1// Copyright 2014 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package http2 6 7import ( 8 "errors" 9) 10 11// fixedBuffer is an io.ReadWriter backed by a fixed size buffer. 12// It never allocates, but moves old data as new data is written. 13type fixedBuffer struct { 14 buf []byte 15 r, w int 16} 17 18var ( 19 errReadEmpty = errors.New("read from empty fixedBuffer") 20 errWriteFull = errors.New("write on full fixedBuffer") 21) 22 23// Read copies bytes from the buffer into p. 24// It is an error to read when no data is available. 25func (b *fixedBuffer) Read(p []byte) (n int, err error) { 26 if b.r == b.w { 27 return 0, errReadEmpty 28 } 29 n = copy(p, b.buf[b.r:b.w]) 30 b.r += n 31 if b.r == b.w { 32 b.r = 0 33 b.w = 0 34 } 35 return n, nil 36} 37 38// Len returns the number of bytes of the unread portion of the buffer. 39func (b *fixedBuffer) Len() int { 40 return b.w - b.r 41} 42 43// Write copies bytes from p into the buffer. 44// It is an error to write more data than the buffer can hold. 45func (b *fixedBuffer) Write(p []byte) (n int, err error) { 46 // Slide existing data to beginning. 47 if b.r > 0 && len(p) > len(b.buf)-b.w { 48 copy(b.buf, b.buf[b.r:b.w]) 49 b.w -= b.r 50 b.r = 0 51 } 52 53 // Write new data. 54 n = copy(b.buf[b.w:], p) 55 b.w += n 56 if n < len(p) { 57 err = errWriteFull 58 } 59 return n, err 60} 61