Use flushHeaders method

As `flush` was deprecated

https://github.com/nodejs/node/blob/master/lib/_http_outgoing.js#L892
nodejs/node#1156

lib/sse-channel.js

@@ -301,19 +301,17 @@ function broadcast(connections, packet) {
 }
 
 /**
- * Calls `flush()` on the response if it exists. This is necessary in the case
+ * Calls `flushHeaders()` on the response if it exists. This is necessary in the case
  * when you are using the `compression` middleware for express.js, where the
  * middleware will wait for a certain amount of data before sending it to the
  * client in order to compress in a more efficient manner.
  *
- * Unfortunately, node has a native (but deprecated) flush() method which will trigger
- * deprecation warnings if called. Thus, we're checking the name of the function.
- * Please open a pull request if you can come up with a cleaner approach to this.
- *
  * @param {Response} response Response object to flush
  */
 function flush(response) {
-    if (response.flush && response.flush.name !== 'deprecated') {
+    if (typeof response.flushHeaders === 'function') {
+        response.flushHeaders();
+    } else if (response.flush && response.flush.name !== 'deprecated') {
         response.flush();
     }
 }

test/sse-channel.test.js

@@ -662,7 +662,7 @@ describe('sse-channel', function() {
         //   - After each broadcast
         var flushes = 0;
         initServer({
-            flush: function() {
+            flushHeaders: function() {
                 flushes++;
             },
             history: [

test/util/server-init.js

@@ -7,8 +7,8 @@ module.exports = function(opts) {
     var channel = new Channel(opts);
 
     var server = http.createServer(function(req, res) {
-        if (opts.flush) {
-            res.flush = opts.flush;
+        if (opts.flushHeaders) {
+            res.flushHeaders = opts.flushHeaders;
         }
 
         channel.addClient(req, res, opts.addClientCallback);