Change res.flush to accept a callback function argument

Author: bijoythomas

README.md

@@ -196,7 +196,8 @@ function shouldCompress (req, res) {
 ### res.flush
 
 This module adds a `res.flush()` method to force the partially-compressed
-response to be flushed to the client.
+response to be flushed to the client. This function accepts a callback which gets
+invoked when the response has been flushed to the client
 
 ## Examples
 

index.js

@@ -79,9 +79,9 @@ function compression (options) {
     var _write = res.write
 
     // flush
-    res.flush = function flush () {
+    res.flush = function flush(cb) {
       if (stream) {
-        stream.flush()
+        stream.flush(cb)
       }
     }
 

test/compression.js

@@ -835,6 +835,80 @@ describe('compression()', function () {
         .end()
     })
 
+    it('should invoke flush callback when supplied for gzip', function (done) {
+      var chunks = 0, callbackInvoked = false;
+      var resp
+      var server = createServer({ threshold: 0 }, function (req, res) {
+        resp = res
+        res.setHeader('Content-Type', 'text/plain')
+        write()
+      })
+
+      function flushCallback() {
+        callbackInvoked = true;
+      }
+
+      function write() {
+        chunks++
+        if (chunks === 20) return resp.end()
+        if (chunks > 20) return chunks--
+        resp.write('..')
+        resp.flush(flushCallback)
+      }
+
+      request(server)
+      .get('/')
+      .set('Accept-Encoding', 'gzip')
+      .request()
+      .on('response', function (res) {
+        assert.equal(res.headers['content-encoding'], 'gzip')
+        res.on('data', write)
+        res.on('end', function(){
+          assert.equal(chunks, 20)
+          assert.equal(callbackInvoked, true)
+          done()
+        })
+      })
+      .end()
+    })
+
+    it('should invoke flush callback when supplied for deflate', function (done) {
+      var chunks = 0, callbackInvoked = false;
+      var resp
+      var server = createServer({ threshold: 0 }, function (req, res) {
+        resp = res
+        res.setHeader('Content-Type', 'text/plain')
+        write()
+      })
+
+      function flushCallback() {
+        callbackInvoked = true;
+      }
+
+      function write() {
+        chunks++
+        if (chunks === 20) return resp.end()
+        if (chunks > 20) return chunks--
+        resp.write('..')
+        resp.flush(flushCallback)
+      }
+
+      request(server)
+      .get('/')
+      .set('Accept-Encoding', 'deflate')
+      .request()
+      .on('response', function (res) {
+        assert.equal(res.headers['content-encoding'], 'deflate')
+        res.on('data', write)
+        res.on('end', function(){
+          assert.equal(chunks, 20)
+          assert.equal(callbackInvoked, true)
+          done()
+        })
+      })
+      .end()
+    })
+
     it('should flush small chunks for deflate', function (done) {
       var chunks = 0
       var next