Make error-handling prettier and handle 404 and 500s

lc/error.py

@@ -33,7 +33,7 @@ class UserExists(LCException):
     name: str
 
     def __str__(self):
-        return f"A user named {self.name} already exists."
+        return f"A user named '{self.name}' already exists."
 
 
 @dataclass
@@ -41,7 +41,7 @@ class NoSuchUser(LCException):
     name: str
 
     def __str__(self):
-        return f"No user named {self.name} exists."
+        return f"No user named '{self.name}' exists."
 
     def http_code(self) -> int:
         return 404
@@ -52,7 +52,7 @@ class NoSuchLink(LCException):
     link_id: int
 
     def __str__(self):
-        return f"No link {self.link_id} exists."
+        return f"No link '{self.link_id}' exists."
 
     def http_code(self) -> int:
         return 404
@@ -138,3 +138,14 @@ class BadTagName(LCException):
 
     def http_code(self) -> int:
         return 400
+
+
+@dataclass
+class BadAddLink(LCException):
+    message: str
+
+    def __str__(self):
+        return f"Error adding link: {self.message}"
+
+    def http_code(self) -> int:
+        return 400

lc/static/main.css

@@ -185,3 +185,16 @@ form > div {
 .deleteconfirm a {
     color: #f00;
 }
+
+.errorpane {
+    display: flex;
+    justify-content: center;
+}
+
+.error {
+    width: 50%;
+}
+
+.error p {
+    margin-left: 2em;
+}

lc/view.py

@@ -103,3 +103,9 @@ class Page(View):
     title: str
     content: str
     user: Optional[Any]
+
+
+@dataclass
+class Error(View):
+    code: int
+    message: str

lc/web.py

@@ -52,6 +52,16 @@ class Endpoint:
         except e.LCException:
             return
 
+    @staticmethod
+    def just_get_user() -> Optional[m.User]:
+        try:
+            return Endpoint().user
+        except:
+            # this is going to catch everything on the off chance that
+            # there's a bug in the user-validation code: this is used
+            # in error handlers, so we should be resilient to that!
+            return None
+
     def api_ok(self, redirect: str, data: dict = {"status": "ok"}) -> ApiOK:
         if flask.request.content_type == "application/x-www-form-urlencoded":
             raise e.LCRedirect(redirect)
@@ -113,13 +123,7 @@ class Endpoint:
             if flask.request.content_type == "application/json":
                 return ({"status": exn.http_code(), "error": str(exn)}, exn.http_code())
             else:
-                page = render(
-                    "main",
-                    v.Page(
-                        title="error", content=f"shit's fucked yo: {exn}", user=None,
-                    ),
-                )
-                return (page, exn.http_code())
+                return (self.render_error(exn), exn.http_code())
         # also maybe we tried to redirect, so just do that
         except e.LCRedirect as exn:
             return flask.redirect(exn.to_path())
@@ -129,16 +133,15 @@ class Endpoint:
         try:
             return self.html(*args, **kwargs)  # type: ignore
         except e.LCException as exn:
-            page = render(
-                "main",
-                v.Page(
-                    title="error", content=f"shit's fucked yo: {exn}", user=self.user,
-                ),
-            )
-            return (page, exn.http_code())
+            return (self.render_error(exn), exn.http_code())
         except e.LCRedirect as exn:
             return flask.redirect(exn.to_path())
 
+    def render_error(self, exn: e.LCException) -> str:
+        error = v.Error(code=exn.http_code(), message=str(exn))
+        page = v.Page(title="error", content=render("error", error), user=self.user)
+        return render("main", page)
+
 
 # Decorators result in some weird code in Python, especially 'cause it
 # doesn't make higher-order functions terse. Let's break this down a
@@ -184,3 +187,21 @@ def render(name: str, data: Optional[v.View] = None) -> str:
     template = LOADER.load_name(name)
     renderer = pystache.Renderer(missing_tags="strict", search_dirs=["templates"])
     return renderer.render(template, data or {})
+
+
+@c.app.errorhandler(404)
+def handle_404(e):
+    user = Endpoint.just_get_user()
+    url = flask.request.path
+    error = v.Error(code=404, message=f"Page {url} not found")
+    page = v.Page(title="not found", content=render("error", error), user=None)
+    return render("main", page)
+
+
+@c.app.errorhandler(500)
+def handle_500(e):
+    user = Endpoint.just_get_user()
+    c.log(f"Internal error: {e}")
+    error = v.Error(code=500, message=f"An unexpected error occurred")
+    page = v.Page(title="500", content=render("error", error), user=None)
+    return render("main", page)

templates/error.mustache

@@ -0,0 +1,6 @@
+<div class="errorpane">
+  <div class="error">
+    <h1>Error ({{code}})</h1>
+    <p>{{message}}</p>
+  </div>
+</div>