Send a real EventSource event for heartbeat

share/doc/src/api/database/changes.rst

@@ -398,6 +398,16 @@ parameter.
 
     }
 
+If you set a heartbeat interval (using the ``heartbeat`` query argument), CouchDB will
+send a ``hearbeat`` event that you can subscribe to with:
+
+.. code-block:: javascript
+
+    source.addEventListener('heartbeat', function () {}, false);
+
+This can be monitored by the client application to restart the EventSource connection if
+needed (i.e. if the TCP connection gets stuck in a half-open state).
+
 .. note::
 
    EventSource connections are subject to cross-origin resource sharing

share/www/script/test/changes.js

@@ -123,7 +123,7 @@ couchTests.changes = function(debug) {
 
     xhr = CouchDB.newXhr();
 
-    //verify the hearbeat newlines are sent
+    //verify the heartbeat newlines are sent
     xhr.open("GET", CouchDB.proxyUrl("/test_suite_db/_changes?feed=continuous&heartbeat=10&timeout=500"), true);
     xhr.send("");
 
@@ -171,6 +171,25 @@ couchTests.changes = function(debug) {
       T(results[1].changes[0].rev == docBar._rev);
     }
 
+    // test that we receive EventSource heartbeat events
+    if (!!window.EventSource) {
+      var source = new EventSource(
+              "/test_suite_db/_changes?feed=eventsource&heartbeat=10");
+
+      var count_heartbeats = 0;
+      source.addEventListener('heartbeat', function () { count_heartbeats = count_heartbeats + 1; } , false);
+
+      waitForSuccess(function() {
+        if (count_heartbeats < 3) {
+          throw "keep waiting";
+        }
+        return true;
+      }, "eventsource-heartbeat");
+
+      T(count_heartbeats >= 3);
+      source.close();
+    }
+
     // test longpolling
     xhr = CouchDB.newXhr();
 

src/couchdb/couch_httpd_db.erl

@@ -105,6 +105,8 @@ handle_changes_req2(Req, Db) ->
                 io_lib:format("\n],\n\"last_seq\":~w}\n", [EndSeq])
             ),
             end_json_response(Resp);
+        (timeout, "eventsource") ->
+            send_chunk(Resp, "event: heartbeat\ndata: \n\n");
         (timeout, _) ->
             send_chunk(Resp, "\n")
         end