Show available routes on 404 page

examples/starlette.py

@@ -3,7 +3,7 @@
 from starlette.applications import Starlette
 from starlette.requests import Request
 from starlette.responses import Response
-from starlette.routing import Route
+from starlette.routing import Mount, Route, WebSocketRoute
 from starlette.templating import Jinja2Templates
 
 from starception import install_error_handler
@@ -72,5 +72,23 @@ def css_view(request: Request) -> Response:
         Route('/css', css_view),
         Route('/template', template_view),
         Route('/javascript', javascript_view),
+        Mount(
+            '/app',
+            routes=[
+                Route('/node', index_view, name='index1'),
+                Mount(
+                    '/nested',
+                    routes=[
+                        Route('/node/{id:int}', index_view, name='nested_node'),
+                        Route('/node/{id:uuid}-{user:str}-{counter:int}', index_view, name='params_node'),
+                        Route('/node2', index_view, name='nested_node'),
+                        Mount('/level2', routes=[Route('/node/{id}', index_view)]),
+                    ],
+                    name='nested',
+                ),
+            ],
+        ),
+        Mount('/subapp', app=Starlette(), name='subapp'),
+        WebSocketRoute('/ws', index_view),
     ],
 )

starception/exception_handler.py

@@ -15,6 +15,8 @@
 from starlette.middleware.errors import ServerErrorMiddleware
 from starlette.requests import Request
 from starlette.responses import HTMLResponse, PlainTextResponse, Response
+from starlette.routing import BaseRoute, Mount, NoMatchFound, Router
+from starlette.types import Receive, Scope, Send
 from urllib.parse import quote_plus
 
 _editor: str = 'none'
@@ -24,6 +26,53 @@
 }
 
 
+@dataclasses.dataclass
+class RouteInfo:
+    methods: typing.List[str]
+    type: str
+    middleware: typing.List[str]
+    path_name: str
+    path_pattern: str
+    endpoint: typing.Any
+
+    @property
+    def endpoint_name(self) -> str:
+        module_name = getattr(self.endpoint, '__module__')
+        base_name = getattr(self.endpoint, '__name__', getattr(self.endpoint.__class__, '__name__'))
+        return f'{module_name}.{base_name}'
+
+
+def collect_routes(routes: typing.Iterable[BaseRoute], prefix: str = '') -> typing.Iterable[RouteInfo]:
+    for route in routes:
+        if isinstance(route, Mount) and len(route.routes):
+            yield from collect_routes(list(route.routes), route.path_format)
+        else:
+            endpoint = getattr(route, 'endpoint', getattr(route, 'app'))
+            yield RouteInfo(
+                methods=getattr(route, 'methods', []) or [],
+                type=type(route).__name__,
+                path_name=getattr(route, 'name', ''),
+                path_pattern=prefix + getattr(route, 'path_format', ''),
+                endpoint=endpoint,
+                middleware=[],
+            )
+
+
+def not_found_renderer(request: Request, exc: BaseException) -> str:
+    routes = list(collect_routes(request.app.routes))
+    return jinja.get_template('custom_exceptions/not_found.html').render(
+        {
+            'routes': routes,
+        }
+    )
+
+
+ExceptionRenderer = typing.Callable[[Request, BaseException], str]
+exception_renderers: typing.Dict[typing.Type[BaseException], ExceptionRenderer] = {
+    NoMatchFound: not_found_renderer,
+}
+
+
 def set_editor(name: str) -> None:
     """
     Set code editor.
@@ -51,7 +100,10 @@ def to_ide_link(path: str, lineno: int) -> str:
     return template.format(path=path, lineno=lineno)
 
 
-def install_error_handler(editor: str = '') -> None:
+def install_error_handler(
+    editor: str = '',
+    custom_exception_renderers: typing.Optional[typing.Dict[typing.Type[BaseException], ExceptionRenderer]] = None,
+) -> None:
     """
     Replace Starlette debug exception handler in-place.
 
@@ -60,10 +112,22 @@ def install_error_handler(editor: str = '') -> None:
     """
     set_editor(editor)
 
+    if custom_exception_renderers:
+        exception_renderers.update(custom_exception_renderers)
+
     def bound_handler(self: ServerErrorMiddleware, request: Request, exc: Exception) -> Response:
         return exception_handler(request, exc)
 
+    original_handler = getattr(Router, 'not_found')
+
+    async def patched_not_found(self: Router, scope: Scope, receive: Receive, send: Send) -> None:
+        if 'app' in scope and scope['app'].debug:
+            raise NoMatchFound('', {})
+        else:
+            await original_handler(self, scope, receive, send)
+
     setattr(ServerErrorMiddleware, 'debug_response', bound_handler)
+    setattr(Router, 'not_found', patched_not_found)
 
 
 def get_relative_filename(path: str) -> str:
@@ -247,6 +311,14 @@ def generate_html(request: Request, exc: Exception, limit: int = 15) -> str:
         )
         cause = getattr(cause, '__cause__')
 
+    custom_exception_block = ''
+    exception_renderer = exception_renderers.get(exc.__class__)
+    if exception_renderer:
+        try:
+            custom_exception_block = exception_renderer(request, exc)
+        except Exception as ex:
+            custom_exception_block = f"Got exception while rendering exception details: {ex.__class__.__name__} {ex}."
+
     template = jinja.get_template('index.html')
     return template.render(
         {
@@ -290,6 +362,7 @@ def generate_html(request: Request, exc: Exception, limit: int = 15) -> str:
                 "Paths": Markup("<br>".join(sys.path)),
             },
             'environment': os.environ,
+            'custom_exception_block': custom_exception_block,
             'solution': getattr(exc, 'solution', None),
         }
     )

starception/templates/custom_exceptions/not_found.html

@@ -0,0 +1,35 @@
+<strong>Available routes</strong>
+<br/>
+<br/>
+<table style="width: 100%;" class="table">
+    <thead>
+    <tr>
+        <th style="text-align: right">Name</th>
+        <th>Methods</th>
+        <th>Path pattern</th>
+        <th>Endpoint</th>
+        <th>Type</th>
+    </tr>
+    </thead>
+    <tbody>
+    {% for route in routes %}
+        <tr>
+            <td style="text-align: right">
+                {{ route.path_name }}
+            </td>
+            <td>
+                {{ route.methods|join(', ') }}
+            </td>
+            <td>
+                {{ route.path_pattern }}
+            </td>
+            <td>
+                {{ route.endpoint_name }}
+            </td>
+            <td>
+                {{ route.type }}
+            </td>
+        </tr>
+    {% endfor %}
+    </tbody>
+</table>

starception/templates/index.html

@@ -65,6 +65,15 @@
                     </div>
                 </header>
             {% endif %}
+
+            {% if loop.index0 == 0 and custom_exception_block %}
+                <div style="padding: 20px 40px 0px 40px;">
+                    <div style="background: var(--snippet-bg); padding: 24px;">
+                        {{ custom_exception_block }}
+                    </div>
+                </div>
+            {% endif %}
+
             <div data-trace-target {% if loop.index0 > 0 %} class="collapsed"{% endif %}>
                 {% if loop.index0 > 0 %}
                     {% if stack_item.solution %}

starception/templates/styles.css

@@ -376,3 +376,20 @@ dd {
 .search-links a:hover {
     text-decoration: underline;
 }
+
+.table {
+    width: 100%;
+}
+
+.table th, .table td {
+    text-align: left;
+    padding: 3px 8px;
+}
+
+.table tbody tr td {
+    border-top: 1px solid var(--data-list-border-color);
+}
+
+.table tbody tr:hover {
+    background-color: var(--data-list-bg-hover);
+}