blob: b883f733a6bdf3e69851cb22ed1098127fb3b568 [file] [log] [blame]
/*
bsdiff.c -- Binary patch generator.
Copyright 2003 Colin Percival
For the terms under which this work may be distributed, please see
the adjoining file "LICENSE".
ChangeLog:
2005-05-05 - Use the modified header struct from bspatch.h; use 32-bit
values throughout.
--Benjamin Smedberg <benjamin@smedbergs.us>
2005-05-18 - Use the same CRC algorithm as bzip2, and leverage the CRC table
provided by libbz2.
--Darin Fisher <darin@meer.net>
2007-11-14 - Changed to use Crc from Lzma library instead of Bzip library
--Rahul Kuchhal
2009-03-31 - Change to use Streams. Added lots of comments.
--Stephen Adams <sra@chromium.org>
2010-05-26 - Use a paged array for V and I. The address space may be too
fragmented for these big arrays to be contiguous.
--Stephen Adams <sra@chromium.org>
2015-08-03 - Extract qsufsort portion to a separate file.
--Samuel Huang <huangs@chromium.org>
2015-08-12 - Interface change to qsufsort search().
--Samuel Huang <huangs@chromium.org>
*/
#include "courgette/third_party/bsdiff.h"
#include <stdlib.h>
#include <algorithm>
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/strings/string_util.h"
#include "base/time/time.h"
#include "courgette/crc.h"
#include "courgette/streams.h"
#include "courgette/third_party/paged_array.h"
#include "courgette/third_party/qsufsort.h"
namespace courgette {
static CheckBool WriteHeader(SinkStream* stream, MBSPatchHeader* header) {
bool ok = stream->Write(header->tag, sizeof(header->tag));
ok &= stream->WriteVarint32(header->slen);
ok &= stream->WriteVarint32(header->scrc32);
ok &= stream->WriteVarint32(header->dlen);
return ok;
}
BSDiffStatus CreateBinaryPatch(SourceStream* old_stream,
SourceStream* new_stream,
SinkStream* patch_stream)
{
base::Time start_bsdiff_time = base::Time::Now();
VLOG(1) << "Start bsdiff";
size_t initial_patch_stream_length = patch_stream->Length();
SinkStreamSet patch_streams;
SinkStream* control_stream_copy_counts = patch_streams.stream(0);
SinkStream* control_stream_extra_counts = patch_streams.stream(1);
SinkStream* control_stream_seeks = patch_streams.stream(2);
SinkStream* diff_skips = patch_streams.stream(3);
SinkStream* diff_bytes = patch_streams.stream(4);
SinkStream* extra_bytes = patch_streams.stream(5);
const uint8* old = old_stream->Buffer();
const int oldsize = static_cast<int>(old_stream->Remaining());
uint32 pending_diff_zeros = 0;
PagedArray<int> I;
PagedArray<int> V;
if (!I.Allocate(oldsize + 1)) {
LOG(ERROR) << "Could not allocate I[], " << ((oldsize + 1) * sizeof(int))
<< " bytes";
return MEM_ERROR;
}
if (!V.Allocate(oldsize + 1)) {
LOG(ERROR) << "Could not allocate V[], " << ((oldsize + 1) * sizeof(int))
<< " bytes";
return MEM_ERROR;
}
base::Time q_start_time = base::Time::Now();
qsuf::qsufsort<PagedArray<int>&>(I, V, old, oldsize);
VLOG(1) << " done qsufsort "
<< (base::Time::Now() - q_start_time).InSecondsF();
V.clear();
const uint8* newbuf = new_stream->Buffer();
const int newsize = static_cast<int>(new_stream->Remaining());
int control_length = 0;
int diff_bytes_length = 0;
int diff_bytes_nonzero = 0;
int extra_bytes_length = 0;
// The patch format is a sequence of triples <copy,extra,seek> where 'copy' is
// the number of bytes to copy from the old file (possibly with mistakes),
// 'extra' is the number of bytes to copy from a stream of fresh bytes, and
// 'seek' is an offset to move to the position to copy for the next triple.
//
// The invariant at the top of this loop is that we are committed to emitting
// a triple for the part of |newbuf| surrounding a 'seed' match near
// |lastscan|. We are searching for a second match that will be the 'seed' of
// the next triple. As we scan through |newbuf|, one of four things can
// happen at the current position |scan|:
//
// 1. We find a nice match that appears to be consistent with the current
// seed. Continue scanning. It is likely that this match will become
// part of the 'copy'.
//
// 2. We find match which does much better than extending the current seed
// old match. Emit a triple for the current seed and take this match as
// the new seed for a new triple. By 'much better' we remove 8 mismatched
// bytes by taking the new seed.
//
// 3. There is not a good match. Continue scanning. These bytes will likely
// become part of the 'extra'.
//
// 4. There is no match because we reached the end of the input, |newbuf|.
// This is how the loop advances through the bytes of |newbuf|:
//
// ...012345678901234567890123456789...
// ssssssssss Seed at |lastscan|
// xxyyyxxyyxy |scan| forward, cases (3)(x) & (1)(y)
// mmmmmmmm New match will start new seed case (2).
// fffffffffffffff |lenf| = scan forward from |lastscan|
// bbbb |lenb| = scan back from new seed |scan|.
// ddddddddddddddd Emit diff bytes for the 'copy'.
// xx Emit extra bytes.
// ssssssssssss |lastscan = scan - lenb| is new seed.
// x Cases (1) and (3) ....
int lastscan = 0, lastpos = 0, lastoffset = 0;
int scan = 0;
int match_length = 0;
while (scan < newsize) {
int pos = 0;
int oldscore = 0; // Count of how many bytes of the current match at |scan|
// extend the match at |lastscan|.
scan += match_length;
for (int scsc = scan; scan < newsize; ++scan) {
match_length = qsuf::search<PagedArray<int>&>(
I, old, oldsize, newbuf + scan, newsize - scan, &pos);
for ( ; scsc < scan + match_length ; scsc++)
if ((scsc + lastoffset < oldsize) &&
(old[scsc + lastoffset] == newbuf[scsc]))
oldscore++;
if ((match_length == oldscore) && (match_length != 0))
break; // Good continuing match, case (1)
if (match_length > oldscore + 8)
break; // New seed match, case (2)
if ((scan + lastoffset < oldsize) &&
(old[scan + lastoffset] == newbuf[scan]))
oldscore--;
// Case (3) continues in this loop until we fall out of the loop (4).
}
if ((match_length != oldscore) || (scan == newsize)) { // Cases (2) and (4)
// This next chunk of code finds the boundary between the bytes to be
// copied as part of the current triple, and the bytes to be copied as
// part of the next triple. The |lastscan| match is extended forwards as
// far as possible provided doing to does not add too many mistakes. The
// |scan| match is extended backwards in a similar way.
// Extend the current match (if any) backwards. |lenb| is the maximal
// extension for which less than half the byte positions in the extension
// are wrong.
int lenb = 0;
if (scan < newsize) { // i.e. not case (4); there is a match to extend.
int score = 0, Sb = 0;
for (int i = 1; (scan >= lastscan + i) && (pos >= i); i++) {
if (old[pos - i] == newbuf[scan - i]) score++;
if (score*2 - i > Sb*2 - lenb) { Sb = score; lenb = i; }
}
}
// Extend the lastscan match forward; |lenf| is the maximal extension for
// which less than half of the byte positions in entire lastscan match are
// wrong. There is a subtle point here: |lastscan| points to before the
// seed match by |lenb| bytes from the previous iteration. This is why
// the loop measures the total number of mistakes in the the match, not
// just the from the match.
int lenf = 0;
{
int score = 0, Sf = 0;
for (int i = 0; (lastscan + i < scan) && (lastpos + i < oldsize); ) {
if (old[lastpos + i] == newbuf[lastscan + i]) score++;
i++;
if (score*2 - i > Sf*2 - lenf) { Sf = score; lenf = i; }
}
}
// If the extended scans overlap, pick a position in the overlap region
// that maximizes the exact matching bytes.
if (lastscan + lenf > scan - lenb) {
int overlap = (lastscan + lenf) - (scan - lenb);
int score = 0;
int Ss = 0, lens = 0;
for (int i = 0; i < overlap; i++) {
if (newbuf[lastscan + lenf - overlap + i] ==
old[lastpos + lenf - overlap + i]) score++;
if (newbuf[scan - lenb + i] == old[pos - lenb + i]) score--;
if (score > Ss) { Ss = score; lens = i + 1; }
}
lenf += lens - overlap;
lenb -= lens;
};
for (int i = 0; i < lenf; i++) {
uint8 diff_byte = newbuf[lastscan + i] - old[lastpos + i];
if (diff_byte) {
++diff_bytes_nonzero;
if (!diff_skips->WriteVarint32(pending_diff_zeros))
return MEM_ERROR;
pending_diff_zeros = 0;
if (!diff_bytes->Write(&diff_byte, 1))
return MEM_ERROR;
} else {
++pending_diff_zeros;
}
}
int gap = (scan - lenb) - (lastscan + lenf);
for (int i = 0; i < gap; i++) {
if (!extra_bytes->Write(&newbuf[lastscan + lenf + i], 1))
return MEM_ERROR;
}
diff_bytes_length += lenf;
extra_bytes_length += gap;
uint32 copy_count = lenf;
uint32 extra_count = gap;
int32 seek_adjustment = ((pos - lenb) - (lastpos + lenf));
if (!control_stream_copy_counts->WriteVarint32(copy_count) ||
!control_stream_extra_counts->WriteVarint32(extra_count) ||
!control_stream_seeks->WriteVarint32Signed(seek_adjustment)) {
return MEM_ERROR;
}
++control_length;
#ifdef DEBUG_bsmedberg
VLOG(1) << StringPrintf("Writing a block: copy: %-8u extra: %-8u seek: "
"%+-9d", copy_count, extra_count,
seek_adjustment);
#endif
lastscan = scan - lenb; // Include the backward extension in seed.
lastpos = pos - lenb; // ditto.
lastoffset = lastpos - lastscan;
}
}
if (!diff_skips->WriteVarint32(pending_diff_zeros))
return MEM_ERROR;
I.clear();
MBSPatchHeader header;
// The string will have a null terminator that we don't use, hence '-1'.
static_assert(sizeof(MBS_PATCH_HEADER_TAG) - 1 == sizeof(header.tag),
"MBS_PATCH_HEADER_TAG must match header field size");
memcpy(header.tag, MBS_PATCH_HEADER_TAG, sizeof(header.tag));
header.slen = oldsize;
header.scrc32 = CalculateCrc(old, oldsize);
header.dlen = newsize;
if (!WriteHeader(patch_stream, &header))
return MEM_ERROR;
size_t diff_skips_length = diff_skips->Length();
if (!patch_streams.CopyTo(patch_stream))
return MEM_ERROR;
VLOG(1) << "Control tuples: " << control_length
<< " copy bytes: " << diff_bytes_length
<< " mistakes: " << diff_bytes_nonzero
<< " (skips: " << diff_skips_length << ")"
<< " extra bytes: " << extra_bytes_length
<< "\nUncompressed bsdiff patch size "
<< patch_stream->Length() - initial_patch_stream_length
<< "\nEnd bsdiff "
<< (base::Time::Now() - start_bsdiff_time).InSecondsF();
return OK;
}
} // namespace courgette