doulouxun6756 2018-12-20 01:49
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ServeHTTP方法从何而来

This has confused me for the last month of learning Go:

func Auth(next http.HandlerFunc) http.HandlerFunc {

    return func(w http.ResponseWriter, r *http.Request) {  // hmmmm

        // ...
        next.ServeHTTP(w, r)
    }
}

here we can see that the Auth func returns type http.HandlerFunc. That type is just a func. So when you call next.ServeHTTP, when/where is that method defined?

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  • douchen5971 2018-12-20 05:35
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    https://golang.org/src/net/http/server.go?s=59707:59754#L1950

    // The HandlerFunc type is an adapter to allow the use of
    // ordinary functions as HTTP handlers. If f is a function
    // with the appropriate signature, HandlerFunc(f) is a
    // Handler that calls f.
    type HandlerFunc func(ResponseWriter, *Request)
    
    // ServeHTTP calls f(w, r).
    func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
        f(w, r)
    }
    

    Literally any function with the signature func(ResponseWriter, *Request) can be cast to a HandlerFunc, which gives it the method ServeHTTP - which then simply calls the function.

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