aboutsummaryrefslogtreecommitdiffstats
path: root/plumbing/format/commitgraph/file.go
blob: 1f82abd754e3de5a61a85be272696ad48eb896a2 (plain) (blame)
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
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
package commitgraph

import (
	"bytes"
	encbin "encoding/binary"
	"errors"
	"io"
	"time"

	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/utils/binary"
)

var (
	// ErrUnsupportedVersion is returned by OpenFileIndex when the commit graph

	// file version is not supported.

	ErrUnsupportedVersion = errors.New("Unsupported version")
	// ErrUnsupportedHash is returned by OpenFileIndex when the commit graph

	// hash function is not supported. Currently only SHA-1 is defined and

	// supported

	ErrUnsupportedHash = errors.New("Unsupported hash algorithm")
	// ErrMalformedCommitGraphFile is returned by OpenFileIndex when the commit

	// graph file is corrupted.

	ErrMalformedCommitGraphFile = errors.New("Malformed commit graph file")

	commitFileSignature    = []byte{'C', 'G', 'P', 'H'}
	oidFanoutSignature     = []byte{'O', 'I', 'D', 'F'}
	oidLookupSignature     = []byte{'O', 'I', 'D', 'L'}
	commitDataSignature    = []byte{'C', 'D', 'A', 'T'}
	extraEdgeListSignature = []byte{'E', 'D', 'G', 'E'}
	lastSignature          = []byte{0, 0, 0, 0}

	parentNone        = uint32(0x70000000)
	parentOctopusUsed = uint32(0x80000000)
	parentOctopusMask = uint32(0x7fffffff)
	parentLast        = uint32(0x80000000)
)

type fileIndex struct {
	reader              io.ReaderAt
	fanout              [256]int
	oidFanoutOffset     int64
	oidLookupOffset     int64
	commitDataOffset    int64
	extraEdgeListOffset int64
}

// OpenFileIndex opens a serialized commit graph file in the format described at

// https://github.com/git/git/blob/master/Documentation/technical/commit-graph-format.txt

func OpenFileIndex(reader io.ReaderAt) (Index, error) {
	fi := &fileIndex{reader: reader}

	if err := fi.verifyFileHeader(); err != nil {
		return nil, err
	}
	if err := fi.readChunkHeaders(); err != nil {
		return nil, err
	}
	if err := fi.readFanout(); err != nil {
		return nil, err
	}

	return fi, nil
}

func (fi *fileIndex) verifyFileHeader() error {
	// Verify file signature

	var signature = make([]byte, 4)
	if _, err := fi.reader.ReadAt(signature, 0); err != nil {
		return err
	}
	if !bytes.Equal(signature, commitFileSignature) {
		return ErrMalformedCommitGraphFile
	}

	// Read and verify the file header

	var header = make([]byte, 4)
	if _, err := fi.reader.ReadAt(header, 4); err != nil {
		return err
	}
	if header[0] != 1 {
		return ErrUnsupportedVersion
	}
	if header[1] != 1 {
		return ErrUnsupportedHash
	}

	return nil
}

func (fi *fileIndex) readChunkHeaders() error {
	var chunkID = make([]byte, 4)
	for i := 0; ; i++ {
		chunkHeader := io.NewSectionReader(fi.reader, 8+(int64(i)*12), 12)
		if _, err := io.ReadAtLeast(chunkHeader, chunkID, 4); err != nil {
			return err
		}
		chunkOffset, err := binary.ReadUint64(chunkHeader)
		if err != nil {
			return err
		}

		if bytes.Equal(chunkID, oidFanoutSignature) {
			fi.oidFanoutOffset = int64(chunkOffset)
		} else if bytes.Equal(chunkID, oidLookupSignature) {
			fi.oidLookupOffset = int64(chunkOffset)
		} else if bytes.Equal(chunkID, commitDataSignature) {
			fi.commitDataOffset = int64(chunkOffset)
		} else if bytes.Equal(chunkID, extraEdgeListSignature) {
			fi.extraEdgeListOffset = int64(chunkOffset)
		} else if bytes.Equal(chunkID, lastSignature) {
			break
		}
	}

	if fi.oidFanoutOffset <= 0 || fi.oidLookupOffset <= 0 || fi.commitDataOffset <= 0 {
		return ErrMalformedCommitGraphFile
	}

	return nil
}

func (fi *fileIndex) readFanout() error {
	fanoutReader := io.NewSectionReader(fi.reader, fi.oidFanoutOffset, 256*4)
	for i := 0; i < 256; i++ {
		fanoutValue, err := binary.ReadUint32(fanoutReader)
		if err != nil {
			return err
		}
		if fanoutValue > 0x7fffffff {
			return ErrMalformedCommitGraphFile
		}
		fi.fanout[i] = int(fanoutValue)
	}
	return nil
}

func (fi *fileIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
	var oid plumbing.Hash

	// Find the hash in the oid lookup table

	var low int
	if h[0] == 0 {
		low = 0
	} else {
		low = fi.fanout[h[0]-1]
	}
	high := fi.fanout[h[0]]
	for low < high {
		mid := (low + high) >> 1
		offset := fi.oidLookupOffset + int64(mid)*20
		if _, err := fi.reader.ReadAt(oid[:], offset); err != nil {
			return 0, err
		}
		cmp := bytes.Compare(h[:], oid[:])
		if cmp < 0 {
			high = mid
		} else if cmp == 0 {
			return mid, nil
		} else {
			low = mid + 1
		}
	}

	return 0, plumbing.ErrObjectNotFound
}

func (fi *fileIndex) GetCommitDataByIndex(idx int) (*CommitData, error) {
	if idx >= fi.fanout[0xff] {
		return nil, plumbing.ErrObjectNotFound
	}

	offset := fi.commitDataOffset + int64(idx)*36
	commitDataReader := io.NewSectionReader(fi.reader, offset, 36)

	treeHash, err := binary.ReadHash(commitDataReader)
	if err != nil {
		return nil, err
	}
	parent1, err := binary.ReadUint32(commitDataReader)
	if err != nil {
		return nil, err
	}
	parent2, err := binary.ReadUint32(commitDataReader)
	if err != nil {
		return nil, err
	}
	genAndTime, err := binary.ReadUint64(commitDataReader)
	if err != nil {
		return nil, err
	}

	var parentIndexes []int
	if parent2&parentOctopusUsed == parentOctopusUsed {
		// Octopus merge

		parentIndexes = []int{int(parent1 & parentOctopusMask)}
		offset := fi.extraEdgeListOffset + 4*int64(parent2&parentOctopusMask)
		buf := make([]byte, 4)
		for {
			_, err := fi.reader.ReadAt(buf, offset)
			if err != nil {
				return nil, err
			}

			parent := encbin.BigEndian.Uint32(buf)
			offset += 4
			parentIndexes = append(parentIndexes, int(parent&parentOctopusMask))
			if parent&parentLast == parentLast {
				break
			}
		}
	} else if parent2 != parentNone {
		parentIndexes = []int{int(parent1 & parentOctopusMask), int(parent2 & parentOctopusMask)}
	} else if parent1 != parentNone {
		parentIndexes = []int{int(parent1 & parentOctopusMask)}
	}

	parentHashes, err := fi.getHashesFromIndexes(parentIndexes)
	if err != nil {
		return nil, err
	}

	return &CommitData{
		TreeHash:      treeHash,
		ParentIndexes: parentIndexes,
		ParentHashes:  parentHashes,
		Generation:    int(genAndTime >> 34),
		When:          time.Unix(int64(genAndTime&0x3FFFFFFFF), 0),
	}, nil
}

func (fi *fileIndex) getHashesFromIndexes(indexes []int) ([]plumbing.Hash, error) {
	hashes := make([]plumbing.Hash, len(indexes))

	for i, idx := range indexes {
		if idx >= fi.fanout[0xff] {
			return nil, ErrMalformedCommitGraphFile
		}

		offset := fi.oidLookupOffset + int64(idx)*20
		if _, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil {
			return nil, err
		}
	}

	return hashes, nil
}

// Hashes returns all the hashes that are available in the index

func (fi *fileIndex) Hashes() []plumbing.Hash {
	hashes := make([]plumbing.Hash, fi.fanout[0xff])
	for i := 0; i < fi.fanout[0xff]; i++ {
		offset := fi.oidLookupOffset + int64(i)*20
		if n, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil || n < 20 {
			return nil
		}
	}
	return hashes
}