Improve exception handling

Re-raise exceptions caught in _dispatch_request.  Added starlette
ExceptionMiddleware to be able to test this gracefully.

responder/api.py

@@ -15,6 +15,7 @@ from starlette.testclient import TestClient
 from starlette.middleware.gzip import GZipMiddleware
 from starlette.middleware.httpsredirect import HTTPSRedirectMiddleware
 from starlette.middleware.cors import CORSMiddleware
+from starlette.exceptions import ExceptionMiddleware
 from apispec import APISpec
 from apispec.ext.marshmallow import MarshmallowPlugin
 from apispec import yaml_utils
@@ -31,6 +32,7 @@ from .statics import (
     DEFAULT_API_THEME, DEFAULT_SESSION_COOKIE, DEFAULT_SECRET_KEY, DEFAULT_CORS_PARAMS
 )
 
+
 # TODO: consider moving status codes here
 class API:
     """The primary web-service class.
@@ -121,6 +123,7 @@ class API:
 
         if self.cors:
             self.add_middleware(CORSMiddleware, **self.cors_params)
+        self.add_middleware(ExceptionMiddleware, debug=debug)
 
         # Jinja enviroment
         self.jinja_env = jinja2.Environment(
@@ -285,6 +288,7 @@ class API:
                         cont = True
                 except Exception:
                     self.default_response(req, resp, error=True)
+                    raise
 
             elif route.is_class_based or cont:
                 try:
@@ -301,8 +305,9 @@ class API:
                     # If it's async, await it.
                     if hasattr(r, "send"):
                         await r
-                except Exception as e:
+                except Exception:
                     self.default_response(req, resp, error=True)
+                    raise
 
                 # Then on_get.
                 method = req.method

tests/test_responder.py

@@ -3,6 +3,8 @@ import yaml
 import responder
 import io
 
+from starlette.responses import PlainTextResponse
+
 
 def test_api_basic_route(api):
     @api.route("/")
@@ -460,12 +462,18 @@ def test_file_uploads(api):
 
 
 def test_500(api):
+    def catcher(request, exc):
+        return PlainTextResponse("Suppressed error", 500)
+
+    api.app.add_exception_handler(ValueError, catcher)
+
     @api.route("/")
     def view(req, resp):
         raise ValueError
 
     r = api.requests.get(api.url_for(view))
     assert not r.ok
+    assert r.content == b'Suppressed error'
 
 
 def test_404(api):