Add widget title API

Adds #130

This is backed by a homeserver's media repository.

config/default.yaml

@@ -25,6 +25,11 @@ upstreams:
 - name: vector
   url: "https://scalar.vector.im/api"
 
+# Homeserver configuration (used to proxy some requests to the homeserver for processing)
+homeserver:
+  name: "t2bot.io"
+  accessToken: "something"
+
 # IPs and CIDR ranges listed here will be blocked from being widgets.
 # Note: Widgets may still be embedded with restricted content, although not through Dimension directly.
 widgetBlacklist:

docs/scalar_server_api.md

@@ -441,3 +441,20 @@ None of these are officially documented, and are subject to change.
 ```
 
 *Note*: Invite person-specific bot on first repository
+
+## GET `/api/widgets/title_lookup?curl=https://t2bot.io&scalar_token=...`
+
+**Response**
+```
+{
+  "page_title_cache_item": {
+    "expires": "2017-12-12T20:11:00.70212938Z",
+    "cached_title": "t2bot.io",
+    "cached_response_err": ""
+  },
+  "error": {
+    "message": ""
+  },
+  "cached_response": false
+}
+```

src/ScalarApi.js

@@ -27,6 +27,46 @@ class ScalarApi {
 
         app.post("/api/v1/scalar/register", this._scalarRegister.bind(this));
         app.get("/api/v1/scalar/checkToken", this._checkScalarToken.bind(this));
+        app.get("/api/v1/scalar/widgets/title_lookup", this._getWidgetTitle.bind(this));
+    }
+
+    _getWidgetTitle(req, res) {
+        res.setHeader("Content-Type", "application/json");
+
+        var token = req.query.scalar_token;
+        var url = req.query.curl;
+
+        if (!token || !url) {
+            res.status(400).send({error: "Missing token or curl"});
+            return;
+        }
+
+        this._db.checkToken(token).then(() => {
+            MatrixLiteClient.getUrlPreview(url).then(preview => {
+                if (!preview["og:title"]) {
+                    res.status(404).send({error:{message:"Could not locate a title for the URL"}});
+                    return;
+                }
+
+                // We need to convert the preview response to what Scalar expects
+                res.status(200).send({
+                    cached_response: false,
+                    page_title_cache_item: {
+                        expires: null, // unused
+                        cached_response_err: null, // unused
+                        cached_title: preview["og:title"],
+                    }
+                });
+            }).catch(err => {
+                res.status(500).send({error: {message: "Failed to get preview"}});
+                log.error("ScalarApi", "Failed to get URL preview");
+                log.error("ScalarApi", err);
+            });
+        }).catch(err => {
+            res.status(401).send({error: {message: "Failed to authenticate token"}});
+            log.warn("ScalarApi", "Failed to authenticate token");
+            log.warn("ScalarApi", err);
+        });
     }
 
     _checkScalarToken(req, res) {

src/matrix/MatrixLiteClient.js

@@ -2,6 +2,7 @@ var request = require('request');
 var log = require("../util/LogService");
 var dns = require("dns-then");
 var Promise = require("bluebird");
+var config = require("config");
 
 /**
  * Represents a lightweight matrix client with minimal functionality
@@ -27,8 +28,22 @@ class MatrixLiteClient {
         });
     }
 
+    /**
+     * Gets a URL preview from the media repo (as provided by the default homeserver)
+     * @param {string} url The URL to get the preview of
+     * @return {Promise<*>} resolves to the raw URL preview
+     */
+    static getUrlPreview(url) {
+        return MatrixLiteClient._do(config.homeserver.name, config.homeserver.accessToken, "GET", "/_matrix/media/r0/preview_url", {url: url}).then((response, body) => {
+            return JSON.parse(response.body);
+        });
+    }
+
     _do(method, endpoint, qs = null, body = null, allowSelfSigned = false) {
-        var serverName = this._openId.matrix_server_name;
+        return MatrixLiteClient._do(this._openId.matrix_server_name, this._openId.access_token, method, endpoint, qs, body, allowSelfSigned);
+    }
+
+    static _do(serverName, accessToken, method, endpoint, qs = null, body = null, allowSelfSigned = false) {
         // HACK: We have to wrap the dns promise in a Bluebird promise just to make sure it works
         var dnsPromise = dns.resolveSrv("_matrix._tcp." + serverName);
         return Promise.resolve(dnsPromise).then(records => {
@@ -43,7 +58,7 @@ class MatrixLiteClient {
             log.verbose("MatrixLiteClient", "Performing request: " + url);
 
             if (!qs) qs = {};
-            qs['access_token'] = this._openId.access_token;
+            if (accessToken) qs['access_token'] = accessToken;
 
             var params = {
                 url: url,