/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package h2c

import (
	"net/http"
	"net/textproto"

	"golang.org/x/net/http/httpguts"
	"golang.org/x/net/http2"
	"golang.org/x/net/http2/h2c" // nolint: depguard
)

func NewHandler(h http.Handler, s *http2.Server) http.Handler {
	return denyH2cUpgrade(h2c.NewHandler(h, s))
}

func denyH2cUpgrade(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if isH2CUpgrade(r.Header) {
			w.WriteHeader(http.StatusMethodNotAllowed)
			_, _ = w.Write([]byte("h2c upgrade not allowed"))
			return
		}
		h.ServeHTTP(w, r)
	})
}

func isH2CUpgrade(h http.Header) bool {
	return httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Upgrade")], "h2c") &&
		httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Connection")], "HTTP2-Settings")
}
