returns error io.EOF.
	func (b *Buffer) ReadByte() (byte, error) {
	if b.empty() {
	// Buffer is empty, reset to recover space.
	b.Reset()
	return 0, io.EOF
	}
	c := b.buf[b.off]
	b.off++
	b.lastRead = opRead
	return c, nil
	}

	// ReadRune reads and returns the next UTF-8-encoded
	// Unicode code point from the buffer.
	// If no bytes are available, the error returned is io.EOF.
	// If the bytes are an erroneous UTF-8 encoding, it
	// consumes one byte and returns U+FFFD, 1.
	func (b *Buffer) ReadRune() (r rune, size int, err error) {
	if b.empty() {
	// Buffer is empty, reset to recover space.
	b.Reset()
	return 0, 0, io.EOF
	}
	c := b.buf[b.off]
	if c < utf8.RuneSelf {
	b.off++
	b.lastRead = opReadRune1
	return rune(c), 1, nil
	}
	r, n := utf8.DecodeRune(b.buf[b.off:])
	b.off += n
	b.lastRead = readOp(n)
	return r, n, nil
	}

	// UnreadRune unreads the last rune returned by ReadRune.
	// If the most recent read or write operation on the buffer was
	// not a successful ReadRune, UnreadRune returns an error. (In this regard
	// it is stricter than UnreadByte, which will unread the last byte
	// from any read operation.)
	func (b *Buffer) UnreadRune() error {
	if b.lastRead <= opInvalid {
	return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
	}
	if b.off >= int(b.lastRead) {
	b.off -= int(b.lastRead)
	}
	b.lastRead = opInvalid
	return nil
	}

	// UnreadByte unreads the last byte returned by the most recent successful
	// read operation that read at least one byte. If a write has happened since
	// the last read, if the last read returned an error, or if the read read zero
	// bytes, UnreadByte returns an error.
	func (b *Buffer) UnreadByte() error {
	if b.lastRead == opInvalid {
	return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
	}
	b.lastRead = opInvalid
	if b.off > 0 {
	b.off--
	}
	return nil
	}

	// ReadBytes reads until the first occurrence of delim in the input,
	// returning a slice containing the data up to and including the delimiter.
	// If ReadBytes encounters an error before finding a delimiter,
	// it returns the data read before the error and the error itself (often io.EOF).
	// ReadBytes returns err != nil if and only if the returned data does not end in
	// delim.
	func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {
	slice, err := b.readSlice(delim)
	// return a copy of slice. The buffer's backing array may
	// be overwritten by later calls.
	line = append(line, slice...)
	return line, err
	}

	// readSlice is like ReadBytes but returns a reference to internal buffer data.
	func (b *Buffer) readSlice(delim byte) (line []byte, err error) {
	i := IndexByte(b.buf[b.off:], delim)
	end := b.off + i + 1
	if i < 0 {
	end = len(b.buf)
	err = io.EOF
	}
	line = b.buf[b.off:end]
	b.off = end
	b.lastRead = opRead
	return line, err
	}

	// ReadString reads until the first occurrence of delim in the input,
	// returning a string containing the data up to and including the delimiter.
	// If ReadString encounters an error before finding a delimiter,
	// it returns the data read before the error and the error itself (often io.EOF).
	// ReadString returns err != nil if and only if the returned data does not end
	// in delim.
	func (b *Buffer) ReadString(delim byte) (line string, err error) {
	slice, err := b.readSlice(delim)
	return string(slice), err
	}

	// NewBuffer creates and initializes a new Buffer using buf as its
	// initial contents. The new Buffer takes ownership of buf, and the
	// caller should not use buf after this call. NewBuffer is intended to
	// prepare a Buffer to read existing data. It can also be used to size
	// the internal buffer for writing. To do that, buf should have the
	// desired capacity but a length of zero.
	//
	// In most cases, new(Buffer) (or just declaring a Buffer variable) is
	// sufficient to initialize a Buffer.
	func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }

	// NewBufferString creates and initializes a new Buffer using string s as its
	// initial contents. It is intended to prepare a buffer to read an existing
	// string.
	//
	// In most cases, new(Buffer) (or just declaring a Buffer variable) is
	// sufficient to initialize a Buffer.
	func NewBufferString(s string) *Buffer {
	return &Buffer{buf: []byte(s)}
	}