Question

I’m using the following to read a packet of data from a DataInputStream (wrapped around a socket).

    DataInputStream ins = ....;
    boolean cleanBreak = true;

    try {

        synchronized (readLock) {

            // read: message length
            int ml = ins.readInt();
            cleanBreak = false;

            // read: message data
            byte[] msg = IO.readBytes(ins, ml);

        }

    } catch (IOException e) {


            final boolean eof = e instanceof EOFException && cleanBreak;

        ...

Using the cleanBreak boolean, I want to determine whether an EOF occurs in the middle of a packet (abruptly) or nicely between two packets. Currently this works when the EOF is in the data part, but not if it’s in the header (the int), e.g. if only 2 more bytes are left when reading the header.

How can I do that?

Answer 1

One way would be to inline readInt:

public final int readInt() throws IOException {
    int ch1 = in.read();
    int ch2 = in.read();
    int ch3 = in.read();
    int ch4 = in.read();
    if ((ch1 | ch2 | ch3 | ch4) < 0)
        throw new EOFException();
    return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
}

And adapt it with a special check for the first byte.