1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
|
// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
//
// Copyright 2013 The Go-MySQL-Driver Authors. All rights reserved.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package mysql
import (
"io"
"net"
"time"
)
const defaultBufSize = 4096
const maxCachedBufSize = 256 * 1024
// A buffer which is used for both reading and writing.
// This is possible since communication on each connection is synchronous.
// In other words, we can't write and read simultaneously on the same connection.
// The buffer is similar to bufio.Reader / Writer but zero-copy-ish
// Also highly optimized for this particular use case.
// This buffer is backed by two byte slices in a double-buffering scheme
type buffer struct {
buf []byte // buf is a byte buffer who's length and capacity are equal.
nc net.Conn
idx int
length int
timeout time.Duration
dbuf [2][]byte // dbuf is an array with the two byte slices that back this buffer
flipcnt uint // flipccnt is the current buffer counter for double-buffering
}
// newBuffer allocates and returns a new buffer.
func newBuffer(nc net.Conn) buffer {
fg := make([]byte, defaultBufSize)
return buffer{
buf: fg,
nc: nc,
dbuf: [2][]byte{fg, nil},
}
}
// flip replaces the active buffer with the background buffer
// this is a delayed flip that simply increases the buffer counter;
// the actual flip will be performed the next time we call `buffer.fill`
func (b *buffer) flip() {
b.flipcnt += 1
}
// fill reads into the buffer until at least _need_ bytes are in it
func (b *buffer) fill(need int) error {
n := b.length
// fill data into its double-buffering target: if we've called
// flip on this buffer, we'll be copying to the background buffer,
// and then filling it with network data; otherwise we'll just move
// the contents of the current buffer to the front before filling it
dest := b.dbuf[b.flipcnt&1]
// grow buffer if necessary to fit the whole packet.
if need > len(dest) {
// Round up to the next multiple of the default size
dest = make([]byte, ((need/defaultBufSize)+1)*defaultBufSize)
// if the allocated buffer is not too large, move it to backing storage
// to prevent extra allocations on applications that perform large reads
if len(dest) <= maxCachedBufSize {
b.dbuf[b.flipcnt&1] = dest
}
}
// if we're filling the fg buffer, move the existing data to the start of it.
// if we're filling the bg buffer, copy over the data
if n > 0 {
copy(dest[:n], b.buf[b.idx:])
}
b.buf = dest
b.idx = 0
for {
if b.timeout > 0 {
if err := b.nc.SetReadDeadline(time.Now().Add(b.timeout)); err != nil {
return err
}
}
nn, err := b.nc.Read(b.buf[n:])
n += nn
switch err {
case nil:
if n < need {
continue
}
b.length = n
return nil
case io.EOF:
if n >= need {
b.length = n
return nil
}
return io.ErrUnexpectedEOF
default:
return err
}
}
}
// returns next N bytes from buffer.
// The returned slice is only guaranteed to be valid until the next read
func (b *buffer) readNext(need int) ([]byte, error) {
if b.length < need {
// refill
if err := b.fill(need); err != nil {
return nil, err
}
}
offset := b.idx
b.idx += need
b.length -= need
return b.buf[offset:b.idx], nil
}
// takeBuffer returns a buffer with the requested size.
// If possible, a slice from the existing buffer is returned.
// Otherwise a bigger buffer is made.
// Only one buffer (total) can be used at a time.
func (b *buffer) takeBuffer(length int) ([]byte, error) {
if b.length > 0 {
return nil, ErrBusyBuffer
}
// test (cheap) general case first
if length <= cap(b.buf) {
return b.buf[:length], nil
}
if length < maxPacketSize {
b.buf = make([]byte, length)
return b.buf, nil
}
// buffer is larger than we want to store.
return make([]byte, length), nil
}
// takeSmallBuffer is shortcut which can be used if length is
// known to be smaller than defaultBufSize.
// Only one buffer (total) can be used at a time.
func (b *buffer) takeSmallBuffer(length int) ([]byte, error) {
if b.length > 0 {
return nil, ErrBusyBuffer
}
return b.buf[:length], nil
}
// takeCompleteBuffer returns the complete existing buffer.
// This can be used if the necessary buffer size is unknown.
// cap and len of the returned buffer will be equal.
// Only one buffer (total) can be used at a time.
func (b *buffer) takeCompleteBuffer() ([]byte, error) {
if b.length > 0 {
return nil, ErrBusyBuffer
}
return b.buf, nil
}
// store stores buf, an updated buffer, if its suitable to do so.
func (b *buffer) store(buf []byte) error {
if b.length > 0 {
return ErrBusyBuffer
} else if cap(buf) <= maxPacketSize && cap(buf) > cap(b.buf) {
b.buf = buf[:cap(buf)]
}
return nil
}
|