Add custom error pages for user errors

Such as 404. We already have separate handling for
internal errors, and Stac API errors.

cubedash/_pages.py

@@ -10,6 +10,7 @@
 from datacube.scripts.dataset import build_dataset_info
 from flask import abort, redirect, request, url_for
 from werkzeug.datastructures import MultiDict
+from werkzeug.exceptions import HTTPException
 
 import cubedash
 from cubedash import _audit, _monitoring
@@ -52,6 +53,19 @@
     _monitoring.init_app_monitoring()
 
 
+@app.errorhandler(HTTPException)
+def handle_exception(e: HTTPException):
+    return (
+        utils.render(
+            "message.html",
+            title=e.code,
+            message=e.description,
+            e=e,
+        ),
+        e.code,
+    )
+
+
 @app.route("/<product_name>")
 @app.route("/<product_name>/<int:year>")
 @app.route("/<product_name>/<int:year>/<int:month>")

cubedash/templates/message.html

@@ -0,0 +1,19 @@
+{% extends "layout/base.html" %}
+
+{#
+A simple page for showing a message to the user.
+
+Such as a 404.
+
+#}
+
+{% set active_page = "message" %}
+
+{% block title %}{{ title }}: {{ message }}{% endblock %}
+
+{% block content %}
+    <div class="panel highlight">
+        <h2>{{ title }}</h2>
+        <p>{{ message }}</p>
+    </div>
+{% endblock %}