Fix exception propogation in Promises

capnp/capabilityHelper.h

@@ -11,6 +11,7 @@ extern "C" {
    ::kj::Promise<void> * call_server_method(PyObject * py_server, char * name, capnp::CallContext< capnp::DynamicStruct, capnp::DynamicStruct> & context);
    PyObject * wrap_kj_exception(kj::Exception &);
    PyObject * wrap_kj_exception_for_reraise(kj::Exception &);
+   PyObject * get_exception_info(PyObject *, PyObject *, PyObject *);
  }
 
 void reraise_kj_exception() {
@@ -36,8 +37,22 @@ void reraise_kj_exception() {
 void check_py_error() {
     PyObject * err = PyErr_Occurred();
     if(err) {
-        // PyErr_Clear();
-        throw std::exception();
+        // TODO: decref references
+        PyObject * ptype, *pvalue, *ptraceback;
+        PyErr_Fetch(&ptype, &pvalue, &ptraceback);
+
+        PyObject * info = get_exception_info(ptype, pvalue, ptraceback);
+
+        PyObject * py_filename = PyTuple_GetItem(info, 0);
+        kj::String filename(kj::heapString(PyBytes_AsString(py_filename)));
+
+        PyObject * py_line = PyTuple_GetItem(info, 1);
+        int line = PyInt_AsLong(py_line);
+
+        PyObject * py_description = PyTuple_GetItem(info, 2);
+        kj::String description(kj::heapString(PyBytes_AsString(py_description)));
+
+        throw kj::Exception(kj::Exception::Nature::OTHER, kj::Exception::Durability::PERMANENT, kj::mv(filename), line, kj::mv(description));
     }
 }
 

capnp/capnp.pyx

@@ -16,6 +16,7 @@ from cython.operator cimport dereference as deref
 cimport async_cpp
 
 from cpython.ref cimport PyObject, Py_INCREF, Py_DECREF
+from cpython.exc cimport PyErr_Clear
 from libc.stdint cimport *
 ctypedef unsigned int uint
 ctypedef uint8_t UInt8
@@ -181,6 +182,7 @@ class KjException(Exception):
         return self.message
 
 cdef public object wrap_kj_exception(capnp.Exception & exception):
+    PyErr_Clear()
     wrapper = _KjExceptionWrapper()._init(exception)
     ret = KjException(wrapper=wrapper)
 
@@ -204,6 +206,13 @@ cdef public object wrap_kj_exception_for_reraise(capnp.Exception & exception):
     ret = KjException(wrapper=wrapper)
     return ret
 
+cdef public object get_exception_info(object exc_type, object exc_obj, object exc_tb):
+    try:
+        return (exc_tb.tb_frame.f_code.co_filename, exc_tb.tb_lineno, repr(exc_type) + ':' + str(exc_obj))
+    except:
+        return ('', 0, "Couldn't determine python exception")
+
+
 ctypedef fused _DynamicStructReaderOrBuilder:
     _DynamicStructReader
     _DynamicStructBuilder

test/test_capability.py

@@ -113,7 +113,7 @@ def test_exception_client(capability):
     client = capability.TestInterface.new_client(BadServer(), loop)
     
     remote = client._send('foo', i=5)
-    with pytest.raises(ValueError):
+    with pytest.raises(capnp.KjException):
         loop.wait(remote)
 
 class BadPipelineServer:
@@ -122,7 +122,7 @@ class BadPipelineServer:
             context.results.s = response.x + '_foo'
             context.results.outBox.cap = capability().TestInterface.new_server(Server(100))
         def _error(error):
-            raise Exception('test')
+            raise Exception('test was a success')
 
         return context.params.inCap.foo(i=context.params.n).then(_then, _error)
 
@@ -137,7 +137,7 @@ def test_exception_chain(capability):
     try:
         loop.wait(remote)
     except Exception as e:
-        assert str(e) == 'test'
+        assert 'test was a success' in str(e)
 
 def test_pipeline_exception(capability):
     loop = capnp.EventLoop()