[PATCH 2 of 8 V7] bookmarks: introduce binary encoding

[Augie Fackler]

On Thu, Nov 10, 2016 at 09:24:56AM +0000, Stanislau Hlebik wrote:
> We can use 32 bytes, but only 20 bytes will be used.
> What’s the point then?

Because some day sha3 or sha256 will be used.

>
> On 11/9/16, 5:22 PM, "Augie Fackler" <raf at durin42.com> wrote:
>
>     On Wed, Nov 02, 2016 at 07:06:44AM -0700, Stanislau Hlebik wrote:
>     > # HG changeset patch
>     > # User Stanislau Hlebik <stash at fb.com>
>     > # Date 1478016027 25200
>     > #      Tue Nov 01 09:00:27 2016 -0700
>     > # Branch stable
>     > # Node ID f3da841e3d47ccbb0be3892b521607c09fdeab13
>     > # Parent  a56a624a8a42b93ec980d2c284756a38719dffe6
>     > bookmarks: introduce binary encoding
>     >
>     > Bookmarks binary encoding will be used for `bookmarks` bundle2 part.
>     > The format is: <4 bytes - bookmark size, big-endian><bookmark>
>     >                <1 byte - 0 if node is empty 1 otherwise><20 bytes node>
>
>     Enough other formats have 32 bytes of space for nodes (eg revlog) that
>     I suspect we should do 32 bytes here too. Thoughts?
>
>     > BookmarksEncodeError and BookmarksDecodeError maybe thrown if input is
>     > incorrect.
>     >
>     > diff --git a/mercurial/bookmarks.py b/mercurial/bookmarks.py
>     > --- a/mercurial/bookmarks.py
>     > +++ b/mercurial/bookmarks.py
>     > @@ -7,8 +7,10 @@
>     >
>     >  from __future__ import absolute_import
>     >
>     > +import StringIO
>     >  import errno
>     >  import os
>     > +import struct
>     >
>     >  from .i18n import _
>     >  from .node import (
>     > @@ -23,6 +25,70 @@
>     >      util,
>     >  )
>     >
>     > +_NONEMPTYNODE = struct.pack('?', False)
>     > +_EMPTYNODE = struct.pack('?', True)
>     > +
>     > +def _unpackbookmarksize(stream):
>     > +    """Returns 0 if stream is empty.
>     > +    """
>     > +
>     > +    expectedsize = struct.calcsize('>i')
>     > +    encodedbookmarksize = stream.read(expectedsize)
>     > +    if len(encodedbookmarksize) == 0:
>     > +        return 0
>     > +    if len(encodedbookmarksize) != expectedsize:
>     > +        raise ValueError(
>     > +            _('cannot decode bookmark size: '
>     > +              'expected size: %d, actual size: %d') %
>     > +            (expectedsize, len(encodedbookmarksize)))
>     > +    return struct.unpack('>i', encodedbookmarksize)[0]
>     > +
>     > +def encodebookmarks(bookmarks):
>     > +    """Encodes bookmark to node mapping to the byte string.
>     > +
>     > +    Format: <4 bytes - bookmark size><bookmark>
>     > +            <1 byte - 0 if node is empty 1 otherwise><20 bytes node>
>     > +    Node may be 20 byte binary string, 40 byte hex string or empty
>     > +    """
>     > +
>     > +    for bookmark, node in bookmarks.iteritems():
>     > +        yield struct.pack('>i', (len(bookmark)))
>     > +        yield encoding.fromlocal(bookmark)
>     > +        if node:
>     > +            if len(node) != 20 and len(node) != 40:
>     > +                raise ValueError(_('node must be 20 or bytes long'))
>     > +            if len(node) == 40:
>     > +                node = bin(node)
>     > +            yield _NONEMPTYNODE
>     > +            yield node
>     > +        else:
>     > +            yield _EMPTYNODE
>     > +
>     > +def decodebookmarks(buf):
>     > +    """Decodes buffer into bookmark to node mapping.
>     > +
>     > +    Node is either 20 bytes or empty.
>     > +    """
>     > +
>     > +    stream = StringIO.StringIO(buf)
>     > +    bookmarks = {}
>     > +    bookmarksize = _unpackbookmarksize(stream)
>     > +    while bookmarksize:
>     > +        bookmark = stream.read(bookmarksize)
>     > +        if len(bookmark) != bookmarksize:
>     > +            raise ValueError(
>     > +                _('cannot decode bookmark: expected size: %d, '
>     > +                'actual size: %d') % (bookmarksize, len(bookmark)))
>     > +        bookmark = encoding.tolocal(bookmark)
>     > +        packedemptynodeflag = stream.read(struct.calcsize('?'))
>     > +        emptynode = struct.unpack('?', packedemptynodeflag)[0]
>     > +        node = ''
>     > +        if not emptynode:
>     > +            node = stream.read(20)
>     > +        bookmarks[bookmark] = node
>     > +        bookmarksize = _unpackbookmarksize(stream)
>     > +    return bookmarks
>     > +
>     >  def _getbkfile(repo):
>     >      """Hook so that extensions that mess with the store can hook bm storage.
>     >
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