streaming: a new API to read from the object store
[git/git.git] / streaming.c
CommitLineData
46bf0438
JH
1/*
2 * Copyright (c) 2011, Google Inc.
3 */
4#include "cache.h"
5#include "streaming.h"
6
7enum input_source {
8 stream_error = -1,
9 incore = 0,
10 loose = 1,
11 pack_non_delta = 2
12};
13
14typedef int (*open_istream_fn)(struct git_istream *,
15 struct object_info *,
16 const unsigned char *,
17 enum object_type *);
18typedef int (*close_istream_fn)(struct git_istream *);
19typedef ssize_t (*read_istream_fn)(struct git_istream *, char *, size_t);
20
21struct stream_vtbl {
22 close_istream_fn close;
23 read_istream_fn read;
24};
25
26#define open_method_decl(name) \
27 int open_istream_ ##name \
28 (struct git_istream *st, struct object_info *oi, \
29 const unsigned char *sha1, \
30 enum object_type *type)
31
32#define close_method_decl(name) \
33 int close_istream_ ##name \
34 (struct git_istream *st)
35
36#define read_method_decl(name) \
37 ssize_t read_istream_ ##name \
38 (struct git_istream *st, char *buf, size_t sz)
39
40/* forward declaration */
41static open_method_decl(incore);
42static open_method_decl(loose);
43static open_method_decl(pack_non_delta);
44
45static open_istream_fn open_istream_tbl[] = {
46 open_istream_incore,
47 open_istream_loose,
48 open_istream_pack_non_delta,
49};
50
51struct git_istream {
52 const struct stream_vtbl *vtbl;
53 unsigned long size; /* inflated size of full object */
54
55 union {
56 struct {
57 char *buf; /* from read_object() */
58 unsigned long read_ptr;
59 } incore;
60
61 struct {
62 int fd; /* open for reading */
63 /* NEEDSWORK: what else? */
64 } loose;
65
66 struct {
67 int fd; /* open for reading */
68 /* NEEDSWORK: what else? */
69 } in_pack;
70 } u;
71};
72
73int close_istream(struct git_istream *st)
74{
75 return st->vtbl->close(st);
76}
77
78ssize_t read_istream(struct git_istream *st, char *buf, size_t sz)
79{
80 return st->vtbl->read(st, buf, sz);
81}
82
83static enum input_source istream_source(const unsigned char *sha1,
84 enum object_type *type,
85 struct object_info *oi)
86{
87 unsigned long size;
88 int status;
89
90 oi->sizep = &size;
91 status = sha1_object_info_extended(sha1, oi);
92 if (status < 0)
93 return stream_error;
94 *type = status;
95
96 switch (oi->whence) {
97 case OI_LOOSE:
98 return loose;
99 case OI_PACKED:
100 if (!oi->u.packed.is_delta && big_file_threshold <= size)
101 return pack_non_delta;
102 /* fallthru */
103 default:
104 return incore;
105 }
106}
107
108struct git_istream *open_istream(const unsigned char *sha1,
109 enum object_type *type,
110 unsigned long *size)
111{
112 struct git_istream *st;
113 struct object_info oi;
114 const unsigned char *real = lookup_replace_object(sha1);
115 enum input_source src = istream_source(real, type, &oi);
116
117 if (src < 0)
118 return NULL;
119
120 st = xmalloc(sizeof(*st));
121 if (open_istream_tbl[src](st, &oi, real, type)) {
122 if (open_istream_incore(st, &oi, real, type)) {
123 free(st);
124 return NULL;
125 }
126 }
127 *size = st->size;
128 return st;
129}
130
131/*****************************************************************
132 *
133 * Loose object stream
134 *
135 *****************************************************************/
136
137static open_method_decl(loose)
138{
139 return -1; /* for now */
140}
141
142
143/*****************************************************************
144 *
145 * Non-delta packed object stream
146 *
147 *****************************************************************/
148
149static open_method_decl(pack_non_delta)
150{
151 return -1; /* for now */
152}
153
154
155/*****************************************************************
156 *
157 * In-core stream
158 *
159 *****************************************************************/
160
161static close_method_decl(incore)
162{
163 free(st->u.incore.buf);
164 return 0;
165}
166
167static read_method_decl(incore)
168{
169 size_t read_size = sz;
170 size_t remainder = st->size - st->u.incore.read_ptr;
171
172 if (remainder <= read_size)
173 read_size = remainder;
174 if (read_size) {
175 memcpy(buf, st->u.incore.buf + st->u.incore.read_ptr, read_size);
176 st->u.incore.read_ptr += read_size;
177 }
178 return read_size;
179}
180
181static struct stream_vtbl incore_vtbl = {
182 close_istream_incore,
183 read_istream_incore,
184};
185
186static open_method_decl(incore)
187{
188 st->u.incore.buf = read_sha1_file_extended(sha1, type, &st->size, 0);
189 st->u.incore.read_ptr = 0;
190 st->vtbl = &incore_vtbl;
191
192 return st->u.incore.buf ? 0 : -1;
193}