mercurial/pure/mpatch.py
author Pierre-Yves David <pierre-yves.david@octobus.net>
Tue, 06 Apr 2021 10:38:27 +0200
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child 48873 5aafc3c5bdec
permissions -rw-r--r--
upgrade: do not hardcore file extension of revlogs This logic already lives inside the `store` module. So lets reuse it instead. Differential Revision: https://phab.mercurial-scm.org/D10317
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# mpatch.py - Python implementation of mpatch.c
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#
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# Copyright 2009 Olivia Mackall <olivia@selenic.com> and others
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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from __future__ import absolute_import
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import struct
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from .. import pycompat
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stringio = pycompat.bytesio
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class mpatchError(Exception):
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    """error raised when a delta cannot be decoded"""
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# This attempts to apply a series of patches in time proportional to
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# the total size of the patches, rather than patches * len(text). This
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# means rather than shuffling strings around, we shuffle around
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# pointers to fragments with fragment lists.
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#
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# When the fragment lists get too long, we collapse them. To do this
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# efficiently, we do all our operations inside a buffer created by
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# mmap and simply use memmove. This avoids creating a bunch of large
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# temporary string buffers.
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def _pull(dst, src, l):  # pull l bytes from src
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    while l:
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        f = src.pop()
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        if f[0] > l:  # do we need to split?
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            src.append((f[0] - l, f[1] + l))
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            dst.append((l, f[1]))
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            return
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        dst.append(f)
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        l -= f[0]
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def _move(m, dest, src, count):
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    """move count bytes from src to dest
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    The file pointer is left at the end of dest.
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    """
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    m.seek(src)
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    buf = m.read(count)
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    m.seek(dest)
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    m.write(buf)
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def _collect(m, buf, list):
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    start = buf
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    for l, p in reversed(list):
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        _move(m, buf, p, l)
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        buf += l
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    return (buf - start, start)
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def patches(a, bins):
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    if not bins:
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        return a
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    plens = [len(x) for x in bins]
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    pl = sum(plens)
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    bl = len(a) + pl
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    tl = bl + bl + pl  # enough for the patches and two working texts
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    b1, b2 = 0, bl
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    if not tl:
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        return a
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    m = stringio()
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    # load our original text
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    m.write(a)
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    frags = [(len(a), b1)]
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    # copy all the patches into our segment so we can memmove from them
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    pos = b2 + bl
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    m.seek(pos)
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    for p in bins:
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        m.write(p)
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    for plen in plens:
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        # if our list gets too long, execute it
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        if len(frags) > 128:
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            b2, b1 = b1, b2
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            frags = [_collect(m, b1, frags)]
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        new = []
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        end = pos + plen
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        last = 0
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        while pos < end:
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            m.seek(pos)
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            try:
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                p1, p2, l = struct.unpack(b">lll", m.read(12))
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            except struct.error:
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                raise mpatchError(b"patch cannot be decoded")
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            _pull(new, frags, p1 - last)  # what didn't change
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            _pull([], frags, p2 - p1)  # what got deleted
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            new.append((l, pos + 12))  # what got added
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            pos += l + 12
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            last = p2
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        frags.extend(reversed(new))  # what was left at the end
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    t = _collect(m, b2, frags)
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    m.seek(t[1])
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    return m.read(t[0])
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def patchedsize(orig, delta):
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    outlen, last, bin = 0, 0, 0
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    binend = len(delta)
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    data = 12
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    while data <= binend:
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        decode = delta[bin : bin + 12]
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        start, end, length = struct.unpack(b">lll", decode)
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        if start > end:
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            break
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        bin = data + length
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        data = bin + 12
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        outlen += start - last
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        last = end
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        outlen += length
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    if bin != binend:
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        raise mpatchError(b"patch cannot be decoded")
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    outlen += orig - last
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    return outlen