1 /*
2  * Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 struct got_delta {
18 	STAILQ_ENTRY(got_delta) entry;
19 	off_t offset;
20 	size_t tslen;
21 	int type;
22 	size_t size;
23 	off_t data_offset;
24 };
25 
26 struct got_delta_chain {
27 	int nentries;
28 	STAILQ_HEAD(, got_delta) entries;
29 };
30 
31 #define GOT_DELTA_CHAIN_RECURSION_MAX	500
32 
33 struct got_delta *got_delta_open(off_t, size_t, int, size_t, off_t);
34 const struct got_error *got_delta_chain_get_base_type(int *,
35     struct got_delta_chain *);
36 const struct got_error *got_delta_get_sizes(uint64_t *, uint64_t *,
37     const uint8_t *, size_t);
38 const struct got_error *got_delta_apply_in_mem(uint8_t *, size_t,
39     const uint8_t *, size_t, uint8_t *, size_t *, size_t);
40 const struct got_error *got_delta_apply(FILE *, const uint8_t *, size_t,
41     FILE *, size_t *);
42 
43 /*
44  * The amount of result data we may keep in RAM while applying deltas.
45  * Data larger than this is written to disk during delta application (slow).
46  */
47 #define GOT_DELTA_RESULT_SIZE_CACHED_MAX	(8 * 1024 * 1024) /* bytes */
48 
49 /*
50  * Definitions for delta data streams.
51  */
52 
53 #define GOT_DELTA_STREAM_LENGTH_MIN	4	/* bytes */
54 
55 /*
56  * A delta stream begins with two size fields. The first specifies the
57  * size of the delta base, and the second describes the expected size of
58  * the data which results from applying the delta to the delta base.
59  *
60  * Each size field uses a variable length encoding:
61  * size0...sizeN form a 7+7+7+...+7 bit integer, where size0 is the
62  * least significant part and sizeN is the most significant part.
63  * If the MSB of a size byte is set, an additional size byte follows.
64  */
65 #define GOT_DELTA_SIZE_VAL_MASK	0x7f
66 #define GOT_DELTA_SIZE_SHIFT	7
67 #define GOT_DELTA_SIZE_MORE	0x80
68 
69 /*
70  * The rest of the delta stream contains copy instructions.
71  *
72  * A base copy instruction copies N bytes starting at offset X from the delta
73  * base to the output. Base copy instructions begin with a byte which has its
74  * MSB set. The remaining bits of this byte describe how many offset and
75  * length value bytes follow.
76  * The offset X is encoded in 1 to 4 bytes, and the length N is encoded in
77  * 1 to 3 bytes. For both values, the first byte contributes the least
78  * significant part and the last byte which is present contributes the
79  * most significant part.
80  * If the offset value is omitted, an offset of zero is implied.
81  * If the length value is omitted, a default length of 65536 bytes is implied.
82  *
83  * An inline copy instruction copies data from the delta stream to the output.
84  * Such instructions begin with one byte which does not have the MSB set
85  * and which specifies the length of the inline data which follows (i.e.
86  * at most 127 bytes). A length value of zero is invalid.
87  */
88 
89 #define GOT_DELTA_BASE_COPY	0x80
90 
91 #define GOT_DELTA_COPY_OFF1	0x01	/* byte 1 of offset is present */
92 #define GOT_DELTA_COPY_OFF2	0x02	/* byte 2 of offset is present */
93 #define GOT_DELTA_COPY_OFF3	0x04	/* byte 3 of offset is present */
94 #define GOT_DELTA_COPY_OFF4	0x08	/* byte 4 of offset is present */
95 
96 #define GOT_DELTA_COPY_LEN1	0x10	/* byte 1 of length is present */
97 #define GOT_DELTA_COPY_LEN2	0x20	/* byte 2 of length is present */
98 #define GOT_DELTA_COPY_LEN3	0x40	/* byte 3 of length is present */
99 
100 #define GOT_DELTA_COPY_DEFAULT_OFF	0x0	/* default offset if omitted */
101 #define GOT_DELTA_COPY_DEFAULT_LEN	0x10000 /* default length if omitted */