/*
 * Minio Cloud Storage, (C) 2017 Minio, Inc.
 *
 * 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 http

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/minio/minio/cmd/logger"
)

var sslRequiredErrMsg = []byte("HTTP/1.0 403 Forbidden\r\n\r\nSSL required")

var badRequestMsg = []byte("HTTP/1.0 400 Bad Request\r\n\r\n")

// HTTP methods.
var methods = []string{
	http.MethodGet,
	http.MethodHead,
	http.MethodPost,
	http.MethodPut,
	http.MethodPatch,
	http.MethodDelete,
	http.MethodConnect,
	http.MethodOptions,
	http.MethodTrace,
	"PRI", // HTTP 2 method
}

// maximum length of above methods + one space.
var methodMaxLen = getMethodMaxLen() + 1

func getMethodMaxLen() int {
	maxLen := 0
	for _, method := range methods {
		if len(method) > maxLen {
			maxLen = len(method)
		}
	}

	return maxLen
}

func isHTTPMethod(s string) bool {
	for _, method := range methods {
		if s == method {
			return true
		}
	}

	return false
}

func getPlainText(bufConn *BufConn) (bool, error) {
	defer bufConn.setReadTimeout()

	if bufConn.canSetReadDeadline() {
		// Set deadline such that we close the connection quickly
		// of no data was received from the Peek()
		bufConn.SetReadDeadline(time.Now().UTC().Add(time.Second * 3))
	}
	b, err := bufConn.Peek(1)
	if err != nil {
		return false, err
	}
	for _, method := range methods {
		if b[0] == method[0] {
			return true, nil
		}
	}
	return false, nil
}

func getMethodResourceHost(bufConn *BufConn, maxHeaderBytes int) (method string, resource string, host string, err error) {
	defer bufConn.setReadTimeout()

	var data []byte
	for dataLen := 1; dataLen < maxHeaderBytes; dataLen++ {
		if bufConn.canSetReadDeadline() {
			// Set deadline such that we close the connection quickly
			// of no data was received from the Peek()
			bufConn.SetReadDeadline(time.Now().UTC().Add(time.Second * 3))
		}

		data, err = bufConn.bufReader.Peek(dataLen)
		if err != nil {
			return "", "", "", err
		}

		tokens := strings.Split(string(data), "\n")
		if len(tokens) < 2 {
			continue
		}

		if method == "" && resource == "" {
			if i := strings.IndexByte(tokens[0], ' '); i == -1 {
				return "", "", "", fmt.Errorf("malformed HTTP request from '%s'", bufConn.LocalAddr())
			}
			httpTokens := strings.SplitN(tokens[0], " ", 3)
			if len(httpTokens) < 3 {
				return "", "", "", fmt.Errorf("malformed HTTP request from '%s'", bufConn.LocalAddr())
			}
			if !isHTTPMethod(httpTokens[0]) {
				return "", "", "", fmt.Errorf("malformed HTTP request, invalid HTTP method '%s' from '%s'",
					httpTokens[0], bufConn.LocalAddr())
			}

			method = httpTokens[0]
			resource = httpTokens[1]
		}

		for _, token := range tokens[1:] {
			if token == "" || !strings.HasSuffix(token, "\r") {
				continue
			}

			// HTTP headers are case insensitive, so we should simply convert
			// each tokens to their lower case form to match 'host' header.
			token = strings.ToLower(token)
			if strings.HasPrefix(token, "host:") {
				host = strings.TrimPrefix(strings.TrimSuffix(token, "\r"), "host:")
				return method, resource, host, nil
			}
		}

		if tokens[len(tokens)-1] == "\r" {
			break
		}
	}

	return "", "", "", fmt.Errorf("malformed HTTP request from %s", bufConn.LocalAddr())
}

type acceptResult struct {
	conn net.Conn
	err  error
}

// httpListener - HTTP listener capable of handling multiple server addresses.
type httpListener struct {
	mutex                  sync.Mutex         // to guard Close() method.
	tcpListeners           []*net.TCPListener // underlaying TCP listeners.
	acceptCh               chan acceptResult  // channel where all TCP listeners write accepted connection.
	doneCh                 chan struct{}      // done channel for TCP listener goroutines.
	tlsConfig              *tls.Config        // TLS configuration
	tcpKeepAliveTimeout    time.Duration
	readTimeout            time.Duration
	writeTimeout           time.Duration
	maxHeaderBytes         int
	updateBytesReadFunc    func(*http.Request, int) // function to be called to update bytes read in BufConn.
	updateBytesWrittenFunc func(*http.Request, int) // function to be called to update bytes written in BufConn.
}

// isRoutineNetErr returns true if error is due to a network timeout,
// connect reset or io.EOF and false otherwise
func isRoutineNetErr(err error) bool {
	if err == nil {
		return false
	}
	if nErr, ok := err.(*net.OpError); ok {
		// Check if the error is a tcp connection reset
		if syscallErr, ok := nErr.Err.(*os.SyscallError); ok {
			if errno, ok := syscallErr.Err.(syscall.Errno); ok {
				return errno == syscall.ECONNRESET
			}
		}
		// Check if the error is a timeout
		return nErr.Timeout()
	}
	// check for io.EOF and also some times io.EOF is wrapped is another error type.
	return err == io.EOF || err.Error() == "EOF"
}

// start - starts separate goroutine for each TCP listener.  A valid insecure/TLS HTTP new connection is passed to httpListener.acceptCh.
func (listener *httpListener) start() {
	listener.acceptCh = make(chan acceptResult)
	listener.doneCh = make(chan struct{})

	// Closure to send acceptResult to acceptCh.
	// It returns true if the result is sent else false if returns when doneCh is closed.
	send := func(result acceptResult, doneCh <-chan struct{}) bool {
		select {
		case listener.acceptCh <- result:
			// Successfully written to acceptCh
			return true
		case <-doneCh:
			// As stop signal is received, close accepted connection.
			if result.conn != nil {
				result.conn.Close()
			}
			return false
		}
	}

	// Closure to handle single connection.
	handleConn := func(tcpConn *net.TCPConn, doneCh <-chan struct{}) {
		// Tune accepted TCP connection.
		tcpConn.SetKeepAlive(true)
		tcpConn.SetKeepAlivePeriod(listener.tcpKeepAliveTimeout)

		bufconn := newBufConn(tcpConn, listener.readTimeout, listener.writeTimeout)
		if listener.tlsConfig != nil {
			ok, err := getPlainText(bufconn)
			if err != nil {
				// Peek could fail legitimately when clients abruptly close
				// connection. E.g. Chrome browser opens connections speculatively to
				// speed up loading of a web page. Peek may also fail due to network
				// saturation on a transport with read timeout set. All other kind of
				// errors should be logged for further investigation. Thanks @brendanashworth.
				if !isRoutineNetErr(err) {
					reqInfo := (&logger.ReqInfo{}).AppendTags("remoteAddr", bufconn.RemoteAddr().String())
					reqInfo.AppendTags("localAddr", bufconn.LocalAddr().String())
					ctx := logger.SetReqInfo(context.Background(), reqInfo)
					logger.LogIf(ctx, err)
				}
				bufconn.Close()
				return
			}

			if ok {
				// As TLS is configured and we got plain text HTTP request,
				// return 403 (forbidden) error.
				bufconn.Write(sslRequiredErrMsg)
				bufconn.Close()
				return
			}

			// As the listener is configured with TLS, try to do TLS handshake, drop the connection if it fails.
			tlsConn := tls.Server(bufconn, listener.tlsConfig)

			if err := tlsConn.Handshake(); err != nil {
				reqInfo := (&logger.ReqInfo{}).AppendTags("remoteAddr", bufconn.RemoteAddr().String())
				reqInfo.AppendTags("localAddr", bufconn.LocalAddr().String())
				ctx := logger.SetReqInfo(context.Background(), reqInfo)
				logger.LogIf(ctx, err)
				bufconn.Close()
				return
			}

			bufconn = newBufConn(tlsConn, listener.readTimeout, listener.writeTimeout)
		}

		method, resource, host, err := getMethodResourceHost(bufconn, listener.maxHeaderBytes)
		if err != nil {
			// Peek could fail legitimately when clients abruptly close
			// connection. E.g. Chrome browser opens connections speculatively to
			// speed up loading of a web page. Peek may also fail due to network
			// saturation on a transport with read timeout set. All other kind of
			// errors should be logged for further investigation. Thanks @brendanashworth.
			if !isRoutineNetErr(err) {
				reqInfo := (&logger.ReqInfo{}).AppendTags("remoteAddr", bufconn.RemoteAddr().String())
				reqInfo.AppendTags("localAddr", bufconn.LocalAddr().String())
				ctx := logger.SetReqInfo(context.Background(), reqInfo)
				logger.LogIf(ctx, err)
				bufconn.Write(badRequestMsg)
			}
			bufconn.Close()
			return
		}

		header := make(http.Header)
		if host != "" {
			header.Add("Host", host)
		}
		bufconn.setRequest(&http.Request{
			Method: method,
			URL:    &url.URL{Path: resource},
			Host:   bufconn.LocalAddr().String(),
			Header: header,
		})
		bufconn.setUpdateFuncs(listener.updateBytesReadFunc, listener.updateBytesWrittenFunc)

		send(acceptResult{bufconn, nil}, doneCh)
	}

	// Closure to handle TCPListener until done channel is closed.
	handleListener := func(tcpListener *net.TCPListener, doneCh <-chan struct{}) {
		for {
			tcpConn, err := tcpListener.AcceptTCP()
			if err != nil {
				// Returns when send fails.
				if !send(acceptResult{nil, err}, doneCh) {
					return
				}
			} else {
				go handleConn(tcpConn, doneCh)
			}
		}
	}

	// Start separate goroutine for each TCP listener to handle connection.
	for _, tcpListener := range listener.tcpListeners {
		go handleListener(tcpListener, listener.doneCh)
	}
}

// Accept - reads from httpListener.acceptCh for one of previously accepted TCP connection and returns the same.
func (listener *httpListener) Accept() (conn net.Conn, err error) {
	result, ok := <-listener.acceptCh
	if ok {
		return result.conn, result.err
	}

	return nil, syscall.EINVAL
}

// Close - closes underneath all TCP listeners.
func (listener *httpListener) Close() (err error) {
	listener.mutex.Lock()
	defer listener.mutex.Unlock()
	if listener.doneCh == nil {
		return syscall.EINVAL
	}

	for i := range listener.tcpListeners {
		listener.tcpListeners[i].Close()
	}
	close(listener.doneCh)

	listener.doneCh = nil
	return nil
}

// Addr - net.Listener interface compatible method returns net.Addr.  In case of multiple TCP listeners, it returns '0.0.0.0' as IP address.
func (listener *httpListener) Addr() (addr net.Addr) {
	addr = listener.tcpListeners[0].Addr()
	if len(listener.tcpListeners) == 1 {
		return addr
	}

	tcpAddr := addr.(*net.TCPAddr)
	if ip := net.ParseIP("0.0.0.0"); ip != nil {
		tcpAddr.IP = ip
	}

	addr = tcpAddr
	return addr
}

// Addrs - returns all address information of TCP listeners.
func (listener *httpListener) Addrs() (addrs []net.Addr) {
	for i := range listener.tcpListeners {
		addrs = append(addrs, listener.tcpListeners[i].Addr())
	}

	return addrs
}

// newHTTPListener - creates new httpListener object which is interface compatible to net.Listener.
// httpListener is capable to
// * listen to multiple addresses
// * controls incoming connections only doing HTTP protocol
func newHTTPListener(serverAddrs []string,
	tlsConfig *tls.Config,
	tcpKeepAliveTimeout time.Duration,
	readTimeout time.Duration,
	writeTimeout time.Duration,
	maxHeaderBytes int,
	updateBytesReadFunc func(*http.Request, int),
	updateBytesWrittenFunc func(*http.Request, int)) (listener *httpListener, err error) {

	var tcpListeners []*net.TCPListener

	// Close all opened listeners on error
	defer func() {
		if err == nil {
			return
		}

		for _, tcpListener := range tcpListeners {
			// Ignore error on close.
			tcpListener.Close()
		}
	}()

	for _, serverAddr := range serverAddrs {
		var l net.Listener
		if l, err = listen("tcp", serverAddr); err != nil {
			if l, err = fallbackListen("tcp", serverAddr); err != nil {
				return nil, err
			}
		}

		tcpListener, ok := l.(*net.TCPListener)
		if !ok {
			return nil, fmt.Errorf("unexpected listener type found %v, expected net.TCPListener", l)
		}

		tcpListeners = append(tcpListeners, tcpListener)
	}

	listener = &httpListener{
		tcpListeners:           tcpListeners,
		tlsConfig:              tlsConfig,
		tcpKeepAliveTimeout:    tcpKeepAliveTimeout,
		readTimeout:            readTimeout,
		writeTimeout:           writeTimeout,
		maxHeaderBytes:         maxHeaderBytes,
		updateBytesReadFunc:    updateBytesReadFunc,
		updateBytesWrittenFunc: updateBytesWrittenFunc,
	}
	listener.start()

	return listener, nil
}