Add extra documentation (in code).

Removed ? from path's regexp, because
"http://cors-anywhere/" + "/domain.com/file" =
"http://cors-anywhere//domain.com/file" SHOULD be an invalid request.

"//domain.com/file" can be resolved to "http://domain.com/file", but
"/domain.com/file" should resolved to http://host/domain.com/file,
but since the host is unknown, the API should just fail.

lib/cors-anywhere.js

@@ -30,8 +30,13 @@ function showUsage(headers, response) {
   }
 }
 
+/**
+ * Check whether the specified hostname is valid.
+ *
+ * @param hostname {string} Host name (excluding port) of requested resource.
+ * @return {boolean} Whether the requested resource can be accessed.
+ */
 function hasNoContent(hostname) {
-  // Show 404 for non-requests. For instance when hostname is favicon.ico, robots.txt, ...
   return !(
     regexp_tld.test(hostname) ||
     net.isIPv4(hostname) ||
@@ -39,8 +44,12 @@ function hasNoContent(hostname) {
   );
 }
 
-// First argument: The response.headers object
-// Second argument: The request object.
+/**
+ * Adds CORS headers to the response headers.
+ *
+ * @param headers {object} Response headers
+ * @param request {ServerRequest}
+ */
 function withCORS(headers, request) {
   var origin = request.headers.origin || 'null';
   headers['access-control-allow-origin'] = origin === 'null' ? '*' : origin;
@@ -61,9 +70,23 @@ function withCORS(headers, request) {
 
   return headers;
 }
+
+/**
+ * @param host {string} Host name (excluding port) of requested resource
+ */
 function isForbidden(host) {
   return false; // TODO
 }
+
+/**
+ * Performs the actual proxy request.
+ *
+ * @param req {ServerRequest} Incoming http request
+ * @param res {ServerResponse} Outgoing (proxied) http request
+ * @param proxy {HttpProxy}
+ * @param full_url {string} Canonical URL of outgoing (proxied) http request.
+ * @param isRequestedOverHttps {boolean} Whether the incoming request originates from https
+ */
 function proxyRequest(req, res, proxy, full_url, isRequestedOverHttps, proxyOptions) {
   if (isForbidden(proxyOptions.host)) {
     res.writeHead(403, 'Refused to visit', withCORS({'Location': full_url}, req));
@@ -142,7 +165,7 @@ var getHandler = exports.getHandler = function(options) {
     } else {
       // Actual request. First, extract the desired URL from the request:
       var full_url, host, hostname, port, path, match, isHttps;
-      match = req.url.match(/^\/?(?:(https?:)?\/\/)?(([^\/?]+?)(?::(\d{0,5})(?=[\/?]|$))?)([\/?][\S\s]*|$)/i);
+      match = req.url.match(/^\/(?:(https?:)?\/\/)?(([^\/?]+?)(?::(\d{0,5})(?=[\/?]|$))?)([\/?][\S\s]*|$)/i);
       //                            ^^^^^^^          ^^^^^^^^      ^^^^^^^                ^^^^^^^^^^^^
       //                          1:protocol       3:hostname     4:port                 5:path + query string
       //                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -162,12 +185,12 @@ var getHandler = exports.getHandler = function(options) {
       } else if (match[4] > 65535) {
         // Port is higher than 65535
         res.writeHead(400, 'Invalid port', cors_headers);
-        res.end();
+        res.end('Invalid port: ' + match[4]);
         return;
       } else if ( hasNoContent(match[3]) ) {
-        // Don't even try to proxy invalid hosts
+        // Don't even try to proxy invalid hosts (such as /favicon.ico, /robots.txt)
         res.writeHead(404, 'Invalid host', cors_headers);
-        res.end();
+        res.end('Invalid host: ' + match[3]);
         return;
       } else if (!hasRequiredHeaders(req.headers)) {
         res.writeHead(400, 'Header required', cors_headers);