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HTTP Request ​

The traditional loading of a page is a http request, e.g. calling the main address https://foodsharing.de calls /src/Modules/Index/IndexController.php which uses other php files to answer the request. The php builds html, css and javascript and sends them to the client.

Other ways to interact with the foodsharing platform are:

REST API ​

Most of the communication between client and server happens via the REST API. API calls are always initiated by the client and responded to by the server.

The javascript code that sends REST API requests is found under /client/src/api and is used by other javascript by import.

Socket.io for notifications and chat ​

The chats have a separate way of communication between client and server. For all other pages the initiative starts at the client, the client sends a request to the (php) server and gets an answer. Each request uses one connection that is closed afterwards. This is not useful for the chats since the server knows that there are new messages and has to tell the client.

For this case there exists a separate nodejs server (on the same machine as the php server but separate). This holds an open connection to each user that has foodsharing.de open on their device. Each time a message arrives at the php server, it sends this information to the nodejs server via a websocket

TODO: explanation what a websocket is, on which server is it, is it the right place to explain it?

which uses the connection to the client to send the message. Note that there can be several connections to each session, of which there can be several for each user. nodejs sends the message to all connections of all addressed users.

The code for the nodejs server is found in /chat/src/index.ts and other files in /chat/src chat/socket.io -> nodejs server, in chat/src/index.ts. There is documentation for all used parts in /chat/node_modules/<modulename>/Readme.md. All nodejs-documentation is found on their webpage.

php server tells websocket that there is a new message

nodejs-server sends message to all open connections of all sessions of all users