Handling http method, accessing query strings & request body

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

type customHandler struct{}

// ServeHTTP implements the http.Handler interface in the net/http package
func (h customHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {

    // ParseForm will parse query string values and make r.Form available
    r.ParseForm()

    // r.Form is map of query string parameters
    // its' type is url.Values, which in turn is a map[string][]string
    queryMap := r.Form

    switch r.Method {
    case http.MethodGet:
        // Handle GET requests
        w.WriteHeader(http.StatusOK)
        w.Write([]byte(fmt.Sprintf("Query string values: %s", queryMap)))
        return
    case http.MethodPost:
        // Handle POST requests
        body, err := ioutil.ReadAll(r.Body)
        if err != nil {
            // Error occurred while parsing request body
            w.WriteHeader(http.StatusBadRequest)
            return
        }
        w.WriteHeader(http.StatusOK)
        w.Write([]byte(fmt.Sprintf("Query string values: %s\nBody posted: %s", queryMap, body)))
        return
    }

    // Other HTTP methods (eg PUT, PATCH, etc) are not handled by the above
    // so inform the client with appropriate status code
    w.WriteHeader(http.StatusMethodNotAllowed)
}

func main() {
    // All URLs will be handled by this function
    // http.Handle, similarly to http.HandleFunc
    // uses the DefaultServeMux
    http.Handle("/", customHandler{})

    // Continue to process new requests until an error occurs
    log.Fatal(http.ListenAndServe(":8080", nil))
}