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 	SIMPLEQ_ENTRY(got_delta) entry;
19 	char *path_packfile;
20 	off_t offset;
21 	size_t tslen;
22 	int type;
23 	size_t size;
24 };
25 
26 struct got_delta_chain {
27 	int nentries;
28 	SIMPLEQ_HEAD(, got_delta) entries;
29 };
30 
31 struct got_delta *got_delta_open(const char *, off_t, size_t, int, size_t);
32 void got_delta_close(struct got_delta *);
33 const struct got_error *got_delta_chain_get_base_type(int *,
34     struct got_delta_chain *);
35 const struct got_error *got_delta_apply(FILE *, const uint8_t *, size_t,
36     FILE *);
37 
38 /*
39  * Definitions for delta data streams.
40  */
41 
42 #define GOT_DELTA_STREAM_LENGTH_MIN	4	/* bytes */
43 
44 /*
45  * A delta stream begins with two size fields. The first specifies the
46  * size of the delta base, and the second describes the expected size of
47  * the data which results from combining the delta base and the delta.
48  *
49  * Each size field uses a variable length encoding:
50  * size0...sizeN form a 7+7+7+...+7 bit integer, where size0 is the
51  * least significant part and sizeN is the most significant part.
52  * If the MSB of a size byte is set, an additional size byte follows.
53  */
54 #define GOT_DELTA_SIZE_VAL_MASK	0x7f
55 #define GOT_DELTA_SIZE_SHIFT	7
56 #define GOT_DELTA_SIZE_MORE	0x80
57 
58 /*
59  * The rest of the delta stream contains copy instructions.
60  *
61  * A base copy instruction tells the delta combiner to copy N bytes starting
62  * at offset X from the delta base to the output. Base copy instructions begin
63  * with a byte which has its MSB set. The remaining bits of this byte describe
64  * how many offset and length value bytes follow.
65  * The offset X is encoded in 1 to 4 bytes, and the length N is encoded in
66  * 1 to 3 bytes. For both values, the first byte contributes the least
67  * significant part and the last byte which is present contributes the
68  * most significant part.
69  * If the offset value is omitted, an offset of zero is implied.
70  * If the length value is omitted, a default length of 65536 bytes is implied.
71  *
72  * An inline copy instruction tells the delta combiner to copy data from
73  * the delta stream to the output.
74  * Such instructions begin with one byte which does not have the MSB set
75  * and which specifies the length of the inline data which follows (i.e.
76  * at most 127 bytes). A length value of zero is invalid.
77  */
78 
79 #define GOT_DELTA_BASE_COPY	0x80
80 
81 #define GOT_DELTA_COPY_OFF1	0x01	/* byte 1 of offset is present */
82 #define GOT_DELTA_COPY_OFF2	0x02	/* byte 2 of offset is present */
83 #define GOT_DELTA_COPY_OFF3	0x04	/* byte 3 of offset is present */
84 #define GOT_DELTA_COPY_OFF4	0x08	/* byte 4 of offset is present */
85 
86 #define GOT_DELTA_COPY_LEN1	0x10	/* byte 1 of length is present */
87 #define GOT_DELTA_COPY_LEN2	0x20	/* byte 2 of length is present */
88 #define GOT_DELTA_COPY_LEN3	0x40	/* byte 3 of length is present */
89 
90 #define GOT_DELTA_COPY_DEFAULT_OFF	0x0	/* default offset if omitted */
91 #define GOT_DELTA_COPY_DEFAULT_LEN	0x10000 /* default length if omitted */