How do I make a PUT request from fetch to my go API?
<p>I am creating a REST API with Go (using Gorilla mux) and a frontend app with React. The GET requests work fine, but I'm having trouble getting the PUT request to work correctly. It makes the OPTIONS preflight request successfully, but never the PUT request. I may be handling it incorrectly on the backend or making the request incorrectly. I'm created a middleware that will add the CORS headers because the gorilla toolkit's CORS handlers weren't allowing the OPTIONS request at all. I have also tried using axios instead of fetch to make sure it wasn't something I was doing incorrectly in the request. I was getting the exact same behavior with axios.</p>

<p>Here is the router:</p>

<pre><code>var V1URLBase string = "/api/v1"

func Load() http.Handler {

    r := mux.NewRouter().StrictSlash(true)

    // Status endpoints
    s := r.PathPrefix(fmt.Sprintf("%s%s", V1URLBase, "/statuses")).Subrouter()

    s.HandleFunc("/", handlers.GetStatuses).
        Methods("GET")
    s.HandleFunc("/{status_id}/", handlers.GetStatus).
        Methods("GET")
    s.HandleFunc("/", handlers.PostStatus).
        Methods("POST")
    s.HandleFunc("/{status_id}/", handlers.PutStatus).
        Methods("PUT")
    s.HandleFunc("/{status_id}/", handlers.DeleteStatus).
        Methods("DELETE")

    // Visit endpoints
    v := r.PathPrefix(fmt.Sprintf("%s%s", V1URLBase, "/visits")).Subrouter()

    v.HandleFunc("/", handlers.GetVisits).
        Methods("GET")
    v.HandleFunc("/{visit_id}/", handlers.GetVisit).
        Methods("GET")
    v.HandleFunc("/", handlers.PostVisit).
        Methods("POST")
    v.HandleFunc("/{visit_id}/", handlers.PutVisit).
        Methods("PUT")
    v.HandleFunc("/{visit_id}/", handlers.DeleteVisit).
        Methods("DELETE")

    // Member endpoints
    m := r.PathPrefix(fmt.Sprintf("%s%s", V1URLBase, "/members")).Subrouter()

    m.HandleFunc("/", handlers.GetMembers).
        Methods("GET")
    m.HandleFunc("/{member_id}/", handlers.GetMember).
        Methods("GET")
    m.HandleFunc("/", handlers.PostMember).
        Methods("POST")
    m.HandleFunc("/{member_id}/", handlers.PutMember).
        Methods("PUT")
    m.HandleFunc("/{member_id}/", handlers.DeleteMember).
        Methods("DELETE")

    // GymLocation endpoints
    gl := r.PathPrefix(fmt.Sprintf("%s%s", V1URLBase, "/gym_locations")).Subrouter()

    gl.HandleFunc("/", handlers.GetGymLocations).
        Methods("GET")
    gl.HandleFunc("/{gym_location_id}/", handlers.GetGymLocation).
        Methods("GET")
    gl.HandleFunc("/", handlers.PostGymLocation).
        Methods("POST")
    gl.HandleFunc("/{gym_location_id}/", handlers.PutGymLocation).
        Methods("PUT")
    gl.HandleFunc("/{gym_location_id}/", handlers.DeleteGymLocation).
        Methods("DELETE")

    router := ghandlers.LoggingHandler(os.Stdout, r)
    router = handlers.WriteCORSHeaders(r)

    return router
}
</code></pre>

<p>Here is the CORS handler:</p>

<pre><code>func WriteCORSHeaders(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        fmt.Println("HIT")
        w.Header().Set("Access-Control-Allow-Origin", r.Header.Get("Origin"))
        w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
        w.Header().Set(
            "Access-Control-Allow-Headers",
            "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization",
        )
        //w.Header().Set("Access-Control-Allow-Credentials", "true")

        if r.Method == "OPTIONS" {
            return
        }

        h.ServeHTTP(w, r)
    })
}
</code></pre>

<p>Here is the PUT handler:</p>

<pre><code>func PutVisit(w http.ResponseWriter, r *http.Request) {
    body, _ := ioutil.ReadAll(r.Body)
    r.Body.Close()

    visitId, err := strconv.ParseInt(mux.Vars(r)[VisitId], 10, 64)
    if err != nil {
        WriteJSON(w, http.StatusBadRequest, APIErrorMessage{Message: InvalidVisitId})
        return
    }

    visit := &amp;models.Visit{}
    err = json.Unmarshal(body, visit)
    if err != nil {
        WriteJSON(w, http.StatusBadRequest, APIErrorMessage{Message: err.Error()})
        return
    }

    updated, err := datastore.UpdateVisit(visitId, *visit)
    if err != nil {
        WriteJSON(w, http.StatusInternalServerError, APIErrorMessage{Message: err.Error()})
        return
    }

    WriteJSON(w, http.StatusOK, updated)
}

func WriteJSON(w http.ResponseWriter, statusCode int, response interface{}) {
    encoder := json.NewEncoder(w)
    w.Header().Set("Content-Type", "application/json; charset=UTF-8")
    w.WriteHeader(statusCode)
    encoder.Encode(response)
}
</code></pre>

<p>Here is the main that starts the server:</p>

<pre><code>func main() {
    r := router.Load()

    http.ListenAndServe(":8080", r)
}
</code></pre>

<p>Here is my request from Reactjs:</p>

<pre><code>export function putVisit(visit) {
  return function(dispatch) {
    return fetch(`http://localhost:8080/api/v1/visits/${visit.visit_id}/`, {
      method: 'PUT',
      headers: {
        'Accept': 'application/json; charset=UTF-8',
        'Content-Type': 'application/json; charset=UTF-8'
      },
      body: JSON.stringify(visit)
    })
      .then(response =&gt; response.json())
      .then(json =&gt;
        dispatch(updateVisit(json))
      )
      .catch(err =&gt;
        console.log(err)
      )
  }
}
</code></pre>