issue #72: WIP

docs/api.rst

@@ -34,14 +34,12 @@ mitogen.core
 .. decorator:: takes_econtext
 
     Decorator that marks a function or class method to automatically receive a
-    kwarg named `econtext`, referencing the
-    :class:`mitogen.core.ExternalContext` active in the context in which the
-    function is being invoked in. The decorator is only meaningful when the
-    function is invoked via :data:`CALL_FUNCTION
-    <mitogen.core.CALL_FUNCTION>`.
-
-    When the function is invoked directly, `econtext` must still be passed to
-    it explicitly.
+    kwarg named `econtext`, referencing the :class:`ExternalContext` active in
+    the context in which the function is being invoked. The decorator is only
+    meaningful when the function is invoked via :data:`CALL_FUNCTION`.
+
+    No special handling occurs when the function is invoked directly.
+
 
 .. currentmodule:: mitogen.core
 .. decorator:: takes_router

mitogen/core.py

@@ -248,39 +248,43 @@ class CallError(Error):
     :py:meth:`Context.call() <mitogen.parent.Context.call>` fails. A copy of
     the traceback from the external context is appended to the exception
     message."""
-    def __init__(self, fmt=None, *args):
-        if not isinstance(fmt, BaseException):
-            Error.__init__(self, fmt, *args)
-        else:
-            e = fmt
-            fmt = '%s: %s' % (qualname(type(e)), e)
-            args = ()
-            tb = sys.exc_info()[2]
-            if tb:
-                fmt += '\n'
-                fmt += ''.join(traceback.format_tb(tb))
-            Error.__init__(self, fmt)
+    #: Fully qualified name of the original exception type, or :data:`None` if
+    #: the :class:`CallError` was constructed with a string argument.
+    type_name = None
 
-    @property
-    def type_name(self):
-        """
-        Return the fully qualified name of the original exception type, or
-        :data:`None` if the :class:`CallError` was raised explcitly.
-        """
-        type_name, sep, _ = self.args[0].partition(':')
-        if sep:
-            return type_name
+    @classmethod
+    def with_type_name(cls, type_name):
+        return type('CallError_' + type_name, (cls,), {
+            'type_name': type_name,
+        })
+
+    @classmethod
+    def from_exception(cls, e=None):
+        e_type, e_val, tb = sys.exc_info()
+        if e is None:
+            e = e_val
+        assert e is not None
+        type_name = qualname(type(e))
+        s = '%s: %s' % (type_name, e)
+        if tb:
+            s += '\n'
+            s += ''.join(traceback.format_tb(tb))
+        return cls.with_type_name(type_name)(s)
 
     def __reduce__(self):
-        return (_unpickle_call_error, (self.args[0],))
+        return (_unpickle_call_error, (self.type_name, self.args[0],))
 
 
-def _unpickle_call_error(s):
+def _unpickle_call_error(type_name, s):
+    if not (type_name is None or
+            (type(type_name) is UnicodeType and
+             len(type_name) < 100)):
+        raise TypeError('cannot unpickle CallError: bad type_name')
     if not (type(s) is UnicodeType and len(s) < 10000):
-        raise TypeError('cannot unpickle CallError: bad input')
-    inst = CallError.__new__(CallError)
-    Exception.__init__(inst, s)
-    return inst
+        raise TypeError('cannot unpickle CallError: bad message')
+    if type_name:
+        return CallError.with_type_name(type_name)(s)
+    return CallError(s)
 
 
 class ChannelError(Error):
@@ -580,8 +584,7 @@ class Message(object):
         try:
             self.data = pickle.dumps(obj, protocol=2)
         except pickle.PicklingError:
-            e = sys.exc_info()[1]
-            self.data = pickle.dumps(CallError(e), protocol=2)
+            self.data = pickle.dumps(CallError.from_exception(), protocol=2)
         return self
 
     def reply(self, msg, router=None, **kwargs):
@@ -2013,7 +2016,7 @@ class Dispatcher(object):
         try:
             chain_id, fn, args, kwargs = self._parse_request(msg)
         except Exception:
-            return None, CallError(sys.exc_info()[1])
+            return None, CallError.from_exception()
 
         if chain_id in self._error_by_chain_id:
             return chain_id, self._error_by_chain_id[chain_id]
@@ -2021,7 +2024,7 @@ class Dispatcher(object):
         try:
             return chain_id, fn(*args, **kwargs)
         except Exception:
-            e = CallError(sys.exc_info()[1])
+            e = CallError.from_exception()
             if chain_id is not None:
                 self._error_by_chain_id[chain_id] = e
             return chain_id, e

mitogen/debug.py

@@ -234,5 +234,4 @@ class ContextDebugger(object):
             method, args, kwargs = msg.unpickle()
             msg.reply(getattr(cls, method)(*args, **kwargs))
         except Exception:
-            e = sys.exc_info()[1]
-            msg.reply(mitogen.core.CallError(e))
+            msg.reply(mitogen.core.CallError.from_exception())

mitogen/error.py

@@ -0,0 +1,127 @@
+# Copyright 2017, David Wilson
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice,
+# this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice,
+# this list of conditions and the following disclaimer in the documentation
+# and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors
+# may be used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+
+"""
+This defines :func:`match` that produces dynamic subclasses of a magical type
+whose :func:`isinstance` returns :data:`True` if the instance being checked is
+a :class:`mitogen.core.CallError` whose original exception type matches a
+parent class in the hierarchy of the the supplied Exception type.
+"""
+
+from __future__ import absolute_import
+import mitogen.core
+
+
+#: Map Exception class -> Matcher class.
+_matcher_by_cls = {}
+
+
+def get_matching_classes(cls):
+    """
+    Given a class, return a list containing it and any base classes, operating
+    recursively such that the returned list contains the entire hierarchy of
+    `cls`.
+    """
+    classes = [cls]
+    for subcls in cls.__bases__:
+        classes.extend(get_matching_classes(subcls))
+    return classes
+
+
+class MatcherMeta(type):
+    def __subclasscheck__(matcher_cls, cls):
+        print('lol2')
+        return (
+            issubclass(cls, mitogen.core.CallError) and
+            (cls.type_name in matcher_cls.type_names)
+        )
+
+    def __instancecheck__(matcher_cls, e):
+        print('lol')
+        return MatcherMeta.__subclasscheck__(matcher_cls, type(e))
+
+
+__metaclass__ = MatcherMeta
+
+
+class Matcher:
+    """
+    This class serves only as a placeholder for its relationship with
+    :meth:`MatcherMeta.__instancecheck__` where the magic happens. A
+    dynamically generated Matcher subclass is returned by :func:`match`, to
+    served only for use with isinstance() internally by the Python exception
+    handling implementation::
+
+        # Create a dynamic subclass of Matcher to match mitogen.core.CallError
+        # instances according to the type of the original exception.
+        matcher_cls = mitogen.error.match(ValueError)
+        try:
+            context.call(func_raising_some_exc)
+
+        # Here Python calls type(matcher_class).__instancecheck__(e):
+        except matcher_cls as e:
+            # e remains bound to the CallError as before.
+            pass
+    """
+    #: Overridden by subclasses generated by :func:`match`.
+    classes = frozenset([])
+
+
+def match(target_cls):
+    """
+    Return a magic for use in :keyword:`except` statements that matches any
+    :class:`mitogen.core.CallError` whose original exception type was
+    `target_cls` or one of its base classes::
+
+        try:
+            context.call(func_raising_some_exc)
+        except mitogen.error.match(ValueError) as e:
+            # handle ValueError.
+            pass
+
+    :param type target_cls:
+        Target class to match.
+
+    :returns:
+        :class:`Matcher` subclass.
+    """
+    try:
+        return _matcher_by_cls[target_cls]
+    except KeyError:
+        name = '%s{%s}' % (
+            mitogen.core.qualname(Matcher),
+            mitogen.core.qualname(target_cls),
+        )
+        matcher_cls = type(name, (Matcher,), {
+            'type_names': frozenset(
+                mitogen.core.qualname(cls)
+                for cls in get_matching_classes(target_cls)
+            )
+        })
+        _matcher_by_cls[target_cls] = matcher_cls
+        return matcher_cls

mitogen/service.py

@@ -365,8 +365,10 @@ class DeduplicatingInvoker(Invoker):
             e = sys.exc_info()[1]
             self._produce_response(key, e)
         except Exception:
-            e = sys.exc_info()[1]
-            self._produce_response(key, mitogen.core.CallError(e))
+            self._produce_response(
+                key,
+                mitogen.core.CallError.from_exception()
+            )
 
         return Service.NO_REPLY
 
@@ -524,8 +526,7 @@ class Pool(object):
         except Exception:
             LOG.exception('%r: while invoking %r of %r',
                           self, method_name, service_name)
-            e = sys.exc_info()[1]
-            msg.reply(mitogen.core.CallError(e))
+            msg.reply(mitogen.core.CallError.from_exception())
 
     def _worker_run(self):
         while not self.closed:
@@ -876,9 +877,7 @@ class FileService(Service):
         try:
             fp = open(path, 'rb', self.IO_SIZE)
         except IOError:
-            msg.reply(mitogen.core.CallError(
-                sys.exc_info()[1]
-            ))
+            msg.reply(mitogen.core.CallError.from_exception())
             return
 
         # Response must arrive first so requestee can begin receive loop,