// Copyright 2014 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 http2 import ( "errors" "fmt" "sync" ) // Buffer chunks are allocated from a pool to reduce pressure on GC. // The maximum wasted space per dataBuffer is 2x the largest size class, // which happens when the dataBuffer has multiple chunks and there is // one unread byte in both the first and last chunks. We use a few size // classes to minimize overheads for servers that typically receive very // small request bodies. // // TODO: Benchmark to determine if the pools are necessary. The GC may have // improved enough that we can instead allocate chunks like this: // make([]byte, max(16<<10, expectedBytesRemaining)) var dataChunkPools = [...]sync.Pool{ {New: func() interface{} { return new([1 << 10]byte) }}, {New: func() interface{} { return new([2 << 10]byte) }}, {New: func() interface{} { return new([4 << 10]byte) }}, {New: func() interface{} { return new([8 << 10]byte) }}, {New: func() interface{} { return new([16 << 10]byte) }}, } func getDataBufferChunk(size int64) []byte { switch { case size <= 1<<10: return dataChunkPools[0].Get().(*[1 << 10]byte)[:] case size <= 2<<10: return dataChunkPools[1].Get().(*[2 << 10]byte)[:] case size <= 4<<10: return dataChunkPools[2].Get().(*[4 << 10]byte)[:] case size <= 8<<10: return dataChunkPools[3].Get().(*[8 << 10]byte)[:] default: return dataChunkPools[4].Get().(*[16 << 10]byte)[:] } } func putDataBufferChunk(p []byte) { switch len(p) { case 1 << 10: dataChunkPools[0].Put((*[1 << 10]byte)(p)) case 2 << 10: dataChunkPools[1].Put((*[2 << 10]byte)(p)) case 4 << 10: dataChunkPools[2].Put((*[4 << 10]byte)(p)) case 8 << 10: dataChunkPools[3].Put((*[8 << 10]byte)(p)) case 16 << 10: dataChunkPools[4].Put((*[16 << 10]byte)(p)) default: panic(fmt.Sprintf("unexpected buffer len=%v", len(p))) } } // dataBuffer is an io.ReadWriter backed by a list of data chunks. // Each dataBuffer is used to read DATA frames on a single stream. // The buffer is divided into chunks so the server can limit the // total memory used by a single connection without limiting the // request body size on any single stream. type dataBuffer struct { chunks [][]byte r int // next byte to read is chunks[0][r] w int // next byte to write is chunks[len(chunks)-1][w] size int // total buffered bytes expected int64 // we expect at least this many bytes in future Write calls (ignored if <= 0) } var errReadEmpty = errors.New("read from empty dataBuffer") // Read copies bytes from the buffer into p. // It is an error to read when no data is available. func (b *dataBuffer) Read(p []byte) (int, error) { if b.size == 0 { return 0, errReadEmpty } var ntotal int for len(p) > 0 && b.size > 0 { readFrom := b.bytesFromFirstChunk() n := copy(p, readFrom) p = p[n:] ntotal += n b.r += n b.size -= n // If the first chunk has been consumed, advance to the next chunk. if b.r == len(b.chunks[0]) { putDataBufferChunk(b.chunks[0]) end := len(b.chunks) - 1 copy(b.chunks[:end], b.chunks[1:]) b.chunks[end] = nil b.chunks = b.chunks[:end] b.r = 0 } } return ntotal, nil } func (b *dataBuffer) bytesFromFirstChunk() []byte { if len(b.chunks) == 1 { return b.chunks[0][b.r:b.w] } return b.chunks[0][b.r:] } // Len returns the number of bytes of the unread portion of the buffer. func (b *dataBuffer) Len() int { return b.size } // Write appends p to the buffer. func (b *dataBuffer) Write(p []byte) (int, error) { ntotal := len(p) for len(p) > 0 { // If the last chunk is empty, allocate a new chunk. Try to allocate // enough to fully copy p plus any additional bytes we expect to // receive. However, this may allocate less than len(p). want := int64(len(p)) if b.expected > want { want = b.expected } chunk := b.lastChunkOrAlloc(want) n := copy(chunk[b.w:], p) p = p[n:] b.w += n b.size += n b.expected -= int64(n) } return ntotal, nil } func (b *dataBuffer) lastChunkOrAlloc(want int64) []byte { if len(b.chunks) != 0 { last := b.chunks[len(b.chunks)-1] if b.w < len(last) { return last } } chunk := getDataBufferChunk(want) b.chunks = append(b.chunks, chunk) b.w = 0 return chunk }