Using OutputStreamWriter to write binary char array

Question

I'm trying to create an array of 16-bit values to send over a socket in network order.

First, I have defined an array to hold the value:

char[] txbuf = new char[32]; // Java "char" is 16-bits

Next, I open the socket and create the OutputStreamWriter:

InetAddress serverAddr = InetAddress.getByName(host);
socket = new Socket(serverAddr, port);
writer = new OutputStreamWriter(socket.getOutputStream(),Charset.forName("UTF-16BE"));

Then I initialize the data to send:

txbuf[0] = 0x1234;
...
txbuf[31] = 0xFFFF;

Finally, I send the data to the socket:

writer.write(txbuf,0,32);
write.flush();

However, the device I am sending the data to is behaving erratically, and I suspect there is some issue with the UTF-16BE conversion actually doing something to the data (filtering characters out?) besides the simple network order translation. Everything works fine in C, but not in the Java port.

I have seen various convoluted schemes for trying to write raw binary data but was trying for what seemed like the simplest and most straightforward method.

Is there a problem with the above scheme?

Are any of the characters you are writing surrogates? Have you looked at the actual data that is being sent? — David Conrad
– David Conrad, Commented Sep 23, 2014 at 22:57
@DavidConrad If I understand what you are saying, if any of the values are in the surrogate range (0xD800..0xDBFF / 0xDC00..0xDFFF) then some translation is going to occur? — Michael
– Michael, Commented Sep 23, 2014 at 23:08
I'm not sure, actually, but I think it's worth investigating. — David Conrad
– David Conrad, Commented Sep 23, 2014 at 23:08
Does the device really understand UTF-16BE? If not, you should be writing bytes, not chars. Don't use chars as though they are 16 bits on the wire. — user207421
– user207421, Commented Sep 23, 2014 at 23:54

Louis Wasserman · Accepted Answer · 2014-09-23 23:26:07Z

3

If you want to write bytes, instead of characters, you should be using the raw OutputStream instead of a Writer. OutputStream deals with bytes, Writer deals with characters, and a charset converts between them.

DataOutputStream writes primitive values to an OutputStream in big-endian order without any byte order marks or other charset issues.

answered Sep 23, 2014 at 23:26

Louis Wasserman

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