// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed 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 caddyhttp

import (
	"bufio"
	"fmt"
	"net"
	"net/http"
	"sync"
)

// httpRedirectListener is listener that checks the first few bytes
// of the request when the server is intended to accept HTTPS requests,
// to respond to an HTTP request with a redirect.
type httpRedirectListener struct {
	net.Listener
}

// Accept waits for and returns the next connection to the listener,
// wrapping it with a httpRedirectConn.
func (l *httpRedirectListener) Accept() (net.Conn, error) {
	c, err := l.Listener.Accept()
	if err != nil {
		return nil, err
	}

	return &httpRedirectConn{
		Conn: c,
		r:    bufio.NewReader(c),
	}, nil
}

type httpRedirectConn struct {
	net.Conn
	once sync.Once
	r    *bufio.Reader
}

// Read tries to peek at the first few bytes of the request, and if we get
// an error reading the headers, and that error was due to the bytes looking
// like an HTTP request, then we perform a HTTP->HTTPS redirect on the same
// port as the original connection.
func (c *httpRedirectConn) Read(p []byte) (int, error) {
	var errReturn error
	c.once.Do(func() {
		firstBytes, err := c.r.Peek(5)
		if err != nil {
			return
		}

		// If the request doesn't look like HTTP, then it's probably
		// TLS bytes and we don't need to do anything.
		if !firstBytesLookLikeHTTP(firstBytes) {
			return
		}

		// Parse the HTTP request, so we can get the Host and URL to redirect to.
		req, err := http.ReadRequest(c.r)
		if err != nil {
			return
		}

		// Build the redirect response, using the same Host and URL,
		// but replacing the scheme with https.
		headers := make(http.Header)
		headers.Add("Location", "https://"+req.Host+req.URL.String())
		resp := &http.Response{
			Proto:      "HTTP/1.0",
			Status:     "308 Permanent Redirect",
			StatusCode: 308,
			ProtoMajor: 1,
			ProtoMinor: 0,
			Header:     headers,
		}

		err = resp.Write(c.Conn)
		if err != nil {
			errReturn = fmt.Errorf("couldn't write HTTP->HTTPS redirect")
			return
		}

		errReturn = fmt.Errorf("redirected HTTP request on HTTPS port")
		c.Conn.Close()
	})

	if errReturn != nil {
		return 0, errReturn
	}

	return c.r.Read(p)
}

// firstBytesLookLikeHTTP reports whether a TLS record header
// looks like it might've been a misdirected plaintext HTTP request.
func firstBytesLookLikeHTTP(hdr []byte) bool {
	switch string(hdr[:5]) {
	case "GET /", "HEAD ", "POST ", "PUT /", "OPTIO":
		return true
	}
	return false
}