[fix] Readd the empty userinfo to url.href

If the userinfo is present but empty, the parsed host is also empty, and
`url.pathname` is not `'/'`, then readd the empty userinfo to `url.href`,
otherwise the original invalid URL might be transformed into a valid one
with `url.pathname` as host.

index.js

@@ -539,6 +539,17 @@ function toString(stringify) {
   } else if (url.password) {
     result += ':'+ url.password;
     result += '@';
+  } else if (
+    url.protocol !== 'file:' &&
+    isSpecial(url.protocol) &&
+    !url.host &&
+    url.pathname !== '/'
+  ) {
+    //
+    // Add back the empty userinfo, otherwise the original invalid URL
+    // might be transformed into a valid one with `url.pathname` as host.
+    //
+    result += '@';
   }
 
   result += url.host + url.pathname;

test/test.js

@@ -771,6 +771,63 @@ describe('url-parse', function () {
       assume(parsed.pathname).equals('/');
       assume(parsed.href).equals('http://user%40:pas%3As%40@www.example.com/');
     });
+
+    it('adds @ to href if auth and host are empty', function () {
+      var parsed, i = 0;
+      var urls = [
+        'http:@/127.0.0.1',
+        'http::@/127.0.0.1',
+        'http:/@/127.0.0.1',
+        'http:/:@/127.0.0.1',
+        'http://@/127.0.0.1',
+        'http://:@/127.0.0.1',
+        'http:///@/127.0.0.1',
+        'http:///:@/127.0.0.1'
+      ];
+
+      for (; i < urls.length; i++) {
+        parsed = parse(urls[i]);
+
+        assume(parsed.protocol).equals('http:');
+        assume(parsed.auth).equals('');
+        assume(parsed.username).equals('');
+        assume(parsed.password).equals('');
+        assume(parsed.host).equals('');
+        assume(parsed.hostname).equals('');
+        assume(parsed.pathname).equals('/127.0.0.1');
+        assume(parsed.href).equals('http://@/127.0.0.1');
+        assume(parsed.toString()).equals('http://@/127.0.0.1');
+      }
+
+      urls = [
+        'http:@/',
+        'http:@',
+        'http::@/',
+        'http::@',
+        'http:/@/',
+        'http:/@',
+        'http:/:@/',
+        'http:/:@',
+        'http://@/',
+        'http://@',
+        'http://:@/',
+        'http://:@'
+      ];
+
+      for (i = 0; i < urls.length; i++) {
+        parsed = parse(urls[i]);
+
+        assume(parsed.protocol).equals('http:');
+        assume(parsed.auth).equals('');
+        assume(parsed.username).equals('');
+        assume(parsed.password).equals('');
+        assume(parsed.host).equals('');
+        assume(parsed.hostname).equals('');
+        assume(parsed.pathname).equals('/');
+        assume(parsed.href).equals('http:///');
+        assume(parsed.toString()).equals('http:///');
+      }
+    });
   });
 
   it('accepts multiple ???', function () {