-
Notifications
You must be signed in to change notification settings - Fork 3.4k
/
buf_reader.go
212 lines (185 loc) · 5 KB
/
buf_reader.go
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
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package utils
import (
"bufio"
"errors"
"fmt"
"io"
)
// bufferedReader is similar to bufio.Reader except
// it will expand the buffer if necessary when asked to Peek
// more bytes than are in the buffer
type bufferedReader struct {
bufferSz int
buf []byte
r, w int
rd io.Reader
err error
}
// NewBufferedReader returns a buffered reader with similar semantics to bufio.Reader
// except Peek will expand the internal buffer if needed rather than return
// an error.
func NewBufferedReader(rd io.Reader, sz int) *bufferedReader {
// if rd is already a buffered reader whose buffer is >= the requested size
// then just return it as is. no need to make a new object.
b, ok := rd.(*bufferedReader)
if ok && len(b.buf) >= sz {
return b
}
r := &bufferedReader{
rd: rd,
}
r.resizeBuffer(sz)
return r
}
func (b *bufferedReader) resetBuffer() {
if b.buf == nil {
b.buf = make([]byte, b.bufferSz)
} else if b.bufferSz > cap(b.buf) {
buf := b.buf
b.buf = make([]byte, b.bufferSz)
copy(b.buf, buf)
} else {
b.buf = b.buf[:b.bufferSz]
}
}
func (b *bufferedReader) resizeBuffer(newSize int) {
b.bufferSz = newSize
b.resetBuffer()
}
func (b *bufferedReader) fill() error {
// slide existing data to the beginning
if b.r > 0 {
copy(b.buf, b.buf[b.r:b.w])
b.w -= b.r
b.r = 0
}
if b.w >= len(b.buf) {
return fmt.Errorf("arrow/bufferedreader: %w", bufio.ErrBufferFull)
}
n, err := io.ReadAtLeast(b.rd, b.buf[b.w:], 1)
if n < 0 {
return fmt.Errorf("arrow/bufferedreader: filling buffer: %w", bufio.ErrNegativeCount)
}
b.w += n
b.err = err
return nil
}
func (b *bufferedReader) readErr() error {
err := b.err
b.err = nil
return err
}
// Buffered returns the number of bytes currently buffered
func (b *bufferedReader) Buffered() int { return b.w - b.r }
// SetBufferSize resets the size of the internal buffer to the desired size.
// Will return an error if newSize is <= 0 or if newSize is less than the size
// of the buffered data.
func (b *bufferedReader) SetBufferSize(newSize int) error {
if newSize <= 0 {
return errors.New("buffer size should be positive")
}
if b.w >= newSize {
return errors.New("cannot shrink read buffer if buffered data remains")
}
b.resizeBuffer(newSize)
return nil
}
// Peek will buffer and return n bytes from the underlying reader without advancing
// the reader itself. If n is larger than the current buffer size, the buffer will
// be expanded to accommodate the extra bytes rather than error.
func (b *bufferedReader) Peek(n int) ([]byte, error) {
if n < 0 {
return nil, fmt.Errorf("arrow/bufferedreader: %w", bufio.ErrNegativeCount)
}
if n > len(b.buf) {
if err := b.SetBufferSize(n); err != nil {
return nil, err
}
}
for b.w-b.r < n && b.w-b.r < len(b.buf) && b.err == nil {
b.fill() // b.w-b.r < len(b.buf) => buffer is not full
}
return b.buf[b.r : b.r+n], b.readErr()
}
// Discard skips the next n bytes either by advancing the internal buffer
// or by reading that many bytes in and throwing them away.
func (b *bufferedReader) Discard(n int) (discarded int, err error) {
if n < 0 {
return 0, fmt.Errorf("arrow/bufferedreader: %w", bufio.ErrNegativeCount)
}
if n == 0 {
return
}
remain := n
for {
skip := b.Buffered()
if skip == 0 {
b.fill()
skip = b.Buffered()
}
if skip > remain {
skip = remain
}
b.r += skip
remain -= skip
if remain == 0 {
return n, nil
}
if b.err != nil {
return n - remain, b.readErr()
}
}
}
func (b *bufferedReader) Read(p []byte) (n int, err error) {
n = len(p)
if n == 0 {
if b.Buffered() > 0 {
return 0, nil
}
return 0, b.readErr()
}
if b.r == b.w {
if b.err != nil {
return 0, b.readErr()
}
if len(p) >= len(b.buf) {
// large read, empty buffer
// read directly into p to avoid extra copy
n, b.err = b.rd.Read(p)
if n < 0 {
return n, fmt.Errorf("arrow/bufferedreader: %w", bufio.ErrNegativeCount)
}
return n, b.readErr()
}
// one read
// don't use b.fill
b.r, b.w = 0, 0
n, b.err = b.rd.Read(b.buf)
if n < 0 {
return n, fmt.Errorf("arrow/bufferedreader: %w", bufio.ErrNegativeCount)
}
if n == 0 {
return 0, b.readErr()
}
b.w += n
}
// copy as much as we can
n = copy(p, b.buf[b.r:b.w])
b.r += n
return n, nil
}