How to make a server middleware in gorilla mux?

Question

go

I need to catch the server's response , get the response body from it and log it, let's say to the console.
Can you tell me how to get access to the response body in middleware?

Answer 1

There is an option to use httptest.ResponseRecorder, I used it earlier to write tests.
https://pkg.go.dev/net/http/httptest#ResponseRecorder
An example would be something like this

func (m *LoggingMiddleware) LogBody(next http.Handler) http.Handler {
    fn := func(w http.ResponseWriter, r *http.Request) {
        wRecorder := httptest.NewRecorder()
        next.ServeHTTP(wRecorder, r)
        resp := wRecorder.Result()
        body, _ := io.ReadAll(resp.Body)
        // не забыть записать ответ в w
    }

    return http.HandlerFunc(fn)
}

An example of its use from the official documentation https://pkg.go.dev/net/http/httptest#example-Respo...
Or, you can make your own responseWriter, pass your writer to the handler, and then, after processing, write the received response server into original responseWriter
Something like this

func (m *LoggingMiddleware) LogBody(next http.Handler) http.Handler {
    fn := func(w http.ResponseWriter, r *http.Request) {
        var buf bytes.Buffer
        logWriter := NewLogToConsoleResponseWriter(&b)
        next.ServeHTTP(logWriter, r)
        // тут у вас в buf будет ответ сервера, с которым можно работать
        // главное потом не забыть записать его в `w`
    }

    return http.HandlerFunc(fn)
}