/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.

"""

# TODO: Something like pread() would make this slightly simpler and

# perhaps more efficient.

# TODO: Could also try to mmap things...

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

# fields in the index record

I_SHA = 0

I_BASE = 1

I_FLAGS = 2

I_OFFSET = 3

I_LEN = 4

class RevfileError(Exception):

    pass

class Revfile:

    def __init__(self, basename):

        # TODO: Option to open readonly

        # TODO: Lock file  while open

        # TODO: advise of random access

        self.basename = basename

        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:

            self.idxfile = open(idxname, 'w+b')

            self.datafile = open(dataname, 'w+b')

            print 'init empty file'

            self.idxfile.write(_HEADER)

            self.idxfile.flush()

        else:

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

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

            h = self.idxfile.read(_RECORDSIZE)

            if h != _HEADER:

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

                                   % (h, self.basename))

    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 = 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(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 _get_full_text(self, idx):

        idxrec = self[idx]

        assert idxrec[I_FLAGS] == 0

        assert idxrec[I_BASE] == _NO_BASE

        l = idxrec[I_LEN]

        if l == 0:

            return ''

        self.datafile.seek(idxrec[I_OFFSET])

        text = self.datafile.read(l)

        if len(text) != l:

            raise RevfileError("short read %d of %d "

                               "getting text for record %d in %r"

                               % (len(text), l, idx, self.basename))

        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"""

        self._seek_index(idx)

        return self._read_next_index()

    def _seek_index(self, idx):

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

    def _read_next_index(self):

        rec = self.idxfile.read(_RECORDSIZE)

        if not rec:

            raise IndexError("end of index file")

        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")

    try:

        cmd = argv[1]

    except IndexError:

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

                         "       revfile add\n"

                         "       revfile get IDX\n")

        return 1

    if cmd == 'add':

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

        print 'added idx %d' % new_idx

    elif cmd == 'dump':

        r.dump()

    elif cmd == 'get':

        try:

            idx = int(argv[2])

        except IndexError:

            sys.stderr.write("usage: revfile get IDX\n")

            return 1

        if idx < 0 or idx >= len(r):

            sys.stderr.write("invalid index %r\n" % idx)

            return 1

        sys.stdout.write(r._get_full_text(idx))

    else:

        sys.stderr.write("unknown command %r\n" % cmd)

        return 1

if __name__ == '__main__':

    import sys

    sys.exit(main(sys.argv) or 0)