What's the proper way to continuously read socket messages through DataInputStream?

Question

I'm trying to build a Java Bittorent client. From what I understand after peers handshake with one another they may start sending messages to each other, often sending messages sporadically.

Using a DataInputStream connection I can read messages, but if I call a read and nothing is on the stream the peers holds. Is there a way I can tell if something is being sent over the stream? Or should I create a new thread that reads the stream for messages continuously from each peer until the client shuts them down shut down?

Answer 1

I think you need to do some major experimenting so that you can start to learn the basics of socket I/O. Trying to answer your question "as is" is difficult, because you don't yet understand enough to ask the question in a manner that it can be answered.

If you want to be able to tell if there is data to read, then you should not use the blocking I/O approach. Instead, you will need to use the APIs known as "NIO", which allow you to "select" a socket that has data to read (i.e. a socket that is associated with a buffer that already has data in it).

This will make much more sense after you write a lot of code and mess it up a few times. The underlying I/O primitives are actually quite primitive (pun intended). In this industry, we just made up lots of complicated terms and function names and API descriptions so that people would think that network communication is magic. It's not. It's generally no more complicated than memcpy().

Answer 2

There is a function in C called select(). In the scenario you've described, you need an equivalent of select in Java. And that is, as cpurdy mentioned, Non-blocking Socket I/O or NIO. Cursory googling returned following links:

• http://tutorials.jenkov.com/java-nio/socket-channel.html
• http://www.owlmountain.com/tutorials/NonBlockingIo.htm
• http://rox-xmlrpc.sourceforge.net/niotut/index.htm

Answer 3

You might want to take a look at the Netty project: http://netty.io/

It is very easy with Netty to get started on network programming.