From 431fbb7d98525299432e3c110ebe554ca658974b Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Mon, 18 May 2020 16:37:41 +0200
Subject: [PATCH 01/23] Proxy res.end(callback) calls correctly

---
 index.js        |  2 +-
 test/session.js | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 9615346c..ad90ff58 100644
--- a/index.js
+++ b/index.js
@@ -272,7 +272,7 @@ function session(options) {
           return ret;
         }
 
-        if (chunk == null) {
+        if (chunk == null || typeof chunk === 'function') {
           ret = true;
           return ret;
         }
diff --git a/test/session.js b/test/session.js
index f0b60fdf..b20da863 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,6 +189,23 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
+  it('should handle res.end(callback) calls', function (done) {
+    var callbackHasBeenCalled = false;
+
+    var server = createServer(null, function (req, res) {
+      function callback() {
+        callbackHasBeenCalled = true;
+      }
+
+      res.end(callback);
+    });
+
+    request(server).get('/').expect(200, '', function () {
+      assert.ok(callbackHasBeenCalled);
+      done();
+    })
+  });
+
   it('should handle res.end(null) calls', function (done) {
     var server = createServer(null, function (req, res) {
       res.end(null)

From 2482cf2c6f6c4ae569acb1a2819f087f94f982e9 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Wed, 20 May 2020 14:23:21 +0200
Subject: [PATCH 02/23] work in progress, doesn't work properly

---
 .gitignore      |  1 +
 index.js        | 30 ++++++++++++++++++++++++-----
 package.json    |  7 ++-----
 test/session.js | 51 ++++++++++++++++++++++++++++++++-----------------
 4 files changed, 62 insertions(+), 27 deletions(-)

diff --git a/.gitignore b/.gitignore
index 207febba..615e06d4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+.idea/
 .nyc_output
 coverage
 node_modules
diff --git a/index.js b/index.js
index ad90ff58..47b3e369 100644
--- a/index.js
+++ b/index.js
@@ -247,7 +247,7 @@ function session(options) {
     var _end = res.end;
     var _write = res.write;
     var ended = false;
-    res.end = function end(chunk, encoding) {
+    res.end = function end() {
       if (ended) {
         return false;
       }
@@ -257,9 +257,25 @@ function session(options) {
       var ret;
       var sync = true;
 
+      var endArguments = arguments;
+      var chunk = endArguments[0];
+      var encoding = endArguments[1];
+
+      console.log('about to shuffle arguments', { chunk: chunk, encoding: encoding });
+
+      // Callback may be the 1st (and only), second, or third argument
+      if (typeof chunk === 'function') {
+        console.log('chunk was function');
+        chunk = null;
+        encoding = null;
+      } else if (typeof encoding === 'function') {
+        console.log('encoding was function');
+        encoding = null;
+      }
+
       function writeend() {
         if (sync) {
-          ret = _end.call(res, chunk, encoding);
+          ret = _end.apply(res, endArguments);
           sync = false;
           return;
         }
@@ -272,7 +288,7 @@ function session(options) {
           return ret;
         }
 
-        if (chunk == null || typeof chunk === 'function') {
+        if (chunk == null) {
           ret = true;
           return ret;
         }
@@ -301,6 +317,7 @@ function session(options) {
       }
 
       if (shouldDestroy(req)) {
+        console.log('shouldDestroy');
         // destroy session
         debug('destroying');
         store.destroy(req.sessionID, function ondestroy(err) {
@@ -317,17 +334,20 @@ function session(options) {
 
       // no session to save
       if (!req.session) {
+        console.log('has no session');
         debug('no session');
-        return _end.call(res, chunk, encoding);
+        return _end.apply(res, endArguments);
       }
 
       if (!touched) {
+        console.log('session was not touched')
         // touch session
         req.session.touch()
         touched = true
       }
 
       if (shouldSave(req)) {
+        console.log('should save')
         req.session.save(function onsave(err) {
           if (err) {
             defer(next, err);
@@ -352,7 +372,7 @@ function session(options) {
         return writetop();
       }
 
-      return _end.call(res, chunk, encoding);
+      return _end.apply(res, endArguments);
     };
 
     // generate the session
diff --git a/package.json b/package.json
index ba2adb65..f0bea203 100644
--- a/package.json
+++ b/package.json
@@ -22,12 +22,9 @@
   "devDependencies": {
     "after": "0.8.2",
     "cookie-parser": "1.4.5",
-    "eslint": "3.19.0",
-    "eslint-plugin-markdown": "1.0.2",
     "express": "4.17.1",
-    "mocha": "7.1.1",
-    "nyc": "15.0.1",
-    "supertest": "4.0.2"
+    "mocha": "2.5.3",
+    "supertest": "1.1.0"
   },
   "files": [
     "session/",
diff --git a/test/session.js b/test/session.js
index b20da863..961d3b37 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,22 +189,39 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  it('should handle res.end(callback) calls', function (done) {
-    var callbackHasBeenCalled = false;
-
-    var server = createServer(null, function (req, res) {
-      function callback() {
-        callbackHasBeenCalled = true;
-      }
-
-      res.end(callback);
-    });
-
-    request(server).get('/').expect(200, '', function () {
-      assert.ok(callbackHasBeenCalled);
-      done();
-    })
-  });
+  // it('should handle res.end(callback) calls', function (done) {
+  //   var callbackHasBeenCalled = false;
+  //
+  //   var server = createServer(null, function (req, res) {
+  //     function callback() {
+  //       callbackHasBeenCalled = true;
+  //     }
+  //
+  //     res.end(callback);
+  //   });
+  //
+  //   request(server).get('/').expect(200, '', function () {
+  //     var nodeVersionStrings = process.versions.node.split('.');
+  //     var nodeVersion = {
+  //       major: Number(nodeVersionStrings[0]),
+  //       minor: Number(nodeVersionStrings[1]),
+  //       patch: Number(nodeVersionStrings[2])
+  //     }
+  //
+  //     console.log('nodejs version', {nodeVersion: nodeVersion });
+  //
+  //     if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+  //       // Node versions prior to 0.11.6 do not support the callback argument
+  //       console.log('callback should NOT be called')
+  //       assert.ok(!callbackHasBeenCalled)
+  //     } else {
+  //       console.log('callback SHOULD be called')
+  //       assert.ok(callbackHasBeenCalled)
+  //     }
+  //
+  //     done()
+  //   })
+  // });
 
   it('should handle res.end(null) calls', function (done) {
     var server = createServer(null, function (req, res) {
@@ -361,7 +378,7 @@ describe('session()', function(){
       })
     })
 
-    it('should have saved session even with multi-write', function (done) {
+    it.only('should have saved session even with multi-write', function (done) {
       var saved = false
       var store = new session.MemoryStore()
       var server = createServer({ store: store }, function (req, res) {

From fa4ba454784a8dbb6f3c76a9ae75de148867a9c2 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Fri, 22 May 2020 17:16:25 +0200
Subject: [PATCH 03/23] --wip-- [skip ci]

---
 index.js        | 26 +++++++++++++++-----------
 test/session.js | 40 ++++++++++++++++++++++------------------
 2 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/index.js b/index.js
index 47b3e369..f8452a5e 100644
--- a/index.js
+++ b/index.js
@@ -247,7 +247,7 @@ function session(options) {
     var _end = res.end;
     var _write = res.write;
     var ended = false;
-    res.end = function end() {
+    res.end = function end(c, e) {
       if (ended) {
         return false;
       }
@@ -257,23 +257,27 @@ function session(options) {
       var ret;
       var sync = true;
 
-      var endArguments = arguments;
+      var endArguments = Array.from(arguments);
+      // var endArguments = arguments;
+      // var chunk = endArguments[0];
+      // var encoding = endArguments[1];
       var chunk = endArguments[0];
       var encoding = endArguments[1];
 
       console.log('about to shuffle arguments', { chunk: chunk, encoding: encoding });
 
-      // Callback may be the 1st (and only), second, or third argument
-      if (typeof chunk === 'function') {
-        console.log('chunk was function');
-        chunk = null;
-        encoding = null;
-      } else if (typeof encoding === 'function') {
-        console.log('encoding was function');
-        encoding = null;
-      }
+      // // Callback may be the 1st (and only), second, or third argument
+      // if (typeof chunk === 'function') {
+      //   console.log('chunk was function');
+      //   chunk = null;
+      //   encoding = null;
+      // } else if (typeof encoding === 'function') {
+      //   console.log('encoding was function');
+      //   encoding = null;
+      // }
 
       function writeend() {
+        console.log('writeend')
         if (sync) {
           ret = _end.apply(res, endArguments);
           sync = false;
diff --git a/test/session.js b/test/session.js
index 961d3b37..66b73b5d 100644
--- a/test/session.js
+++ b/test/session.js
@@ -342,12 +342,12 @@ describe('session()', function(){
       }
 
       request(server)
-      .get('/')
-      .expect(200, 'session saved', function (err) {
-        if (err) return done(err)
-        assert.ok(saved)
-        done()
-      })
+        .get('/')
+        .expect(200, 'session saved', function (err) {
+          if (err) return done(err)
+          assert.ok(saved)
+          done()
+        })
     })
 
     it('should have saved session even with empty response', function (done) {
@@ -370,12 +370,12 @@ describe('session()', function(){
       }
 
       request(server)
-      .get('/')
-      .expect(200, '', function (err) {
-        if (err) return done(err)
-        assert.ok(saved)
-        done()
-      })
+        .get('/')
+        .expect(200, '', function (err) {
+          if (err) return done(err)
+          assert.ok(saved)
+          done()
+        })
     })
 
     it.only('should have saved session even with multi-write', function (done) {
@@ -399,12 +399,15 @@ describe('session()', function(){
       }
 
       request(server)
-      .get('/')
-      .expect(200, 'hello, world', function (err) {
-        if (err) return done(err)
-        assert.ok(saved)
-        done()
-      })
+        .get('/')
+        .expect(200, 'hello, world', function (err) {
+          if (err) {
+            console.error('got err', { err });
+            return done(err)
+          }
+          assert.ok(saved)
+          done()
+        })
     })
 
     it('should have saved session even with non-chunked response', function (done) {
@@ -560,6 +563,7 @@ describe('session()', function(){
       .get('/')
       .expect(shouldSetCookie('sessid'))
       .expect(200, 'session created', function (err, res) {
+        console.log('inside done');
         if (err) return done(err)
         var val = cookie(res).replace(/...\./, '.')
 

From 7f70f947d3d3183c6f9605537e1412e2b8724930 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Fri, 22 May 2020 17:22:30 +0200
Subject: [PATCH 04/23] it works

---
 index.js              | 32 +++++++++++-----------
 test/session.js       | 62 +++++++++++++++++++------------------------
 test/support/utils.js | 12 +++++++++
 3 files changed, 56 insertions(+), 50 deletions(-)

diff --git a/index.js b/index.js
index f8452a5e..6af64aaf 100644
--- a/index.js
+++ b/index.js
@@ -247,7 +247,7 @@ function session(options) {
     var _end = res.end;
     var _write = res.write;
     var ended = false;
-    res.end = function end(c, e) {
+    res.end = function end(chunk, encoding, callback) {
       if (ended) {
         return false;
       }
@@ -257,29 +257,29 @@ function session(options) {
       var ret;
       var sync = true;
 
-      var endArguments = Array.from(arguments);
+      var endArguments = [chunk, encoding, callback];
       // var endArguments = arguments;
       // var chunk = endArguments[0];
       // var encoding = endArguments[1];
-      var chunk = endArguments[0];
-      var encoding = endArguments[1];
 
       console.log('about to shuffle arguments', { chunk: chunk, encoding: encoding });
 
-      // // Callback may be the 1st (and only), second, or third argument
-      // if (typeof chunk === 'function') {
-      //   console.log('chunk was function');
-      //   chunk = null;
-      //   encoding = null;
-      // } else if (typeof encoding === 'function') {
-      //   console.log('encoding was function');
-      //   encoding = null;
-      // }
+      // Callback may be the 1st (and only), second, or third argument
+      if (typeof chunk === 'function') {
+        console.log('chunk was function');
+        callback = chunk;
+        chunk = null;
+        encoding = null;
+      } else if (typeof encoding === 'function') {
+        console.log('encoding was function');
+        callback = encoding;
+        encoding = null;
+      }
 
       function writeend() {
         console.log('writeend')
         if (sync) {
-          ret = _end.apply(res, endArguments);
+          ret = _end.call(res, chunk, encoding, callback);
           sync = false;
           return;
         }
@@ -340,7 +340,7 @@ function session(options) {
       if (!req.session) {
         console.log('has no session');
         debug('no session');
-        return _end.apply(res, endArguments);
+        return _end.call(res, chunk, encoding, callback);
       }
 
       if (!touched) {
@@ -376,7 +376,7 @@ function session(options) {
         return writetop();
       }
 
-      return _end.apply(res, endArguments);
+      return _end.call(res, chunk, encoding, callback);
     };
 
     // generate the session
diff --git a/test/session.js b/test/session.js
index 66b73b5d..c7ca548c 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,39 +189,33 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  // it('should handle res.end(callback) calls', function (done) {
-  //   var callbackHasBeenCalled = false;
-  //
-  //   var server = createServer(null, function (req, res) {
-  //     function callback() {
-  //       callbackHasBeenCalled = true;
-  //     }
-  //
-  //     res.end(callback);
-  //   });
-  //
-  //   request(server).get('/').expect(200, '', function () {
-  //     var nodeVersionStrings = process.versions.node.split('.');
-  //     var nodeVersion = {
-  //       major: Number(nodeVersionStrings[0]),
-  //       minor: Number(nodeVersionStrings[1]),
-  //       patch: Number(nodeVersionStrings[2])
-  //     }
-  //
-  //     console.log('nodejs version', {nodeVersion: nodeVersion });
-  //
-  //     if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-  //       // Node versions prior to 0.11.6 do not support the callback argument
-  //       console.log('callback should NOT be called')
-  //       assert.ok(!callbackHasBeenCalled)
-  //     } else {
-  //       console.log('callback SHOULD be called')
-  //       assert.ok(callbackHasBeenCalled)
-  //     }
-  //
-  //     done()
-  //   })
-  // });
+  it.only('should handle res.end(callback) calls', function (done) {
+    var callbackHasBeenCalled = false;
+
+    var server = createServer(null, function (req, res) {
+      function callback() {
+        callbackHasBeenCalled = true;
+      }
+
+      res.end(callback);
+    });
+
+    request(server).get('/').expect(200, '', function () {
+      const nodeVersion = utils.getNodeVersion();
+
+      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+        // Node versions prior to 0.11.6 do not support the callback argument,
+        // so it should not have been called.
+        console.log('callback should NOT be called')
+        assert.ok(!callbackHasBeenCalled)
+      } else {
+        console.log('callback SHOULD be called')
+        assert.ok(callbackHasBeenCalled)
+      }
+
+      done()
+    })
+  });
 
   it('should handle res.end(null) calls', function (done) {
     var server = createServer(null, function (req, res) {
@@ -378,7 +372,7 @@ describe('session()', function(){
         })
     })
 
-    it.only('should have saved session even with multi-write', function (done) {
+    it('should have saved session even with multi-write', function (done) {
       var saved = false
       var store = new session.MemoryStore()
       var server = createServer({ store: store }, function (req, res) {
diff --git a/test/support/utils.js b/test/support/utils.js
index 0f13ba6a..ea56da35 100644
--- a/test/support/utils.js
+++ b/test/support/utils.js
@@ -2,6 +2,7 @@
 
 module.exports.parseSetCookie = parseSetCookie
 module.exports.writePatch = writePatch
+module.exports.getNodeVersion = getNodeVersion
 
 function parseSetCookie (header) {
   var match
@@ -40,3 +41,14 @@ function writePatch (res) {
     return _write.apply(this, arguments)
   }
 }
+
+function getNodeVersion () {
+  var nodeVersionStrings = process.versions.node.split('.');
+  var nodeVersion = {
+    major: Number(nodeVersionStrings[0]),
+    minor: Number(nodeVersionStrings[1]),
+    patch: Number(nodeVersionStrings[2])
+  }
+
+  return nodeVersion;
+}

From 2c8a4ed8ecd7e5f7cd6f5a9638f61946f266e74b Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:09:16 +0200
Subject: [PATCH 05/23] clean up

---
 test/session.js | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/test/session.js b/test/session.js
index c7ca548c..5c55f5bb 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,7 +189,7 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  it.only('should handle res.end(callback) calls', function (done) {
+  it('should handle res.end(callback) calls', function (done) {
     var callbackHasBeenCalled = false;
 
     var server = createServer(null, function (req, res) {
@@ -395,10 +395,7 @@ describe('session()', function(){
       request(server)
         .get('/')
         .expect(200, 'hello, world', function (err) {
-          if (err) {
-            console.error('got err', { err });
-            return done(err)
-          }
+          if (err) return done(err)
           assert.ok(saved)
           done()
         })

From 38327907cbc0c53f5cf78e3e389826f34298ce2a Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:10:05 +0200
Subject: [PATCH 06/23] remove console.log statements

---
 test/session.js | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/test/session.js b/test/session.js
index 5c55f5bb..ea28a7ff 100644
--- a/test/session.js
+++ b/test/session.js
@@ -206,10 +206,8 @@ describe('session()', function(){
       if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
         // Node versions prior to 0.11.6 do not support the callback argument,
         // so it should not have been called.
-        console.log('callback should NOT be called')
         assert.ok(!callbackHasBeenCalled)
       } else {
-        console.log('callback SHOULD be called')
         assert.ok(callbackHasBeenCalled)
       }
 
@@ -554,7 +552,6 @@ describe('session()', function(){
       .get('/')
       .expect(shouldSetCookie('sessid'))
       .expect(200, 'session created', function (err, res) {
-        console.log('inside done');
         if (err) return done(err)
         var val = cookie(res).replace(/...\./, '.')
 

From e909d4a186bfd5f22a3fca6ff94c5691e8b1c4df Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:12:04 +0200
Subject: [PATCH 07/23] remove more debug stuff

---
 index.js | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/index.js b/index.js
index 6af64aaf..536114e3 100644
--- a/index.js
+++ b/index.js
@@ -257,27 +257,17 @@ function session(options) {
       var ret;
       var sync = true;
 
-      var endArguments = [chunk, encoding, callback];
-      // var endArguments = arguments;
-      // var chunk = endArguments[0];
-      // var encoding = endArguments[1];
-
-      console.log('about to shuffle arguments', { chunk: chunk, encoding: encoding });
-
       // Callback may be the 1st (and only), second, or third argument
       if (typeof chunk === 'function') {
-        console.log('chunk was function');
         callback = chunk;
         chunk = null;
         encoding = null;
       } else if (typeof encoding === 'function') {
-        console.log('encoding was function');
         callback = encoding;
         encoding = null;
       }
 
       function writeend() {
-        console.log('writeend')
         if (sync) {
           ret = _end.call(res, chunk, encoding, callback);
           sync = false;
@@ -321,7 +311,6 @@ function session(options) {
       }
 
       if (shouldDestroy(req)) {
-        console.log('shouldDestroy');
         // destroy session
         debug('destroying');
         store.destroy(req.sessionID, function ondestroy(err) {
@@ -338,20 +327,17 @@ function session(options) {
 
       // no session to save
       if (!req.session) {
-        console.log('has no session');
         debug('no session');
         return _end.call(res, chunk, encoding, callback);
       }
 
       if (!touched) {
-        console.log('session was not touched')
         // touch session
         req.session.touch()
         touched = true
       }
 
       if (shouldSave(req)) {
-        console.log('should save')
         req.session.save(function onsave(err) {
           if (err) {
             defer(next, err);

From 655b36f63c64e1d5680538113a2a31846002f719 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:21:17 +0200
Subject: [PATCH 08/23] minimize diff

---
 .gitignore      |  1 -
 test/session.js | 36 ++++++++++++++++++------------------
 2 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/.gitignore b/.gitignore
index 615e06d4..207febba 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,3 @@
-.idea/
 .nyc_output
 coverage
 node_modules
diff --git a/test/session.js b/test/session.js
index ea28a7ff..a87a590c 100644
--- a/test/session.js
+++ b/test/session.js
@@ -334,12 +334,12 @@ describe('session()', function(){
       }
 
       request(server)
-        .get('/')
-        .expect(200, 'session saved', function (err) {
-          if (err) return done(err)
-          assert.ok(saved)
-          done()
-        })
+      .get('/')
+      .expect(200, 'session saved', function (err) {
+        if (err) return done(err)
+        assert.ok(saved)
+        done()
+      })
     })
 
     it('should have saved session even with empty response', function (done) {
@@ -362,12 +362,12 @@ describe('session()', function(){
       }
 
       request(server)
-        .get('/')
-        .expect(200, '', function (err) {
-          if (err) return done(err)
-          assert.ok(saved)
-          done()
-        })
+      .get('/')
+      .expect(200, '', function (err) {
+        if (err) return done(err)
+        assert.ok(saved)
+        done()
+      })
     })
 
     it('should have saved session even with multi-write', function (done) {
@@ -391,12 +391,12 @@ describe('session()', function(){
       }
 
       request(server)
-        .get('/')
-        .expect(200, 'hello, world', function (err) {
-          if (err) return done(err)
-          assert.ok(saved)
-          done()
-        })
+      .get('/')
+      .expect(200, 'hello, world', function (err) {
+        if (err) return done(err)
+        assert.ok(saved)
+        done()
+      })
     })
 
     it('should have saved session even with non-chunked response', function (done) {

From afa311d728223de2f4af1f09c1e1e2ab9d51ae3a Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:24:35 +0200
Subject: [PATCH 09/23] revert package.json changes

---
 package.json | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/package.json b/package.json
index f0bea203..ba2adb65 100644
--- a/package.json
+++ b/package.json
@@ -22,9 +22,12 @@
   "devDependencies": {
     "after": "0.8.2",
     "cookie-parser": "1.4.5",
+    "eslint": "3.19.0",
+    "eslint-plugin-markdown": "1.0.2",
     "express": "4.17.1",
-    "mocha": "2.5.3",
-    "supertest": "1.1.0"
+    "mocha": "7.1.1",
+    "nyc": "15.0.1",
+    "supertest": "4.0.2"
   },
   "files": [
     "session/",

From b6bce2debe96088786db34ef2ad83352bcabfd11 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 20:26:52 +0200
Subject: [PATCH 10/23] simplify node version test util

---
 test/support/utils.js | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/test/support/utils.js b/test/support/utils.js
index ea56da35..a0ace1ff 100644
--- a/test/support/utils.js
+++ b/test/support/utils.js
@@ -43,12 +43,11 @@ function writePatch (res) {
 }
 
 function getNodeVersion () {
-  var nodeVersionStrings = process.versions.node.split('.');
-  var nodeVersion = {
-    major: Number(nodeVersionStrings[0]),
-    minor: Number(nodeVersionStrings[1]),
-    patch: Number(nodeVersionStrings[2])
-  }
+  var nodeVersionNumbers = process.versions.node.split('.').map(Number);
 
-  return nodeVersion;
+  return {
+    major: nodeVersionNumbers[0],
+    minor: nodeVersionNumbers[1],
+    patch: nodeVersionNumbers[2]
+  }
 }

From 76e3c106e802007ccb22811c0883629e20b144ad Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 21:31:48 +0200
Subject: [PATCH 11/23] test all cases & make it work when passing (data,
 callback)

---
 index.js        |  2 +-
 test/session.js | 54 ++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index 536114e3..d120ff9d 100644
--- a/index.js
+++ b/index.js
@@ -274,7 +274,7 @@ function session(options) {
           return;
         }
 
-        _end.call(res);
+        _end.call(res, callback);
       }
 
       function writetop() {
diff --git a/test/session.js b/test/session.js
index a87a590c..27850f69 100644
--- a/test/session.js
+++ b/test/session.js
@@ -201,7 +201,59 @@ describe('session()', function(){
     });
 
     request(server).get('/').expect(200, '', function () {
-      const nodeVersion = utils.getNodeVersion();
+      var nodeVersion = utils.getNodeVersion();
+
+      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+        // Node versions prior to 0.11.6 do not support the callback argument,
+        // so it should not have been called.
+        assert.ok(!callbackHasBeenCalled)
+      } else {
+        assert.ok(callbackHasBeenCalled)
+      }
+
+      done()
+    })
+  });
+
+  it('should handle res.end(data, callback) calls', function (done) {
+    var callbackHasBeenCalled = false;
+
+    var server = createServer(null, function (req, res) {
+      function callback() {
+        callbackHasBeenCalled = true;
+      }
+
+      res.end('hello', callback);
+    });
+
+    request(server).get('/').expect(200, 'hello', function () {
+      var nodeVersion = utils.getNodeVersion();
+
+      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+        // Node versions prior to 0.11.6 do not support the callback argument,
+        // so it should not have been called.
+        assert.ok(!callbackHasBeenCalled)
+      } else {
+        assert.ok(callbackHasBeenCalled)
+      }
+
+      done()
+    })
+  });
+
+  it('should handle res.end(data, encoding, callback) calls', function (done) {
+    var callbackHasBeenCalled = false;
+
+    var server = createServer(null, function (req, res) {
+      function callback() {
+        callbackHasBeenCalled = true;
+      }
+
+      res.end('hello', 'utf8', callback);
+    });
+
+    request(server).get('/').expect(200, 'hello', function () {
+      var nodeVersion = utils.getNodeVersion();
 
       if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
         // Node versions prior to 0.11.6 do not support the callback argument,

From 3591378df335a990efc5aba384b545c51aa51df1 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 21:35:45 +0200
Subject: [PATCH 12/23] pull tests into describe block

---
 test/session.js | 120 ++++++++++++++++++++++++------------------------
 1 file changed, 61 insertions(+), 59 deletions(-)

diff --git a/test/session.js b/test/session.js
index 27850f69..b7695b7a 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,82 +189,84 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  it('should handle res.end(callback) calls', function (done) {
-    var callbackHasBeenCalled = false;
+  describe('res.end() proxy', function () {
+    it('should correctly handle callback as only argument', function (done) {
+      var callbackHasBeenCalled = false;
 
-    var server = createServer(null, function (req, res) {
-      function callback() {
-        callbackHasBeenCalled = true;
-      }
+      var server = createServer(null, function (req, res) {
+        function callback() {
+          callbackHasBeenCalled = true;
+        }
 
-      res.end(callback);
-    });
+        res.end(callback);
+      });
 
-    request(server).get('/').expect(200, '', function () {
-      var nodeVersion = utils.getNodeVersion();
+      request(server).get('/').expect(200, '', function () {
+        var nodeVersion = utils.getNodeVersion();
 
-      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-        // Node versions prior to 0.11.6 do not support the callback argument,
-        // so it should not have been called.
-        assert.ok(!callbackHasBeenCalled)
-      } else {
-        assert.ok(callbackHasBeenCalled)
-      }
+        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+          // Node versions prior to 0.11.6 do not support the callback argument,
+          // so it should not have been called.
+          assert.ok(!callbackHasBeenCalled)
+        } else {
+          assert.ok(callbackHasBeenCalled)
+        }
 
-      done()
-    })
-  });
+        done()
+      })
+    });
 
-  it('should handle res.end(data, callback) calls', function (done) {
-    var callbackHasBeenCalled = false;
+    it('should correctly handle callback as second argument', function (done) {
+      var callbackHasBeenCalled = false;
 
-    var server = createServer(null, function (req, res) {
-      function callback() {
-        callbackHasBeenCalled = true;
-      }
+      var server = createServer(null, function (req, res) {
+        function callback() {
+          callbackHasBeenCalled = true;
+        }
 
-      res.end('hello', callback);
-    });
+        res.end('hello', callback);
+      });
 
-    request(server).get('/').expect(200, 'hello', function () {
-      var nodeVersion = utils.getNodeVersion();
+      request(server).get('/').expect(200, 'hello', function () {
+        var nodeVersion = utils.getNodeVersion();
 
-      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-        // Node versions prior to 0.11.6 do not support the callback argument,
-        // so it should not have been called.
-        assert.ok(!callbackHasBeenCalled)
-      } else {
-        assert.ok(callbackHasBeenCalled)
-      }
+        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+          // Node versions prior to 0.11.6 do not support the callback argument,
+          // so it should not have been called.
+          assert.ok(!callbackHasBeenCalled)
+        } else {
+          assert.ok(callbackHasBeenCalled)
+        }
 
-      done()
-    })
-  });
+        done()
+      })
+    });
 
-  it('should handle res.end(data, encoding, callback) calls', function (done) {
-    var callbackHasBeenCalled = false;
+    it('should correctly handle callback as third argument', function (done) {
+      var callbackHasBeenCalled = false;
 
-    var server = createServer(null, function (req, res) {
-      function callback() {
-        callbackHasBeenCalled = true;
-      }
+      var server = createServer(null, function (req, res) {
+        function callback() {
+          callbackHasBeenCalled = true;
+        }
 
-      res.end('hello', 'utf8', callback);
-    });
+        res.end('hello', 'utf8', callback);
+      });
 
-    request(server).get('/').expect(200, 'hello', function () {
-      var nodeVersion = utils.getNodeVersion();
+      request(server).get('/').expect(200, 'hello', function () {
+        var nodeVersion = utils.getNodeVersion();
 
-      if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-        // Node versions prior to 0.11.6 do not support the callback argument,
-        // so it should not have been called.
-        assert.ok(!callbackHasBeenCalled)
-      } else {
-        assert.ok(callbackHasBeenCalled)
-      }
+        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
+          // Node versions prior to 0.11.6 do not support the callback argument,
+          // so it should not have been called.
+          assert.ok(!callbackHasBeenCalled)
+        } else {
+          assert.ok(callbackHasBeenCalled)
+        }
 
-      done()
-    })
+        done()
+      })
+    });
   });
 
   it('should handle res.end(null) calls', function (done) {

From 0a5d51a571073aafb29140a83b267c4ef5f09b5e Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 21:41:06 +0200
Subject: [PATCH 13/23] extract node version support stuff to variable

---
 test/session.js | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/test/session.js b/test/session.js
index b7695b7a..560ecf48 100644
--- a/test/session.js
+++ b/test/session.js
@@ -190,6 +190,12 @@ describe('session()', function(){
   })
 
   describe('res.end() proxy', function () {
+    var nodeVersion = utils.getNodeVersion();
+
+    // Node versions prior to 0.11.6 do not support the callback argument,
+    // so the callback should not have been called.
+    var nodeVersionSupportsResEndCallback = nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6));
+
     it('should correctly handle callback as only argument', function (done) {
       var callbackHasBeenCalled = false;
 
@@ -202,11 +208,7 @@ describe('session()', function(){
       });
 
       request(server).get('/').expect(200, '', function () {
-        var nodeVersion = utils.getNodeVersion();
-
-        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-          // Node versions prior to 0.11.6 do not support the callback argument,
-          // so it should not have been called.
+        if (nodeVersionSupportsResEndCallback) {
           assert.ok(!callbackHasBeenCalled)
         } else {
           assert.ok(callbackHasBeenCalled)
@@ -228,11 +230,7 @@ describe('session()', function(){
       });
 
       request(server).get('/').expect(200, 'hello', function () {
-        var nodeVersion = utils.getNodeVersion();
-
-        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-          // Node versions prior to 0.11.6 do not support the callback argument,
-          // so it should not have been called.
+        if (nodeVersionSupportsResEndCallback) {
           assert.ok(!callbackHasBeenCalled)
         } else {
           assert.ok(callbackHasBeenCalled)
@@ -256,9 +254,7 @@ describe('session()', function(){
       request(server).get('/').expect(200, 'hello', function () {
         var nodeVersion = utils.getNodeVersion();
 
-        if (nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6))) {
-          // Node versions prior to 0.11.6 do not support the callback argument,
-          // so it should not have been called.
+        if (nodeVersionSupportsResEndCallback) {
           assert.ok(!callbackHasBeenCalled)
         } else {
           assert.ok(callbackHasBeenCalled)

From f93f99565acc4bb89c9b6ea6e2ed5aabadac5815 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 21:51:30 +0200
Subject: [PATCH 14/23] switch from call to apply

---
 index.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/index.js b/index.js
index d120ff9d..53e1269a 100644
--- a/index.js
+++ b/index.js
@@ -269,12 +269,12 @@ function session(options) {
 
       function writeend() {
         if (sync) {
-          ret = _end.call(res, chunk, encoding, callback);
+          ret = _end.apply(res, [chunk, encoding, callback]);
           sync = false;
           return;
         }
 
-        _end.call(res, callback);
+        _end.apply(res, [callback]);
       }
 
       function writetop() {
@@ -328,7 +328,7 @@ function session(options) {
       // no session to save
       if (!req.session) {
         debug('no session');
-        return _end.call(res, chunk, encoding, callback);
+        return _end.apply(res, [chunk, encoding, callback]);
       }
 
       if (!touched) {
@@ -362,7 +362,7 @@ function session(options) {
         return writetop();
       }
 
-      return _end.call(res, chunk, encoding, callback);
+      return _end.apply(res, [chunk, encoding, callback]);
     };
 
     // generate the session

From 6e88688bcc5b4d25b5142a74f6a295efeaaac0cb Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@lehmann.tech>
Date: Tue, 26 May 2020 22:06:16 +0200
Subject: [PATCH 15/23] mutate arguments to Make It Work

---
 index.js | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/index.js b/index.js
index 53e1269a..3d5aed84 100644
--- a/index.js
+++ b/index.js
@@ -257,6 +257,8 @@ function session(options) {
       var ret;
       var sync = true;
 
+      var endArgs = arguments;
+
       // Callback may be the 1st (and only), second, or third argument
       if (typeof chunk === 'function') {
         callback = chunk;
@@ -269,7 +271,7 @@ function session(options) {
 
       function writeend() {
         if (sync) {
-          ret = _end.apply(res, [chunk, encoding, callback]);
+          ret = _end.apply(res, endArgs);
           sync = false;
           return;
         }
@@ -294,12 +296,15 @@ function session(options) {
           chunk = !Buffer.isBuffer(chunk)
             ? Buffer.from(chunk, encoding)
             : chunk;
+          endArgs[0] = chunk;
           encoding = undefined;
+          endArgs[1] = encoding;
 
           if (chunk.length !== 0) {
             debug('split response');
             ret = _write.call(res, chunk.slice(0, chunk.length - 1));
             chunk = chunk.slice(chunk.length - 1, chunk.length);
+            endArgs[0] = chunk;
             return ret;
           }
         }
@@ -328,7 +333,7 @@ function session(options) {
       // no session to save
       if (!req.session) {
         debug('no session');
-        return _end.apply(res, [chunk, encoding, callback]);
+        return _end.apply(res, endArgs);
       }
 
       if (!touched) {
@@ -362,7 +367,7 @@ function session(options) {
         return writetop();
       }
 
-      return _end.apply(res, [chunk, encoding, callback]);
+      return _end.apply(res, endArgs);
     };
 
     // generate the session

From 647edce5f952d3c3426f17b524e2c33555078a54 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Wed, 27 May 2020 14:45:01 +0200
Subject: [PATCH 16/23] update

---
 test/session.js | 81 ++++++++++++++++++++++++++++---------------------
 1 file changed, 46 insertions(+), 35 deletions(-)

diff --git a/test/session.js b/test/session.js
index 560ecf48..6e7bef47 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,81 +189,91 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  describe('res.end() proxy', function () {
+  describe.only('res.end() proxy', function () {
     var nodeVersion = utils.getNodeVersion();
 
-    // Node versions prior to 0.11.6 do not support the callback argument,
-    // so the callback should not have been called.
-    var nodeVersionSupportsResEndCallback = nodeVersion.major === 0 && (nodeVersion.minor < 11 || (nodeVersion.minor === 11 && nodeVersion.patch < 6));
+    // Node versions prior to 0.11.6 do not explicitly support the callback argument.
+    // These versions, if given a callback as the…
+    //   - first argument, throw a TypeError
+    //   - second argument, execute the callback (by accident)
+    //   - third argument, ignore the callback
+    var nodeVersionSupportsResEndCallback = nodeVersion.major > 0 || nodeVersion.minor > 11 || (nodeVersion.minor === 11 && nodeVersion.patch >= 6);
 
     it('should correctly handle callback as only argument', function (done) {
-      var callbackHasBeenCalled = false;
+      var callbackHasBeenCalled = false
 
       var server = createServer(null, function (req, res) {
         function callback() {
-          callbackHasBeenCalled = true;
+          callbackHasBeenCalled = true
         }
 
-        res.end(callback);
+        try {
+          res.end(callback)
+        } catch (err) {
+          // The res#end proxy passes on the arguments exactly as provided,
+          // so we expect a TypeError in versions that don't support the callback.
+          // This is a way of notifying the test client that an error occurred.
+          res.writeHead(500)
+          res.end(err.message)
+        }
       });
 
-      request(server).get('/').expect(200, '', function () {
-        if (nodeVersionSupportsResEndCallback) {
-          assert.ok(!callbackHasBeenCalled)
-        } else {
-          assert.ok(callbackHasBeenCalled)
-        }
+      var call = request(server).get('/');
 
-        done()
-      })
+      if (nodeVersionSupportsResEndCallback) {
+        call.expect(200, '', function () {
+          assert.ok(callbackHasBeenCalled)
+          done()
+        })
+      } else {
+        call.expect(500, 'first argument must be a string or Buffer', done)
+      }
     });
 
     it('should correctly handle callback as second argument', function (done) {
-      var callbackHasBeenCalled = false;
+      var callbackHasBeenCalled = false
 
       var server = createServer(null, function (req, res) {
         function callback() {
-          callbackHasBeenCalled = true;
+          callbackHasBeenCalled = true
         }
 
-        res.end('hello', callback);
+        res.end('hello', callback)
       });
 
       request(server).get('/').expect(200, 'hello', function () {
-        if (nodeVersionSupportsResEndCallback) {
-          assert.ok(!callbackHasBeenCalled)
-        } else {
-          assert.ok(callbackHasBeenCalled)
-        }
-
+        // Passing the callback as the second argument works on all versions of Node,
+        // seemingly by accident. The encoding parameter is passed to afterWrite,
+        // which supports that it might be a callback.
+        assert.ok(callbackHasBeenCalled)
         done()
       })
-    });
+    })
 
     it('should correctly handle callback as third argument', function (done) {
-      var callbackHasBeenCalled = false;
+      var callbackHasBeenCalled = false
 
       var server = createServer(null, function (req, res) {
         function callback() {
-          callbackHasBeenCalled = true;
+          callbackHasBeenCalled = true
         }
 
-        res.end('hello', 'utf8', callback);
+        res.end('hello', 'utf8', callback)
       });
 
       request(server).get('/').expect(200, 'hello', function () {
-        var nodeVersion = utils.getNodeVersion();
-
+        // The third argument is completely ignored on Node versions
+        // that do not support the callback.
         if (nodeVersionSupportsResEndCallback) {
-          assert.ok(!callbackHasBeenCalled)
-        } else {
           assert.ok(callbackHasBeenCalled)
+        } else {
+          assert.ok(!callbackHasBeenCalled)
         }
 
         done()
       })
-    });
-  });
+    })
+  })
 
   it('should handle res.end(null) calls', function (done) {
     var server = createServer(null, function (req, res) {
@@ -2367,8 +2377,9 @@ function createServer (options, respond) {
 }
 
 function createRequestListener(opts, fn) {
-  var _session = createSession(opts)
+  // var _session = createSession(opts)
   var respond = fn || end
+  var _session = respond;
 
   return function onRequest(req, res) {
     var server = this

From 94a85cd3bd9206affe64c1fce29bccfe6737130c Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Wed, 27 May 2020 15:13:50 +0200
Subject: [PATCH 17/23] what

---
 index.js        | 32 +++++++++++++++++++++++---------
 test/session.js |  9 ++++-----
 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/index.js b/index.js
index 3d5aed84..1c578a07 100644
--- a/index.js
+++ b/index.js
@@ -259,14 +259,26 @@ function session(options) {
 
       var endArgs = arguments;
 
-      // Callback may be the 1st (and only), second, or third argument
-      if (typeof chunk === 'function') {
-        callback = chunk;
-        chunk = null;
-        encoding = null;
-      } else if (typeof encoding === 'function') {
-        callback = encoding;
-        encoding = null;
+      var callbackArgumentIndex = typeof chunk === 'function'
+        ? 0
+        : typeof encoding === 'function'
+        ? 1
+        : 2;
+
+      // Callback may be the first, second, or third argument.
+      // If provided, it must be the last argument.
+      switch (callbackArgumentIndex) {
+        case 0: {
+          callback = chunk;
+          chunk = null;
+          encoding = null;
+          break;
+        }
+        case 1: {
+          callback = encoding;
+          encoding = null;
+          break;
+        }
       }
 
       function writeend() {
@@ -276,7 +288,9 @@ function session(options) {
           return;
         }
 
-        _end.apply(res, [callback]);
+        var argumentsWithoutChunkOrEncoding = [null, null, null];
+        argumentsWithoutChunkOrEncoding[callbackArgumentIndex] = callback;
+        _end.apply(res, argumentsWithoutChunkOrEncoding);
       }
 
       function writetop() {
diff --git a/test/session.js b/test/session.js
index 6e7bef47..43b7a3c5 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,7 +189,7 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  describe.only('res.end() proxy', function () {
+  describe('res.end() proxy', function () {
     var nodeVersion = utils.getNodeVersion();
 
     // Node versions prior to 0.11.6 do not explicitly support the callback argument.
@@ -235,6 +235,7 @@ describe('session()', function(){
 
       var server = createServer(null, function (req, res) {
         function callback() {
+          console.log('what');
           callbackHasBeenCalled = true
         }
 
@@ -243,8 +244,7 @@ describe('session()', function(){
 
       request(server).get('/').expect(200, 'hello', function () {
         // Passing the callback as the second argument works on all versions of Node,
-        // seemingly by accident. The encoding parameter is passed to afterWrite,
-        // which supports that it might be a callback.
+        // seemingly by accident.
         assert.ok(callbackHasBeenCalled)
         done()
       })
@@ -2377,9 +2377,8 @@ function createServer (options, respond) {
 }
 
 function createRequestListener(opts, fn) {
-  // var _session = createSession(opts)
+  var _session = createSession(opts)
   var respond = fn || end
-  var _session = respond;
 
   return function onRequest(req, res) {
     var server = this

From c9abb7e3b960b680ab5c8f4ddc07d6839ad5d4a6 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Wed, 27 May 2020 15:18:26 +0200
Subject: [PATCH 18/23] wat

---
 index.js        | 19 +++++++------------
 test/session.js |  2 +-
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/index.js b/index.js
index 1c578a07..87348a4f 100644
--- a/index.js
+++ b/index.js
@@ -267,18 +267,13 @@ function session(options) {
 
       // Callback may be the first, second, or third argument.
       // If provided, it must be the last argument.
-      switch (callbackArgumentIndex) {
-        case 0: {
-          callback = chunk;
-          chunk = null;
-          encoding = null;
-          break;
-        }
-        case 1: {
-          callback = encoding;
-          encoding = null;
-          break;
-        }
+      if (callbackArgumentIndex === 0) {
+        callback = chunk;
+        chunk = null;
+        encoding = null;
+      } else if (callbackArgumentIndex === 1) {
+        callback = encoding;
+        encoding = null;
       }
 
       function writeend() {
diff --git a/test/session.js b/test/session.js
index 43b7a3c5..f9505188 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,7 +189,7 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  describe('res.end() proxy', function () {
+  describe.only('res.end() proxy', function () {
     var nodeVersion = utils.getNodeVersion();
 
     // Node versions prior to 0.11.6 do not explicitly support the callback argument.

From 5fce3e3dac1e23697d42f937a8663de59c0c8d6f Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Wed, 27 May 2020 17:53:33 +0200
Subject: [PATCH 19/23] still WIP

---
 index.js        | 21 ++++++++++++++++++---
 test/session.js | 50 +++++++++++++++++++++++++------------------------
 2 files changed, 44 insertions(+), 27 deletions(-)

diff --git a/index.js b/index.js
index 87348a4f..13ece8cc 100644
--- a/index.js
+++ b/index.js
@@ -265,6 +265,7 @@ function session(options) {
         ? 1
         : 2;
 
+      debug('callbackArgumentIndex', callbackArgumentIndex)
       // Callback may be the first, second, or third argument.
       // If provided, it must be the last argument.
       if (callbackArgumentIndex === 0) {
@@ -277,6 +278,7 @@ function session(options) {
       }
 
       function writeend() {
+        debug('writeend', { sync: sync })
         if (sync) {
           ret = _end.apply(res, endArgs);
           sync = false;
@@ -285,6 +287,7 @@ function session(options) {
 
         var argumentsWithoutChunkOrEncoding = [null, null, null];
         argumentsWithoutChunkOrEncoding[callbackArgumentIndex] = callback;
+        debug('applying _end with', { argumentsWithoutChunkOrEncoding: argumentsWithoutChunkOrEncoding })
         _end.apply(res, argumentsWithoutChunkOrEncoding);
       }
 
@@ -333,7 +336,11 @@ function session(options) {
           }
 
           debug('destroyed');
-          writeend();
+          try {
+            writeend();
+          } catch (err) {
+            next(err);
+          }
         });
 
         return writetop();
@@ -357,7 +364,11 @@ function session(options) {
             defer(next, err);
           }
 
-          writeend();
+          try {
+            writeend();
+          } catch (err) {
+            next(err);
+          }
         });
 
         return writetop();
@@ -370,7 +381,11 @@ function session(options) {
           }
 
           debug('touched');
-          writeend();
+          try {
+            writeend();
+          } catch (err) {
+            next(err);
+          }
         });
 
         return writetop();
diff --git a/test/session.js b/test/session.js
index f9505188..c27aa72d 100644
--- a/test/session.js
+++ b/test/session.js
@@ -189,7 +189,7 @@ describe('session()', function(){
     .expect(200, 'Hello, world!', done);
   })
 
-  describe.only('res.end() proxy', function () {
+  describe('res.end() proxy', function () {
     var nodeVersion = utils.getNodeVersion();
 
     // Node versions prior to 0.11.6 do not explicitly support the callback argument.
@@ -207,30 +207,24 @@ describe('session()', function(){
           callbackHasBeenCalled = true
         }
 
-        try {
-          res.end(callback)
-        } catch (err) {
-          // The res#end proxy passes on the arguments exactly as provided,
-          // so we expect a TypeError in versions that don't support the callback.
-          // This is a way of notifying the test client that an error occurred.
-          res.writeHead(500)
-          res.end(err.message)
-        }
-      });
-
-      var call = request(server).get('/');
-
-      if (nodeVersionSupportsResEndCallback) {
-        call.expect(200, '', function () {
-          assert.ok(callbackHasBeenCalled)
+        server.once('error', function onerror (err) {
+          assert.ok(err)
+          assert.strictEqual(err.message, 'first argument must be a string or Buffer')
           done()
         })
-      } else {
-        call.expect(500, 'first argument must be a string or Buffer', done)
-      }
+
+        res.end(callback)
+      });
+
+      request(server)
+      .get('/')
+      .expect(200, '', function () {
+        assert.ok(callbackHasBeenCalled)
+        done()
+      })
     });
 
-    it('should correctly handle callback as second argument', function (done) {
+    it.only('should correctly handle callback as second argument', function (done) {
       var callbackHasBeenCalled = false
 
       var server = createServer(null, function (req, res) {
@@ -239,11 +233,17 @@ describe('session()', function(){
           callbackHasBeenCalled = true
         }
 
+        console.log('ending');
         res.end('hello', callback)
       });
 
-      request(server).get('/').expect(200, 'hello', function () {
-        // Passing the callback as the second argument works on all versions of Node,
+      request(server).get('/').expect(200, 'hello', function (err, response) {
+        if (err) {
+          console.log('err', err);
+        }
+        console.log('response', response.text);
+
+        // Passing the callback as the second argument works on all Node versions,
         // seemingly by accident.
         assert.ok(callbackHasBeenCalled)
         done()
@@ -267,7 +267,7 @@ describe('session()', function(){
         if (nodeVersionSupportsResEndCallback) {
           assert.ok(callbackHasBeenCalled)
         } else {
-          assert.ok(!callbackHasBeenCalled)
+          assert.strictEqual(callbackHasBeenCalled, false)
         }
 
         done()
@@ -2384,6 +2384,7 @@ function createRequestListener(opts, fn) {
     var server = this
 
     _session(req, res, function (err) {
+      console.log('err inside _session next', err)
       if (err && !res._header) {
         res.statusCode = err.status || 500
         res.end(err.message)
@@ -2395,6 +2396,7 @@ function createRequestListener(opts, fn) {
         return
       }
 
+      console.log('calling respond')
       respond(req, res)
     })
   }

From d4856f82efcf3acc4dfcf9d96945a1c89074f860 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Thu, 28 May 2020 13:39:55 +0200
Subject: [PATCH 20/23] clean up

---
 index.js        | 14 +++++++++-----
 test/session.js | 28 ++++++++++++----------------
 2 files changed, 21 insertions(+), 21 deletions(-)

diff --git a/index.js b/index.js
index 13ece8cc..14e777e5 100644
--- a/index.js
+++ b/index.js
@@ -257,17 +257,18 @@ function session(options) {
       var ret;
       var sync = true;
 
+      // Keep a reference to the original arguments so we can preserve their
+      // order when passing them on to the original _end()
       var endArgs = arguments;
 
+      // The callback argument is optional. If provided, it may be the
+      // first, second, or third argument, and must be the last argument.
       var callbackArgumentIndex = typeof chunk === 'function'
         ? 0
         : typeof encoding === 'function'
         ? 1
         : 2;
 
-      debug('callbackArgumentIndex', callbackArgumentIndex)
-      // Callback may be the first, second, or third argument.
-      // If provided, it must be the last argument.
       if (callbackArgumentIndex === 0) {
         callback = chunk;
         chunk = null;
@@ -278,16 +279,19 @@ function session(options) {
       }
 
       function writeend() {
-        debug('writeend', { sync: sync })
         if (sync) {
           ret = _end.apply(res, endArgs);
           sync = false;
           return;
         }
 
+        // This differs very slightly from (undocumented) Node behaviour in versions
+        // prior to 0.11.6 (which introduced callback support), because we explicitly
+        // call write() followed by end().
+        // The behaviour seems unintentional, as the callback is invoked immediately
+        // after write(), as opposed to after end().
         var argumentsWithoutChunkOrEncoding = [null, null, null];
         argumentsWithoutChunkOrEncoding[callbackArgumentIndex] = callback;
-        debug('applying _end with', { argumentsWithoutChunkOrEncoding: argumentsWithoutChunkOrEncoding })
         _end.apply(res, argumentsWithoutChunkOrEncoding);
       }
 
diff --git a/test/session.js b/test/session.js
index c27aa72d..1d1d6224 100644
--- a/test/session.js
+++ b/test/session.js
@@ -192,11 +192,7 @@ describe('session()', function(){
   describe('res.end() proxy', function () {
     var nodeVersion = utils.getNodeVersion();
 
-    // Node versions prior to 0.11.6 do not explicitly support the callback argument.
-    // These versions, if given a callback as the…
-    //   - first argument, throw a TypeError
-    //   - second argument, execute the callback (by accident)
-    //   - third argument, ignore the callback
+    // Support for the callback argument was added in Node 0.11.6.
     var nodeVersionSupportsResEndCallback = nodeVersion.major > 0 || nodeVersion.minor > 11 || (nodeVersion.minor === 11 && nodeVersion.patch >= 6);
 
     it('should correctly handle callback as only argument', function (done) {
@@ -229,23 +225,25 @@ describe('session()', function(){
 
       var server = createServer(null, function (req, res) {
         function callback() {
-          console.log('what');
           callbackHasBeenCalled = true
         }
 
-        console.log('ending');
         res.end('hello', callback)
       });
 
-      request(server).get('/').expect(200, 'hello', function (err, response) {
-        if (err) {
-          console.log('err', err);
+      request(server).get('/').expect(200, 'hello', function () {
+        if (nodeVersionSupportsResEndCallback) {
+          assert.ok(callbackHasBeenCalled)
+        } else {
+          // This is (very slightly) different from the default Node behaviour,
+          // where the callback is invoked if `chunk` is a non-empty string or Buffer.
+          // This behaviour is undocumented, and seemingly happens unintentionally
+          // when the chunk and encoding are passed to write(), and in turn to
+          // afterWrite(), which considers the encoding argument to possibly be
+          // a function, and invokes it.
+          assert.strictEqual(callbackHasBeenCalled, false)
         }
-        console.log('response', response.text);
 
-        // Passing the callback as the second argument works on all Node versions,
-        // seemingly by accident.
-        assert.ok(callbackHasBeenCalled)
         done()
       })
     })
@@ -2384,7 +2382,6 @@ function createRequestListener(opts, fn) {
     var server = this
 
     _session(req, res, function (err) {
-      console.log('err inside _session next', err)
       if (err && !res._header) {
         res.statusCode = err.status || 500
         res.end(err.message)
@@ -2396,7 +2393,6 @@ function createRequestListener(opts, fn) {
         return
       }
 
-      console.log('calling respond')
       respond(req, res)
     })
   }

From a5b85af36977f505b6dfb03b1ccd2cd319bdeaa1 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Thu, 28 May 2020 13:43:46 +0200
Subject: [PATCH 21/23] don't use .only

---
 test/session.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/session.js b/test/session.js
index 1d1d6224..26c69fc1 100644
--- a/test/session.js
+++ b/test/session.js
@@ -220,7 +220,7 @@ describe('session()', function(){
       })
     });
 
-    it.only('should correctly handle callback as second argument', function (done) {
+    it('should correctly handle callback as second argument', function (done) {
       var callbackHasBeenCalled = false
 
       var server = createServer(null, function (req, res) {

From 3a5df79c1892ac6fa8cbd04381c80299d0aa07ae Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Thu, 28 May 2020 13:57:37 +0200
Subject: [PATCH 22/23] don't overwrite second argument if it isn't encoding

---
 index.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 14e777e5..12f94815 100644
--- a/index.js
+++ b/index.js
@@ -314,7 +314,9 @@ function session(options) {
             : chunk;
           endArgs[0] = chunk;
           encoding = undefined;
-          endArgs[1] = encoding;
+          if (callbackArgumentIndex !== 1) {
+            endArgs[1] = encoding;
+          }
 
           if (chunk.length !== 0) {
             debug('split response');

From a578c5010ebeefea7aa3b348cbad559d2cdb1f99 Mon Sep 17 00:00:00 2001
From: Martin Lehmann <martin@folio.no>
Date: Thu, 28 May 2020 14:29:54 +0200
Subject: [PATCH 23/23] don't assert or call done if not required

---
 test/session.js | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/test/session.js b/test/session.js
index 26c69fc1..f7e4b01f 100644
--- a/test/session.js
+++ b/test/session.js
@@ -203,7 +203,7 @@ describe('session()', function(){
           callbackHasBeenCalled = true
         }
 
-        server.once('error', function onerror (err) {
+        server.on('error', function onerror (err) {
           assert.ok(err)
           assert.strictEqual(err.message, 'first argument must be a string or Buffer')
           done()
@@ -215,8 +215,12 @@ describe('session()', function(){
       request(server)
       .get('/')
       .expect(200, '', function () {
-        assert.ok(callbackHasBeenCalled)
-        done()
+        if (nodeVersionSupportsResEndCallback) {
+          // If the Node version does not support the callback,
+          // the error listener will make the necessary assertions.
+          assert.ok(callbackHasBeenCalled)
+          done()
+        }
       })
     });