url: fix surrogate handling in encodeAuth()

Currently, the legacy URL stringifier miscalculates the offset of an
extra surrogate, causing the high surrogate to be included unescaped:

    > url.format({ auth: '\uD83D\uDE00', hostname: 'a' })
    '//%F0%9F%98%80�@a'

PR-URL: https://github.com/nodejs/node/pull/11387
Backport-of: https://github.com/nodejs/node/pull/11161

lib/url.js

@@ -948,6 +948,24 @@ function spliceOne(list, index) {
 var hexTable = new Array(256);
 for (var i = 0; i < 256; ++i)
   hexTable[i] = '%' + ((i < 16 ? '0' : '') + i.toString(16)).toUpperCase();
+
+// These characters do not need escaping:
+// ! - . _ ~
+// ' ( ) * :
+// digits
+// alpha (uppercase)
+// alpha (lowercase)
+const noEscapeAuth = [
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x00 - 0x0F
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x10 - 0x1F
+  0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, // 0x20 - 0x2F
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, // 0x30 - 0x3F
+  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x40 - 0x4F
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, // 0x50 - 0x5F
+  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x60 - 0x6F
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0  // 0x70 - 0x7F
+];
+
 function encodeAuth(str) {
   // faster encodeURIComponent alternative for encoding auth uri components
   var out = '';
@@ -955,37 +973,28 @@ function encodeAuth(str) {
   for (var i = 0; i < str.length; ++i) {
     var c = str.charCodeAt(i);
 
-    // These characters do not need escaping:
-    // ! - . _ ~
-    // ' ( ) * :
-    // digits
-    // alpha (uppercase)
-    // alpha (lowercase)
-    if (c === 0x21 || c === 0x2D || c === 0x2E || c === 0x5F || c === 0x7E ||
-        (c >= 0x27 && c <= 0x2A) ||
-        (c >= 0x30 && c <= 0x3A) ||
-        (c >= 0x41 && c <= 0x5A) ||
-        (c >= 0x61 && c <= 0x7A)) {
-      continue;
-    }
-
-    if (i - lastPos > 0)
-      out += str.slice(lastPos, i);
-
-    lastPos = i + 1;
-
-    // Other ASCII characters
+    // ASCII
     if (c < 0x80) {
+      if (noEscapeAuth[c] === 1)
+        continue;
+      if (lastPos < i)
+        out += str.slice(lastPos, i);
+      lastPos = i + 1;
       out += hexTable[c];
       continue;
     }
 
+    if (lastPos < i)
+      out += str.slice(lastPos, i);
+
     // Multi-byte characters ...
     if (c < 0x800) {
+      lastPos = i + 1;
       out += hexTable[0xC0 | (c >> 6)] + hexTable[0x80 | (c & 0x3F)];
       continue;
     }
     if (c < 0xD800 || c >= 0xE000) {
+      lastPos = i + 1;
       out += hexTable[0xE0 | (c >> 12)] +
              hexTable[0x80 | ((c >> 6) & 0x3F)] +
              hexTable[0x80 | (c & 0x3F)];
@@ -998,6 +1007,7 @@ function encodeAuth(str) {
       c2 = str.charCodeAt(i) & 0x3FF;
     else
       c2 = 0;
+    lastPos = i + 1;
     c = 0x10000 + (((c & 0x3FF) << 10) | c2);
     out += hexTable[0xF0 | (c >> 18)] +
            hexTable[0x80 | ((c >> 12) & 0x3F)] +

test/parallel/test-url.js

@@ -891,8 +891,19 @@ var parseTests = {
     pathname: '/*',
     path: '/*',
     href: 'https:///*'
-  }
+  },
 
+  // surrogate in auth
+  'http://%F0%9F%98%80@www.example.com/': {
+    href: 'http://%F0%9F%98%80@www.example.com/',
+    slashes: true,
+    protocol: 'http:',
+    auth: '\uD83D\uDE00',
+    host: 'www.example.com',
+    hostname: 'www.example.com',
+    pathname: '/',
+    path: '/'
+  }
 };
 
 for (const u in parseTests) {