Dinesh Belwalkar | e63f7f9 | 2019-11-22 23:11:16 +0000 | [diff] [blame^] | 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 | |
| 5 | package http2 |
| 6 | |
| 7 | import ( |
| 8 | "errors" |
| 9 | "fmt" |
| 10 | "sync" |
| 11 | ) |
| 12 | |
| 13 | // Buffer chunks are allocated from a pool to reduce pressure on GC. |
| 14 | // The maximum wasted space per dataBuffer is 2x the largest size class, |
| 15 | // which happens when the dataBuffer has multiple chunks and there is |
| 16 | // one unread byte in both the first and last chunks. We use a few size |
| 17 | // classes to minimize overheads for servers that typically receive very |
| 18 | // small request bodies. |
| 19 | // |
| 20 | // TODO: Benchmark to determine if the pools are necessary. The GC may have |
| 21 | // improved enough that we can instead allocate chunks like this: |
| 22 | // make([]byte, max(16<<10, expectedBytesRemaining)) |
| 23 | var ( |
| 24 | dataChunkSizeClasses = []int{ |
| 25 | 1 << 10, |
| 26 | 2 << 10, |
| 27 | 4 << 10, |
| 28 | 8 << 10, |
| 29 | 16 << 10, |
| 30 | } |
| 31 | dataChunkPools = [...]sync.Pool{ |
| 32 | {New: func() interface{} { return make([]byte, 1<<10) }}, |
| 33 | {New: func() interface{} { return make([]byte, 2<<10) }}, |
| 34 | {New: func() interface{} { return make([]byte, 4<<10) }}, |
| 35 | {New: func() interface{} { return make([]byte, 8<<10) }}, |
| 36 | {New: func() interface{} { return make([]byte, 16<<10) }}, |
| 37 | } |
| 38 | ) |
| 39 | |
| 40 | func getDataBufferChunk(size int64) []byte { |
| 41 | i := 0 |
| 42 | for ; i < len(dataChunkSizeClasses)-1; i++ { |
| 43 | if size <= int64(dataChunkSizeClasses[i]) { |
| 44 | break |
| 45 | } |
| 46 | } |
| 47 | return dataChunkPools[i].Get().([]byte) |
| 48 | } |
| 49 | |
| 50 | func putDataBufferChunk(p []byte) { |
| 51 | for i, n := range dataChunkSizeClasses { |
| 52 | if len(p) == n { |
| 53 | dataChunkPools[i].Put(p) |
| 54 | return |
| 55 | } |
| 56 | } |
| 57 | panic(fmt.Sprintf("unexpected buffer len=%v", len(p))) |
| 58 | } |
| 59 | |
| 60 | // dataBuffer is an io.ReadWriter backed by a list of data chunks. |
| 61 | // Each dataBuffer is used to read DATA frames on a single stream. |
| 62 | // The buffer is divided into chunks so the server can limit the |
| 63 | // total memory used by a single connection without limiting the |
| 64 | // request body size on any single stream. |
| 65 | type dataBuffer struct { |
| 66 | chunks [][]byte |
| 67 | r int // next byte to read is chunks[0][r] |
| 68 | w int // next byte to write is chunks[len(chunks)-1][w] |
| 69 | size int // total buffered bytes |
| 70 | expected int64 // we expect at least this many bytes in future Write calls (ignored if <= 0) |
| 71 | } |
| 72 | |
| 73 | var errReadEmpty = errors.New("read from empty dataBuffer") |
| 74 | |
| 75 | // Read copies bytes from the buffer into p. |
| 76 | // It is an error to read when no data is available. |
| 77 | func (b *dataBuffer) Read(p []byte) (int, error) { |
| 78 | if b.size == 0 { |
| 79 | return 0, errReadEmpty |
| 80 | } |
| 81 | var ntotal int |
| 82 | for len(p) > 0 && b.size > 0 { |
| 83 | readFrom := b.bytesFromFirstChunk() |
| 84 | n := copy(p, readFrom) |
| 85 | p = p[n:] |
| 86 | ntotal += n |
| 87 | b.r += n |
| 88 | b.size -= n |
| 89 | // If the first chunk has been consumed, advance to the next chunk. |
| 90 | if b.r == len(b.chunks[0]) { |
| 91 | putDataBufferChunk(b.chunks[0]) |
| 92 | end := len(b.chunks) - 1 |
| 93 | copy(b.chunks[:end], b.chunks[1:]) |
| 94 | b.chunks[end] = nil |
| 95 | b.chunks = b.chunks[:end] |
| 96 | b.r = 0 |
| 97 | } |
| 98 | } |
| 99 | return ntotal, nil |
| 100 | } |
| 101 | |
| 102 | func (b *dataBuffer) bytesFromFirstChunk() []byte { |
| 103 | if len(b.chunks) == 1 { |
| 104 | return b.chunks[0][b.r:b.w] |
| 105 | } |
| 106 | return b.chunks[0][b.r:] |
| 107 | } |
| 108 | |
| 109 | // Len returns the number of bytes of the unread portion of the buffer. |
| 110 | func (b *dataBuffer) Len() int { |
| 111 | return b.size |
| 112 | } |
| 113 | |
| 114 | // Write appends p to the buffer. |
| 115 | func (b *dataBuffer) Write(p []byte) (int, error) { |
| 116 | ntotal := len(p) |
| 117 | for len(p) > 0 { |
| 118 | // If the last chunk is empty, allocate a new chunk. Try to allocate |
| 119 | // enough to fully copy p plus any additional bytes we expect to |
| 120 | // receive. However, this may allocate less than len(p). |
| 121 | want := int64(len(p)) |
| 122 | if b.expected > want { |
| 123 | want = b.expected |
| 124 | } |
| 125 | chunk := b.lastChunkOrAlloc(want) |
| 126 | n := copy(chunk[b.w:], p) |
| 127 | p = p[n:] |
| 128 | b.w += n |
| 129 | b.size += n |
| 130 | b.expected -= int64(n) |
| 131 | } |
| 132 | return ntotal, nil |
| 133 | } |
| 134 | |
| 135 | func (b *dataBuffer) lastChunkOrAlloc(want int64) []byte { |
| 136 | if len(b.chunks) != 0 { |
| 137 | last := b.chunks[len(b.chunks)-1] |
| 138 | if b.w < len(last) { |
| 139 | return last |
| 140 | } |
| 141 | } |
| 142 | chunk := getDataBufferChunk(want) |
| 143 | b.chunks = append(b.chunks, chunk) |
| 144 | b.w = 0 |
| 145 | return chunk |
| 146 | } |