414 lines
13 KiB
Go
414 lines
13 KiB
Go
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package bufio
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// Simple byte buffer for marshaling data.
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import (
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"bytes"
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"errors"
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"io"
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"unicode/utf8"
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)
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// A Buffer is a variable-sized buffer of bytes with Read and Write methods.
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// The zero value for Buffer is an empty buffer ready to use.
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type Buffer struct {
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buf []byte // contents are the bytes buf[off : len(buf)]
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off int // read at &buf[off], write at &buf[len(buf)]
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runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune
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bootstrap [64]byte // memory to hold first slice; helps small buffers (Printf) avoid allocation.
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lastRead readOp // last read operation, so that Unread* can work correctly.
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}
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// The readOp constants describe the last action performed on
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// the buffer, so that UnreadRune and UnreadByte can
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// check for invalid usage.
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type readOp int
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const (
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opInvalid readOp = iota // Non-read operation.
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opReadRune // Read rune.
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opRead // Any other read operation.
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)
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// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
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var ErrTooLarge = errors.New("bytes.Buffer: too large")
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// Bytes returns a slice of the contents of the unread portion of the buffer;
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// len(b.Bytes()) == b.Len(). If the caller changes the contents of the
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// returned slice, the contents of the buffer will change provided there
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// are no intervening method calls on the Buffer.
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func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
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// String returns the contents of the unread portion of the buffer
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// as a string. If the Buffer is a nil pointer, it returns "<nil>".
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func (b *Buffer) String() string {
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if b == nil {
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// Special case, useful in debugging.
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return "<nil>"
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}
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return string(b.buf[b.off:])
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}
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// Len returns the number of bytes of the unread portion of the buffer;
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// b.Len() == len(b.Bytes()).
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func (b *Buffer) Len() int { return len(b.buf) - b.off }
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// Truncate discards all but the first n unread bytes from the buffer.
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// It panics if n is negative or greater than the length of the buffer.
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func (b *Buffer) Truncate(n int) {
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b.lastRead = opInvalid
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switch {
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case n < 0 || n > b.Len():
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panic("bytes.Buffer: truncation out of range")
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case n == 0:
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// Reuse buffer space.
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b.off = 0
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}
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b.buf = b.buf[0 : b.off+n]
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}
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// Reset resets the buffer so it has no content.
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// b.Reset() is the same as b.Truncate(0).
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func (b *Buffer) Reset() { b.Truncate(0) }
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// grow grows the buffer to guarantee space for n more bytes.
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// It returns the index where bytes should be written.
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// If the buffer can't grow it will panic with ErrTooLarge.
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func (b *Buffer) grow(n int) int {
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m := b.Len()
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// If buffer is empty, reset to recover space.
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if m == 0 && b.off != 0 {
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b.Truncate(0)
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}
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if len(b.buf)+n > cap(b.buf) {
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var buf []byte
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if b.buf == nil && n <= len(b.bootstrap) {
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buf = b.bootstrap[0:]
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} else if m+n <= cap(b.buf)/2 {
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// We can slide things down instead of allocating a new
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// slice. We only need m+n <= cap(b.buf) to slide, but
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// we instead let capacity get twice as large so we
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// don't spend all our time copying.
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copy(b.buf[:], b.buf[b.off:])
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buf = b.buf[:m]
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} else {
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// not enough space anywhere
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buf = makeSlice(2*cap(b.buf) + n)
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copy(buf, b.buf[b.off:])
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}
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b.buf = buf
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b.off = 0
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}
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b.buf = b.buf[0 : b.off+m+n]
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return b.off + m
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}
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// Grow grows the buffer's capacity, if necessary, to guarantee space for
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// another n bytes. After Grow(n), at least n bytes can be written to the
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// buffer without another allocation.
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// If n is negative, Grow will panic.
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// If the buffer can't grow it will panic with ErrTooLarge.
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func (b *Buffer) Grow(n int) {
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if n < 0 {
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panic("bytes.Buffer.Grow: negative count")
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}
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m := b.grow(n)
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b.buf = b.buf[0:m]
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}
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// Write appends the contents of p to the buffer, growing the buffer as
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// needed. The return value n is the length of p; err is always nil. If the
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// buffer becomes too large, Write will panic with ErrTooLarge.
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func (b *Buffer) Write(p []byte) (n int, err error) {
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b.lastRead = opInvalid
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m := b.grow(len(p))
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return copy(b.buf[m:], p), nil
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}
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// WriteString appends the contents of s to the buffer, growing the buffer as
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// needed. The return value n is the length of s; err is always nil. If the
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// buffer becomes too large, WriteString will panic with ErrTooLarge.
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func (b *Buffer) WriteString(s string) (n int, err error) {
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b.lastRead = opInvalid
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m := b.grow(len(s))
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return copy(b.buf[m:], s), nil
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}
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// MinRead is the minimum slice size passed to a Read call by
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// Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
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// what is required to hold the contents of r, ReadFrom will not grow the
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// underlying buffer.
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const MinRead = 512
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// ReadFrom reads data from r until EOF and appends it to the buffer, growing
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// the buffer as needed. The return value n is the number of bytes read. Any
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// error except io.EOF encountered during the read is also returned. If the
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// buffer becomes too large, ReadFrom will panic with ErrTooLarge.
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func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
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b.lastRead = opInvalid
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// If buffer is empty, reset to recover space.
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if b.off >= len(b.buf) {
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b.Truncate(0)
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}
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for {
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if free := cap(b.buf) - len(b.buf); free < MinRead {
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// not enough space at end
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newBuf := b.buf
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if b.off+free < MinRead {
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// not enough space using beginning of buffer;
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// double buffer capacity
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newBuf = makeSlice(2*cap(b.buf) + MinRead)
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}
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copy(newBuf, b.buf[b.off:])
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b.buf = newBuf[:len(b.buf)-b.off]
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b.off = 0
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}
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m, e := r.Read(b.buf[len(b.buf):cap(b.buf)])
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b.buf = b.buf[0 : len(b.buf)+m]
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n += int64(m)
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if e == io.EOF {
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break
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}
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if e != nil {
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return n, e
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}
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}
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return n, nil // err is EOF, so return nil explicitly
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}
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// makeSlice allocates a slice of size n. If the allocation fails, it panics
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// with ErrTooLarge.
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func makeSlice(n int) []byte {
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// If the make fails, give a known error.
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defer func() {
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if recover() != nil {
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panic(ErrTooLarge)
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}
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}()
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return make([]byte, n)
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}
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// WriteTo writes data to w until the buffer is drained or an error occurs.
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// The return value n is the number of bytes written; it always fits into an
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// int, but it is int64 to match the io.WriterTo interface. Any error
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// encountered during the write is also returned.
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func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
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b.lastRead = opInvalid
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if b.off < len(b.buf) {
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nBytes := b.Len()
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m, e := w.Write(b.buf[b.off:])
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if m > nBytes {
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panic("bytes.Buffer.WriteTo: invalid Write count")
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}
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b.off += m
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n = int64(m)
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if e != nil {
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return n, e
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}
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// all bytes should have been written, by definition of
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// Write method in io.Writer
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if m != nBytes {
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return n, io.ErrShortWrite
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}
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}
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// Buffer is now empty; reset.
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b.Truncate(0)
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return
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}
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// WriteByte appends the byte c to the buffer, growing the buffer as needed.
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// The returned error is always nil, but is included to match bufio.Writer's
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// WriteByte. If the buffer becomes too large, WriteByte will panic with
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// ErrTooLarge.
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func (b *Buffer) WriteByte(c byte) error {
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b.lastRead = opInvalid
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m := b.grow(1)
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b.buf[m] = c
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return nil
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}
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// WriteRune appends the UTF-8 encoding of Unicode code point r to the
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// buffer, returning its length and an error, which is always nil but is
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// included to match bufio.Writer's WriteRune. The buffer is grown as needed;
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// if it becomes too large, WriteRune will panic with ErrTooLarge.
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func (b *Buffer) WriteRune(r rune) (n int, err error) {
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if r < utf8.RuneSelf {
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b.WriteByte(byte(r))
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return 1, nil
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}
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n = utf8.EncodeRune(b.runeBytes[0:], r)
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b.Write(b.runeBytes[0:n])
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return n, nil
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}
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// Read reads the next len(p) bytes from the buffer or until the buffer
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// is drained. The return value n is the number of bytes read. If the
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// buffer has no data to return, err is io.EOF (unless len(p) is zero);
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// otherwise it is nil.
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func (b *Buffer) Read(p []byte) (n int, err error) {
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b.lastRead = opInvalid
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if b.off >= len(b.buf) {
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// Buffer is empty, reset to recover space.
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b.Truncate(0)
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if len(p) == 0 {
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return
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}
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return 0, io.EOF
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}
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n = copy(p, b.buf[b.off:])
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b.off += n
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if n > 0 {
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b.lastRead = opRead
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}
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return
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}
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// Next returns a slice containing the next n bytes from the buffer,
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// advancing the buffer as if the bytes had been returned by Read.
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// If there are fewer than n bytes in the buffer, Next returns the entire buffer.
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// The slice is only valid until the next call to a read or write method.
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func (b *Buffer) Next(n int) []byte {
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b.lastRead = opInvalid
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m := b.Len()
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if n > m {
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n = m
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}
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data := b.buf[b.off : b.off+n]
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b.off += n
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if n > 0 {
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b.lastRead = opRead
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}
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return data
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}
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// ReadByte reads and returns the next byte from the buffer.
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// If no byte is available, it returns error io.EOF.
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func (b *Buffer) ReadByte() (c byte, err error) {
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b.lastRead = opInvalid
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if b.off >= len(b.buf) {
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// Buffer is empty, reset to recover space.
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b.Truncate(0)
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return 0, io.EOF
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}
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c = b.buf[b.off]
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b.off++
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b.lastRead = opRead
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return c, nil
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}
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// ReadRune reads and returns the next UTF-8-encoded
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// Unicode code point from the buffer.
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// If no bytes are available, the error returned is io.EOF.
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// If the bytes are an erroneous UTF-8 encoding, it
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// consumes one byte and returns U+FFFD, 1.
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func (b *Buffer) ReadRune() (r rune, size int, err error) {
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b.lastRead = opInvalid
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if b.off >= len(b.buf) {
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// Buffer is empty, reset to recover space.
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b.Truncate(0)
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return 0, 0, io.EOF
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}
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b.lastRead = opReadRune
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c := b.buf[b.off]
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if c < utf8.RuneSelf {
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b.off++
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return rune(c), 1, nil
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}
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r, n := utf8.DecodeRune(b.buf[b.off:])
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b.off += n
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return r, n, nil
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}
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// UnreadRune unreads the last rune returned by ReadRune.
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// If the most recent read or write operation on the buffer was
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// not a ReadRune, UnreadRune returns an error. (In this regard
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// it is stricter than UnreadByte, which will unread the last byte
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// from any read operation.)
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func (b *Buffer) UnreadRune() error {
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if b.lastRead != opReadRune {
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return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
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}
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b.lastRead = opInvalid
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if b.off > 0 {
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_, n := utf8.DecodeLastRune(b.buf[0:b.off])
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b.off -= n
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}
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return nil
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}
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// UnreadByte unreads the last byte returned by the most recent
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// read operation. If write has happened since the last read, UnreadByte
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// returns an error.
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func (b *Buffer) UnreadByte() error {
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if b.lastRead != opReadRune && b.lastRead != opRead {
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return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
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}
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b.lastRead = opInvalid
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if b.off > 0 {
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b.off--
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}
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return nil
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}
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// ReadBytes reads until the first occurrence of delim in the input,
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// returning a slice containing the data up to and including the delimiter.
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// If ReadBytes encounters an error before finding a delimiter,
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// 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
|
||
|
|
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)}
|
||
|
|
}
|