Java: Remove first UTF string from byte array

Question

I'm trying to remove a written string from a byte array and maintain the original separate objects:

byte[] data... // this is populated with the following:
// 00094E6966747943686174001C00074D657373616765000B4372616674656446757279000474657374
// to string using converter : "    ChannelMessageUsernametest"
// notice that tab/whitespace, ignore quotes
// The byte array was compiled by writing the following (writeUTF from a writer):
// Channel
// Message
// Username
// test

Now I'm trying to strip Channel from the byte array:

ByteArrayDataInput input = ByteStreams.newDataInput(message);
String channel = input.readUTF(); // Channel, don't want this
String message = input.readUTF(); // Message
// works good, but I don't want Channel,
// and I can't remove it from the data before it arrives,
// I have to work with what I have

Here is my problem:

byte[] newData = Arrays.copyOfRange(data, channel.length() + 2, data.length)
// I use Arrays.copyOfRange to strip the whitespace (I assume it's not needed)
// As well, since it's inclusive of length size, I have to add 1 more,
// resulting in channel.length() + 1
// ...
ByteArrayDataInput newInput = ByteStreams.newDataInput(message);
String channel = newInput.readUTF(); // MessageUsernametext

See how I lose the separation of the objects, how can I keep the original "sections" of objects in the original byte[] data inside byte[] newData.

It's safe to assume that String channel (before and after stripping) is a string
It's NOT safe to assume that every object is a string, assume everything is random, because it is

yawkat · Accepted Answer · 2014-04-25 18:09:09Z

1

As long as you can guarantee that channel is always in a reasonable character range (for example alphanumeric), changing the channel.length() + 2 to channel.length() + 4 should be sufficient.

answered Apr 25, 2014 at 18:09

yawkat

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Tjaart · Accepted Answer · 2016-05-08 19:16:13Z

0

Java Strings have 16-bit elements, so it is safe to convert a byte array into a String, although not as memory efficient:

private byte[] removeElements(byte[] data, int fromIndex, int len) {
       String str1 = new String(data).substring(0,fromIndex);
       String str2 = new String(data).substring(fromIndex+len,data.length);
       return (str1+str2).getBytes();
}

In the same manner, you can also search for a String inside the byte array:

private int findStringInByteArray(byte[] mainByte, String str, int fromIndex) {
    String main = new String(mainByte);
    return main.indexOf(str,fromIndex);
}

Now you can call these methods together:

byte[] newData = removeElements(
    data,
    findStringInByteArray(data,channel,0),
    channel.length() );

edited May 8, 2016 at 19:16

answered May 8, 2016 at 18:45

Tjaart

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