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
|
// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed 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 buffer
import (
"fmt"
"reflect"
"unsafe"
"github.com/jacobsa/fuse/internal/fusekernel"
)
// OutMessageHeaderSize is the size of the leading header in every
// properly-constructed OutMessage. Reset brings the message back to this size.
const OutMessageHeaderSize = int(unsafe.Sizeof(fusekernel.OutHeader{}))
// OutMessage provides a mechanism for constructing a single contiguous fuse
// message from multiple segments, where the first segment is always a
// fusekernel.OutHeader message.
//
// Must be initialized with Reset.
type OutMessage struct {
header fusekernel.OutHeader
Sglist [][]byte
}
// Reset resets m so that it's ready to be used again. Afterward, the contents
// are solely a zeroed fusekernel.OutHeader struct.
func (m *OutMessage) Reset() {
m.header = fusekernel.OutHeader{}
m.Sglist = nil
}
// OutHeader returns a pointer to the header at the start of the message.
func (m *OutMessage) OutHeader() *fusekernel.OutHeader {
return &m.header
}
// Grow adds a new buffer of <n> bytes to the message, returning a pointer to
// the start of the new segment, which is guaranteed to be zeroed.
func (m *OutMessage) Grow(n int) unsafe.Pointer {
b := make([]byte, n)
m.Append(b)
p := unsafe.Pointer(&b[0])
return p
}
// ShrinkTo shrinks m to the given size. It panics if the size is greater than
// Len() or less than OutMessageHeaderSize.
func (m *OutMessage) ShrinkTo(n int) {
if n < OutMessageHeaderSize || n > m.Len() {
panic(fmt.Sprintf(
"ShrinkTo(%d) out of range (current Len: %d)",
n,
m.Len()))
}
if n == OutMessageHeaderSize {
m.Sglist = nil
} else {
i := 1
n -= OutMessageHeaderSize
for len(m.Sglist) > i && n >= len(m.Sglist[i]) {
n -= len(m.Sglist[i])
i++
}
if n > 0 {
m.Sglist[i] = m.Sglist[i][0:n]
i++
}
m.Sglist = m.Sglist[0:i]
}
}
// Append is equivalent to growing by len(src), then copying src over the new
// segment. Int panics if there is not enough room available.
func (m *OutMessage) Append(src ...[]byte) {
if m.Sglist == nil {
// First element of Sglist is pre-filled with a pointer to the header
// to allow sending it with a single writev() call without copying the
// slice again
m.Sglist = append(m.Sglist, m.OutHeaderBytes())
}
m.Sglist = append(m.Sglist, src...)
return
}
// AppendString is like Append, but accepts string input.
func (m *OutMessage) AppendString(src string) {
m.Append([]byte(src))
return
}
// Len returns the current size of the message, including the leading header.
func (m *OutMessage) Len() int {
if m.Sglist == nil {
return OutMessageHeaderSize
}
// First element of Sglist is the header, so we don't need to count it here
r := 0
for _, b := range m.Sglist {
r += len(b)
}
return r
}
// OutHeaderBytes returns a byte slice containing the current header.
func (m *OutMessage) OutHeaderBytes() []byte {
l := OutMessageHeaderSize
sh := reflect.SliceHeader{
Data: uintptr(unsafe.Pointer(&m.header)),
Len: l,
Cap: l,
}
return *(*[]byte)(unsafe.Pointer(&sh))
}
|
