Allow url_prefix to be only the path

* Define utils function `get_base_url`.
 * If url_prefix start with `/` construct base URL using protocol and host form request.
 * Update SERVER.md with description of new `url_prefix` option.

SERVER.md

@@ -28,6 +28,12 @@ url_prefix: 'https://your-domain:8888'
 # or
 url_prefix: 'https://your-domain:8888/your-path'
 ```
+
+If you do not know the protocol and host, you can define only subpath as `url_prefix`. Full URL will be constructed from the request.
+```yaml
+url_prefix: '/your-path'
+```
+
 > Nginx or Apache configure? Please check out Wiki ;-)
 
 ## Keeping verdaccio running forever

lib/index-web.js

@@ -9,6 +9,7 @@ let Handlebars = require('handlebars');
 let renderReadme = require('render-readme');
 let Search = require('./search');
 let Middleware = require('./middleware');
+let Utils = require('./utils');
 let match = Middleware.match;
 let validate_name = Middleware.validate_name;
 let validate_pkg = Middleware.validate_package;
@@ -43,9 +44,7 @@ module.exports = function(config, auth, storage) {
     template = Handlebars.compile(fs.readFileSync(require.resolve('./GUI/index.hbs'), 'utf8'));
   }
   app.get('/', function(req, res, next) {
-    let base = config.url_prefix
+    let base = Utils.get_base_url(req.protocol, req.get('host'), config.url_prefix);
-             ? config.url_prefix.replace(/\/$/, '')
-             : req.protocol + '://' + req.get('host');
     res.setHeader('Content-Type', 'text/html');
 
     storage.get_local(function(err, packages) {

lib/utils.js

@@ -80,6 +80,27 @@ function validate_metadata(object, name) {
 	return object;
 }
 
+/**
+ * Create base url for registry.
+ * @param {String} protocol
+ * @param {String} host
+ * @param {String} prefix
+ * @return {String} base registry url
+ */
+function get_base_url(protocol, host, prefix) {
+	let result = protocol + '://' + host;
+
+	if (prefix) {
+		prefix = prefix.replace(/\/$/, '');
+
+		result = (prefix.indexOf('/') === 0)
+			? result + prefix
+			: prefix;
+	}
+
+	return result;
+}
+
 /**
  * Iterate a packages's versions and filter each original tarbal url.
  * @param {*} pkg
@@ -98,13 +119,9 @@ function filter_tarball_urls(pkg, req, config) {
 			return _url;
 		}
 		const filename = URL.parse(_url).pathname.replace(/^.*\//, '');
-		let result;
+		const base = get_base_url(req.protocol, req.headers.host, config.url_prefix);
-		if (config.url_prefix != null) {
+
-			result = config.url_prefix.replace(/\/$/, '');
+		return `${base}/${pkg.name.replace(/\//g, '%2f')}/-/${filename}`;
-		} else {
-			result = `${req.protocol}://${req.headers.host}`;
-		}
-		return `${result}/${pkg.name.replace(/\//g, '%2f')}/-/${filename}`;
 	};
 
 	for (let ver in pkg.versions) {
@@ -263,6 +280,7 @@ module.exports.parse_address = parse_address;
 module.exports.get_version = get_version;
 module.exports.normalize_dist_tags = normalize_dist_tags;
 module.exports.tag_version = tag_version;
+module.exports.get_base_url = get_base_url;
 module.exports.filter_tarball_urls = filter_tarball_urls;
 module.exports.validate_metadata = validate_metadata;
 module.exports.is_object = is_object;