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Test the code and see what happens.

You could read and write more than one byte at a time using a byte array.

Do your first testing using the localhost address on one PC for easier debugging. Add lots of println statements to see what the code is doing.

Maybe if they are on Windows, they right-clicked on the file and asked for the file's properties.

It's possible to use a smaller array. In the read loop, read some bytes and write them to the...