One of the messages that the client above sends is 0 bytes long. What would happen on a tcp socket when sending this message?

When using TCP to send a stream of individual messages, why is it still possible to send a 0-byte message (and receive it on the other side)? (For example, you can put an empty file on a website and download it. Why?)

When running the programs using "./example_server 4000" and "./example_client 127.0.0.1 4000" on the same machine I get the following output: $ /example_server 4000 msg 1: Hi msg 2: Hi again msg 3: Why am I just saying 'Hi' msg 4: Why are you not answering $ ./example_client 127.0.0.1 4000 msg 1: Hi msg 2: Hi again msg 3: Why am I just saying 'Hi'? msg 4: Why are you not answering? msg 6: Bye. msg 5: Explain why the output differs! Propose changes to the code to make the programs work as intended