aboutsummaryrefslogtreecommitdiffstats
path: root/plumbing/protocol/packp/advrefs_decode.go
blob: df824a98e9161c7ebf6347480ba4486d9e540f9e (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
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
package packp

import (
	"bytes"
	"encoding/hex"
	"errors"
	"fmt"
	"io"

	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/format/pktline"
)

// A AdvRefsDecoder reads and decodes AdvRef values from an input stream.
type AdvRefsDecoder struct {
	s     *pktline.Scanner // a pkt-line scanner from the input stream
	line  []byte           // current pkt-line contents, use parser.nextLine() to make it advance
	nLine int              // current pkt-line number for debugging, begins at 1
	hash  plumbing.Hash    // last hash read
	err   error            // sticky error, use the parser.error() method to fill this out
	data  *AdvRefs         // parsed data is stored here
}

// ErrEmpty is returned by Decode when there was no advertised-message at all
var ErrEmpty = errors.New("empty advertised-ref message")

// NewAdvRefsDecoder returns a new decoder that reads from r.
//
// Will not read more data from r than necessary.
func NewAdvRefsDecoder(r io.Reader) *AdvRefsDecoder {
	return &AdvRefsDecoder{
		s: pktline.NewScanner(r),
	}
}

// Decode reads the next advertised-refs message form its input and
// stores it in the value pointed to by v.
func (d *AdvRefsDecoder) Decode(v *AdvRefs) error {
	d.data = v

	for state := decodePrefix; state != nil; {
		state = state(d)
	}

	return d.err
}

type decoderStateFn func(*AdvRefsDecoder) decoderStateFn

// fills out the parser stiky error
func (d *AdvRefsDecoder) error(format string, a ...interface{}) {
	d.err = fmt.Errorf("pkt-line %d: %s", d.nLine,
		fmt.Sprintf(format, a...))
}

// Reads a new pkt-line from the scanner, makes its payload available as
// p.line and increments p.nLine.  A successful invocation returns true,
// otherwise, false is returned and the sticky error is filled out
// accordingly.  Trims eols at the end of the payloads.
func (d *AdvRefsDecoder) nextLine() bool {
	d.nLine++

	if !d.s.Scan() {
		if d.err = d.s.Err(); d.err != nil {
			return false
		}

		if d.nLine == 1 {
			d.err = ErrEmpty
			return false
		}

		d.error("EOF")
		return false
	}

	d.line = d.s.Bytes()
	d.line = bytes.TrimSuffix(d.line, eol)

	return true
}

// The HTTP smart prefix is often followed by a flush-pkt.
func decodePrefix(d *AdvRefsDecoder) decoderStateFn {
	if ok := d.nextLine(); !ok {
		return nil
	}

	// If the repository is empty, we receive a flush here (SSH).
	if isFlush(d.line) {
		d.err = ErrEmpty
		return nil
	}

	if isPrefix(d.line) {
		tmp := make([]byte, len(d.line))
		copy(tmp, d.line)
		d.data.Prefix = append(d.data.Prefix, tmp)
		if ok := d.nextLine(); !ok {
			return nil
		}
	}

	if isFlush(d.line) {
		d.data.Prefix = append(d.data.Prefix, pktline.Flush)
		if ok := d.nextLine(); !ok {
			return nil
		}
	}

	return decodeFirstHash
}

func isPrefix(payload []byte) bool {
	return payload[0] == '#'
}

func isFlush(payload []byte) bool {
	return len(payload) == 0
}

// If the first hash is zero, then a no-refs is comming. Otherwise, a
// list-of-refs is comming, and the hash will be followed by the first
// advertised ref.
func decodeFirstHash(p *AdvRefsDecoder) decoderStateFn {
	// If the repository is empty, we receive a flush here (HTTP).
	if isFlush(p.line) {
		p.err = ErrEmpty
		return nil
	}

	if len(p.line) < hashSize {
		p.error("cannot read hash, pkt-line too short")
		return nil
	}

	if _, err := hex.Decode(p.hash[:], p.line[:hashSize]); err != nil {
		p.error("invalid hash text: %s", err)
		return nil
	}

	p.line = p.line[hashSize:]

	if p.hash.IsZero() {
		return decodeSkipNoRefs
	}

	return decodeFirstRef
}

// Skips SP "capabilities^{}" NUL
func decodeSkipNoRefs(p *AdvRefsDecoder) decoderStateFn {
	if len(p.line) < len(noHeadMark) {
		p.error("too short zero-id ref")
		return nil
	}

	if !bytes.HasPrefix(p.line, noHeadMark) {
		p.error("malformed zero-id ref")
		return nil
	}

	p.line = p.line[len(noHeadMark):]

	return decodeCaps
}

// decode the refname, expectes SP refname NULL
func decodeFirstRef(l *AdvRefsDecoder) decoderStateFn {
	if len(l.line) < 3 {
		l.error("line too short after hash")
		return nil
	}

	if !bytes.HasPrefix(l.line, sp) {
		l.error("no space after hash")
		return nil
	}
	l.line = l.line[1:]

	chunks := bytes.SplitN(l.line, null, 2)
	if len(chunks) < 2 {
		l.error("NULL not found")
		return nil
	}
	ref := chunks[0]
	l.line = chunks[1]

	if bytes.Equal(ref, []byte(head)) {
		l.data.Head = &l.hash
	} else {
		l.data.References[string(ref)] = l.hash
	}

	return decodeCaps
}

func decodeCaps(p *AdvRefsDecoder) decoderStateFn {
	if len(p.line) == 0 {
		return decodeOtherRefs
	}

	for _, c := range bytes.Split(p.line, sp) {
		name, values := readCapability(c)
		p.data.Capabilities.Add(name, values...)
	}

	return decodeOtherRefs
}

// The refs are either tips (obj-id SP refname) or a peeled (obj-id SP refname^{}).
// If there are no refs, then there might be a shallow or flush-ptk.
func decodeOtherRefs(p *AdvRefsDecoder) decoderStateFn {
	if ok := p.nextLine(); !ok {
		return nil
	}

	if bytes.HasPrefix(p.line, shallow) {
		return decodeShallow
	}

	if len(p.line) == 0 {
		return nil
	}

	saveTo := p.data.References
	if bytes.HasSuffix(p.line, peeled) {
		p.line = bytes.TrimSuffix(p.line, peeled)
		saveTo = p.data.Peeled
	}

	ref, hash, err := readRef(p.line)
	if err != nil {
		p.error("%s", err)
		return nil
	}
	saveTo[ref] = hash

	return decodeOtherRefs
}

// Reads a ref-name
func readRef(data []byte) (string, plumbing.Hash, error) {
	chunks := bytes.Split(data, sp)
	switch {
	case len(chunks) == 1:
		return "", plumbing.ZeroHash, fmt.Errorf("malformed ref data: no space was found")
	case len(chunks) > 2:
		return "", plumbing.ZeroHash, fmt.Errorf("malformed ref data: more than one space found")
	default:
		return string(chunks[1]), plumbing.NewHash(string(chunks[0])), nil
	}
}

// Keeps reading shallows until a flush-pkt is found
func decodeShallow(p *AdvRefsDecoder) decoderStateFn {
	if !bytes.HasPrefix(p.line, shallow) {
		p.error("malformed shallow prefix, found %q... instead", p.line[:len(shallow)])
		return nil
	}
	p.line = bytes.TrimPrefix(p.line, shallow)

	if len(p.line) != hashSize {
		p.error(fmt.Sprintf(
			"malformed shallow hash: wrong length, expected 40 bytes, read %d bytes",
			len(p.line)))
		return nil
	}

	text := p.line[:hashSize]
	var h plumbing.Hash
	if _, err := hex.Decode(h[:], text); err != nil {
		p.error("invalid hash text: %s", err)
		return nil
	}

	p.data.Shallows = append(p.data.Shallows, h)

	if ok := p.nextLine(); !ok {
		return nil
	}

	if len(p.line) == 0 {
		return nil // succesfull parse of the advertised-refs message
	}

	return decodeShallow
}