/brz/remove-bazaar

#! /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.

"""

import sys, zlib, struct, mdiff, stat, os, sha

from binascii import hexlify

factor = 10

_RECORDSIZE = 48

_HEADER = "bzr revfile v1\n"

_HEADER = _HEADER + ('\xff' * (_RECORDSIZE - len(_HEADER)))

_NO_BASE = 0xFFFFFFFFL

class RevfileError(Exception):

    pass

class Revfile:

    def __init__(self, basename):

        self.basename = basename

        self.idxfile = open(basename + '.irev', 'r+b')

        self.datafile = open(basename + '.drev', 'r+b')

        if self.last_idx() == -1:

            print 'init empty file'

            self.idxfile.write(_HEADER)

            self.idxfile.flush()

        else:

            h = self.idxfile.read(_RECORDSIZE)

            if h != _HEADER:

                raise RevfileError("bad header %r in index of %r"

                                   % (h, self.basename))

    def last_idx(self):

        """Return last index already present, or -1 if none."""

        l = os.fstat(self.idxfile.fileno())[stat.ST_SIZE]

        if l == 0:

            return -1

        if l % _RECORDSIZE:

            raise RevfileError("bad length %d on index of %r" % (l, self.basename))

        return (l / _RECORDSIZE) - 1

    def revision(self, rev):

        base = self.index[rev][0]

        start = self.index[base][1]

        end = self.index[rev][1] + self.index[rev][2]

        f = open(self.datafile())

        f.seek(start)

        data = f.read(end - start)

        last = self.index[base][2]

        text = zlib.decompress(data[:last])

        for r in range(base + 1, rev + 1):

            s = self.index[r][2]

            b = zlib.decompress(data[last:last + s])

            text = mdiff.bpatch(text, b)

            last = last + s

        return text    

    def add_full_text(self, t):

        """Add a full text to the file.

        This is not compressed against any reference version.

        Returns the index for that text."""

        idx = self.last_idx() + 1

        self.datafile.seek(0, 2)        # to end

        self.idxfile.seek(0, 2)

        assert self.idxfile.tell() == _RECORDSIZE * idx

        data_offset = self.datafile.tell()

        assert isinstance(t, str) # not unicode or anything wierd

        self.datafile.write(t)

        self.datafile.flush()

        entry = sha.new(t).digest()

        entry += struct.pack(">IIII12x", 0xFFFFFFFFL, 0, data_offset, len(t))

        assert len(entry) == _RECORDSIZE

        self.idxfile.write(entry)

        self.idxfile.flush()

        return idx

    def __len__(self):

        return int(self.last_idx())

    def __getitem__(self, idx):

        self.idxfile.seek((idx + 1) * _RECORDSIZE)

        rec = self.idxfile.read(_RECORDSIZE)

        if not rec:

            raise IndexError("no record %d in index for %r" % (idx, self.basename))

        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 addrevision(self, text, changeset):

        t = self.tip()

        n = t + 1

        if not n % factor:

            data = zlib.compress(text)

            base = n

        else:

            prev = self.revision(t)

            data = zlib.compress(mdiff.bdiff(prev, text))

            base = self.index[t][0]

        offset = 0

        if t >= 0:

            offset = self.index[t][1] + self.index[t][2]

        self.index.append((base, offset, len(data), changeset))

        entry = struct.pack(">llll", base, offset, len(data), changeset)

        open(self.indexfile(), "a").write(entry)

        open(self.datafile(), "a").write(data)

    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_BASE:

                f.write("(none)   ")

            else:

                f.write("#%-7d " % rec[1])

            f.write("%8x %8d %8d\n" % (rec[2], rec[3], rec[4]))

def main(argv):

    r = Revfile("testrev")

    if len(argv) < 2:

        sys.stderr.write("usage: revfile dump\n"

                         "       revfile add\n")

        sys.exit(1)

    if argv[1] == 'add':

        new_idx = r.add_full_text(sys.stdin.read())

        print 'added idx %d' % new_idx

    elif argv[1] == 'dump':

        r.dump()

    else:

        sys.stderr.write("unknown command %r\n" % argv[1])

        sys.exit(1)

if __name__ == '__main__':

    import sys

    main(sys.argv)