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
|
package gitdiff
import (
"errors"
"fmt"
"io"
)
// BinaryApplier applies binary changes described in a fragment to source data.
// The applier must be closed after use.
type BinaryApplier struct {
dst io.Writer
src io.ReaderAt
closed bool
dirty bool
}
// NewBinaryApplier creates an BinaryApplier that reads data from src and
// writes modified data to dst.
func NewBinaryApplier(dst io.Writer, src io.ReaderAt) *BinaryApplier {
a := BinaryApplier{
dst: dst,
src: src,
}
return &a
}
// ApplyFragment applies the changes in the fragment f and writes the result to
// dst. ApplyFragment can be called at most once.
//
// If an error occurs while applying, ApplyFragment returns an *ApplyError that
// annotates the error with additional information. If the error is because of
// a conflict between a fragment and the source, the wrapped error will be a
// *Conflict.
func (a *BinaryApplier) ApplyFragment(f *BinaryFragment) error {
if f == nil {
return applyError(errors.New("nil fragment"))
}
if a.closed {
return applyError(errApplierClosed)
}
if a.dirty {
return applyError(errApplyInProgress)
}
// mark an apply as in progress, even if it fails before making changes
a.dirty = true
switch f.Method {
case BinaryPatchLiteral:
if _, err := a.dst.Write(f.Data); err != nil {
return applyError(err)
}
case BinaryPatchDelta:
if err := applyBinaryDeltaFragment(a.dst, a.src, f.Data); err != nil {
return applyError(err)
}
default:
return applyError(fmt.Errorf("unsupported binary patch method: %v", f.Method))
}
return nil
}
// Close writes any data following the last applied fragment and prevents
// future calls to ApplyFragment.
func (a *BinaryApplier) Close() (err error) {
if a.closed {
return nil
}
a.closed = true
if !a.dirty {
_, err = copyFrom(a.dst, a.src, 0)
} else {
// do nothing, applying a binary fragment copies all data
}
return err
}
func applyBinaryDeltaFragment(dst io.Writer, src io.ReaderAt, frag []byte) error {
srcSize, delta := readBinaryDeltaSize(frag)
if err := checkBinarySrcSize(src, srcSize); err != nil {
return err
}
dstSize, delta := readBinaryDeltaSize(delta)
for len(delta) > 0 {
op := delta[0]
if op == 0 {
return errors.New("invalid delta opcode 0")
}
var n int64
var err error
switch op & 0x80 {
case 0x80:
n, delta, err = applyBinaryDeltaCopy(dst, op, delta[1:], src)
case 0x00:
n, delta, err = applyBinaryDeltaAdd(dst, op, delta[1:])
}
if err != nil {
return err
}
dstSize -= n
}
if dstSize != 0 {
return errors.New("corrupt binary delta: insufficient or extra data")
}
return nil
}
// readBinaryDeltaSize reads a variable length size from a delta-encoded binary
// fragment, returing the size and the unused data. Data is encoded as:
//
// [[1xxxxxxx]...] [0xxxxxxx]
//
// in little-endian order, with 7 bits of the value per byte.
func readBinaryDeltaSize(d []byte) (size int64, rest []byte) {
shift := uint(0)
for i, b := range d {
size |= int64(b&0x7F) << shift
shift += 7
if b <= 0x7F {
return size, d[i+1:]
}
}
return size, nil
}
// applyBinaryDeltaAdd applies an add opcode in a delta-encoded binary
// fragment, returning the amount of data written and the usused part of the
// fragment. An add operation takes the form:
//
// [0xxxxxx][[data1]...]
//
// where the lower seven bits of the opcode is the number of data bytes
// following the opcode. See also pack-format.txt in the Git source.
func applyBinaryDeltaAdd(w io.Writer, op byte, delta []byte) (n int64, rest []byte, err error) {
size := int(op)
if len(delta) < size {
return 0, delta, errors.New("corrupt binary delta: incomplete add")
}
_, err = w.Write(delta[:size])
return int64(size), delta[size:], err
}
// applyBinaryDeltaCopy applies a copy opcode in a delta-encoded binary
// fragment, returing the amount of data written and the unused part of the
// fragment. A copy operation takes the form:
//
// [1xxxxxxx][offset1][offset2][offset3][offset4][size1][size2][size3]
//
// where the lower seven bits of the opcode determine which non-zero offset and
// size bytes are present in little-endian order: if bit 0 is set, offset1 is
// present, etc. If no offset or size bytes are present, offset is 0 and size
// is 0x10000. See also pack-format.txt in the Git source.
func applyBinaryDeltaCopy(w io.Writer, op byte, delta []byte, src io.ReaderAt) (n int64, rest []byte, err error) {
const defaultSize = 0x10000
unpack := func(start, bits uint) (v int64) {
for i := uint(0); i < bits; i++ {
mask := byte(1 << (i + start))
if op&mask > 0 {
if len(delta) == 0 {
err = errors.New("corrupt binary delta: incomplete copy")
return
}
v |= int64(delta[0]) << (8 * i)
delta = delta[1:]
}
}
return
}
offset := unpack(0, 4)
size := unpack(4, 3)
if err != nil {
return 0, delta, err
}
if size == 0 {
size = defaultSize
}
// TODO(bkeyes): consider pooling these buffers
b := make([]byte, size)
if _, err := src.ReadAt(b, offset); err != nil {
return 0, delta, err
}
_, err = w.Write(b)
return size, delta, err
}
func checkBinarySrcSize(r io.ReaderAt, size int64) error {
ok, err := isLen(r, size)
if err != nil {
return err
}
if !ok {
return &Conflict{"fragment src size does not match actual src size"}
}
return nil
}
|
