How to tell if Java SSLSocket has data available?

Question

When I was using regular Sockets, I could call getInputStream() and use available() to see how many bytes were available. I switched to SSLSocket, but now available() always returns 0 for some reason. When I read instead, I can still get data. How can I tell if there is data available in an SSLSocket so that I can service it without blocking if there is no data?

Notes:

• I cannot call read() on the InputStream or the thread will block. I would like non-blocking in my implementation.
• available() returns 0 even though there is data for SSLSocket's InputStream.

Answer 1

There is no way to do this. Your streams cannot tell you the length of the data without first decrypting it. available() will always return 0 for SSLSocket.

As mentioned in this chat, the reason you wanted to check for data is to prevent read() from blocking when called, so you can handle multiple connections on a single thread, instead of a Thread per Client system.

Instead, use a non-blocking alternative. java.nio currently doesn't have it's own SSL implementation of SocketChannel, but you can find one online (like here) or create your own.

With this system, you can register a Selector to every channel, and manage them all using the "selector thread". I wrote an example of how to use a selector here (scroll down to Using a Selector).

With non-blocking IO, you to handle multiple clients per thread, allowing you to scale up. This method of managing channels was brought up due to the C10k Problem

Answer 2

I assume you fixed your problem, but for those like me, I found a much easier solution. If you perform a read, then the available() method fills up for what was decrypted. How to use and abuse this? Read a single byte with a very low SoTimeout on your socket, if you catch a SocketTimeoutException, then the connection is empty, if not, prepend that byte you read to your future interpretation of the message. Until in.available() == 0 again, just roll with it.