Re-apply "Fix URL decoding in HTTP library"

runtime/bin/http_utils.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _HttpUtils {
   static String decodeUrlEncodedString(String urlEncoded) {
-    void invalidEscape() {
-      // TODO(sgjesse): Handle the error.
+    // First check the string for any encoding.
+    int index = 0;
+    bool encoded = false;
+    while (!encoded && index < urlEncoded.length) {
+      encoded = urlEncoded[index] == "+" || urlEncoded[index] == "%";
+      index++;
     }
+    if (!encoded) return urlEncoded;
+    index--;
 
-    StringBuffer result = new StringBuffer();
-    for (int ii = 0; urlEncoded.length > ii; ++ii) {
-      if ('+' == urlEncoded[ii]) {
-        result.add(' ');
-      } else if ('%' == urlEncoded[ii] &&
-                 urlEncoded.length - 2 > ii) {
-        try {
-          int charCode =
-            Math.parseInt('0x' + urlEncoded.substring(ii + 1, ii + 3));
-          if (charCode <= 0x7f) {
-            result.add(new String.fromCharCodes([charCode]));
-            ii += 2;
+    // Start decoding from the first encoded character.
+    List<int> bytes = new List<int>();
+    for (int i = 0; i < index; i++) bytes.add(urlEncoded.charCodeAt(i));
+    for (int i = index; i < urlEncoded.length; i++) {
+      if (urlEncoded[i] == "+") {
+        bytes.add(32);
+      } else if (urlEncoded[i] == "%") {
+        if (urlEncoded.length - i < 2) {
+          throw new HttpException("Invalid URL encoding");
+        }
+        int byte = 0;
+        for (int j = 0; j < 2; j++) {
+          var charCode = urlEncoded.charCodeAt(i + j + 1);
+          if (0x30 <= charCode && charCode <= 0x39) {
+            byte = byte * 16 + charCode - 0x30;
+          } else if (0x41 <= charCode && charCode <= 0x46) {
+            byte = byte * 16 + charCode - 0x37;
+          } else if (0x61 <= charCode && charCode <= 0x66) {
+            byte = byte * 16 + charCode - 0x57;
           } else {
-            invalidEscape();
-            return '';
+            throw new HttpException("Invalid URL encoding");
           }
-        } catch (BadNumberFormatException ignored) {
-          invalidEscape();
-          return '';
         }
+        bytes.add(byte);
+        i += 2;
       } else {
-        result.add(urlEncoded[ii]);
+        bytes.add(urlEncoded.charCodeAt(i));
       }
     }
-    return result.toString();
+    return decodeUtf8(bytes);
   }
 
   static Map<String, String> splitQueryString(String queryString) {
     Map<String, String> result = new Map<String, String>();
     int currentPosition = 0;
     while (currentPosition < queryString.length) {
       int position = queryString.indexOf("=", currentPosition);
       if (position == -1) {
         break;
       }
@@ skipping 175 matching lines @@
       minutes = expectNum(":");
       seconds = expectNum(" ");
       expect("GMT");
     }
     expectEnd();
     TimeZone utc = new TimeZone.utc();
     return new Date.withTimeZone(
         year, month + 1, day, hours, minutes, seconds, 0, utc);
   }
 }