294 lines
9.1 KiB
Go
294 lines
9.1 KiB
Go
// 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 util
|
|
|
|
// This a copy of Go std bytes.Buffer with some modification
|
|
// and some features stripped.
|
|
|
|
import (
|
|
"bytes"
|
|
"io"
|
|
)
|
|
|
|
// 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 (Printf) avoid allocation.
|
|
}
|
|
|
|
// 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 panics if n is negative or greater than the length of the buffer.
|
|
func (b *Buffer) Truncate(n int) {
|
|
switch {
|
|
case n < 0 || n > b.Len():
|
|
panic("leveldb/util.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 bytes.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
|
|
}
|
|
|
|
// Alloc allocs n bytes of slice from the buffer, growing the buffer as
|
|
// needed. If n is negative, Alloc will panic.
|
|
// If the buffer can't grow it will panic with bytes.ErrTooLarge.
|
|
func (b *Buffer) Alloc(n int) []byte {
|
|
if n < 0 {
|
|
panic("leveldb/util.Buffer.Alloc: negative count")
|
|
}
|
|
m := b.grow(n)
|
|
return b.buf[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 bytes.ErrTooLarge.
|
|
func (b *Buffer) Grow(n int) {
|
|
if n < 0 {
|
|
panic("leveldb/util.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 bytes.ErrTooLarge.
|
|
func (b *Buffer) Write(p []byte) (n int, err error) {
|
|
m := b.grow(len(p))
|
|
return copy(b.buf[m:], p), 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 bytes.ErrTooLarge.
|
|
func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
|
|
// 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 bytes.ErrTooLarge.
|
|
func makeSlice(n int) []byte {
|
|
// If the make fails, give a known error.
|
|
defer func() {
|
|
if recover() != nil {
|
|
panic(bytes.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) {
|
|
if b.off < len(b.buf) {
|
|
nBytes := b.Len()
|
|
m, e := w.Write(b.buf[b.off:])
|
|
if m > nBytes {
|
|
panic("leveldb/util.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
|
|
// bytes.ErrTooLarge.
|
|
func (b *Buffer) WriteByte(c byte) error {
|
|
m := b.grow(1)
|
|
b.buf[m] = c
|
|
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 io.EOF (unless len(p) is zero);
|
|
// otherwise it is nil.
|
|
func (b *Buffer) Read(p []byte) (n int, err error) {
|
|
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
|
|
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 {
|
|
m := b.Len()
|
|
if n > m {
|
|
n = m
|
|
}
|
|
data := b.buf[b.off : b.off+n]
|
|
b.off += n
|
|
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) {
|
|
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++
|
|
return c, 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 := bytes.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
|
|
return line, 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} }
|