How do I decipher garbled/gibberish characters in my networking program

Question

I am working on a client-server networking app in Java SE. I am using stings terminated by a newline from client to server and the server responds with a null terminated string.
In the output window of Netbeans IDE I am finding some gibberish characters amongst the strings that I send and receive.

I can't figure out what these characters are they mostly look like a rectagular box, when I paste that line containing the character in Notepad++ all the characters following and including that character disapear.

How could I know what characters are appearing in the output sreen of the IDE?

Answer 1

This is probably just binary data. Most of it will look like gibberish when interpreted as ascii. Make sure you are writing exact number of bytes to the socket, and not some nice number like 4096. Best would be if you can post your code so we can help you find the error(s).

Answer 2

If the response you are getting back from the server is supposed to be human readable text, then this is probably a character encoding problem. For example, if the client and server are both written in Java, it is likely that they using/assuming different character encodings for the text. (It is also possible that the response is not supposed to be human readable text. In that case, the client should not be trying to interpret it as text ... so this question is moot.)

You typically see boxes (splats) when a program tries to render some character code that it does not understand. This maybe a real character (e.g. a Japanese character, mathematical symbol or the like) or it could be an artifact caused by a mismatch between the character sets used for encoding and decoding the text.

To try and figure out what is going on, try modifying your client-side code to read the response as bytes rather than characters, and then output the bytes to the console in hexadecimal. Then post those bytes in your question, together with the displayed characters that you currently see.

If you understand character set naming and have some ideas what the character sets are likely to be, the UNIX / Linux iconv utility may be helpful. Emacs has extensive support for displaying / editing files in a wide range of character encodings. (Even plain old Wordpad can help, if this is just a problem with line termination sequences; e.g. "\n" versus "\r\n" versus "\n\r".)

(I'd avoid trying to diagnose this by copy and pasting. The copy and paste process may itself "mangle" the data, causing you further confusion.)