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 "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))
23var dataChunkPools = [...]sync.Pool{
24 {New: func() interface{} { return new([1 << 10]byte) }},
25 {New: func() interface{} { return new([2 << 10]byte) }},
26 {New: func() interface{} { return new([4 << 10]byte) }},
27 {New: func() interface{} { return new([8 << 10]byte) }},
28 {New: func() interface{} { return new([16 << 10]byte) }},
29}
30
31func getDataBufferChunk(size int64) []byte {
32 switch {
33 case size <= 1<<10:
34 return dataChunkPools[0].Get().(*[1 << 10]byte)[:]
35 case size <= 2<<10:
36 return dataChunkPools[1].Get().(*[2 << 10]byte)[:]
37 case size <= 4<<10:
38 return dataChunkPools[2].Get().(*[4 << 10]byte)[:]
39 case size <= 8<<10:
40 return dataChunkPools[3].Get().(*[8 << 10]byte)[:]
41 default:
42 return dataChunkPools[4].Get().(*[16 << 10]byte)[:]
43 }
44}
45
46func putDataBufferChunk(p []byte) {
47 switch len(p) {
48 case 1 << 10:
49 dataChunkPools[0].Put((*[1 << 10]byte)(p))
50 case 2 << 10:
51 dataChunkPools[1].Put((*[2 << 10]byte)(p))
52 case 4 << 10:
53 dataChunkPools[2].Put((*[4 << 10]byte)(p))
54 case 8 << 10:
55 dataChunkPools[3].Put((*[8 << 10]byte)(p))
56 case 16 << 10:
57 dataChunkPools[4].Put((*[16 << 10]byte)(p))
58 default:
59 panic(fmt.Sprintf("unexpected buffer len=%v", len(p)))
60 }
61}
62
63// dataBuffer is an io.ReadWriter backed by a list of data chunks.
64// Each dataBuffer is used to read DATA frames on a single stream.
65// The buffer is divided into chunks so the server can limit the
66// total memory used by a single connection without limiting the
67// request body size on any single stream.
68type dataBuffer struct {
69 chunks [][]byte
70 r int // next byte to read is chunks[0][r]
71 w int // next byte to write is chunks[len(chunks)-1][w]
72 size int // total buffered bytes
73 expected int64 // we expect at least this many bytes in future Write calls (ignored if <= 0)
74}
75
76var errReadEmpty = errors.New("read from empty dataBuffer")
77
78// Read copies bytes from the buffer into p.
79// It is an error to read when no data is available.
80func (b *dataBuffer) Read(p []byte) (int, error) {
81 if b.size == 0 {
82 return 0, errReadEmpty
83 }
84 var ntotal int
85 for len(p) > 0 && b.size > 0 {
86 readFrom := b.bytesFromFirstChunk()
87 n := copy(p, readFrom)
88 p = p[n:]
89 ntotal += n
90 b.r += n
91 b.size -= n
92 // If the first chunk has been consumed, advance to the next chunk.
93 if b.r == len(b.chunks[0]) {
94 putDataBufferChunk(b.chunks[0])
95 end := len(b.chunks) - 1
96 copy(b.chunks[:end], b.chunks[1:])
97 b.chunks[end] = nil
98 b.chunks = b.chunks[:end]
99 b.r = 0
100 }
101 }
102 return ntotal, nil
103}
104
105func (b *dataBuffer) bytesFromFirstChunk() []byte {
106 if len(b.chunks) == 1 {
107 return b.chunks[0][b.r:b.w]
108 }
109 return b.chunks[0][b.r:]
110}
111
112// Len returns the number of bytes of the unread portion of the buffer.
113func (b *dataBuffer) Len() int {
114 return b.size
115}
116
117// Write appends p to the buffer.
118func (b *dataBuffer) Write(p []byte) (int, error) {
119 ntotal := len(p)
120 for len(p) > 0 {
121 // If the last chunk is empty, allocate a new chunk. Try to allocate
122 // enough to fully copy p plus any additional bytes we expect to
123 // receive. However, this may allocate less than len(p).
124 want := int64(len(p))
125 if b.expected > want {
126 want = b.expected
127 }
128 chunk := b.lastChunkOrAlloc(want)
129 n := copy(chunk[b.w:], p)
130 p = p[n:]
131 b.w += n
132 b.size += n
133 b.expected -= int64(n)
134 }
135 return ntotal, nil
136}
137
138func (b *dataBuffer) lastChunkOrAlloc(want int64) []byte {
139 if len(b.chunks) != 0 {
140 last := b.chunks[len(b.chunks)-1]
141 if b.w < len(last) {
142 return last
143 }
144 }
145 chunk := getDataBufferChunk(want)
146 b.chunks = append(b.chunks, chunk)
147 b.w = 0
148 return chunk
149}