Use 200-style conneg on timegate.

Browsers don't support time-based content negotiation with redirection.
Since time-based content negotiation happens using an additional HTTP
request header (Accept-Datetime), a CORS preflight request is needed.
Unfortunately, browsers disallow redirects for such cross-origin requests
that require a preflight request.
Therefore, we cannot use 302-style content negotiation in the browser.

Author: RubenVerborgh

config/config-defaults.json

@@ -26,10 +26,10 @@
 
   "controllers": [
     "SummaryController",
+    "TimegateController",
     "TriplePatternFragmentsController",
     "AssetsController",
     "DereferenceController",
-    "TimegateController",
     "NotFoundController"
   ],
 

lib/controllers/Controller.js

@@ -69,7 +69,8 @@ Controller.prototype._handleNotAcceptable = function (request, response, next) {
 // Finds an appropriate view using content negotiation
 Controller.prototype._negotiateView = function (viewName, request, response) {
   // Indicate that the response is content-negotiated
-  response.setHeader('Vary', 'Accept');
+  var vary = response.getHeader('Vary');
+  response.setHeader('Vary', 'Accept' + (vary ? ', ' + vary : ''));
   // Negotiate a view
   var viewMatch = this._views.matchView(viewName, request);
   response.setHeader('Content-Type', viewMatch.responseType || viewMatch.type);

lib/controllers/TimegateController.js

@@ -41,34 +41,40 @@ function TimegateController(options) {
 }
 Controller.extend(TimegateController);
 
-// Tries to serve the requested Timegate
+// Perform time negotiation if applicable
 TimegateController.prototype._handleRequest = function (request, response, next) {
-  var self = this, timegateMatch = this._matcher && this._matcher.exec(request.url),
-      datasource = timegateMatch && timegateMatch[1];
-  if (datasource && this._timemaps[datasource]) {
-    // retrieve Accept-Datetime & construct memento link
-    var acceptDatetime = toDate(request.headers['accept-datetime']), // If no datetime is present, return most recent one
-        memento = this._getClosestMemento(this._timemaps[datasource].timemap, acceptDatetime);
-
-    // memento invalid, go to next
-    if (!memento) next();
-
-    // Construct memento and Original url
-    var mementoUrl = url.format(_.assign(request.parsedUrl, { pathname: memento.dataSource})),
-        parsedOriginalUrl = this._timemaps[datasource].originalBaseURL ? // If originalBaseURL is present, the original is external
-                            _.assign(url.parse(this._timemaps[datasource].originalBaseURL), { query: request.parsedUrl.query }) :
-                            _.defaults({ pathname: datasource }, request.parsedUrl),
-        originalUrl = url.format(parsedOriginalUrl);
-
-    response.writeHead(303, {
-      'Location': mementoUrl,
-      'Vary': 'Accept, Accept-Datetime',
-      'Link': '<' + originalUrl + '>;rel="original", <' + mementoUrl + '>;rel="memento";datetime="' + memento.interval[0].toUTCString() + '"'
-    });
-    response.end();
+  var self = this, timegateMatch = this._matcher.exec(request.url),
+      datasource = timegateMatch && timegateMatch[1],
+      timemapDetails = datasource && this._timemaps[datasource];
+  if (timemapDetails) {
+    // Try to find the memento closest to the requested date
+    var acceptDatetime = toDate(request.headers['accept-datetime']),
+        memento = this._getClosestMemento(timemapDetails.timemap, acceptDatetime);
+    if (memento) {
+      // Determine the URL of the memento
+      var mementoUrl = _.assign(request.parsedUrl, { pathname: memento.dataSource });
+      mementoUrl = url.format(mementoUrl);
+
+      // Determine the URL of the original resource
+      var originalBaseURL = timemapDetails.originalBaseURL, originalUrl;
+      if (!originalBaseURL)
+        originalUrl = _.defaults({ pathname: datasource }, request.parsedUrl);
+      else
+        originalUrl = _.assign(url.parse(originalBaseURL), { query: request.parsedUrl.query });
+      originalUrl = url.format(originalUrl);
+
+      // Perform 200-style negotiation (https://tools.ietf.org/html/rfc7089#section-4.1.2)
+      response.setHeader('Link', '<' + originalUrl + '>;rel="original",' +
+                                 '<' + mementoUrl  + '>;rel="memento";' +
+                                 'datetime="' + memento.interval[0].toUTCString() + '"');
+      response.setHeader('Vary', 'Accept-Datetime');
+      response.setHeader('Content-Location', mementoUrl);
+      // Set request URL to the memento URL, which should be handled by a next controller
+      request.url = mementoUrl.replace(/^[^:]+:\/\/[^\/]+/, '');
+      delete request.parsedUrl;
+    }
   }
-  else
-    next();
+  next();
 };
 
 /*