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
|
package pack
import (
"bytes"
"encoding/binary"
"fmt"
"hash"
"io"
)
const (
// indexMagicWidth is the width of the magic header of packfiles version
// 2 and newer.
indexMagicWidth = 4
// indexVersionWidth is the width of the version following the magic
// header.
indexVersionWidth = 4
// indexV2Width is the total width of the header in V2.
indexV2Width = indexMagicWidth + indexVersionWidth
// indexV1Width is the total width of the header in V1.
indexV1Width = 0
// indexFanoutEntries is the number of entries in the fanout table.
indexFanoutEntries = 256
// indexFanoutEntryWidth is the width of each entry in the fanout table.
indexFanoutEntryWidth = 4
// indexFanoutWidth is the width of the entire fanout table.
indexFanoutWidth = indexFanoutEntries * indexFanoutEntryWidth
// indexOffsetV1Start is the location of the first object outside of the
// V1 header.
indexOffsetV1Start = indexV1Width + indexFanoutWidth
// indexOffsetV2Start is the location of the first object outside of the
// V2 header.
indexOffsetV2Start = indexV2Width + indexFanoutWidth
// indexObjectCRCWidth is the width of the CRC accompanying each object
// in V2.
indexObjectCRCWidth = 4
// indexObjectSmallOffsetWidth is the width of the small offset encoded
// into each object.
indexObjectSmallOffsetWidth = 4
// indexObjectLargeOffsetWidth is the width of the optional large offset
// encoded into the small offset.
indexObjectLargeOffsetWidth = 8
)
var (
// ErrShortFanout is an error representing situations where the entire
// fanout table could not be read, and is thus too short.
ErrShortFanout = fmt.Errorf("gitobj/pack: too short fanout table")
// indexHeader is the first four "magic" bytes of index files version 2
// or newer.
indexHeader = []byte{0xff, 0x74, 0x4f, 0x63}
)
// DecodeIndex decodes an index whose underlying data is supplied by "r".
//
// DecodeIndex reads only the header and fanout table, and does not eagerly
// parse index entries.
//
// If there was an error parsing, it will be returned immediately.
func DecodeIndex(r io.ReaderAt, hash hash.Hash) (*Index, error) {
version, err := decodeIndexHeader(r, hash)
if err != nil {
return nil, err
}
fanout, err := decodeIndexFanout(r, version.Width())
if err != nil {
return nil, err
}
return &Index{
version: version,
fanout: fanout,
r: r,
}, nil
}
// decodeIndexHeader determines which version the index given by "r" is.
func decodeIndexHeader(r io.ReaderAt, hash hash.Hash) (IndexVersion, error) {
hdr := make([]byte, 4)
if _, err := r.ReadAt(hdr, 0); err != nil {
return nil, err
}
if bytes.Equal(hdr, indexHeader) {
vb := make([]byte, 4)
if _, err := r.ReadAt(vb, 4); err != nil {
return nil, err
}
version := binary.BigEndian.Uint32(vb)
switch version {
case 1:
return &V1{hash: hash}, nil
case 2:
return &V2{hash: hash}, nil
}
return nil, &UnsupportedVersionErr{uint32(version)}
}
return &V1{hash: hash}, nil
}
// decodeIndexFanout decodes the fanout table given by "r" and beginning at the
// given offset.
func decodeIndexFanout(r io.ReaderAt, offset int64) ([]uint32, error) {
b := make([]byte, 256*4)
if _, err := r.ReadAt(b, offset); err != nil {
if err == io.EOF {
return nil, ErrShortFanout
}
return nil, err
}
fanout := make([]uint32, 256)
for i, _ := range fanout {
fanout[i] = binary.BigEndian.Uint32(b[(i * 4):])
}
return fanout, nil
}
|
