add header in http.Handler,but not take effect

[damozhiying]

grpc-gateway rest server

srv := &http.Server{
		Addr:         httpPort,
		ReadTimeout:  60 * time.Second,
		WriteTimeout: 60 * time.Second,
		// add handler with middleware
		Handler: middleware.AddRequestID(
			middleware.AddLogger(log.WithField("gateway", "rest"), handler)),
	}

AddLogger code

func AddLogger(logger *logrus.Entry, h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		ctx := r.Context()

h.ServeHTTP(w, r)

w.Header().Set("Grpc-Metadata-Yyyyyyyyyyyyyyyy-Request-ID", "fadfadsfadsf")
		w.Header()["TEST-HEADER-EKY"] = []string{"TEST-HEADER-EKY-110"}
		hs["TEST-HEADER-EKY-1"] = []string{"TEST-HEADER-EKY-110-1"}
		w.Header().Set("Access-Control-Allow-Origin", "*")

browser f12 show

Content-Type →application/json
Lxf--Abc-Www-Authenticate →222222222xxxxxxxxxx
Lxf--Content-Type →application/grpc
Lxf--Grpc-Metadata-Some-Key →222222222xxxxxxxxxx
Lxf--Www-Authenticate →222222222xxxxxxxxxx
Date →Mon, 23 Nov 2020 01:18:04 GMT
Content-Length →120

[johanbrandhorst]

You can't use net/http like this. Headers can only be set before you start writing to the body, and calling h.ServeHTTP is going to write to the body before you're setting the headers (see https://golang.org/pkg/net/http/#ResponseWriter). In your last issue, I suggested you use a header matcher, which is documented here: https://grpc-ecosystem.github.io/grpc-gateway/docs/mapping/customizingyourgateway/#set-http-headers. If you want to set headers in a middleware wrapper you might have to do it before calling ServeHTTP.

Closing as this is not an issue with the grpc-gateway.