~bzr-pqm/bzr/bzr.dev

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
#! /usr/bin/env python

# (C) 2005 Canonical Ltd

# based on an idea by Matt Mackall
# modified to squish into bzr by Martin Pool

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


"""Packed file revision storage.

A Revfile holds the text history of a particular source file, such
as Makefile.  It can represent a tree of text versions for that
file, allowing for microbranches within a single repository.

This is stored on disk as two files: an index file, and a data file.
The index file is short and always read completely into memory; the
data file is much longer and only the relevant bits of it,
identified by the index file, need to be read.

Each text version is identified by the SHA-1 of the full text of
that version.  It also has a sequence number within the file.

The index file has a short header and then a sequence of fixed-length
records:

* byte[20]    SHA-1 of text (as binary, not hex)
* uint32      sequence number this is based on, or -1 for full text
* uint32      flags: 1=zlib compressed
* uint32      offset in text file of start
* uint32      length of compressed delta in text file
* uint32[3]   reserved

total 48 bytes.

The header is also 48 bytes for tidyness and easy calculation.

Both the index and the text are only ever appended to; a consequence
is that sequence numbers are stable references.  But not every
repository in the world will assign the same sequence numbers,
therefore the SHA-1 is the only universally unique reference.

This is meant to scale to hold 100,000 revisions of a single file, by
which time the index file will be ~4.8MB and a bit big to read
sequentially.

Some of the reserved fields could be used to implement a (semi?)
balanced tree indexed by SHA1 so we can much more efficiently find the
index associated with a particular hash.  For 100,000 revs we would be
able to find it in about 17 random reads, which is not too bad.

This performs pretty well except when trying to calculate deltas of
really large files.  For that the main thing would be to plug in
something faster than difflib, which is after all pure Python.
Another approach is to just store the gzipped full text of big files,
though perhaps that's too perverse?

The iter method here will generally read through the whole index file
in one go.  With readahead in the kernel and python/libc (typically
128kB) this means that there should be no seeks and often only one
read() call to get everything into memory.
"""
 

# TODO: Something like pread() would make this slightly simpler and
# perhaps more efficient.

# TODO: Could also try to mmap things...  Might be faster for the
# index in particular?

# TODO: Some kind of faster lookup of SHAs?  The bad thing is that probably means
# rewriting existing records, which is not so nice.

# TODO: Something to check that regions identified in the index file
# completely butt up and do not overlap.  Strictly it's not a problem
# if there are gaps and that can happen if we're interrupted while
# writing to the datafile.  Overlapping would be very bad though.

# TODO: Shouldn't need to lock if we always write in append mode and
# then ftell after writing to see where it went.  In any case we
# assume the whole branch is protected by a lock.

import sys, zlib, struct, mdiff, stat, os, sha
from binascii import hexlify, unhexlify

_RECORDSIZE = 48

_HEADER = "bzr revfile v1\n"
_HEADER = _HEADER + ('\xff' * (_RECORDSIZE - len(_HEADER)))
_NO_RECORD = 0xFFFFFFFFL

# fields in the index record
I_SHA = 0
I_BASE = 1
I_FLAGS = 2
I_OFFSET = 3
I_LEN = 4

FL_GZIP = 1

# maximum number of patches in a row before recording a whole text.
CHAIN_LIMIT = 10


class RevfileError(Exception):
    pass

class LimitHitException(Exception):
    pass

class Revfile(object):
    def __init__(self, basename, mode):
        # TODO: Lock file  while open

        # TODO: advise of random access

        self.basename = basename

        if mode not in ['r', 'w']:
            raise RevfileError("invalid open mode %r" % mode)
        self.mode = mode
        
        idxname = basename + '.irev'
        dataname = basename + '.drev'

        idx_exists = os.path.exists(idxname)
        data_exists = os.path.exists(dataname)

        if idx_exists != data_exists:
            raise RevfileError("half-assed revfile")
        
        if not idx_exists:
            if mode == 'r':
                raise RevfileError("Revfile %r does not exist" % basename)
            
            self.idxfile = open(idxname, 'w+b')
            self.datafile = open(dataname, 'w+b')
            
            self.idxfile.write(_HEADER)
            self.idxfile.flush()
        else:
            if mode == 'r':
                diskmode = 'rb'
            else:
                diskmode = 'r+b'
                
            self.idxfile = open(idxname, diskmode)
            self.datafile = open(dataname, diskmode)
            
            h = self.idxfile.read(_RECORDSIZE)
            if h != _HEADER:
                raise RevfileError("bad header %r in index of %r"
                                   % (h, self.basename))


    def _check_index(self, idx):
        if idx < 0 or idx > len(self):
            raise RevfileError("invalid index %r" % idx)

    def _check_write(self):
        if self.mode != 'w':
            raise RevfileError("%r is open readonly" % self.basename)


    def find_sha(self, s):
        assert isinstance(s, str)
        assert len(s) == 20
        
        for idx, idxrec in enumerate(self):
            if idxrec[I_SHA] == s:
                return idx
        else:
            return _NO_RECORD



    def _add_compressed(self, text_sha, data, base, compress):
        # well, maybe compress
        flags = 0
        if compress:
            data_len = len(data)
            if data_len > 50:
                # don't do compression if it's too small; it's unlikely to win
                # enough to be worthwhile
                compr_data = zlib.compress(data)
                compr_len = len(compr_data)
                if compr_len < data_len:
                    data = compr_data
                    flags = FL_GZIP
                    ##print '- compressed %d -> %d, %.1f%%' \
                    ##      % (data_len, compr_len, float(compr_len)/float(data_len) * 100.0)
        return self._add_raw(text_sha, data, base, flags)
        


    def _add_raw(self, text_sha, data, base, flags):
        """Add pre-processed data, can be either full text or delta.

        This does the compression if that makes sense."""
        idx = len(self)
        self.datafile.seek(0, 2)        # to end
        self.idxfile.seek(0, 2)
        assert self.idxfile.tell() == _RECORDSIZE * (idx + 1)
        data_offset = self.datafile.tell()

        assert isinstance(data, str) # not unicode or anything weird

        self.datafile.write(data)
        self.datafile.flush()

        assert isinstance(text_sha, str)
        entry = text_sha
        entry += struct.pack(">IIII12x", base, flags, data_offset, len(data))
        assert len(entry) == _RECORDSIZE

        self.idxfile.write(entry)
        self.idxfile.flush()

        return idx
        


    def _add_full_text(self, text, text_sha, compress):
        """Add a full text to the file.

        This is not compressed against any reference version.

        Returns the index for that text."""
        return self._add_compressed(text_sha, text, _NO_RECORD, compress)


    # NOT USED
    def _choose_base(self, seed, base):
        while seed & 3 == 3:
            if base == _NO_RECORD:
                return _NO_RECORD
            idxrec = self[base]
            if idxrec[I_BASE] == _NO_RECORD:
                return base

            base = idxrec[I_BASE]
            seed >>= 2
                
        return base        # relative to this full text
        


    def _add_delta(self, text, text_sha, base, compress):
        """Add a text stored relative to a previous text."""
        self._check_index(base)

        try:
            base_text = self.get(base, CHAIN_LIMIT)
        except LimitHitException:
            return self._add_full_text(text, text_sha, compress)
        
        data = mdiff.bdiff(base_text, text)


        if True: # paranoid early check for bad diff
            result = mdiff.bpatch(base_text, data)
            assert result == text
            
        
        # If the delta is larger than the text, we might as well just
        # store the text.  (OK, the delta might be more compressible,
        # but the overhead of applying it probably still makes it
        # bad, and I don't want to compress both of them to find out.)
        if len(data) >= len(text):
            return self._add_full_text(text, text_sha, compress)
        else:
            return self._add_compressed(text_sha, data, base, compress)


    def add(self, text, base=None, compress=True):
        """Add a new text to the revfile.

        If the text is already present them its existing id is
        returned and the file is not changed.

        If compress is true then gzip compression will be used if it
        reduces the size.

        If a base index is specified, that text *may* be used for
        delta compression of the new text.  Delta compression will
        only be used if it would be a size win and if the existing
        base is not at too long of a delta chain already.
        """
        if base == None:
            base = _NO_RECORD
        
        self._check_write()
        
        text_sha = sha.new(text).digest()

        idx = self.find_sha(text_sha)
        if idx != _NO_RECORD:
            # TODO: Optional paranoid mode where we read out that record and make sure
            # it's the same, in case someone ever breaks SHA-1.
            return idx                  # already present
        
        # base = self._choose_base(ord(text_sha[0]), base)

        if base == _NO_RECORD:
            return self._add_full_text(text, text_sha, compress)
        else:
            return self._add_delta(text, text_sha, base, compress)



    def get(self, idx, recursion_limit=None):
        """Retrieve text of a previous revision.

        If recursion_limit is an integer then walk back at most that
        many revisions and then raise LimitHitException, indicating
        that we ought to record a new file text instead of another
        delta.  Don't use this when trying to get out an existing
        revision."""
        
        idxrec = self[idx]
        base = idxrec[I_BASE]
        if base == _NO_RECORD:
            text = self._get_full_text(idx, idxrec)
        else:
            text = self._get_patched(idx, idxrec, recursion_limit)

        if sha.new(text).digest() != idxrec[I_SHA]:
            raise RevfileError("corrupt SHA-1 digest on record %d in %s"
                               % (idx, self.basename))

        return text



    def _get_raw(self, idx, idxrec):
        flags = idxrec[I_FLAGS]
        if flags & ~FL_GZIP:
            raise RevfileError("unsupported index flags %#x on index %d"
                               % (flags, idx))
        
        l = idxrec[I_LEN]
        if l == 0:
            return ''

        self.datafile.seek(idxrec[I_OFFSET])

        data = self.datafile.read(l)
        if len(data) != l:
            raise RevfileError("short read %d of %d "
                               "getting text for record %d in %r"
                               % (len(data), l, idx, self.basename))

        if flags & FL_GZIP:
            data = zlib.decompress(data)

        return data
        

    def _get_full_text(self, idx, idxrec):
        assert idxrec[I_BASE] == _NO_RECORD

        text = self._get_raw(idx, idxrec)

        return text


    def _get_patched(self, idx, idxrec, recursion_limit):
        base = idxrec[I_BASE]
        assert base >= 0
        assert base < idx    # no loops!

        if recursion_limit == None:
            sub_limit = None
        else:
            sub_limit = recursion_limit - 1
            if sub_limit < 0:
                raise LimitHitException()
            
        base_text = self.get(base, sub_limit)
        patch = self._get_raw(idx, idxrec)

        text = mdiff.bpatch(base_text, patch)

        return text



    def __len__(self):
        """Return number of revisions."""
        l = os.fstat(self.idxfile.fileno())[stat.ST_SIZE]
        if l % _RECORDSIZE:
            raise RevfileError("bad length %d on index of %r" % (l, self.basename))
        if l < _RECORDSIZE:
            raise RevfileError("no header present in index of %r" % (self.basename))
        return int(l / _RECORDSIZE) - 1


    def __getitem__(self, idx):
        """Index by sequence id returns the index field"""
        ## TODO: Can avoid seek if we just moved there...
        self._seek_index(idx)
        idxrec = self._read_next_index()
        if idxrec == None:
            raise IndexError("no index %d" % idx)
        else:
            return idxrec


    def _seek_index(self, idx):
        if idx < 0:
            raise RevfileError("invalid index %r" % idx)
        self.idxfile.seek((idx + 1) * _RECORDSIZE)



    def __iter__(self):
        """Read back all index records.

        Do not seek the index file while this is underway!"""
        ## sys.stderr.write(" ** iter called ** \n")
        self._seek_index(0)
        while True:
            idxrec = self._read_next_index()
            if not idxrec:
                break
            yield idxrec
        

    def _read_next_index(self):
        rec = self.idxfile.read(_RECORDSIZE)
        if not rec:
            return None
        elif len(rec) != _RECORDSIZE:
            raise RevfileError("short read of %d bytes getting index %d from %r"
                               % (len(rec), idx, self.basename))
        
        return struct.unpack(">20sIIII12x", rec)

        
    def dump(self, f=sys.stdout):
        f.write('%-8s %-40s %-8s %-8s %-8s %-8s\n' 
                % tuple('idx sha1 base flags offset len'.split()))
        f.write('-------- ---------------------------------------- ')
        f.write('-------- -------- -------- --------\n')

        for i, rec in enumerate(self):
            f.write("#%-7d %40s " % (i, hexlify(rec[0])))
            if rec[1] == _NO_RECORD:
                f.write("(none)   ")
            else:
                f.write("#%-7d " % rec[1])
                
            f.write("%8x %8d %8d\n" % (rec[2], rec[3], rec[4]))


    def total_text_size(self):
        """Return the sum of sizes of all file texts.

        This is how much space they would occupy if they were stored without
        delta and gzip compression.

        As a side effect this completely validates the Revfile, checking that all
        texts can be reproduced with the correct SHA-1."""
        t = 0L
        for idx in range(len(self)):
            t += len(self.get(idx))
        return t


    def check(self, pb=None):
        """Extract every version and check its hash."""
        total = len(self)
        for i in range(total):
            if pb:
                pb.update("check revision", i, total)
            # the get method implicitly checks the SHA-1
            self.get(i)
        if pb:
            pb.clear()
        


def main(argv):
    try:
        cmd = argv[1]
        filename = argv[2]
    except IndexError:
        sys.stderr.write("usage: revfile dump REVFILE\n"
                         "       revfile add REVFILE < INPUT\n"
                         "       revfile add-delta REVFILE BASE < INPUT\n"
                         "       revfile add-series REVFILE BASE FILE...\n"
                         "       revfile get REVFILE IDX\n"
                         "       revfile find-sha REVFILE HEX\n"
                         "       revfile total-text-size REVFILE\n"
                         "       revfile last REVFILE\n")
        return 1

    if filename.endswith('.drev') or filename.endswith('.irev'):
        filename = filename[:-5]

    def rw():
        return Revfile(filename, 'w')

    def ro():
        return Revfile(filename, 'r')

    if cmd == 'add':
        print rw().add(sys.stdin.read())
    elif cmd == 'add-delta':
        print rw().add(sys.stdin.read(), int(argv[3]))
    elif cmd == 'add-series':
        r = rw()
        rev = int(argv[3])
        for fn in argv[4:]:
            print rev
            rev = r.add(file(fn).read(), rev)
    elif cmd == 'dump':
        ro().dump()
    elif cmd == 'get':
        try:
            idx = int(argv[3])
        except IndexError:
            sys.stderr.write("usage: revfile get FILE IDX\n")
            return 1

        r = ro()

        if idx < 0 or idx >= len(r):
            sys.stderr.write("invalid index %r\n" % idx)
            return 1

        sys.stdout.write(r.get(idx))
    elif cmd == 'find-sha':
        try:
            s = unhexlify(argv[3])
        except IndexError:
            sys.stderr.write("usage: revfile find-sha FILE HEX\n")
            return 1

        idx = ro().find_sha(s)
        if idx == _NO_RECORD:
            sys.stderr.write("no such record\n")
            return 1
        else:
            print idx
    elif cmd == 'total-text-size':
        print ro().total_text_size()
    elif cmd == 'last':
        print len(ro())-1
    elif cmd == 'check':
        import bzrlib.progress
        pb = bzrlib.progress.ProgressBar()
        ro().check(pb)
    else:
        sys.stderr.write("unknown command %r\n" % cmd)
        return 1
    

if __name__ == '__main__':
    import sys
    sys.exit(main(sys.argv) or 0)