Change res.flush to accept a callback function argument (#227)

* Change res.flush to accept a callback function argument

* test: add callback invocation check for flush in brotli compression

* fix lint

* deps: update mocha to version 10.8.2 and add --exit option

---------

Co-authored-by: Bijoy Thomas <[email protected]>

Author: bjohansebas

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)
       }
     }
 

package.json

@@ -27,7 +27,7 @@
     "eslint-plugin-node": "^11.1.0",
     "eslint-plugin-promise": "^5.2.0",
     "eslint-plugin-standard": "^4.1.0",
-    "mocha": "^9.2.2",
+    "mocha": "^10.8.2",
     "nyc": "^15.1.0",
     "supertest": "^6.2.3"
   },
@@ -41,7 +41,7 @@
   },
   "scripts": {
     "lint": "eslint .",
-    "test": "mocha --check-leaks --reporter spec",
+    "test": "mocha --check-leaks --exit --reporter spec",
     "test-ci": "nyc --reporter=lcov --reporter=text npm test",
     "test-cov": "nyc --reporter=html --reporter=text npm test"
   }

test/compression.js

@@ -835,6 +835,117 @@ describe('compression()', function () {
         .end()
     })
 
+    it('should invoke flush callback when supplied for gzip', function (done) {
+      var chunks = 0; var 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 brotli', function (done) {
+      var chunks = 0; var 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', 'br')
+        .request()
+        .on('response', function (res) {
+          assert.equal(res.headers['content-encoding'], 'br')
+          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; var 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