Skip host check if scheme is explicitly set

Fixes https://github.com/Rob--W/cors-anywhere/issues/14

This allows CORS anywhere to be forwards-compatible with the surge
of new gTLDs.

lib/cors-anywhere.js

@@ -258,7 +258,7 @@ var getHandler = exports.getHandler = function(options, proxy) {
       return;
     }
 
-    if (!isValidHostName(location.hostname)) {
+    if (!/^\/https?:/.test(req.url) && !isValidHostName(location.hostname)) {
       // Don't even try to proxy invalid hosts (such as /favicon.ico, /robots.txt)
       res.writeHead(404, 'Invalid host', cors_headers);
       res.end('Invalid host: ' + location.hostname);

test/setup.js

@@ -97,3 +97,7 @@ echoheaders('http://example.com');
 echoheaders('http://example.com:1337');
 echoheaders('https://example.com');
 echoheaders('https://example.com:1337');
+
+nock('http://robots.txt')
+  .get('/')
+  .reply(200, 'this is http://robots.txt');

test/test.js

@@ -78,6 +78,13 @@ describe('Basic functionality', function() {
       .expect(404, 'Invalid host: robots.txt', done);
   });
 
+  it('GET /http://robots.txt should be proxied', function(done) {
+    request(cors_anywhere)
+      .get('/http://robots.txt')
+      .expect('Access-Control-Allow-Origin', '*')
+      .expect(200, 'this is http://robots.txt', done);
+  });
+
   it('GET /example.com', function(done) {
     request(cors_anywhere)
       .get('/example.com')