Add basic fallback error handler (#46)

This commit adds a proper basic fallback error handler that shows debeug information and the context of when the error has occured.

This replaces the default Sanic error handler which does not show any debug information when development mode is off.

The styling for the error handler is very basic and serves as a placeholder until a proper design can be done for it.

This will likely be a v0.3.0 feature rather than v0.1.0 one.

locales/en_US/LC_MESSAGES/priviblur.po

@@ -133,6 +133,24 @@ msgstr "Priviblur was unable to complete the request to Tumblr before timing out
 msgid "priviblur_error_invalid_internal_tumblr_redirect"
 msgstr "Error: Tumblr HTTP 301 redirect points to foreign URL"
 
+msgid "priviblur_error_generic"
+msgstr "An unknown exception has occured!"
+
+msgid "priviblur_error_generic_description"
+msgstr "It looks like you have found a bug in Priviblur."
+
+msgid "priviblur_error_generic_description_2"
+msgstr "Please report it here at GitHub"
+
+msgid "priviblur_error_generic_technical_details_error_name"
+msgstr "Error: {0}"
+
+msgid "priviblur_error_generic_technical_details_error_message"
+msgstr "Message: {0}"
+
+msgid "priviblur_error_generic_technical_details_error_context"
+msgstr "Context:"
+
 msgid "post_community_label_mature_heading"
 msgstr "Community Label: Mature"
 

src/exceptions/error_handlers/_base.py

@@ -1,3 +1,5 @@
+import inspect
+
 class ErrorHandlerGroup:
     """Manages and registers error handler functions for specific exceptions
 
@@ -24,3 +26,35 @@ def register_handlers_into_app(self, app):
         for handler, exceptions in self.registered_handlers.items():
             for exception in exceptions:
                 app.error_handler.add(exception, handler)
+
+
+def create_user_friendly_error_message(request, exception):
+    # Taken from https://github.com/searxng/searxng/blob/f5eb56b63f250c7804e5e1cf4426e550bc933906/searx/metrics/error_recorder.py
+    exception_class = exception.__class__
+    exception_name = exception_class.__qualname__
+    exception_module = exception_class.__module__
+
+    if exception_module is None or exception_module == str.__class__.__module__:
+        processed_exception_name = exception_name
+    else:
+        processed_exception_name = f"{exception_module}.{exception_name}"
+
+    exception_message = str(exception) or None
+
+    frame = inspect.trace()
+    context = []
+
+    for trace in reversed(frame):
+        if trace.filename.startswith(request.app.ctx.PRIVIBLUR_PARENT_DIR_PATH):
+            local_path = trace.filename[len(request.app.ctx.PRIVIBLUR_PARENT_DIR_PATH) + 1:]
+        else:
+            local_path = trace.filename
+        occurrence = f"File \"{local_path}\" line {trace.lineno}: in {trace.function}"
+
+        # Add code context is applicable
+        if trace.code_context:
+            occurrence = f"{occurrence}\n  {trace.code_context[0].strip()}"
+
+        context.append(occurrence)
+
+    return processed_exception_name, exception_message, '\n'.join(context)

src/exceptions/error_handlers/miscellaneous_errors.py

@@ -49,3 +49,20 @@ async def invalid_redirect(request, exception):
         },
     status=502
     )
+
+
+@miscellaneous_errors.register(Exception)
+async def generic_error(request, exception):
+    name, message, context = _base.create_user_friendly_error_message(request, exception)
+
+    return await sanic_ext.render(
+        "misc/generic_error.jinja",
+        context={
+            "app": request.app,
+            "exception": exception,
+            "exception_name": name,
+            "exception_message": message,
+            "exception_context": context,
+        },
+    status=500
+    )

src/server.py

@@ -1,9 +1,7 @@
 import os
-import asyncio
 import logging
 import urllib.parse
 import functools
-import copy
 
 import sanic
 import aiohttp
@@ -61,6 +59,9 @@
 app.ctx.PRIVIBLUR_CONFIG = config
 app.ctx.translate = i18n.translate
 
+app.ctx.PRIVIBLUR_PARENT_DIR_PATH = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+
+
 @app.listener("before_server_start")
 async def initialize(app):
     priviblur_backend = app.ctx.PRIVIBLUR_CONFIG.backend

src/templates/misc/generic_error.jinja

@@ -0,0 +1,80 @@
+{# Displays information about some generic exception to the user #}
+
+{% extends "base.jinja" %}
+{% block head %}
+<style>
+#priviblur-error > div {
+    background-color: var(--color-top-level-card-bg);
+    border-radius: 25px;
+    padding: 25px;
+    max-width: 100%;
+}
+
+#priviblur-error h2 {
+    margin: 0;
+}
+
+#priviblur-error {
+    color: var(--color-text);
+}
+
+#priviblur-error details {
+    margin-top: 20px;
+}
+
+#priviblur-error pre {
+    text-wrap: wrap;
+}
+
+#priviblur-error a {
+    text-decoration: underline;
+}
+
+#error-header {
+    font-size: 16px;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 10px;
+}
+
+@media screen and (min-width: 768px) {
+    #priviblur-error pre {
+        text-wrap: nowrap;
+    }
+
+    #priviblur-error > div {
+        max-width: unset;
+        width: fit-content;
+    }
+}
+
+}
+</style>
+
+{% endblock %}
+{% block title %}Error{% endblock %}
+
+{% block center %}
+<section id="priviblur-error">
+    <div class="card">
+        <div id="error-header">
+            <h2>{{translate(request.ctx.language, "priviblur_error_generic")}}</h2>
+            <p>{{translate(request.ctx.language, "priviblur_error_generic_description")}}</p>
+            <a href="https://github.com/syeopite/priviblur/issues/new">{{translate(request.ctx.language, "priviblur_error_generic_description_2")}}</a>
+        </div>
+
+        <div>
+            <details open="">
+            <summary>Technical details</summary>
+                <pre>{{translate(request.ctx.language, "priviblur_error_generic_technical_details_error_name", substitution=exception_name)}}</pre>
+                {% if exception_message %}<pre>{{translate(request.ctx.language, "priviblur_error_generic_technical_details_error_message", substitution='"' + exception_message + '"')}}</pre>{% endif %}
+                <pre>{{-translate(request.ctx.language, "priviblur_error_generic_technical_details_error_context")}}</pre>
+                <pre>{{exception_context}}</pre>
+            </details>
+        </div>
+
+    </div>
+</section>
+{%- endblock %}