java.net.URLDecode.decode(st) does not decode encoded surrogate pairs correctly

Name: dfR10049 Date: 12/09/2000



Javadoc for java.net.URLDecode.decode(String s) states:

    Decodes a x-www-form-urlencoded string. UTF-8 is used to determine what
    characters are represented by any consecutive sequences of the form "%xy".

The string "\uD800\uDC00" is a surrogate pair and encoded as "%3F%ED%B0%80"
(by URLEncoder.encode(s) method) according to UTF-8. But "%3F%ED%B0%80" is
not decoded as "\uD800\uDC00". This behavior is not correct.

Please see an example demonstrating the bug below:
----------- DecoderTest.java ----------------
import java.net.*;

public class DecoderTest {

   public static void main(String args[]) {

        String surrogatePair = "\uD800\uDC00";
               // a string of surrogate pairs can be expressed as 4 bytes (UTF-8)

        String encoded = URLEncoder.encode(surrogatePair);
        String decoded = URLDecoder.decode(encoded);

        System.out.println("encoded: " + encoded);

        System.out.println("decoded: " + decoded);
        System.out.print (" ");
        printBytes(decoded);
        System.out.println("surrogatePair: " + surrogatePair);
        System.out.print (" ");
        printBytes(surrogatePair);


        if (encoded.equals(decoded))
            System.out.println("Test passed");
        else
            System.out.println("Test failed");
   };

   static void printBytes(String s) {
       try {
           byte[] arr = s.getBytes("UTF-8");
           for (int i = 0; i < arr.length; i++) {
               char ch1 = Character.forDigit((arr[i] >> 4) & 0xF, 16);
               char ch2 = Character.forDigit(arr[i] & 0xF, 16);
               System.out.print(ch1 + "" + ch2 + " ");
           }
           System.out.println();
       } catch (java.io.UnsupportedEncodingException e) {
       }

   }
}
#----------------- output from the test ----------------------
encoded: %3F%ED%B0%80
decoded: ??
         3f ed b0 80
surrogatePair: ?
         f0 90 80 80
Test failed
#-------------------------------------------------------------

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