[PATCH 02 of 14 V3] util: implement varint functions

[Augie Fackler]

On Sat, Jan 20, 2018 at 12:47:07AM +0100, Boris Feld wrote:
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc at gmail.com>
> # Date 1516398755 -3600
> #      Fri Jan 19 22:52:35 2018 +0100
> # Node ID 5dbc3c53c923b8d11b5efcaf0f415b3d8c8c5180
> # Parent  15f7795f96a5f9acb3ed2e640fcec82f3ccd6f53
> # EXP-Topic b2-stream
> # Available At https://bitbucket.org/octobus/mercurial-devel/
> #              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 5dbc3c53c923
> util: implement varint functions
>

also candidates for netutil imo, or maybe protoutil (readexactly also
fits in the same bucket)

> This will be useful in an incoming version-2 of the stream format.
>
> diff --git a/mercurial/util.py b/mercurial/util.py
> --- a/mercurial/util.py
> +++ b/mercurial/util.py
> @@ -3874,3 +3874,73 @@ def readexactly(stream, n):
>                             " (got %d bytes, expected %d)")
>                            % (len(s), n))
>      return s
> +
> +def uvarintencode(value):
> +    """Encode an unsigned integer value to a varint.
> +
> +    A varint is a variable length integer of 1 or more bytes. Each byte
> +    except the last has the most significant bit set. The lower 7 bits of
> +    each byte store the 2's complement representation, least significant group
> +    first.
> +
> +    >>> uvarintencode(0)
> +    '\\x00'
> +    >>> uvarintencode(1)
> +    '\\x01'
> +    >>> uvarintencode(127)
> +    '\\x7f'
> +    >>> uvarintencode(1337)
> +    '\\xb9\\n'
> +    >>> uvarintencode(65536)
> +    '\\x80\\x80\\x04'
> +    >>> uvarintencode(-1)
> +    Traceback (most recent call last):
> +        ...
> +    ProgrammingError: negative value for uvarint: -1
> +    """
> +    if value < 0:
> +        raise error.ProgrammingError('negative value for uvarint: %d'
> +                                     % value)
> +    bits = value & 0x7f
> +    value >>= 7
> +    bytes = []
> +    while value:
> +        bytes.append(pycompat.bytechr(0x80 | bits))
> +        bits = value & 0x7f
> +        value >>= 7
> +    bytes.append(pycompat.bytechr(bits))
> +
> +    return ''.join(bytes)
> +
> +def uvarintdecodestream(fh):
> +    """Decode an unsigned variable length integer from a stream.
> +
> +    The passed argument is anything that has a ``.read(N)`` method.
> +
> +    >>> try:
> +    ...     from StringIO import StringIO as BytesIO
> +    ... except ImportError:
> +    ...     from io import BytesIO
> +    >>> uvarintdecodestream(BytesIO(b'\\x00'))
> +    0
> +    >>> uvarintdecodestream(BytesIO(b'\\x01'))
> +    1
> +    >>> uvarintdecodestream(BytesIO(b'\\x7f'))
> +    127
> +    >>> uvarintdecodestream(BytesIO(b'\\xb9\\n'))
> +    1337
> +    >>> uvarintdecodestream(BytesIO(b'\\x80\\x80\\x04'))
> +    65536
> +    >>> uvarintdecodestream(BytesIO(b'\\x80'))
> +    Traceback (most recent call last):
> +        ...
> +    Abort: stream ended unexpectedly (got 0 bytes, expected 1)
> +    """
> +    result = 0
> +    shift = 0
> +    while True:
> +        byte = ord(readexactly(fh, 1))
> +        result |= ((byte & 0x7f) << shift)
> +        if not (byte & 0x80):
> +            return result
> +        shift += 7