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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";
)
// Copy from string to byte array at offset doff. Assume there's room.
func copyString(dst []byte, doff int, str string) {
for soff := 0; soff < len(str); soff++ {
dst[doff] = str[soff];
doff++;
}
}
// Copy from bytes to byte array at offset doff. Assume there's room.
func copyBytes(dst []byte, doff int, src []byte) {
if len(src) == 1 {
dst[doff] = src[0];
return;
}
copy(dst[doff:], src);
}
// 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)]
oneByte [1]byte; // avoid allocation of slice on each WriteByte
}
// Bytes returns the contents of the unread portion of the buffer;
// len(b.Bytes()) == b.Len().
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) {
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) }
// 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) {
m := b.Len();
n = len(p);
if len(b.buf)+n > cap(b.buf) {
// not enough space at end
buf := b.buf;
if m+n > cap(b.buf) {
// not enough space anywhere
buf = make([]byte, 2*cap(b.buf)+n)
}
copyBytes(buf, 0, b.buf[b.off:b.off+m]);
b.buf = buf;
b.off = 0;
}
b.buf = b.buf[0 : b.off+m+n];
copyBytes(b.buf, b.off+m, p);
return n, 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) {
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[b.off : 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) {
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
}
}
return;
}
// 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) {
m := b.Len();
n = len(s);
if len(b.buf)+n > cap(b.buf) {
// not enough space at end
buf := b.buf;
if m+n > cap(b.buf) {
// not enough space anywhere
buf = make([]byte, 2*cap(b.buf)+n)
}
copyBytes(buf, 0, b.buf[b.off:b.off+m]);
b.buf = buf;
b.off = 0;
}
b.buf = b.buf[0 : b.off+m+n];
copyString(b.buf, b.off+m, s);
return n, nil;
}
// 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.oneByte[0] = c;
b.Write(&b.oneByte);
return 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) {
if b.off >= len(b.buf) {
return 0, os.EOF
}
m := b.Len();
n = len(p);
if n > m {
// more bytes requested than available
n = m
}
copyBytes(p, 0, b.buf[b.off:b.off+n]);
b.off += n;
return n, err;
}
// 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) {
if b.off >= len(b.buf) {
return 0, os.EOF
}
c = b.buf[b.off];
b.off++;
return c, nil;
}
// NewBuffer creates and initializes a new Buffer
// using buf as its initial contents.
func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }
// NewBufferString creates and initializes a new Buffer
// using string s as its initial contents.
func NewBufferString(s string) *Buffer {
buf := make([]byte, len(s));
copyString(buf, 0, s);
return &Buffer{buf: buf};
}
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