Refactored to sanic.pages.error module. Traceback and style tuning. Print also headers, and for other than 500 errors as well. 500 error message text UX workaround.

sanic/errorpages.py

@@ -23,7 +23,7 @@ from traceback import extract_tb
 from sanic.exceptions import BadRequest, SanicException
 from sanic.helpers import STATUS_CODES
 from sanic.response import html, json, text
-from sanic.pages.base import ErrorPage
+from sanic.pages.error import ErrorPage
 
 dumps: t.Callable[..., str]
 try:
@@ -160,7 +160,13 @@ class HTMLRenderer(BaseRenderer):
     )
 
     def _page(self, full: bool) -> HTTPResponse:
-        page = ErrorPage(super().title, super().text, sys.exc_info()[1], full=full)
+        page = ErrorPage(
+            title=super().title,
+            text=super().text,
+            request=self.request,
+            exc=self.exception,
+            full=full,
+        )
         return html(page.render(), status=self.status, headers=self.headers)
 
     def full(self) -> HTTPResponse:

sanic/pages/autoindex.py

@@ -24,6 +24,7 @@ class AutoIndex(BasePage):
         table.autoindex td:first-child { flex: 1; }
         table.autoindex td:nth-child(2) { text-align: right; }
         table.autoindex td:last-child {  text-align: right; }
+        span.icon { margin-right: 1rem; }
         """
     )
     TITLE = "File browser"

sanic/pages/base.py

@@ -16,12 +16,15 @@ class BasePage(ABC):
             display: flex; align-items: center; justify-content: space-between;
             background: #555; color: #e1e1e1;
         }
+        main { padding-bottom: 3rem; }
+        h2 { margin: 2rem 0 1rem 0; }
         a:visited { color: inherit; }
         a { text-decoration: none; color: #88f; }
         a:hover, a:focus { text-decoration: underline; outline: none; }
         #logo { height: 2.5rem; }
-        table { width: 100%; max-width: 1200px; }
-        span.icon { margin-right: 1rem; }
+        .smalltext { font-size: 1rem; }
+        .nobr { white-space: nowrap; }
+        table { width: 100%; max-width: 1200px; word-break: break-all; }
         @media (prefers-color-scheme: dark) {
             html { background: #111; color: #ccc; }
         }
@@ -50,24 +53,3 @@ class BasePage(ABC):
     @abstractmethod
     def _body(self) -> None:
         ...
-
-
-class ErrorPage(BasePage):
-    TITLE = "Error while handling your request"
-
-    def __init__(self, title: str, text: str, exc: Exception, full: bool) -> None:
-        super().__init__()
-        self.title = title
-        self.text = text
-        self.exc = exc
-        self.full = full
-
-    def _body(self) -> None:
-        with self.doc.main:
-            self.doc.h1(f"⚠️ {self.title}")
-            if self.full and self.exc:
-                from niceback import html_traceback
-                self.doc(html_traceback(self.exc))
-            else:
-                self.doc.p(self.text)
-

sanic/pages/error.py

@@ -0,0 +1,40 @@
+from .base import BasePage
+from sanic.request import Request
+
+from html5tagger import E
+from niceback import html_traceback, inspector
+
+# Avoid showing the request in the traceback variable inspectors
+inspector.blacklist_types += Request,
+
+class ErrorPage(BasePage):
+    def __init__(self, title: str, text: str, request: Request, exc: Exception, full: bool) -> None:
+        super().__init__()
+        # Internal server errors come with the text of the exception, which we don't want to show to the user.
+        # FIXME: This needs to be done some place else but I am not digging into that now.
+        if "Internal Server Error" in title:
+            text = "The application encountered an unexpected error and could not continue."
+        self.TITLE = E(f"App {request.app.name} cannot handle your request")
+        self.title = title
+        self.text = text
+        self.request = request
+        self.exc = exc
+        self.full = full
+
+    def _body(self) -> None:
+        with self.doc.main:
+            self.doc.h1(f"⚠️ {self.title}").p(self.text)
+            if not self.request.app.debug:
+                return
+            # Show additional details in debug mode, open by default for 500 errors
+            with self.doc.details(open=self.full, class_="smalltext"):
+                self.doc.summary("Details for developers (Sanic debug mode only)")
+                if self.exc:
+                    self.doc.h2(f"Exception in {self.request.route.name}:")
+                    # skip_outmost=1 to hide Sanic.handle_request
+                    self.doc(html_traceback(self.exc, skip_outmost=1))
+
+                self.doc.h2(f"{self.request.method} {self.request.path}")
+                with self.doc.table(id="request-headers"):
+                    for k, v in self.request.headers.items():
+                        self.doc.tr.td(f"{k}:", class_="nobr").td(v)