D2948: wireproto: syntax for encoding CBOR into frames

[Josef 'Jeff' Sipek]

On Wed, Mar 28, 2018 at 22:06:17 +0000, indygreg (Gregory Szorc) wrote:
> indygreg updated this revision to Diff 7352.
> 
> REPOSITORY
>   rHG Mercurial
> 
> CHANGES SINCE LAST UPDATE
>   https://phab.mercurial-scm.org/D2948?vs=7327&id=7352
> 
> REVISION DETAIL
>   https://phab.mercurial-scm.org/D2948
> 
> AFFECTED FILES
>   mercurial/debugcommands.py
>   mercurial/utils/stringutil.py
>   mercurial/wireprotoframing.py
>   tests/test-wireproto-serverreactor.py
> 
> CHANGE DETAILS
> 
...
> diff --git a/mercurial/wireprotoframing.py b/mercurial/wireprotoframing.py
> --- a/mercurial/wireprotoframing.py
> +++ b/mercurial/wireprotoframing.py
> @@ -16,6 +16,7 @@
>  from .i18n import _
>  from .thirdparty import (
>      attr,
> +    cbor,
>  )
>  from . import (
>      error,
> @@ -156,6 +157,9 @@
>  def makeframefromhumanstring(s):
>      """Create a frame from a human readable string
>  
> +    DANGER: NOT SAFE TO USE WITH UNTRUSTED INPUT BECAUSE OF POTENTIAL
> +    eval() USAGE. DO NOT USE IN CORE.
> +
>      Strings have the form:
>  
>          <request-id> <stream-id> <stream-flags> <type> <flags> <payload>
> @@ -169,6 +173,11 @@
>      named constant.
>  
>      Flags can be delimited by `|` to bitwise OR them together.
> +
> +    If the payload begins with ``cbor:``, the following string will be
> +    evaluated as Python code and the resulting object will be fed into
> +    a CBOR encoder. Otherwise, the payload is interpreted as a Python
> +    byte string literal.
>      """

Um, why?  Why not just *always* wrap byte strings in CBOR?  The overhead
will be 1-9 bytes depending on the length (short strings will use 1-2 bytes
of overhead), then there's no need to prefix anything with "cbor:".  Any
string <4GB in size will incur 5 bytes overhead.  Which is (IMO) acceptable.

Jeff.

>      fields = s.split(b' ', 5)
>      requestid, streamid, streamflags, frametype, frameflags, payload = fields
> @@ -196,7 +205,11 @@
>          else:
>              finalflags |= int(flag)
>  
> -    payload = stringutil.unescapestr(payload)
> +    if payload.startswith(b'cbor:'):
> +        payload = cbor.dumps(stringutil.evalpython(payload[5:]), canonical=True)
> +
> +    else:
> +        payload = stringutil.unescapestr(payload)
>  
>      return makeframe(requestid=requestid, streamid=streamid,
>                       streamflags=finalstreamflags, typeid=frametype,
> diff --git a/mercurial/utils/stringutil.py b/mercurial/utils/stringutil.py
> --- a/mercurial/utils/stringutil.py
> +++ b/mercurial/utils/stringutil.py
> @@ -9,6 +9,7 @@
>  
>  from __future__ import absolute_import
>  
> +import __future__
>  import codecs
>  import re as remod
>  import textwrap
> @@ -286,3 +287,29 @@
>      If s is not a valid boolean, returns None.
>      """
>      return _booleans.get(s.lower(), None)
> +
> +def evalpython(s):
> +    """Evaluate a string containing a Python expression.
> +
> +    THIS FUNCTION IS NOT SAFE TO USE ON UNTRUSTED INPUT. IT'S USE SHOULD BE
> +    LIMITED TO DEVELOPER-FACING FUNCTIONALITY.
> +    """
> +    globs = {
> +        r'__builtins__': {
> +            r'None': None,
> +            r'False': False,
> +            r'True': True,
> +            r'int': int,
> +            r'set': set,
> +            r'tuple': tuple,
> +            # Don't need to expose dict and list because we can use
> +            # literals.
> +        },
> +    }
> +
> +    # We can't use eval() directly because it inherits compiler
> +    # flags from this module and we need unicode literals for Python 3
> +    # compatibility.
> +    code = compile(s, r'<string>', r'eval',
> +                   __future__.unicode_literals.compiler_flag, True)
> +    return eval(code, globs, {})
> diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
> --- a/mercurial/debugcommands.py
> +++ b/mercurial/debugcommands.py
> @@ -2785,7 +2785,10 @@
>      or a flag name for stream flags or frame flags, respectively. Values are
>      resolved to integers and then bitwise OR'd together.
>  
> -    ``payload`` is is evaluated as a Python byte string literal.
> +    ``payload`` represents the raw frame payload. If it begins with
> +    ``cbor:``, the following string is evaluated as Python code and the
> +    resulting object is fed into a CBOR encoder. Otherwise it is interpreted
> +    as a Python byte string literal.
>      """
>      opts = pycompat.byteskwargs(opts)
>  
> 
> 
> 
> To: indygreg, #hg-reviewers
> Cc: mercurial-devel
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