In my application, why does readInt() always throw an EOFException?

Question

(Forgive me because I do not write in Java very often.)

I'm writing a client-side network application in Java and I'm having an interesting issue. Every call to readInt() throws an EOFException. The variable is of type DataInputStream (initialized as: DataInputStream din = new DataInputStream(new BufferedInputStream(sock.getInputStream())); where sock is of type Socket).

Now, sock.isInputShutdown() returns false and socket.isConnected() returns true. I'm assuming that this means that I have a valid connection to the other machine I'm connecting to. I've also performed other checks to ensure that I'm properly connected to the other machine.

Is it possible that the DataInputStream was not set up correctly? Are there any preconditions that I have missed?

Any help is greatly appreciated.

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@tofubeer: I actually wrote 17 bytes to the socket. The socket is connected to another machine and I'm waiting on input from that machine (I'm sorry if this was unclear). I successfully read from the stream (to initiate a handshake) first and this worked just fine. I'm checking now to see if my sent-requests are malformed, but I don't think they are. Also, I tried reading a single byte from the stream (via read()) and it returned -1.

Answer 1

Are you writing 4 bytes to the socket? According to the JavaDoc it will throw an EOFException if this stream reaches the end before reading all the bytes.

Try calling readByte() 4 times in a row instead of readInt() and see what happens (likely not all of them will work).

Edit (given your edit).

Find out how many times you can call read() before you get the -1.

When read() returns -1 it means that it has hit the end of file.

Also find out what each read() returns to make sure what you are reading in is what you actually wrote out.

It sounds like a problem either with the read code reading more than you thing while doing the handshake or the other side not writing what you think it is writing.

Answer 2

Some things to check:

• Did the handshake consume more than 13 bytes, leaving less than four for the readInt()?
• Was the integer you want to read written via DataOutputStream.writeInt()?
• Did you flush the stream from the sender?

Edit: I took a look at the Java sources (I have the 1.4 sources on my desktop, not sure which version you're using) and the problem might be in BufferedInputStream. DataInputStream.readInt() is just calling BufferedInputStream.read() four times. BufferedInputStream.read() is calling BufferedInputStream.fill() if its buffer is exhausted (e.g., if its first read only got 16 bytes). BufferedInputStream.fill() calls the underlying InputStream's read(byte[], int, int) method, which by contract might not actually read anything! If this happens, BufferedInputStream.read() will return an erroneous EOF.

This is all assuming that I'm reading all of this correctly, which might not be the case. I only took a quick peek at the sources.

I suspect that your BufferedInputStream is only getting the first 16 bytes of the stream in its first read. I'd be curious what your DataInputStream's available() returns right before the readInt. If you're not already, I'd suggest you flush your OutputStream after writing the int you can't read as a possible workaround.