D2948: wireproto: syntax for encoding CBOR into frames

[Gregory Szorc]

On Thu, Mar 29, 2018 at 9:36 AM, Josef 'Jeff' Sipek <jeffpc at josefsipek.net>
wrote:

> 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.
>

We may end up in that state. There was code emitting non-CBOR data and I
didn't want to scope bloat the commit.


>
> >      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
> > _______________________________________________
> > Mercurial-devel mailing list
> > Mercurial-devel at mercurial-scm.org
> > https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
>
> --
> Si hoc legere scis nimium eruditionis habes.
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