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/*
* Licensed under a two-clause BSD-style license.
* See LICENSE for details.
*/

#include "git-compat-util.h"
#include "sliding_window.h"
#include "line_buffer.h"
#include "svndiff.h"

/*
* svndiff0 applier
*
* See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
*
* svndiff0 ::= 'SVN\0' window*
* window ::= int int int int int instructions inline_data;
* instructions ::= instruction*;
* instruction ::= view_selector int int
* | copyfrom_data int
* | packed_view_selector int
* | packed_copyfrom_data
* ;
* view_selector ::= copyfrom_source
* | copyfrom_target
* ;
* copyfrom_source ::= # binary 00 000000;
* copyfrom_target ::= # binary 01 000000;
* copyfrom_data ::= # binary 10 000000;
* packed_view_selector ::= # view_selector OR-ed with 6 bit value;
* packed_copyfrom_data ::= # copyfrom_data OR-ed with 6 bit value;
* int ::= highdigit* lowdigit;
* highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
* lowdigit ::= # 7 bit value;
*/

#define INSN_MASK 0xc0
#define INSN_COPYFROM_SOURCE 0x00
#define INSN_COPYFROM_TARGET 0x40
#define INSN_COPYFROM_DATA 0x80
#define OPERAND_MASK 0x3f

#define VLI_CONTINUE 0x80
#define VLI_DIGIT_MASK 0x7f
#define VLI_BITS_PER_DIGIT 7

struct window {
struct sliding_view *in;
struct strbuf out;
struct strbuf instructions;
struct strbuf data;
};

#define WINDOW_INIT(w) { (w), STRBUF_INIT, STRBUF_INIT, STRBUF_INIT }

static void window_release(struct window *ctx)
{
strbuf_release(&ctx->out);
strbuf_release(&ctx->instructions);
strbuf_release(&ctx->data);
}

static int write_strbuf(struct strbuf *sb, FILE *out)
{
if (fwrite(sb->buf, 1, sb->len, out) == sb->len) /* Success. */
return 0;
return error("cannot write delta postimage: %s", strerror(errno));
}

static int error_short_read(struct line_buffer *input)
{
if (buffer_ferror(input))
return error("error reading delta: %s", strerror(errno));
return error("invalid delta: unexpected end of file");
}

static int read_chunk(struct line_buffer *delta, off_t *delta_len,
struct strbuf *buf, size_t len)
{
strbuf_reset(buf);
if (len > *delta_len ||
buffer_read_binary(delta, buf, len) != len)
return error_short_read(delta);
*delta_len -= buf->len;
return 0;
}

static int read_magic(struct line_buffer *in, off_t *len)
{
static const char magic[] = {'S', 'V', 'N', '\0'};
struct strbuf sb = STRBUF_INIT;

if (read_chunk(in, len, &sb, sizeof(magic))) {
strbuf_release(&sb);
return -1;
}
if (memcmp(sb.buf, magic, sizeof(magic))) {
strbuf_release(&sb);
return error("invalid delta: unrecognized file type");
}
strbuf_release(&sb);
return 0;
}

static int read_int(struct line_buffer *in, uintmax_t *result, off_t *len)
{
uintmax_t rv = 0;
off_t sz;
for (sz = *len; sz; sz--) {
const int ch = buffer_read_char(in);
if (ch == EOF)
break;

rv <<= VLI_BITS_PER_DIGIT;
rv += (ch & VLI_DIGIT_MASK);
if (ch & VLI_CONTINUE)
continue;

*result = rv;
*len = sz - 1;
return 0;
}
return error_short_read(in);
}

static int parse_int(const char **buf, size_t *result, const char *end)
{
size_t rv = 0;
const char *pos;
for (pos = *buf; pos != end; pos++) {
unsigned char ch = *pos;

rv <<= VLI_BITS_PER_DIGIT;
rv += (ch & VLI_DIGIT_MASK);
if (ch & VLI_CONTINUE)
continue;

*result = rv;
*buf = pos + 1;
return 0;
}
return error("invalid delta: unexpected end of instructions section");
}

static int read_offset(struct line_buffer *in, off_t *result, off_t *len)
{
uintmax_t val;
if (read_int(in, &val, len))
return -1;
if (val > maximum_signed_value_of_type(off_t))
return error("unrepresentable offset in delta: %"PRIuMAX"", val);
*result = val;
return 0;
}

static int read_length(struct line_buffer *in, size_t *result, off_t *len)
{
uintmax_t val;
if (read_int(in, &val, len))
return -1;
if (val > SIZE_MAX)
return error("unrepresentable length in delta: %"PRIuMAX"", val);
*result = val;
return 0;
}

static int copyfrom_source(struct window *ctx, const char **instructions,
size_t nbytes, const char *insns_end)
{
size_t offset;
if (parse_int(instructions, &offset, insns_end))
return -1;
if (unsigned_add_overflows(offset, nbytes) ||
offset + nbytes > ctx->in->width)
return error("invalid delta: copies source data outside view");
strbuf_add(&ctx->out, ctx->in->buf.buf + offset, nbytes);
return 0;
}

static int copyfrom_target(struct window *ctx, const char **instructions,
size_t nbytes, const char *instructions_end)
{
size_t offset;
if (parse_int(instructions, &offset, instructions_end))
return -1;
if (offset >= ctx->out.len)
return error("invalid delta: copies from the future");
for (; nbytes > 0; nbytes--)
strbuf_addch(&ctx->out, ctx->out.buf[offset++]);
return 0;
}

static int copyfrom_data(struct window *ctx, size_t *data_pos, size_t nbytes)
{
const size_t pos = *data_pos;
if (unsigned_add_overflows(pos, nbytes) ||
pos + nbytes > ctx->data.len)
return error("invalid delta: copies unavailable inline data");
strbuf_add(&ctx->out, ctx->data.buf + pos, nbytes);
*data_pos += nbytes;
return 0;
}

static int parse_first_operand(const char **buf, size_t *out, const char *end)
{
size_t result = (unsigned char) *(*buf)++ & OPERAND_MASK;
if (result) { /* immediate operand */
*out = result;
return 0;
}
return parse_int(buf, out, end);
}

static int execute_one_instruction(struct window *ctx,
const char **instructions, size_t *data_pos)
{
unsigned int instruction;
const char *insns_end = ctx->instructions.buf + ctx->instructions.len;
size_t nbytes;
assert(ctx);
assert(instructions && *instructions);
assert(data_pos);

instruction = (unsigned char) **instructions;
if (parse_first_operand(instructions, &nbytes, insns_end))
return -1;
switch (instruction & INSN_MASK) {
case INSN_COPYFROM_SOURCE:
return copyfrom_source(ctx, instructions, nbytes, insns_end);
case INSN_COPYFROM_TARGET:
return copyfrom_target(ctx, instructions, nbytes, insns_end);
case INSN_COPYFROM_DATA:
return copyfrom_data(ctx, data_pos, nbytes);
default:
return error("invalid delta: unrecognized instruction");
}
}

static int apply_window_in_core(struct window *ctx)
{
const char *instructions;
size_t data_pos = 0;

/*
* Fill ctx->out.buf using data from the source, target,
* and inline data views.
*/
for (instructions = ctx->instructions.buf;
instructions != ctx->instructions.buf + ctx->instructions.len;
)
if (execute_one_instruction(ctx, &instructions, &data_pos))
return -1;
if (data_pos != ctx->data.len)
return error("invalid delta: does not copy all inline data");
return 0;
}

static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
struct sliding_view *preimage, FILE *out)
{
struct window ctx = WINDOW_INIT(preimage);
size_t out_len;
size_t instructions_len;
size_t data_len;
assert(delta_len);

/* "source view" offset and length already handled; */
if (read_length(delta, &out_len, delta_len) ||
read_length(delta, &instructions_len, delta_len) ||
read_length(delta, &data_len, delta_len) ||
read_chunk(delta, delta_len, &ctx.instructions, instructions_len) ||
read_chunk(delta, delta_len, &ctx.data, data_len))
goto error_out;
strbuf_grow(&ctx.out, out_len);
if (apply_window_in_core(&ctx))
goto error_out;
if (ctx.out.len != out_len) {
error("invalid delta: incorrect postimage length");
goto error_out;
}
if (write_strbuf(&ctx.out, out))
goto error_out;
window_release(&ctx);
return 0;
error_out:
window_release(&ctx);
return -1;
}

int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
struct sliding_view *preimage, FILE *postimage)
{
assert(delta && preimage && postimage);

if (read_magic(delta, &delta_len))
return -1;
while (delta_len) { /* For each window: */
off_t pre_off = pre_off; /* stupid GCC... */
size_t pre_len;

if (read_offset(delta, &pre_off, &delta_len) ||
read_length(delta, &pre_len, &delta_len) ||
move_window(preimage, pre_off, pre_len) ||
apply_one_window(delta, &delta_len, preimage, postimage))
return -1;
}
return 0;
}
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