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)]
 	runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune
 	bootstrap [64]byte          // memory to hold first slice; helps small buffers (Printf) avoid allocation.
 	lastRead  readOp            // last read operation, so that Unread* can work correctly.
 }

 // The readOp constants describe the last action performed on
 // the buffer, so that UnreadRune and UnreadByte can
 // check for invalid usage.
 type readOp int

 const (
 	opInvalid  readOp = iota // Non-read operation.
 	opReadRune               // Read rune.
 	opRead                   // Any other read operation.
 )

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

 // Bytes returns a slice of the contents of the unread portion of the buffer;
 // len(b.Bytes()) == b.Len().  If the caller changes the contents of the
 // returned slice, the contents of the buffer will change provided there
 // are no intervening method calls on the Buffer.
 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>".
 func (b *Buffer) String() string {
 	if b == nil {
 		// Special case, useful in debugging.
 		return "<nil>"
 	}
 	return string(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.
 // It panics if n is negative or greater than the length of the buffer.
 func (b *Buffer) Truncate(n int) {
 	b.lastRead = opInvalid
 	switch {
 	case n < 0 || n > b.Len():
 		panic("bytes.Buffer: truncation out of range")
 	case n == 0:
 		// Reuse buffer space.
 		b.off = 0
 	}
 	b.buf = b.buf[0 : b.off+n]
 }

 // Reset resets the buffer so it has no content.
 // b.Reset() is the same as b.Truncate(0).
 func (b *Buffer) Reset() { b.Truncate(0) }

 // 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.Truncate(0)
 	}
 	if len(b.buf)+n > cap(b.buf) {
 		var buf []byte
 		if b.buf == nil && n <= len(b.bootstrap) {
 			buf = b.bootstrap[0:]
 		} else if m+n <= cap(b.buf)/2 {
 			// We can slide things down instead of allocating a new
 			// slice. We only need m+n <= cap(b.buf) 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:])
 			buf = b.buf[:m]
 		} else {
 			// not enough space anywhere
 			buf = makeSlice(2*cap(b.buf) + n)
 			copy(buf, b.buf[b.off:])
 		}
 		b.buf = buf
 		b.off = 0
 	}
 	b.buf = b.buf[0 : b.off+m+n]
 	return b.off + 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[0: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 := 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 := 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
 	// If buffer is empty, reset to recover space.
 	if b.off >= len(b.buf) {
 		b.Truncate(0)
 	}
 	for {
 		if free := cap(b.buf) - len(b.buf); free < MinRead {
 			// not enough space at end
 			newBuf := b.buf
 			if b.off+free < MinRead {
 				// not enough space using beginning of buffer;
 				// double buffer capacity
 				newBuf = makeSlice(2*cap(b.buf) + MinRead)
 			}
 			copy(newBuf, b.buf[b.off:])
 			b.buf = newBuf[:len(b.buf)-b.off]
 			b.off = 0
 		}
 		m, e := r.Read(b.buf[len(b.buf):cap(b.buf)])
 		b.buf = b.buf[0 : len(b.buf)+m]
 		n += int64(m)
 		if e == io.EOF {
 			break
 		}
 		if e != nil {
 			return n, e
 		}
 	}
 	return n, nil // err is EOF, so return nil explicitly
 }

 // 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 b.off < len(b.buf) {
 		nBytes := b.Len()
 		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.Truncate(0)
 	return
 }

 // 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 := 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
 	}
 	n = utf8.EncodeRune(b.runeBytes[0:], r)
 	b.Write(b.runeBytes[0: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.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
 		b.Truncate(0)
 		if len(p) == 0 {
 			return
 		}
 		return 0, io.EOF
 	}
 	n = copy(p, b.buf[b.off:])
 	b.off += n
 	if n > 0 {
 		b.lastRead = opRead
 	}
 	return
 }

 // 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() (c byte, err error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
 		b.Truncate(0)
 		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) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
 		b.Truncate(0)
 		return 0, 0, io.EOF
 	}
 	b.lastRead = opReadRune
 	c := b.buf[b.off]
 	if c < utf8.RuneSelf {
 		b.off++
 		return rune(c), 1, nil
 	}
 	r, n := utf8.DecodeRune(b.buf[b.off:])
 	b.off += 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 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 != opReadRune {
 		return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
 	}
 	b.lastRead = opInvalid
 	if b.off > 0 {
 		_, n := utf8.DecodeLastRune(b.buf[0:b.off])
 		b.off -= n
 	}
 	return nil
 }

 // UnreadByte unreads the last byte returned by the most recent
 // read operation.  If write has happened since the last read, UnreadByte
 // returns an error.
 func (b *Buffer) UnreadByte() error {
 	if b.lastRead != opReadRune && b.lastRead != opRead {
 		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a 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
 }

 // 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.  It 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)]
	runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune
	bootstrap [64]byte // memory to hold first slice; helps small buffers (Printf) avoid allocation.
	lastRead readOp // last read operation, so that Unread* can work correctly.
	}

	// The readOp constants describe the last action performed on
	// the buffer, so that UnreadRune and UnreadByte can
	// check for invalid usage.
	type readOp int

	const (
	opInvalid readOp = iota // Non-read operation.
	opReadRune // Read rune.
	opRead // Any other read operation.
	)

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

	// Bytes returns a slice of the contents of the unread portion of the buffer;
	// len(b.Bytes()) == b.Len(). If the caller changes the contents of the
	// returned slice, the contents of the buffer will change provided there
	// are no intervening method calls on the Buffer.
	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>".
	func (b *Buffer) String() string {
	if b == nil {
	// Special case, useful in debugging.
	return "<nil>"
	}
	return string(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.
	// It panics if n is negative or greater than the length of the buffer.
	func (b *Buffer) Truncate(n int) {
	b.lastRead = opInvalid
	switch {
	case n < 0 \|\| n > b.Len():
	panic("bytes.Buffer: truncation out of range")
	case n == 0:
	// Reuse buffer space.
	b.off = 0
	}
	b.buf = b.buf[0 : b.off+n]
	}

	// Reset resets the buffer so it has no content.
	// b.Reset() is the same as b.Truncate(0).
	func (b *Buffer) Reset() { b.Truncate(0) }

	// 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.Truncate(0)
	}
	if len(b.buf)+n > cap(b.buf) {
	var buf []byte
	if b.buf == nil && n <= len(b.bootstrap) {
	buf = b.bootstrap[0:]
	} else if m+n <= cap(b.buf)/2 {
	// We can slide things down instead of allocating a new
	// slice. We only need m+n <= cap(b.buf) 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:])
	buf = b.buf[:m]
	} else {
	// not enough space anywhere
	buf = makeSlice(2*cap(b.buf) + n)
	copy(buf, b.buf[b.off:])
	}
	b.buf = buf
	b.off = 0
	}
	b.buf = b.buf[0 : b.off+m+n]
	return b.off + 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[0: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 := 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 := 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
	// If buffer is empty, reset to recover space.
	if b.off >= len(b.buf) {
	b.Truncate(0)
	}
	for {
	if free := cap(b.buf) - len(b.buf); free < MinRead {
	// not enough space at end
	newBuf := b.buf
	if b.off+free < MinRead {
	// not enough space using beginning of buffer;
	// double buffer capacity
	newBuf = makeSlice(2*cap(b.buf) + MinRead)
	}
	copy(newBuf, b.buf[b.off:])
	b.buf = newBuf[:len(b.buf)-b.off]
	b.off = 0
	}
	m, e := r.Read(b.buf[len(b.buf):cap(b.buf)])
	b.buf = b.buf[0 : len(b.buf)+m]
	n += int64(m)
	if e == io.EOF {
	break
	}
	if e != nil {
	return n, e
	}
	}
	return n, nil // err is EOF, so return nil explicitly
	}

	// 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 b.off < len(b.buf) {
	nBytes := b.Len()
	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.Truncate(0)
	return
	}

	// 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 := 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
	}
	n = utf8.EncodeRune(b.runeBytes[0:], r)
	b.Write(b.runeBytes[0: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.off >= len(b.buf) {
	// Buffer is empty, reset to recover space.
	b.Truncate(0)
	if len(p) == 0 {
	return
	}
	return 0, io.EOF
	}
	n = copy(p, b.buf[b.off:])
	b.off += n
	if n > 0 {
	b.lastRead = opRead
	}
	return
	}

	// 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() (c byte, err error) {
	b.lastRead = opInvalid
	if b.off >= len(b.buf) {
	// Buffer is empty, reset to recover space.
	b.Truncate(0)
	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) {
	b.lastRead = opInvalid
	if b.off >= len(b.buf) {
	// Buffer is empty, reset to recover space.
	b.Truncate(0)
	return 0, 0, io.EOF
	}
	b.lastRead = opReadRune
	c := b.buf[b.off]
	if c < utf8.RuneSelf {
	b.off++
	return rune(c), 1, nil
	}
	r, n := utf8.DecodeRune(b.buf[b.off:])
	b.off += 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 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 != opReadRune {
	return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
	}
	b.lastRead = opInvalid
	if b.off > 0 {
	_, n := utf8.DecodeLastRune(b.buf[0:b.off])
	b.off -= n
	}
	return nil
	}

	// UnreadByte unreads the last byte returned by the most recent
	// read operation. If write has happened since the last read, UnreadByte
	// returns an error.
	func (b *Buffer) UnreadByte() error {
	if b.lastRead != opReadRune && b.lastRead != opRead {
	return errors.New("bytes.Buffer: UnreadByte: previous operation was not a 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
	}

	// 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. It 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)}
	}