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// 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 (
"io"
"os"
"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.
)
// 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 }
// Truncate discards all but the first n unread bytes from the buffer.
// It is an error to call b.Truncate(n) with n > b.Len().
func (b *Buffer) Truncate(n int) {
b.lastRead = opInvalid
if 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 buffer to guarantee space for n more bytes.
// Return index where bytes should be written.
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 {
// not enough space anywhere
buf = make([]byte, 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
}
// Write appends the contents of p to the buffer. The return
// value n is the length of p; err is always nil.
func (b *Buffer) Write(p []byte) (n int, err os.Error) {
b.lastRead = opInvalid
m := b.grow(len(p))
copy(b.buf[m:], p)
return len(p), nil
}
// WriteString appends the contents of s to the buffer. The return
// value n is the length of s; err is always nil.
func (b *Buffer) WriteString(s string) (n int, err os.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.
// The return value n is the number of bytes read.
// Any error except os.EOF encountered during the read
// is also returned.
func (b *Buffer) ReadFrom(r io.Reader) (n int64, err os.Error) {
b.lastRead = opInvalid
// If buffer is empty, reset to recover space.
if b.off >= len(b.buf) {
b.Truncate(0)
}
for {
if cap(b.buf)-len(b.buf) < MinRead {
var newBuf []byte
// can we get space without allocation?
if b.off+cap(b.buf)-len(b.buf) >= MinRead {
// reuse beginning of buffer
newBuf = b.buf[0 : len(b.buf)-b.off]
} else {
// not enough space at end; put space on end
newBuf = make([]byte, len(b.buf)-b.off, 2*(cap(b.buf)-b.off)+MinRead)
}
copy(newBuf, b.buf[b.off:])
b.buf = newBuf
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 == os.EOF {
break
}
if e != nil {
return n, e
}
}
return n, nil // err is EOF, so return nil explicitly
}
// WriteTo writes data to w until the buffer is drained or an error
// occurs. The return value n is the number of bytes written.
// Any error encountered during the write is also returned.
func (b *Buffer) WriteTo(w io.Writer) (n int64, err os.Error) {
b.lastRead = opInvalid
for b.off < len(b.buf) {
m, e := w.Write(b.buf[b.off:])
n += int64(m)
b.off += m
if e != nil {
return n, e
}
}
// Buffer is now empty; reset.
b.Truncate(0)
return
}
// WriteByte appends the byte c to the buffer.
// The returned error is always nil, but is included
// to match bufio.Writer's WriteByte.
func (b *Buffer) WriteByte(c byte) os.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.
func (b *Buffer) WriteRune(r int) (n int, err os.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 os.EOF even if len(p) is zero;
// otherwise it is nil.
func (b *Buffer) Read(p []byte) (n int, err os.Error) {
b.lastRead = opInvalid
if b.off >= len(b.buf) {
// Buffer is empty, reset to recover space.
b.Truncate(0)
return 0, os.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 os.EOF.
func (b *Buffer) ReadByte() (c byte, err os.Error) {
b.lastRead = opInvalid
if b.off >= len(b.buf) {
// Buffer is empty, reset to recover space.
b.Truncate(0)
return 0, os.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 os.EOF.
// If the bytes are an erroneous UTF-8 encoding, it
// consumes one byte and returns U+FFFD, 1.
func (b *Buffer) ReadRune() (r int, size int, err os.Error) {
b.lastRead = opInvalid
if b.off >= len(b.buf) {
// Buffer is empty, reset to recover space.
b.Truncate(0)
return 0, 0, os.EOF
}
b.lastRead = opReadRune
c := b.buf[b.off]
if c < utf8.RuneSelf {
b.off++
return int(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() os.Error {
if b.lastRead != opReadRune {
return os.ErrorString("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() os.Error {
if b.lastRead == opReadRune || b.lastRead == opRead {
return os.ErrorString("bytes.Buffer: UnreadByte: previous operation was not a read")
}
b.lastRead = opInvalid
if b.off > 0 {
b.off--
}
return nil
}
// 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 to size the internal buffer for writing. To do that,
// buf should have the desired capacity but a length of zero.
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.
func NewBufferString(s string) *Buffer {
return &Buffer{buf: []byte(s)}
}