Extract middleware served by host header

lib/cartodb/middleware/served-by-host-header.js

@@ -0,0 +1,11 @@
+const os = require('os');
+
+module.exports = function servedByHostHeader () {
+    const hostname = os.hostname().split('.')[0];
+
+    return function servedByHostHeaderMiddleware (req, res, next) {
+        res.set('X-Served-By-Host', hostname);
+
+        next();
+    };
+};

lib/cartodb/server.js

@@ -50,6 +50,7 @@ var StatsBackend = require('./backends/stats');
 
 const lzmaMiddleware = require('./middleware/lzma');
 const errorMiddleware = require('./middleware/error-middleware');
+const servedByHostHeader = require('./middleware/served-by-host-header');
 
 module.exports = function(serverOptions) {
     // Make stats client globally accessible
@@ -364,13 +365,7 @@ function bootstrap(opts) {
 
     app.use(bodyParser.json());
 
-    app.use(function bootstrap$prepareRequestResponse(req, res, next) {
-        if (global.environment && global.environment.api_hostname) {
-            res.set('X-Served-By-Host', global.environment.api_hostname);
-        }
-
-        next();
-    });
+    app.use(servedByHostHeader());
 
     app.use(stats({
         enabled: opts.useProfiler,