A simple client/server example
------------------------------

... with one message sent and recieved.

I googled "c client server example" and found

  https://www.programminglogic.com/
  example-of-client-server-program-in-c-using-sockets-and-tcp/
  
which has the code here ... though I made some modifications,
an a few includes, prints, closing things, and changing the
names and definitions to be clearer to me.

Reading the man pages for these system calls is helpful;
see for exampe http://manpages.ubuntu.com/manpages/bionic/man2 .

The HOST address should match in the server.c and client.c.
If it's set to 127.0.0.1, the "localhost" or "loopback" address,
then both processes must be running on this machine.

If it's set to this hosts IP address (which I'm just doing
explicitly here rather than asking the system for it;
"host shannon.marlboro.college" will look it up), then
the client and server can be both here or on two different
network connected computers.

This code compiled fine on my mac (10.14.1 with xcode installed)
as well as on shannon.marlboro.college (ubuntu). Running
the server on shannon and the client on my mac worked
as expected.

getting the web page
--------------------

 $ curl htps://... > example.html

compiling it
------------

 $ make client
 cc client.c -o client
 $ make server
 cc server.c -o server

running it
----------

This can be done on one terminal with the server in the background.

 $ ./server &
 [1] 21833
 Server: listening on port 7891 ...
 $ ./client
 Server: connection established.
 Server: message sent.
 Server exiting.
 Client: connection established.
 Client: received: "The server says 'Hi there!'"
 Client exiting.
 [1]+  Done                    ./server
 
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