Andrew's git - gitweb.git/blob

   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
  47struct 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
  56static void window_release(struct window *ctx)
  57{
  58        strbuf_release(&ctx->out);
  59        strbuf_release(&ctx->instructions);
  60        strbuf_release(&ctx->data);
  61}
  62
  63static 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
  70static 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
  77static 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
  89static 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
 106static 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
 127static 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
 146static 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
 157static 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
 168static 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
 181static 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
 194static 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
 205static 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
 215static 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
 240static 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
 259static 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;
 286error_out:
 287        window_release(&ctx);
 288        return rv;
 289}
 290
 291int 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}