listen to 'error' event on the server until listen has finished

fastify.js

@@ -170,13 +170,26 @@ function build (options) {
       if (listening) {
         return _cb(new Error('Fastify is already listening'))
       }
+
+      server.on('error', wrap)
       if (hasAddress) {
-        server.listen(port, address, _cb)
+        server.listen(port, address, wrap)
       } else {
-        server.listen(port, _cb)
+        server.listen(port, wrap)
       }
       listening = true
     })
+
+    function wrap (err) {
+      server.removeListener('error', wrap)
+      if (_cb) {
+        _cb(err)
+      } else {
+        // this will crash the process
+        // it will go to 'uncaughtException'
+        throw err
+      }
+    }
   }
 
   function startHooks (req, res, params, store) {

test/listen.test.js

@@ -72,3 +72,16 @@ test('double listen errors', t => {
     })
   })
 })
+
+test('listen twice on the same port', t => {
+  t.plan(2)
+  const fastify = Fastify()
+  fastify.listen(0, (err) => {
+    t.error(err)
+    const s2 = Fastify()
+    s2.listen(fastify.server.address().port, (err) => {
+      fastify.close()
+      t.ok(err)
+    })
+  })
+})