Add support for delta JSON, to squeeze the request size down further.
[remoteglot] / www / serve-analysis.js
index c970c00..cc1d2dd 100644 (file)
@@ -8,6 +8,7 @@ var url = require('url');
 var querystring = require('querystring');
 var path = require('path');
 var zlib = require('zlib');
+var delta = require('./js/json_delta.js');
 
 // Constants.
 var json_filename = '/srv/analysis.sesse.net/www/analysis.json';
@@ -15,6 +16,11 @@ var json_filename = '/srv/analysis.sesse.net/www/analysis.json';
 // The current contents of the file to hand out, and its last modified time.
 var json = undefined;
 
+// The last five timestamps, and diffs from them to the latest version.
+var history_to_keep = 5;
+var historic_json = [];
+var diff_json = {};
+
 // The list of clients that are waiting for new data to show up.
 // Uniquely keyed by request_id so that we can take them out of
 // the queue if they close the socket.
@@ -35,21 +41,59 @@ var touch_timer = undefined;
 var viewer_count_override = undefined;
 
 var replace_json = function(new_json_contents, mtime) {
+       // Generate the list of diffs from the last five versions.
+       if (json !== undefined) {
+               // If two versions have the same mtime, clients could have either.
+               // Note the fact, so that we never insert it.
+               if (json.last_modified == mtime) {
+                       json.invalid_base = true;
+               }
+               if (!json.invalid_base) {
+                       historic_json.push(json);
+                       if (historic_json.length > history_to_keep) {
+                               historic_json.shift();
+                       }
+               }
+       }
+
        var new_json = {
                parsed: JSON.parse(new_json_contents),
                plain: new_json_contents,
                last_modified: mtime
        };
+       create_json_historic_diff(new_json, historic_json.slice(0), {}, function(new_diff_json) {
+               // gzip the new version (non-delta), and put it into place.
+               zlib.gzip(new_json_contents, function(err, buffer) {
+                       if (err) throw err;
 
-       // gzip the new version, and put it into place.
-       zlib.gzip(new_json_contents, function(err, buffer) {
-               if (err) throw err;
+                       new_json.gzip = buffer;
+                       json = new_json;
+                       diff_json = new_diff_json;
 
-               new_json.gzip = buffer;
-               json = new_json;
+                       // Finally, wake up any sleeping clients.
+                       possibly_wakeup_clients();
+               });
+       });
+}
 
-               // Finally, wake up any sleeping clients.
-               possibly_wakeup_clients();
+var create_json_historic_diff = function(new_json, history_left, new_diff_json, cb) {
+       if (history_left.length == 0) {
+               cb(new_diff_json);
+               return;
+       }
+
+       var histobj = history_left.shift();
+       var diff = delta.JSON_delta.diff(histobj.parsed, new_json.parsed);
+       var diff_text = JSON.stringify(diff);
+       zlib.gzip(diff_text, function(err, buffer) {
+               if (err) throw err;
+               new_diff_json[histobj.last_modified] = {
+                       plain: diff,
+                       text: diff_text,
+                       gzip: buffer,
+                       last_modified: new_json.last_modified,
+               };
+               create_json_historic_diff(new_json, history_left, new_diff_json, cb);
        });
 }
 
@@ -87,6 +131,7 @@ var possibly_wakeup_clients = function() {
        for (var i in sleeping_clients) {
                mark_recently_seen(sleeping_clients[i].unique);
                send_json(sleeping_clients[i].response,
+                         sleeping_clients[i].ims,
                          sleeping_clients[i].accept_gzip,
                          num_viewers);
        }
@@ -114,10 +159,12 @@ var handle_viewer_override = function(request, u, response) {
                response.end();
        }
 }
-var send_json = function(response, accept_gzip, num_viewers) {
+var send_json = function(response, ims, accept_gzip, num_viewers) {
+       var this_json = diff_json[ims] || json;
+
        var headers = {
                'Content-Type': 'text/json',
-               'X-Remoteglot-Last-Modified': json.last_modified,
+               'X-Remoteglot-Last-Modified': this_json.last_modified,
                'X-Remoteglot-Num-Viewers': num_viewers,
                'Access-Control-Expose-Headers': 'X-Remoteglot-Last-Modified, X-Remoteglot-Num-Viewers',
                'Expires': 'Mon, 01 Jan 1970 00:00:00 UTC',
@@ -127,10 +174,10 @@ var send_json = function(response, accept_gzip, num_viewers) {
        if (accept_gzip) {
                headers['Content-Encoding'] = 'gzip';
                response.writeHead(200, headers);
-               response.write(json.gzip);
+               response.write(this_json.gzip);
        } else {
                response.writeHead(200, headers);
-               response.write(json.text);
+               response.write(this_json.text);
        }
        response.end();
 }
@@ -203,7 +250,7 @@ server.on('request', function(request, response) {
        // If we already have something newer than what the user has,
        // just send it out and be done with it.
        if (json !== undefined && (!ims || json.last_modified > ims)) {
-               send_json(response, accept_gzip, count_viewers());
+               send_json(response, ims, accept_gzip, count_viewers());
                return;
        }
 
@@ -214,6 +261,7 @@ server.on('request', function(request, response) {
        client.request_id = request_id;
        client.accept_gzip = accept_gzip;
        client.unique = unique;
+       client.ims = ims;
        sleeping_clients[request_id++] = client;
 
        request.socket.client = client;