mmo-project/fortran/server/README.md

# server

The server implementation is as simple as I could make it.

I found a library called mod_dill from the [tcp-client-server demo code](https://github.com/modern-fortran/tcp-client-server) from a book on modern fortran. This gave me a simple TCP interface to send and recieve "messages".

Originally I had tried saving formatted fortran data into a string and trying to send that, but when you convert the fortran string to a c-string it oftend became garbled and unusable when sent through the tcp connection so I stopped using that method.

I found in [fpm](https://fpm.fortran-lang.org/index.html) [official registry](https://registry-frontend.vercel.app/) a json library which would make it *much* easier to deal with data transfer.

The simplest way to implement the communcation between the server and clients would be a series of tcp requests and responses.

- request
  - int :: request_type
    - ping # 0
    - login # 1
    - logout # 2
    - move # 3
  - str(24) :: username
  - double :: x_pos
  - double :: y_pos

- response
    - array :: records
      - str(24) :: username
      - str(24) :: color
      - double :: x_pos
      - double :: y_pos

For each request, the same response is returned with is a list of the logged in users.

The commands that can be sent to the server are logging in, logging out, moving, and the default "ping" which is essentially a noop from the servers pov.

The server uses the same sqlite library as the [www implementation](../www/README.md).

The server loop is:
1. listen for connection
2. read message from client
3. convert c string to fortran string
4. convert the fortran string to a json object
5. run the command from the json object
6. create a json array of the logged in users and send to client.