byte[] to RubyString for string xor in JRuby Java Extension

Question

I'm trying to implement a Java extension for JRuby to perform string xors. I'm just uncertain how to type cast a byte array into a RubyString:

public static RubyString xor(ThreadContext context,  IRubyObject self, RubyString x, RubyString y) {
    byte[] xBytes = x.getBytes();
    byte[] yBytes = y.getBytes();

    int length = yBytes.length < xBytes.length ? yBytes.length : xBytes.length;

    for(int i = 0; i < length; i++) {
        xBytes[i] = (byte) (xBytes[i] ^ yBytes[i]);
    }

    // How to return a RubyString with xBytes as its content?
}

Also, how would one perform the same operation in-place (i.e. xs value is updated)?

There are constructors on RubyString that accept a byte[] here org.jruby.RubyString.RubyString(Ruby runtime, RubyClass rubyClass, byte[] value) not sure if that's applicable in this instance? — xkickflip
– xkickflip, Commented Jul 13, 2015 at 3:47
Looks promising. Any idea what the rubyClass argument is supposed to be? — fny
– fny, Commented Jul 13, 2015 at 4:00
Not sure about that argument unfortunately. I've used Jruby for years, but haven't tried writing an extension before. Dropping by the #jruby channel on freenode irc may be the quickest way to get some more info — xkickflip
– xkickflip, Commented Jul 13, 2015 at 4:03

fny · Accepted Answer · 2015-07-15 21:44:23Z

1

return context.runtime.newString(new ByteList(xBytes, false));

edited Jul 15, 2015 at 21:44

fny

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answered Jul 14, 2015 at 10:42

kares

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1 Comment

VP. Over a year ago

What is this? Some explanation would be nice. If you don't want to do that, post a comment.

fny · Accepted Answer · 2015-07-15 21:41:37Z

0

You'll first need to wrap the bytes in a ByteList: new ByteList(xBytes, false). The last parameter (Boolean copy) dictates whether to wrap a copy of the Byte array.

To update the string in place, use [RubyString#setValue()][2]:

x.setValue(new ByteList(xBytes, false);
return x;

To return a new RubyString, you can pass that list to the current runtime's #newString():

return context.runtime.newString(new ByteList(xBytes, false));

edited Jul 15, 2015 at 21:41

answered Jul 13, 2015 at 4:22

fny

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