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vcs-svn: parse svndiff0 window header

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Each window in a subversion delta (svndiff0-format file) starts with a
window header, consisting of five integers with variable-length
representation:

	source view offset
	source view length
	output length
	instructions length
	auxiliary data length

Parse it.  The result is not usable for deltas with nonempty postimage
yet; in fact, this only adds support for deltas without any
instructions or auxiliary data.  This is a good place to stop, though,
since that little support lets us add some simple passing tests
concerning error handling to the test suite.

Improved-by: Ramkumar Ramachandra <artagnon@gmail.com>
Improved-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
This commit is contained in:
Jonathan Nieder
2010-10-13 04:21:43 -05:00
parent ddcc8c5b46
commit 252712111f
2 changed files with 142 additions and 6 deletions
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92
vcs-svn/svndiff.c
View File

@ -13,8 +13,16 @@
* See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
*
* svndiff0 ::= 'SVN\0' window*
* window ::= int int int int int instructions inline_data;
* int ::= highdigit* lowdigit;
* highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
* lowdigit ::= # 7 bit value;
*/
#define VLI_CONTINUE 0x80
#define VLI_DIGIT_MASK 0x7f
#define VLI_BITS_PER_DIGIT 7
static int error_short_read(struct line_buffer *input)
{
if (buffer_ferror(input))
@ -28,17 +36,84 @@ static int read_magic(struct line_buffer *in, off_t *len)
struct strbuf sb = STRBUF_INIT;
if (*len < sizeof(magic) ||
buffer_read_binary(in, &sb, sizeof(magic)) != sizeof(magic))
return error_short_read(in);
buffer_read_binary(in, &sb, sizeof(magic)) != sizeof(magic)) {
error_short_read(in);
strbuf_release(&sb);
return -1;
}
if (memcmp(sb.buf, magic, sizeof(magic)))
if (memcmp(sb.buf, magic, sizeof(magic))) {
strbuf_release(&sb);
return error("invalid delta: unrecognized file type");
}
*len -= sizeof(magic);
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 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 apply_one_window(struct line_buffer *delta, off_t *delta_len)
{
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))
return -1;
if (instructions_len)
return error("What do you think I am? A delta applier?");
if (data_len)
return error("No support for inline data yet");
return 0;
}
int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
struct sliding_view *preimage, FILE *postimage)
{
@ -46,7 +121,14 @@ int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
if (read_magic(delta, &delta_len))
return -1;
if (delta_len)
return error("What do you think I am? A delta applier?");
while (delta_len) { /* For each window: */
off_t pre_off;
size_t pre_len;
if (read_offset(delta, &pre_off, &delta_len) ||
read_length(delta, &pre_len, &delta_len) ||
apply_one_window(delta, &delta_len))
return -1;
}
return 0;
}