python: Robust exception handling in callbacks.

* lang/python/helpers.c (pygpgme_stash_callback_exception): New
function.
(pygpgme_raise_callback_exception): Likewise.
(pyPassphraseCb): Stash python errors.
* lang/python/helpers.h (pygpgme_raise_callback_exception): New
prototype.
* lang/python/pyme/core.py ({Context,Data}.__init__): Move common
initialization to superclass.
(Context.set_progress_cb): Hand in 'self'.
* lang/python/pyme/util.py (GpgmeWrapper.__init__): New function.
(GpgmeWrapper.__getattr__): Raise stashed exceptions.
* lang/python/tests/Makefile.am (py_tests): Add new test.
* lang/python/tests/t-callbacks.py: New file.

Signed-off-by: Justus Winter <justus@gnupg.org>

lang/python/helpers.c

@@ -17,6 +17,8 @@
 #    License along with this library; if not, write to the Free Software
 #    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
 */
+
+#include <assert.h>
 #include <stdio.h>
 #include <gpgme.h>
 #include <stdlib.h>
@@ -59,12 +61,84 @@ void pygpgme_clear_generic_cb(PyObject **cb) {
   Py_DECREF(*cb);
 }
 
+/* Exception support for callbacks.  */
+#define EXCINFO	"_callback_excinfo"
+
+static void pygpgme_stash_callback_exception(PyObject *self)
+{
+  PyObject *ptype, *pvalue, *ptraceback, *excinfo;
+
+  PyErr_Fetch(&ptype, &pvalue, &ptraceback);
+  excinfo = PyTuple_New(3);
+  PyTuple_SetItem(excinfo, 0, ptype);
+
+  if (pvalue)
+    PyTuple_SetItem(excinfo, 1, pvalue);
+  else {
+    Py_INCREF(Py_None);
+    PyTuple_SetItem(excinfo, 1, Py_None);
+  }
+
+  if (ptraceback)
+    PyTuple_SetItem(excinfo, 2, ptraceback);
+  else {
+    Py_INCREF(Py_None);
+    PyTuple_SetItem(excinfo, 2, Py_None);
+  }
+
+  PyObject_SetAttrString(self, EXCINFO, excinfo);
+}
+
+PyObject *pygpgme_raise_callback_exception(PyObject *self)
+{
+  PyObject *ptype, *pvalue, *ptraceback, *excinfo;
+
+  if (! PyObject_HasAttrString(self, EXCINFO))
+    goto leave;
+
+  excinfo = PyObject_GetAttrString(self, EXCINFO);
+  if (! PyTuple_Check(excinfo))
+    {
+      Py_DECREF(excinfo);
+      goto leave;
+    }
+
+  ptype = PyTuple_GetItem(excinfo, 0);
+  Py_INCREF(excinfo);
+
+  pvalue = PyTuple_GetItem(excinfo, 1);
+  if (pvalue == Py_None)
+    pvalue = NULL;
+  else
+    Py_INCREF(pvalue);
+
+  ptraceback = PyTuple_GetItem(excinfo, 2);
+  if (ptraceback == Py_None)
+    ptraceback = NULL;
+  else
+    Py_INCREF(ptraceback);
+
+  Py_DECREF(excinfo);
+  PyErr_Restore(ptype, pvalue, ptraceback);
+
+  Py_INCREF(Py_None);
+  PyObject_SetAttrString(self, EXCINFO, Py_None);
+
+  return NULL; /* Raise exception.  */
+
+ leave:
+  Py_INCREF(Py_None);
+  return Py_None;
+}
+#undef EXCINFO
+
 static gpgme_error_t pyPassphraseCb(void *hook,
 				    const char *uid_hint,
 				    const char *passphrase_info,
 				    int prev_was_bad,
 				    int fd) {
   PyObject *pyhook = (PyObject *) hook;
+  PyObject *self = NULL;
   PyObject *func = NULL;
   PyObject *args = NULL;
   PyObject *retval = NULL;
@@ -73,12 +147,13 @@ static gpgme_error_t pyPassphraseCb(void *hook,
 
   pygpgme_exception_init();
 
-  if (PyTuple_Check(pyhook)) {
+  assert (PyTuple_Check(pyhook));
-    func = PyTuple_GetItem(pyhook, 0);
+  self = PyTuple_GetItem(pyhook, 0);
-    dataarg = PyTuple_GetItem(pyhook, 1);
+  func = PyTuple_GetItem(pyhook, 1);
+  if (PyTuple_Size(pyhook) == 3) {
+    dataarg = PyTuple_GetItem(pyhook, 2);
     args = PyTuple_New(4);
   } else {
-    func = pyhook;
     args = PyTuple_New(3);
   }
 
@@ -90,6 +165,11 @@ static gpgme_error_t pyPassphraseCb(void *hook,
   else
     PyTuple_SetItem(args, 0, PyUnicode_DecodeUTF8(uid_hint, strlen (uid_hint),
                                                   "strict"));
+  if (PyErr_Occurred()) {
+    Py_DECREF(args);
+    err_status = gpg_error(GPG_ERR_GENERAL);
+    goto leave;
+  }
 
   PyTuple_SetItem(args, 1, PyBytes_FromString(passphrase_info));
   PyTuple_SetItem(args, 2, PyBool_FromLong((long)prev_was_bad));
@@ -117,7 +197,8 @@ static gpgme_error_t pyPassphraseCb(void *hook,
           PyErr_Format(PyExc_TypeError,
                        "expected str or bytes from passphrase callback, got %s",
                        retval->ob_type->tp_name);
-          return gpg_error(GPG_ERR_GENERAL);
+          err_status = gpg_error(GPG_ERR_GENERAL);
+          goto leave;
         }
 
       write(fd, buf, len);
@@ -126,6 +207,10 @@ static gpgme_error_t pyPassphraseCb(void *hook,
     }
   }
 
+ leave:
+  if (err_status)
+    pygpgme_stash_callback_exception(self);
+
   return err_status;
 }
 

lang/python/helpers.h

@@ -30,6 +30,7 @@ void pygpgme_exception_init(void);
 gpgme_error_t pygpgme_exception2code(void);
 
 void pygpgme_clear_generic_cb(PyObject **cb);
+PyObject *pygpgme_raise_callback_exception(PyObject *self);
 
 void pygpgme_set_passphrase_cb(gpgme_ctx_t ctx, PyObject *cb,
 			       PyObject **freelater);

lang/python/pyme/core.py

@@ -54,14 +54,14 @@ class Context(GpgmeWrapper):
 
     def __init__(self, wrapped=None):
         if wrapped:
-            self.wrapped = wrapped
             self.own = False
         else:
             tmp = pygpgme.new_gpgme_ctx_t_p()
             errorcheck(pygpgme.gpgme_new(tmp))
-            self.wrapped = pygpgme.gpgme_ctx_t_p_value(tmp)
+            wrapped = pygpgme.gpgme_ctx_t_p_value(tmp)
             pygpgme.delete_gpgme_ctx_t_p(tmp)
             self.own = True
+        super().__init__(wrapped)
         self.last_passcb = None
         self.last_progresscb = None
 
@@ -167,9 +167,9 @@ class Context(GpgmeWrapper):
         else:
             self.last_passcb = pygpgme.new_PyObject_p_p()
             if hook == None:
-                hookdata = func
+                hookdata = (self, func)
             else:
-                hookdata = (func, hook)
+                hookdata = (self, func, hook)
         pygpgme.pygpgme_set_passphrase_cb(self.wrapped, hookdata, self.last_passcb)
 
     def set_progress_cb(self, func, hook=None):
@@ -282,7 +282,7 @@ class Data(GpgmeWrapper):
         that file.
 
         Any other use will result in undefined or erroneous behavior."""
-        self.wrapped = None
+        super().__init__(None)
         self.last_readcb = None
 
         if cbs != None:

lang/python/pyme/util.py

@@ -32,6 +32,11 @@ def process_constants(starttext, dict):
 class GpgmeWrapper(object):
     """Base class all Pyme wrappers for GPGME functionality.  Not to be
     instantiated directly."""
+
+    def __init__(self, wrapped):
+        self._callback_excinfo = None
+        self.wrapped = wrapped
+
     def __repr__(self):
         return '<instance of %s.%s with GPG object at %s>' % \
                (__name__, self.__class__.__name__,
@@ -78,11 +83,16 @@ class GpgmeWrapper(object):
 
         if self._errorcheck(name):
             def _funcwrap(slf, *args, **kwargs):
-                return errorcheck(func(slf.wrapped, *args, **kwargs),
+                result = func(slf.wrapped, *args, **kwargs)
-                                  "Invocation of " + name)
+                if slf._callback_excinfo:
+                    pygpgme.pygpgme_raise_callback_exception(slf)
+                return errorcheck(result, "Invocation of " + name)
         else:
             def _funcwrap(slf, *args, **kwargs):
-                return func(slf.wrapped, *args, **kwargs)
+                result = func(slf.wrapped, *args, **kwargs)
+                if slf._callback_excinfo:
+                    pygpgme.pygpgme_raise_callback_exception(slf)
+                return result
 
         _funcwrap.__doc__ = getattr(func, "__doc__")
 

lang/python/tests/Makefile.am

@@ -29,6 +29,7 @@ TESTS_ENVIRONMENT = GNUPGHOME=$(abs_builddir) \
 	PYTHONPATH=`echo $(abs_builddir)/../build/lib.*`
 
 py_tests = t-wrapper.py \
+	t-callbacks.py \
 	t-data.py \
 	t-encrypt.py \
 	t-encrypt-sym.py \

lang/python/tests/t-callbacks.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2016 g10 Code GmbH
+#
+# This file is part of GPGME.
+#
+# GPGME is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# GPGME is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General
+# Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, see <http://www.gnu.org/licenses/>.
+
+import os
+from pyme import core, constants
+import support
+
+support.init_gpgme(constants.PROTOCOL_OpenPGP)
+
+c = core.Context()
+c.set_pinentry_mode(constants.PINENTRY_MODE_LOOPBACK)
+
+source = core.Data("Hallo Leute\n")
+sink = core.Data()
+
+# Valid passphrases, both as string and bytes.
+for passphrase in ('foo', b'foo'):
+    def passphrase_cb(hint, desc, prev_bad, hook=None):
+        assert hook == passphrase
+        return hook
+
+    c.set_passphrase_cb(passphrase_cb, passphrase)
+    c.op_encrypt([], 0, source, sink)
+
+# Returning an invalid type.
+def passphrase_cb(hint, desc, prev_bad, hook=None):
+    return 0
+
+c.set_passphrase_cb(passphrase_cb, None)
+try:
+    c.op_encrypt([], 0, source, sink)
+except Exception as e:
+    assert type(e) == TypeError
+    assert str(e) == "expected str or bytes from passphrase callback, got int"
+else:
+    assert False, "Expected an error, got none"
+
+# Raising an exception inside callback.
+myException = Exception()
+def passphrase_cb(hint, desc, prev_bad, hook=None):
+    raise myException
+
+c.set_passphrase_cb(passphrase_cb, None)
+try:
+    c.op_encrypt([], 0, source, sink)
+except Exception as e:
+    assert e == myException
+else:
+    assert False, "Expected an error, got none"
+
+# Wrong kind of callback function.
+def bad_passphrase_cb():
+    pass
+
+c.set_passphrase_cb(bad_passphrase_cb, None)
+try:
+    c.op_encrypt([], 0, source, sink)
+except Exception as e:
+    assert type(e) == TypeError
+else:
+    assert False, "Expected an error, got none"