FIX: Check for permalinks before showing the 404 page

Limitations: the user profile "open external links in new tab setting" is
slightly broken for "External URL" permalinks.

Remove the copy from the admin permalinks page stating that this doesn't work.

app/assets/javascripts/discourse/lib/url.js

@@ -24,7 +24,6 @@ const SERVER_SIDE_ONLY = [
   /^\/posts\/\d+\/raw/,
   /^\/raw\/\d+/,
   /^\/wizard/,
-  /^\/go\//, // EXPERIMENTAL: https://meta.discourse.org/t/-/142605
   /\.rss$/,
   /\.json$/,
   /^\/admin\/upgrade$/,

app/assets/javascripts/discourse/routes/unknown.js

@@ -1,8 +1,22 @@
-import DiscourseRoute from "discourse/routes/discourse";
 import { ajax } from "discourse/lib/ajax";
+import DiscourseURL from "discourse/lib/url";
+import DiscourseRoute from "discourse/routes/discourse";
 
 export default DiscourseRoute.extend({
-  model() {
-    return ajax("/404-body", { dataType: "html" });
+  model(params, transition) {
+    const path = params.path;
+    return ajax("/permalink-check.json", {
+      data: { path }
+    }).then(results => {
+      if (results.found) {
+        // Avoid polluting the history stack for external links
+        transition.abort();
+        DiscourseURL.routeTo(results.target_url);
+        return "";
+      } else {
+        // 404 body HTML
+        return results.html;
+      }
+    });
   }
 });

app/controllers/permalinks_controller.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class PermalinksController < ApplicationController
-  skip_before_action :check_xhr, :preload_json
+  skip_before_action :check_xhr, :preload_json, only: [:show]
 
   def show
     url = request.fullpath
@@ -17,4 +17,28 @@ class PermalinksController < ApplicationController
     end
   end
 
+  def check
+    begin
+      raise Discourse::NotFound if params[:path].blank?
+
+      permalink = Permalink.find_by_url(params[:path])
+
+      raise Discourse::NotFound unless permalink
+
+      data = {
+        found: true,
+        internal: permalink.external_url.nil?,
+        target_url: permalink.target_url,
+      }
+
+      render json: MultiJson.dump(data)
+    rescue Discourse::NotFound
+      data = {
+        found: false,
+        html: build_not_found_page(status: 200),
+      }
+      render json: MultiJson.dump(data)
+    end
+  end
+
 end

config/locales/client.en.yml

@@ -4578,7 +4578,7 @@ en:
 
       permalink:
         title: "Permalinks"
-        description: "Please note this only applies to external sources, links posted on your forum will not be redirected."
+        description: "Redirections to apply for URLs not known by the forum."
         url: "URL"
         topic_id: "Topic ID"
         topic_title: "Topic"

config/routes.rb

@@ -954,6 +954,8 @@ Discourse::Application.routes.draw do
 
   resources :csp_reports, only: [:create]
 
+  get "/permalink-check", to: 'permalinks#check'
+
   get "*url", to: 'permalinks#show', constraints: PermalinkConstraint.new
   end
 end

test/javascripts/acceptance/unknown-test.js.es6

@@ -1,8 +1,49 @@
 import { acceptance } from "helpers/qunit-helpers";
+import pretender from "helpers/create-pretender";
 acceptance("Unknown");
 
-QUnit.test("Unknown URL", async assert => {
-  assert.expect(1);
+QUnit.test("Permalink Unknown URL", async assert => {
   await visit("/url-that-doesn't-exist");
   assert.ok(exists(".page-not-found"), "The not found content is present");
 });
+
+QUnit.test("Permalink URL to a Topic", async assert => {
+  pretender.get("/permalink-check.json", () => {
+    return [
+      200,
+      { "Content-Type": "application/json" },
+      {
+        found: true,
+        internal: true,
+        target_url: "/t/internationalization-localization/280"
+      }
+    ];
+  });
+
+  await visit("/viewtopic.php?f=8&t=280");
+  assert.ok(exists(".topic-post"));
+});
+
+QUnit.test("Permalink URL to a static page", async assert => {
+  pretender.get("/permalink-check.json", () => {
+    return [
+      200,
+      { "Content-Type": "application/json" },
+      {
+        found: true,
+        internal: true,
+        target_url: "/faq"
+      }
+    ];
+  });
+
+  await visit("/not-the-url-for-faq");
+
+  // body is outside of #ember-testing-container and needs to be targeted
+  // through document instead of find
+  assert.ok(
+    document.querySelector("body.static-faq"),
+    "routed to the faq page"
+  );
+  assert.ok(exists(".body-page"));
+});

test/javascripts/helpers/create-pretender.js.es6

@@ -267,12 +267,11 @@ export function applyDefaultHandlers(pretender) {
   pretender.put("/t/:id/recover", success);
   pretender.put("/t/:id/publish", success);
 
-  pretender.get("/404-body", () => {
-    return [
-      200,
-      { "Content-Type": "text/html" },
-      "<div class='page-not-found'>not found</div>"
-    ];
+  pretender.get("/permalink-check.json", () => {
+    return response({
+      found: false,
+      html: "<div class='page-not-found'>not found</div>"
+    });
   });
 
   pretender.delete("/draft.json", success);