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