// Copyright (c) 2019 The BFE 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.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package bfe_tls partially implements TLS 1.2, as specified in RFC 5246.
package bfe_tls

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"io/ioutil"
	"net"
	"strings"
	"sync"
	"time"
)

// Server returns a new TLS server side connection
// using conn as the underlying transport.
// The configuration config must be non-nil and must have
// at least one certificate.
func Server(conn net.Conn, config *Config) *Conn {
	return &Conn{conn: conn, config: config}
}

// Client returns a new TLS client side connection
// using conn as the underlying transport.
// The config cannot be nil: users must set either ServerName or
// InsecureSkipVerify in the config.
func Client(conn net.Conn, config *Config) *Conn {
	return &Conn{conn: conn, config: config, isClient: true}
}

// A listener implements a network listener (net.Listener) for TLS connections.
type listener struct {
	net.Listener
	config *Config
	lock   sync.RWMutex // lock for config
}

// Accept waits for and returns the next incoming TLS connection.
// The returned connection c is a *tls.Conn.
func (l *listener) Accept() (c net.Conn, err error) {
	c, err = l.Listener.Accept()
	if err != nil {
		return
	}

	l.lock.RLock()
	c = Server(c, l.config)
	l.lock.RUnlock()
	return
}

// NewListener creates a Listener which accepts connections from an inner
// Listener and wraps each connection with Server.
// The configuration config must be non-nil and must have
// at least one certificate.
func NewListener(inner net.Listener, config *Config) net.Listener {
	l := new(listener)
	l.Listener = inner
	l.config = config
	return l
}

// UpdateListener updates config for tls listener
/*
 * Params:
 *     - ln  : a tls listener
 *     - conf: a tls config
 *
 * Return:
 *     - error
 *
 * Note:
 *     1. tls.listener will not modify tls.Config and just pass it
 * to accepted Connection.
 *     2. tls.Conn will just read tls.Config during handshake and
 * data transfer phase
 *     3. MUST specify a new tls.config when called
 */
func UpdateListener(ln net.Listener, conf *Config) error {
	l, ok := ln.(*listener)
	if !ok {
		return errors.New("tls.UpdateListener: type not tls.listener")
	}

	l.lock.Lock()
	defer l.lock.Unlock()

	if l.config == conf {
		return errors.New("tls.UpdateListener: not safe to modify config in use")
	}

	l.config = conf
	return nil
}

// Listen creates a TLS listener accepting connections on the
// given network address using net.Listen.
// The configuration config must be non-nil and must have
// at least one certificate.
func Listen(network, laddr string, config *Config) (net.Listener, error) {
	if config == nil || len(config.Certificates) == 0 {
		return nil, errors.New("tls.Listen: no certificates in configuration")
	}
	l, err := net.Listen(network, laddr)
	if err != nil {
		return nil, err
	}
	return NewListener(l, config), nil
}

type timeoutError struct{}

func (timeoutError) Error() string   { return "tls: DialWithDialer timed out" }
func (timeoutError) Timeout() bool   { return true }
func (timeoutError) Temporary() bool { return true }

// DialWithDialer connects to the given network address using dialer.Dial and
// then initiates a TLS handshake, returning the resulting TLS connection. Any
// timeout or deadline given in the dialer apply to connection and TLS
// handshake as a whole.
//
// DialWithDialer interprets a nil configuration as equivalent to the zero
// configuration; see the documentation of Config for the defaults.
func DialWithDialer(dialer *net.Dialer, network, addr string, config *Config) (*Conn, error) {
	// We want the Timeout and Deadline values from dialer to cover the
	// whole process: TCP connection and TLS handshake. This means that we
	// also need to start our own timers now.
	timeout := dialer.Timeout

	if !dialer.Deadline.IsZero() {
		deadlineTimeout := dialer.Deadline.Sub(time.Now())
		if timeout == 0 || deadlineTimeout < timeout {
			timeout = deadlineTimeout
		}
	}

	var errChannel chan error

	if timeout != 0 {
		errChannel = make(chan error, 2)
		time.AfterFunc(timeout, func() {
			errChannel <- timeoutError{}
		})
	}

	rawConn, err := dialer.Dial(network, addr)
	if err != nil {
		return nil, err
	}

	colonPos := strings.LastIndex(addr, ":")
	if colonPos == -1 {
		colonPos = len(addr)
	}
	hostname := addr[:colonPos]

	if config == nil {
		config = defaultConfig()
	}
	// If no ServerName is set, infer the ServerName
	// from the hostname we're connecting to.
	if config.ServerName == "" {
		// Make a copy to avoid polluting argument or default.
		c := config.Clone()
		c.ServerName = hostname
		config = c
	}

	conn := Client(rawConn, config)

	if timeout == 0 {
		err = conn.Handshake()
	} else {
		go func() {
			errChannel <- conn.Handshake()
		}()

		err = <-errChannel
	}

	if err != nil {
		rawConn.Close()
		return nil, err
	}

	return conn, nil
}

// Dial connects to the given network address using net.Dial
// and then initiates a TLS handshake, returning the resulting
// TLS connection.
// Dial interprets a nil configuration as equivalent to
// the zero configuration; see the documentation of Config
// for the defaults.
func Dial(network, addr string, config *Config) (*Conn, error) {
	return DialWithDialer(new(net.Dialer), network, addr, config)
}

// LoadX509KeyPair reads and parses a public/private key pair from a pair of
// files. The files must contain PEM encoded data.
func LoadX509KeyPair(certFile, keyFile string) (cert Certificate, err error) {
	// try third party loader
	if keyPairLoader != nil {
		return keyPairLoader.LoadX509KeyPair(certFile, keyFile)
	}

	certPEMBlock, err := ioutil.ReadFile(certFile)
	if err != nil {
		return
	}
	keyPEMBlock, err := ioutil.ReadFile(keyFile)
	if err != nil {
		return
	}
	return X509KeyPair(certPEMBlock, keyPEMBlock)
}

// X509KeyPair parses a public/private key pair from a pair of
// PEM encoded data.
func X509KeyPair(certPEMBlock, keyPEMBlock []byte) (cert Certificate, err error) {
	var certDERBlock *pem.Block
	for {
		certDERBlock, certPEMBlock = pem.Decode(certPEMBlock)
		if certDERBlock == nil {
			break
		}
		if certDERBlock.Type == "CERTIFICATE" {
			cert.Certificate = append(cert.Certificate, certDERBlock.Bytes)
		}
	}

	if len(cert.Certificate) == 0 {
		err = errors.New("crypto/tls: failed to parse certificate PEM data")
		return
	}
	cert.buildCertMsg() // prebuild cert message for tls handshake

	var keyDERBlock *pem.Block
	for {
		keyDERBlock, keyPEMBlock = pem.Decode(keyPEMBlock)
		if keyDERBlock == nil {
			err = errors.New("crypto/tls: failed to parse key PEM data")
			return
		}
		if keyDERBlock.Type == "PRIVATE KEY" || strings.HasSuffix(keyDERBlock.Type, " PRIVATE KEY") {
			break
		}
	}

	cert.PrivateKey, err = parsePrivateKey(keyDERBlock.Bytes)
	if err != nil {
		return
	}

	// We don't need to parse the public key for TLS, but we so do anyway
	// to check that it looks sane and matches the private key.
	x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
	if err != nil {
		return
	}

	switch pub := x509Cert.PublicKey.(type) {
	case *rsa.PublicKey:
		priv, ok := cert.PrivateKey.(*rsa.PrivateKey)
		if !ok {
			err = errors.New("crypto/tls: private key type does not match public key type")
			return
		}
		if pub.N.Cmp(priv.N) != 0 {
			err = errors.New("crypto/tls: private key does not match public key")
			return
		}
	case *ecdsa.PublicKey:
		priv, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
		if !ok {
			err = errors.New("crypto/tls: private key type does not match public key type")
			return
		}
		if pub.X.Cmp(priv.X) != 0 || pub.Y.Cmp(priv.Y) != 0 {
			err = errors.New("crypto/tls: private key does not match public key")
			return
		}
	default:
		err = errors.New("crypto/tls: unknown public key algorithm")
		return
	}

	return
}

// Attempt to parse the given private key DER block. OpenSSL 0.9.8 generates
// PKCS#1 private keys by default, while OpenSSL 1.0.0 generates PKCS#8 keys.
// OpenSSL ecparam generates SEC1 EC private keys for ECDSA. We try all three.
func parsePrivateKey(der []byte) (crypto.PrivateKey, error) {
	if key, err := x509.ParsePKCS1PrivateKey(der); err == nil {
		return key, nil
	}
	if key, err := x509.ParsePKCS8PrivateKey(der); err == nil {
		switch key := key.(type) {
		case *rsa.PrivateKey, *ecdsa.PrivateKey:
			return key, nil
		default:
			return nil, errors.New("crypto/tls: found unknown private key type in PKCS#8 wrapping")
		}
	}
	if key, err := x509.ParseECPrivateKey(der); err == nil {
		return key, nil
	}

	return nil, errors.New("crypto/tls: failed to parse private key")
}
