how can i pass http request headers through metadata?

[hhniao]

i trid this, it is not work,
for example, i wanna pass Accept-Language or Language or any other header to service.
it is cant pass.

err = conn.Invoke(callCtx(c), "/"+s.GrpcCall.gw.Service+"."+s.GrpcCall.gw.Endpoint, request, response)
func callCtx(c *gin.Context) context.Context {
	r := c.Request
	// create context
	myContext := ctx.FromRequest(r)
	// get context from http handler wrappers
	md, ok := metadata.FromContext(r.Context())
	if !ok {
		md = make(metadata.Metadata)
	}
	// fill contex with http headers
	md["Host"] = r.Host
	md["Method"] = r.Method
	// get canonical headers
	for k := range r.Header {
		// may be need to get all values for key like r.Header.Values() provide in go 1.14
		md[textproto.CanonicalMIMEHeaderKey(k)] = r.Header.Get(k)
	}

	// merge context with overwrite
	myContext = metadata.MergeContext(myContext, md, true)
	return myContext
}