~bzr-pqm/bzr/bzr.dev

#! /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 os

import sha

import stat

import struct

import sys

import zlib

from binascii import hexlify, unhexlify

import bzrlib.mdiff as mdiff

_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)