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_errno("cannot write delta postimage");
  68 }
  69
  70 static int error_short_read(struct line_buffer *input)
  71 {
  72         if (buffer_ferror(input))
  73                 return error_errno("error reading delta");
  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         assert(*delta_len >= 0);
  81         strbuf_reset(buf);
  82         if (len > (uintmax_t) *delta_len ||
  83             buffer_read_binary(delta, buf, len) != len)
  84                 return error_short_read(delta);
  85         *delta_len -= buf->len;
  86         return 0;
  87 }
  88
  89 static int read_magic(struct line_buffer *in, off_t *len)
  90 {
  91         static const char magic[] = {'S', 'V', 'N', '\0'};
  92         struct strbuf sb = STRBUF_INIT;
  93
  94         if (read_chunk(in, len, &sb, sizeof(magic))) {
  95                 strbuf_release(&sb);
  96                 return -1;
  97         }
  98         if (memcmp(sb.buf, magic, sizeof(magic))) {
  99                 strbuf_release(&sb);
 100                 return error("invalid delta: unrecognized file type");
 101         }
 102         strbuf_release(&sb);
 103         return 0;
 104 }
 105
 106 static int read_int(struct line_buffer *in, uintmax_t *result, off_t *len)
 107 {
 108         uintmax_t rv = 0;
 109         off_t sz;
 110         for (sz = *len; sz; sz--) {
 111                 const int ch = buffer_read_char(in);
 112                 if (ch == EOF)
 113                         break;
 114
 115                 rv <<= VLI_BITS_PER_DIGIT;
 116                 rv += (ch & VLI_DIGIT_MASK);
 117                 if (ch & VLI_CONTINUE)
 118                         continue;
 119
 120                 *result = rv;
 121                 *len = sz - 1;
 122                 return 0;
 123         }
 124         return error_short_read(in);
 125 }
 126
 127 static int parse_int(const char **buf, size_t *result, const char *end)
 128 {
 129         size_t rv = 0;
 130         const char *pos;
 131         for (pos = *buf; pos != end; pos++) {
 132                 unsigned char ch = *pos;
 133
 134                 rv <<= VLI_BITS_PER_DIGIT;
 135                 rv += (ch & VLI_DIGIT_MASK);
 136                 if (ch & VLI_CONTINUE)
 137                         continue;
 138
 139                 *result = rv;
 140                 *buf = pos + 1;
 141                 return 0;
 142         }
 143         return error("invalid delta: unexpected end of instructions section");
 144 }
 145
 146 static int read_offset(struct line_buffer *in, off_t *result, off_t *len)
 147 {
 148         uintmax_t val;
 149         if (read_int(in, &val, len))
 150                 return -1;
 151         if (val > maximum_signed_value_of_type(off_t))
 152                 return error("unrepresentable offset in delta: %"PRIuMAX"", val);
 153         *result = val;
 154         return 0;
 155 }
 156
 157 static int read_length(struct line_buffer *in, size_t *result, off_t *len)
 158 {
 159         uintmax_t val;
 160         if (read_int(in, &val, len))
 161                 return -1;
 162         if (val > SIZE_MAX)
 163                 return error("unrepresentable length in delta: %"PRIuMAX"", val);
 164         *result = val;
 165         return 0;
 166 }
 167
 168 static int copyfrom_source(struct window *ctx, const char **instructions,
 169                            size_t nbytes, const char *insns_end)
 170 {
 171         size_t offset;
 172         if (parse_int(instructions, &offset, insns_end))
 173                 return -1;
 174         if (unsigned_add_overflows(offset, nbytes) ||
 175             offset + nbytes > ctx->in->width)
 176                 return error("invalid delta: copies source data outside view");
 177         strbuf_add(&ctx->out, ctx->in->buf.buf + offset, nbytes);
 178         return 0;
 179 }
 180
 181 static int copyfrom_target(struct window *ctx, const char **instructions,
 182                            size_t nbytes, const char *instructions_end)
 183 {
 184         size_t offset;
 185         if (parse_int(instructions, &offset, instructions_end))
 186                 return -1;
 187         if (offset >= ctx->out.len)
 188                 return error("invalid delta: copies from the future");
 189         for (; nbytes > 0; nbytes--)
 190                 strbuf_addch(&ctx->out, ctx->out.buf[offset++]);
 191         return 0;
 192 }
 193
 194 static int copyfrom_data(struct window *ctx, size_t *data_pos, size_t nbytes)
 195 {
 196         const size_t pos = *data_pos;
 197         if (unsigned_add_overflows(pos, nbytes) ||
 198             pos + nbytes > ctx->data.len)
 199                 return error("invalid delta: copies unavailable inline data");
 200         strbuf_add(&ctx->out, ctx->data.buf + pos, nbytes);
 201         *data_pos += nbytes;
 202         return 0;
 203 }
 204
 205 static int parse_first_operand(const char **buf, size_t *out, const char *end)
 206 {
 207         size_t result = (unsigned char) *(*buf)++ & OPERAND_MASK;
 208         if (result) {   /* immediate operand */
 209                 *out = result;
 210                 return 0;
 211         }
 212         return parse_int(buf, out, end);
 213 }
 214
 215 static int execute_one_instruction(struct window *ctx,
 216                                 const char **instructions, size_t *data_pos)
 217 {
 218         unsigned int instruction;
 219         const char *insns_end = ctx->instructions.buf + ctx->instructions.len;
 220         size_t nbytes;
 221         assert(ctx);
 222         assert(instructions && *instructions);
 223         assert(data_pos);
 224
 225         instruction = (unsigned char) **instructions;
 226         if (parse_first_operand(instructions, &nbytes, insns_end))
 227                 return -1;
 228         switch (instruction & INSN_MASK) {
 229         case INSN_COPYFROM_SOURCE:
 230                 return copyfrom_source(ctx, instructions, nbytes, insns_end);
 231         case INSN_COPYFROM_TARGET:
 232                 return copyfrom_target(ctx, instructions, nbytes, insns_end);
 233         case INSN_COPYFROM_DATA:
 234                 return copyfrom_data(ctx, data_pos, nbytes);
 235         default:
 236                 return error("invalid delta: unrecognized instruction");
 237         }
 238 }
 239
 240 static int apply_window_in_core(struct window *ctx)
 241 {
 242         const char *instructions;
 243         size_t data_pos = 0;
 244
 245         /*
 246          * Fill ctx->out.buf using data from the source, target,
 247          * and inline data views.
 248          */
 249         for (instructions = ctx->instructions.buf;
 250              instructions != ctx->instructions.buf + ctx->instructions.len;
 251              )
 252                 if (execute_one_instruction(ctx, &instructions, &data_pos))
 253                         return -1;
 254         if (data_pos != ctx->data.len)
 255                 return error("invalid delta: does not copy all inline data");
 256         return 0;
 257 }
 258
 259 static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
 260                             struct sliding_view *preimage, FILE *out)
 261 {
 262         int rv = -1;
 263         struct window ctx = WINDOW_INIT(preimage);
 264         size_t out_len;
 265         size_t instructions_len;
 266         size_t data_len;
 267         assert(delta_len);
 268
 269         /* "source view" offset and length already handled; */
 270         if (read_length(delta, &out_len, delta_len) ||
 271             read_length(delta, &instructions_len, delta_len) ||
 272             read_length(delta, &data_len, delta_len) ||
 273             read_chunk(delta, delta_len, &ctx.instructions, instructions_len) ||
 274             read_chunk(delta, delta_len, &ctx.data, data_len))
 275                 goto error_out;
 276         strbuf_grow(&ctx.out, out_len);
 277         if (apply_window_in_core(&ctx))
 278                 goto error_out;
 279         if (ctx.out.len != out_len) {
 280                 rv = error("invalid delta: incorrect postimage length");
 281                 goto error_out;
 282         }
 283         if (write_strbuf(&ctx.out, out))
 284                 goto error_out;
 285         rv = 0;
 286 error_out:
 287         window_release(&ctx);
 288         return rv;
 289 }
 290
 291 int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
 292                         struct sliding_view *preimage, FILE *postimage)
 293 {
 294         assert(delta && preimage && postimage && delta_len >= 0);
 295
 296         if (read_magic(delta, &delta_len))
 297                 return -1;
 298         while (delta_len) {     /* For each window: */
 299                 off_t pre_off = -1;
 300                 size_t pre_len;
 301
 302                 if (read_offset(delta, &pre_off, &delta_len) ||
 303                     read_length(delta, &pre_len, &delta_len) ||
 304                     move_window(preimage, pre_off, pre_len) ||
 305                     apply_one_window(delta, &delta_len, preimage, postimage))
 306                         return -1;
 307         }
 308         return 0;
 309 }