Go doesn't understand how http.Server Handler calls functions attached to empty structs

php editor Banana is here to answer a question about the Go language: Go does not understand how the http.Server Handler calls a function attached to an empty structure. In the Go language, http.Server is a structure used to process HTTP requests, and the Handler field is an interface type. An interface type is a special type that defines a set of methods. When we assign a function to the Handler field, the Go language will use the reflection mechanism to call the function. However, if we attach a function to an empty structure, the Go language will not understand how to call the function correctly. This is because when a method is called on an empty structure, the actual object instance cannot be obtained. To solve this problem, we can use closures or methods with receivers.

Question content

I have a simple web server code, but I don't understand this code:

Handler: app.routes(),

const webport = "80"

type config struct {}

func main() {

    app := config{}
    log.printf("starting broker service on port %s\n",webport)
    srv := &http.server{
        addr: fmt.sprintf(":%s",webport),
        handler:app.routes(),
    }

    err := srv.listenandserve()
    if(err != nil) {
        log.panic(err)
    }
}

In the routing file:

func (app *config) routes() http.handler {
    mux := chi.newrouter()
    mux.use(cors.handler(cors.options{
        allowedorigins: []string{"http://*","https://*"},
        allowedmethods: []string{"get", "post", "delete","put","options"},
        allowedheaders: []string{"accept","authorization","content-type","x-csrf-token"},
        exposedheaders: []string{"link"},
        allowcredentials:true,
        maxage:300,
    }))

    mux.use(middleware.heartbeat("/ping"))
    mux.post("/",app.broker)

    return mux
}

This is effective, the routes() function called when a request is received, But how does this routes() know to be triggered when it's attached to an empty struct?

app := Config{}

Where does the application know about routes()?

What is func (app *config) in function?

Workaround

The route is attached to the http server as shown below.

srv := &http.server{
   addr: ":8081", // port
   handler: app.routes() // a handler to invoke
 }

routes is a method of the config structure. Even if config is empty, we can still call the routes method as in the code.

 cfg := Config{}
 r := cfg.routes()

config structure acts here as a method receiver.

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