vcs-svn/svndiff.c

   1 /*
   2  * Licensed under a two-clause BSD-style license.
   3  * See LICENSE for details.
   4  */
   5
   6 #include "git-compat-util.h"
   7 #include "sliding_window.h"
   8 #include "line_buffer.h"
   9 #include "svndiff.h"
  10
  11 /*
  12  * svndiff0 applier
  13  *
  14  * See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
  15  *
  16  * svndiff0 ::= 'SVN\0' window*
  17  * window ::= int int int int int instructions inline_data;
  18  * instructions ::= instruction*;
  19  * instruction ::= view_selector int int
  20  *   | copyfrom_data int
  21  *   | packed_view_selector int
  22  *   | packed_copyfrom_data
  23  *   ;
  24  * view_selector ::= copyfrom_source
  25  *   | copyfrom_target
  26  *   ;
  27  * copyfrom_source ::= # binary 00 000000;
  28  * copyfrom_target ::= # binary 01 000000;
  29  * copyfrom_data ::= # binary 10 000000;
  30  * packed_view_selector ::= # view_selector OR-ed with 6 bit value;
  31  * packed_copyfrom_data ::= # copyfrom_data OR-ed with 6 bit value;
  32  * int ::= highdigit* lowdigit;
  33  * highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
  34  * lowdigit ::= # 7 bit value;
  35  */
  36
  37 #define INSN_MASK       0xc0
  38 #define INSN_COPYFROM_SOURCE    0x00
  39 #define INSN_COPYFROM_TARGET    0x40
  40 #define INSN_COPYFROM_DATA      0x80
  41 #define OPERAND_MASK    0x3f
  42
  43 #define VLI_CONTINUE    0x80
  44 #define VLI_DIGIT_MASK  0x7f
  45 #define VLI_BITS_PER_DIGIT 7
  46
  47 struct window {
  48         struct sliding_view *in;
  49         struct strbuf out;
  50         struct strbuf instructions;
  51         struct strbuf data;
  52 };
  53
  54 #define WINDOW_INIT(w)  { (w), STRBUF_INIT, STRBUF_INIT, STRBUF_INIT }
  55
  56 static void window_release(struct window *ctx)
  57 {
  58         strbuf_release(&ctx->out);
  59         strbuf_release(&ctx->instructions);
  60         strbuf_release(&ctx->data);
  61 }
  62
  63 static int write_strbuf(struct strbuf *sb, FILE *out)
  64 {
  65         if (fwrite(sb->buf, 1, sb->len, out) == sb->len)        /* Success. */
  66                 return 0;
  67         return error("cannot write delta postimage: %s", strerror(errno));
  68 }
  69
  70 static int error_short_read(struct line_buffer *input)
  71 {
  72         if (buffer_ferror(input))
  73                 return error("error reading delta: %s", strerror(errno));
  74         return error("invalid delta: unexpected end of file");
  75 }
  76
  77 static int read_chunk(struct line_buffer *delta, off_t *delta_len,
  78                       struct strbuf *buf, size_t len)
  79 {
  80         strbuf_reset(buf);
  81         if (len > *delta_len ||
  82             buffer_read_binary(delta, buf, len) != len)
  83                 return error_short_read(delta);
  84         *delta_len -= buf->len;
  85         return 0;
  86 }
  87
  88 static int read_magic(struct line_buffer *in, off_t *len)
  89 {
  90         static const char magic[] = {'S', 'V', 'N', '\0'};
  91         struct strbuf sb = STRBUF_INIT;
  92
  93         if (read_chunk(in, len, &sb, sizeof(magic))) {
  94                 strbuf_release(&sb);
  95                 return -1;
  96         }
  97         if (memcmp(sb.buf, magic, sizeof(magic))) {
  98                 strbuf_release(&sb);
  99                 return error("invalid delta: unrecognized file type");
 100         }
 101         strbuf_release(&sb);
 102         return 0;
 103 }
 104
 105 static int read_int(struct line_buffer *in, uintmax_t *result, off_t *len)
 106 {
 107         uintmax_t rv = 0;
 108         off_t sz;
 109         for (sz = *len; sz; sz--) {
 110                 const int ch = buffer_read_char(in);
 111                 if (ch == EOF)
 112                         break;
 113
 114                 rv <<= VLI_BITS_PER_DIGIT;
 115                 rv += (ch & VLI_DIGIT_MASK);
 116                 if (ch & VLI_CONTINUE)
 117                         continue;
 118
 119                 *result = rv;
 120                 *len = sz - 1;
 121                 return 0;
 122         }
 123         return error_short_read(in);
 124 }
 125
 126 static int parse_int(const char **buf, size_t *result, const char *end)
 127 {
 128         size_t rv = 0;
 129         const char *pos;
 130         for (pos = *buf; pos != end; pos++) {
 131                 unsigned char ch = *pos;
 132
 133                 rv <<= VLI_BITS_PER_DIGIT;
 134                 rv += (ch & VLI_DIGIT_MASK);
 135                 if (ch & VLI_CONTINUE)
 136                         continue;
 137
 138                 *result = rv;
 139                 *buf = pos + 1;
 140                 return 0;
 141         }
 142         return error("invalid delta: unexpected end of instructions section");
 143 }
 144
 145 static int read_offset(struct line_buffer *in, off_t *result, off_t *len)
 146 {
 147         uintmax_t val;
 148         if (read_int(in, &val, len))
 149                 return -1;
 150         if (val > maximum_signed_value_of_type(off_t))
 151                 return error("unrepresentable offset in delta: %"PRIuMAX"", val);
 152         *result = val;
 153         return 0;
 154 }
 155
 156 static int read_length(struct line_buffer *in, size_t *result, off_t *len)
 157 {
 158         uintmax_t val;
 159         if (read_int(in, &val, len))
 160                 return -1;
 161         if (val > SIZE_MAX)
 162                 return error("unrepresentable length in delta: %"PRIuMAX"", val);
 163         *result = val;
 164         return 0;
 165 }
 166
 167 static int copyfrom_source(struct window *ctx, const char **instructions,
 168                            size_t nbytes, const char *insns_end)
 169 {
 170         size_t offset;
 171         if (parse_int(instructions, &offset, insns_end))
 172                 return -1;
 173         if (unsigned_add_overflows(offset, nbytes) ||
 174             offset + nbytes > ctx->in->width)
 175                 return error("invalid delta: copies source data outside view");
 176         strbuf_add(&ctx->out, ctx->in->buf.buf + offset, nbytes);
 177         return 0;
 178 }
 179
 180 static int copyfrom_target(struct window *ctx, const char **instructions,
 181                            size_t nbytes, const char *instructions_end)
 182 {
 183         size_t offset;
 184         if (parse_int(instructions, &offset, instructions_end))
 185                 return -1;
 186         if (offset >= ctx->out.len)
 187                 return error("invalid delta: copies from the future");
 188         for (; nbytes > 0; nbytes--)
 189                 strbuf_addch(&ctx->out, ctx->out.buf[offset++]);
 190         return 0;
 191 }
 192
 193 static int copyfrom_data(struct window *ctx, size_t *data_pos, size_t nbytes)
 194 {
 195         const size_t pos = *data_pos;
 196         if (unsigned_add_overflows(pos, nbytes) ||
 197             pos + nbytes > ctx->data.len)
 198                 return error("invalid delta: copies unavailable inline data");
 199         strbuf_add(&ctx->out, ctx->data.buf + pos, nbytes);
 200         *data_pos += nbytes;
 201         return 0;
 202 }
 203
 204 static int parse_first_operand(const char **buf, size_t *out, const char *end)
 205 {
 206         size_t result = (unsigned char) *(*buf)++ & OPERAND_MASK;
 207         if (result) {   /* immediate operand */
 208                 *out = result;
 209                 return 0;
 210         }
 211         return parse_int(buf, out, end);
 212 }
 213
 214 static int execute_one_instruction(struct window *ctx,
 215                                 const char **instructions, size_t *data_pos)
 216 {
 217         unsigned int instruction;
 218         const char *insns_end = ctx->instructions.buf + ctx->instructions.len;
 219         size_t nbytes;
 220         assert(ctx);
 221         assert(instructions && *instructions);
 222         assert(data_pos);
 223
 224         instruction = (unsigned char) **instructions;
 225         if (parse_first_operand(instructions, &nbytes, insns_end))
 226                 return -1;
 227         switch (instruction & INSN_MASK) {
 228         case INSN_COPYFROM_SOURCE:
 229                 return copyfrom_source(ctx, instructions, nbytes, insns_end);
 230         case INSN_COPYFROM_TARGET:
 231                 return copyfrom_target(ctx, instructions, nbytes, insns_end);
 232         case INSN_COPYFROM_DATA:
 233                 return copyfrom_data(ctx, data_pos, nbytes);
 234         default:
 235                 return error("invalid delta: unrecognized instruction");
 236         }
 237 }
 238
 239 static int apply_window_in_core(struct window *ctx)
 240 {
 241         const char *instructions;
 242         size_t data_pos = 0;
 243
 244         /*
 245          * Fill ctx->out.buf using data from the source, target,
 246          * and inline data views.
 247          */
 248         for (instructions = ctx->instructions.buf;
 249              instructions != ctx->instructions.buf + ctx->instructions.len;
 250              )
 251                 if (execute_one_instruction(ctx, &instructions, &data_pos))
 252                         return -1;
 253         if (data_pos != ctx->data.len)
 254                 return error("invalid delta: does not copy all inline data");
 255         return 0;
 256 }
 257
 258 static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
 259                             struct sliding_view *preimage, FILE *out)
 260 {
 261         struct window ctx = WINDOW_INIT(preimage);
 262         size_t out_len;
 263         size_t instructions_len;
 264         size_t data_len;
 265         assert(delta_len);
 266
 267         /* "source view" offset and length already handled; */
 268         if (read_length(delta, &out_len, delta_len) ||
 269             read_length(delta, &instructions_len, delta_len) ||
 270             read_length(delta, &data_len, delta_len) ||
 271             read_chunk(delta, delta_len, &ctx.instructions, instructions_len) ||
 272             read_chunk(delta, delta_len, &ctx.data, data_len))
 273                 goto error_out;
 274         strbuf_grow(&ctx.out, out_len);
 275         if (apply_window_in_core(&ctx))
 276                 goto error_out;
 277         if (ctx.out.len != out_len) {
 278                 error("invalid delta: incorrect postimage length");
 279                 goto error_out;
 280         }
 281         if (write_strbuf(&ctx.out, out))
 282                 goto error_out;
 283         window_release(&ctx);
 284         return 0;
 285 error_out:
 286         window_release(&ctx);
 287         return -1;
 288 }
 289
 290 int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
 291                         struct sliding_view *preimage, FILE *postimage)
 292 {
 293         assert(delta && preimage && postimage);
 294
 295         if (read_magic(delta, &delta_len))
 296                 return -1;
 297         while (delta_len) {     /* For each window: */
 298                 off_t pre_off = pre_off; /* stupid GCC... */
 299                 size_t pre_len;
 300
 301                 if (read_offset(delta, &pre_off, &delta_len) ||
 302                     read_length(delta, &pre_len, &delta_len) ||
 303                     move_window(preimage, pre_off, pre_len) ||
 304                     apply_one_window(delta, &delta_len, preimage, postimage))
 305                         return -1;
 306         }
 307         return 0;
 308 }