Adding Promise support for "getHost".

README.md

@@ -172,8 +172,11 @@ E.g.,
 ```js
 
   function coinToss() { return Math.random() > .5 }
-  function getHost() { return coinToss() ? 'http://yahoo.com' : 'http://google.com' }
-
+  function getHost() {
+    var host = coinToss() ? 'http://yahoo.com' : 'http://google.com';
+    return coinToss() ? Promise.resolve(host) : host;
+  }
+
   app.use(proxy(getHost, {
     memoizeHost: false
   }))
@@ -451,7 +454,7 @@ app.use('/', proxy('internalhost.example.com', {
     proxyReqOpts.ca =  [caCert, intermediaryCert]
     return proxyReqOpts;
   }
-})
+}))
 ```
 
 

app/steps/resolveProxyHost.js

@@ -2,18 +2,20 @@
 var requestOptions = require('../../lib/requestOptions');
 
 function resolveProxyHost(container) {
-  var parsedHost;
+  var promise;
 
   if (container.options.memoizeHost && container.options.memoizedHost) {
-    parsedHost = container.options.memoizedHost;
+    promise = Promise.resolve(container.options.memoizedHost);
   } else {
-    parsedHost = requestOptions.parseHost(container);
+    promise = Promise.resolve(requestOptions.parseHost(container));
   }
 
-  container.proxy.reqBuilder.host = parsedHost.host;
-  container.proxy.reqBuilder.port = container.options.port || parsedHost.port;
-  container.proxy.requestModule = parsedHost.module;
-  return Promise.resolve(container);
+  return promise.then(function(parsedHost) {
+    container.proxy.reqBuilder.host = parsedHost.host;
+    container.proxy.reqBuilder.port = container.options.port || parsedHost.port;
+    container.proxy.requestModule = parsedHost.module;
+    return container;
+  });
 }
 
 module.exports = resolveProxyHost;

lib/requestOptions.js

@@ -24,29 +24,34 @@ function parseHost(Container) {
   var host = Container.params.host;
   var req =  Container.user.req;
   var options = Container.options;
-  host = (typeof host === 'function') ? host(req) : host.toString();
-
-  if (!host) {
-    return new Error('Empty host parameter');
-  }
-
-  if (!/http(s)?:\/\//.test(host)) {
-    host = 'http://' + host;
-  }
-
-  var parsed = url.parse(host);
-
-  if (!parsed.hostname) {
-    return new Error('Unable to parse hostname, possibly missing protocol://?');
-  }
-
-  var ishttps = options.https || parsed.protocol === 'https:';
-
-  return {
-    host: parsed.hostname,
-    port: parsed.port || (ishttps ? 443 : 80),
-    module: ishttps ? https : http,
-  };
+  host = (typeof host === 'function') ? host(req) : host;
+
+  return Promise
+    .resolve(host)
+    .then(function(host) {
+      if (!host) {
+        throw new Error('Empty host parameter');
+      }
+      host = host.toString();
+
+      if (!/http(s)?:\/\//.test(host)) {
+        host = 'http://' + host;
+      }
+
+      var parsed = url.parse(host);
+
+      if (!parsed.hostname) {
+        return new Error('Unable to parse hostname, possibly missing protocol://?');
+      }
+
+      var ishttps = options.https || parsed.protocol === 'https:';
+
+      return {
+        host: parsed.hostname,
+        port: parsed.port || (ishttps ? 443 : 80),
+        module: ishttps ? https : http,
+      };
+  });
 }
 
 function reqHeaders(req, options) {

test/host.js

@@ -45,3 +45,29 @@ describe('host can be a dynamic function', function() {
       });
   });
 });
+
+describe('host is a promise', function() {
+
+  this.timeout(10000);
+
+  var app = express();
+  var proxyApp = express();
+  var port = Math.floor(Math.random() * 10000);
+
+  var hostFn = function(req) {
+    return Promise.resolve('localhost:' + req.params.port);
+  };
+
+  app.use('/proxy-promise/:port', proxy(hostFn, { memoizeHost: false }));
+
+  proxyApp
+    .get('/', function(req, res) { res.sendStatus(201); })
+    .listen(port);
+
+  it('host returns a promise that should be resolved and its value is the host URL.', function(done) {
+    request(app)
+      .get('/proxy-promise/' + port)
+      .expect(201)
+      .end(done);
+  });
+});