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

Augie Fackler raf at durin42.com
Wed Nov 9 12:22:19 EST 2016


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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