// 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

import (
	"container/list"
	"crypto"
	"crypto/rand"
	"crypto/x509"
	"fmt"
	"io"
	"math/big"
	"strings"
	"sync"
	"time"

	"golang.org/x/crypto/ocsp"
)

const (
	VersionSSL30 = 0x0300
	VersionTLS10 = 0x0301
	VersionTLS11 = 0x0302
	VersionTLS12 = 0x0303
)

const (
	minPlaintext    = 1024         // length plaintext payload that fit into a signle TCP segment
	maxPlaintext    = 16384        // maximum plaintext payload length
	maxCiphertext   = 16384 + 2048 // maximum ciphertext payload length
	recordHeaderLen = 5            // record header length
	maxHandshake    = 65536        // maximum handshake we support (protocol max is 16 MB)

	minVersion = VersionSSL30
	maxVersion = VersionTLS12

	ticketKeyNameLen = 16 // length for session ticket key name
)

// the following grade (A, B, C) is defined by
// www.ssllabs.com
// Grade A+: no ssl3, tls1.0, tls1.1 && no RC4 ciphers
// Grade A: no ssl3 && no RC4 ciphers
// Grade B: ssl3 is ok only with RC4 cipher, or
//
//	modern version(>=tls10) with no RC4 cipher
//
// Grade C: ssl3 is ok only with RC4 cipher
const (
	GradeAPlus = "A+"
	GradeA     = "A"
	GradeB     = "B"
	GradeC     = "C"
)

/*
 * Note: Google's servers use small TLS records that fit into a sing TCP segment
 * for the first ~1 MB of data, increase record size to 16 KB after that to optimize throughput,
 * and then reset record size back to a single segment after ~1 second of inactivity
 * - lather, rinse, repeat.
 *
 * For more information, see:
 *     http://chimera.labs.oreilly.com/books/1230000000545/ch04.html#TLS_RECORD_SIZE
 */
var (
	initPlaintext   int           = minPlaintext                   // initial length of plaintext payload
	bytesThreshold  int           = 1024 * 1024                    // 1 MB
	inactiveSeconds time.Duration = time.Duration(1 * time.Second) // 1 second
)

// TLS record types.
type recordType uint8

const (
	recordTypeChangeCipherSpec recordType = 20
	recordTypeAlert            recordType = 21
	recordTypeHandshake        recordType = 22
	recordTypeApplicationData  recordType = 23
)

// TLS handshake message types.
const (
	typeClientHello        uint8 = 1
	typeServerHello        uint8 = 2
	typeNewSessionTicket   uint8 = 4
	typeCertificate        uint8 = 11
	typeServerKeyExchange  uint8 = 12
	typeCertificateRequest uint8 = 13
	typeServerHelloDone    uint8 = 14
	typeCertificateVerify  uint8 = 15
	typeClientKeyExchange  uint8 = 16
	typeFinished           uint8 = 20
	typeCertificateStatus  uint8 = 22
	typeNextProtocol       uint8 = 67 // Not IANA assigned
)

// TLS compression types.
const (
	compressionNone uint8 = 0
)

// TLS extension numbers
const (
	extensionServerName          uint16 = 0
	extensionStatusRequest       uint16 = 5
	extensionSupportedCurves     uint16 = 10
	extensionSupportedPoints     uint16 = 11
	extensionSignatureAlgorithms uint16 = 13
	extensionALPN                uint16 = 16
	extensionPadding             uint16 = 21
	extensionSessionTicket       uint16 = 35
	extensionNextProtoNeg        uint16 = 13172 // not IANA assigned
	extensionRenegotiationInfo   uint16 = 0xff01
)

// TLS signaling cipher suite values
const (
	scsvRenegotiation uint16 = 0x00ff
)

// CurveID is the type of a TLS identifier for an elliptic curve. See
// http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-8
type CurveID uint16

const (
	CurveP256 CurveID = 23
	CurveP384 CurveID = 24
	CurveP521 CurveID = 25
)

// TLS Elliptic Curve Point Formats
// http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-9
const (
	pointFormatUncompressed uint8 = 0
)

// TLS CertificateStatusType (RFC 3546)
const (
	statusTypeOCSP uint8 = 1
)

// Certificate types (for certificateRequestMsg)
const (
	certTypeRSASign    = 1 // A certificate containing an RSA key
	certTypeDSSSign    = 2 // A certificate containing a DSA key
	certTypeRSAFixedDH = 3 // A certificate containing a static DH key
	certTypeDSSFixedDH = 4 // A certificate containing a static DH key

	// See RFC4492 sections 3 and 5.5.
	certTypeECDSASign      = 64 // A certificate containing an ECDSA-capable public key, signed with ECDSA.
	certTypeRSAFixedECDH   = 65 // A certificate containing an ECDH-capable public key, signed with RSA.
	certTypeECDSAFixedECDH = 66 // A certificate containing an ECDH-capable public key, signed with ECDSA.

	// Rest of these are reserved by the TLS spec
)

// Hash functions for TLS 1.2 (See RFC 5246, section A.4.1)
const (
	hashSHA1   uint8 = 2
	hashSHA256 uint8 = 4
)

// Signature algorithms for TLS 1.2 (See RFC 5246, section A.4.1)
const (
	signatureRSA   uint8 = 1
	signatureECDSA uint8 = 3
)

// signatureAndHash mirrors the TLS 1.2, SignatureAndHashAlgorithm struct. See
// RFC 5246, section A.4.1.
type signatureAndHash struct {
	hash, signature uint8
}

// supportedSKXSignatureAlgorithms contains the signature and hash algorithms
// that the code advertises as supported in a TLS 1.2 ClientHello.
var supportedSKXSignatureAlgorithms = []signatureAndHash{
	{hashSHA256, signatureRSA},
	{hashSHA256, signatureECDSA},
	{hashSHA1, signatureRSA},
	{hashSHA1, signatureECDSA},
}

// supportedClientCertSignatureAlgorithms contains the signature and hash
// algorithms that the code advertises as supported in a TLS 1.2
// CertificateRequest.
var supportedClientCertSignatureAlgorithms = []signatureAndHash{
	{hashSHA256, signatureRSA},
	{hashSHA256, signatureECDSA},
}

// ConnectionState records basic TLS details about the connection.
type ConnectionState struct {
	Version                    uint16                // TLS version used by the connection (e.g. VersionTLS12)
	HandshakeComplete          bool                  // TLS handshake is complete
	DidResume                  bool                  // connection resumes a previous TLS connection
	CipherSuite                uint16                // cipher suite in use (TLS_RSA_WITH_RC4_128_SHA, ...)
	OcspStaple                 bool                  // use ocsp staple (in server side)
	NegotiatedProtocolIsMutual bool                  // negotiated protocol was advertised by server
	NegotiatedProtocol         string                // negotiated next protocol (from Config.NextProtos)
	ServerName                 string                // server name requested by client, if any (server side only)
	HandshakeTime              time.Duration         // TLS handshake time (in server side)
	PeerCertificates           []*x509.Certificate   // certificate chain presented by remote peer
	VerifiedChains             [][]*x509.Certificate // verified chains built from PeerCertificates
	ClientRandom               []byte                // random in client hello
	ServerRandom               []byte                // random in server hello
	MasterSecret               []byte                // master secret used by the connection
	ClientCiphers              []uint16              // ciphers supported by client
	ClientAuth                 bool                  // enable TLS Client Authentication
	ClientCAName               string                // TLS client CA name
	JA3Raw                     string                // JA3 fingerprint string for TLS Client
	JA3Hash                    string                // JA3 fingerprint hash for TLS Client
}

// ClientAuthType declares the policy the server will follow for
// TLS Client Authentication.
type ClientAuthType int

const (
	NoClientCert ClientAuthType = iota
	RequestClientCert
	RequireAnyClientCert
	VerifyClientCertIfGiven
	RequireAndVerifyClientCert
)

// ClientSessionState contains the state needed by clients to resume TLS
// sessions.
type ClientSessionState struct {
	sessionTicket      []uint8             // Encrypted ticket used for session resumption with server
	vers               uint16              // SSL/TLS version negotiated for the session
	cipherSuite        uint16              // Ciphersuite negotiated for the session
	masterSecret       []byte              // MasterSecret generated by client on a full handshake
	serverCertificates []*x509.Certificate // Certificate chain presented by the server
}

// ClientSessionCache is a cache of ClientSessionState objects that can be used
// by a client to resume a TLS session with a given server. ClientSessionCache
// implementations should expect to be called concurrently from different
// goroutines.
type ClientSessionCache interface {
	// Get searches for a ClientSessionState associated with the given key.
	// On return, ok is true if one was found.
	Get(sessionKey string) (session *ClientSessionState, ok bool)

	// Put adds the ClientSessionState to the cache with the given key.
	Put(sessionKey string, cs *ClientSessionState)
}

type ServerSessionCache interface {
	// Get searches for a sessionState associated with the given key.
	// On return, ok is true if one was found.
	Get(sessionKey string) (sessionState []byte, ok bool)

	// Put adds the sessionState to the cache with the given key.
	Put(sessionKey string, sessionState []byte) error
}

type MultiCertificate interface {
	// Get certificate for the given conn
	Get(c *Conn) *Certificate
}

// multiply certificate policy for thirdparty
var tlsMultiCertificate MultiCertificate

func SetTlsMultiCertificate(m MultiCertificate) {
	tlsMultiCertificate = m
}

type NextProtoConf interface {
	// Get next protos for the given conn
	Get(c *Conn) []string
}

// Rule represents customized tls config for specific conn in server side
type Rule struct {
	// NextProtos is a list of supported, application level protocols.
	NextProtos NextProtoConf

	// Security Grade
	Grade string

	// enable TLS Client Authentication
	ClientAuth bool

	// client CA certificate
	ClientCAs *x509.CertPool

	// client CA name
	ClientCAName string

	// client CRL pool
	ClientCRLPool *CRLPool

	// enable Chacha20-poly1305 cipher suites
	Chacha20 bool

	// enable Dynamic TLS record size
	DynamicRecord bool
}

type ServerRule interface {
	// Get tls rule for the given conn
	Get(c *Conn) *Rule
}

// A Config structure is used to configure a TLS client or server.
// After one has been passed to a TLS function it must not be
// modified. A Config may be reused; the tls package will also not
// modify it.
type Config struct {
	// Rand provides the source of entropy for nonces and RSA blinding.
	// If Rand is nil, TLS uses the cryptographic random reader in package
	// crypto/rand.
	// The Reader must be safe for use by multiple goroutines.
	Rand io.Reader

	// Time returns the current time as the number of seconds since the epoch.
	// If Time is nil, TLS uses time.Now.
	Time func() time.Time

	// Certificates contains one or more certificate chains
	// to present to the other side of the connection.
	// Server configurations must include at least one certificate.
	Certificates []Certificate

	// NameToCertificate maps from a certificate name to an element of
	// Certificates. Note that a certificate name can be of the form
	// '*.example.com' and so doesn't have to be a domain name as such.
	// See Config.BuildNameToCertificate
	// The nil value causes the first element of Certificates to be used
	// for all connections.
	NameToCertificate map[string]*Certificate

	// VerifyPeerCertificate, if not nil, is called after normal
	// certificate verification by either a TLS client or server. It
	// receives the raw ASN.1 certificates provided by the peer and also
	// any verified chains that normal processing found. If it returns a
	// non-nil error, the handshake is aborted and that error results.
	//
	// If normal verification fails then the handshake will abort before
	// considering this callback. If normal verification is disabled by
	// setting InsecureSkipVerify, or (for a server) when ClientAuth is
	// RequestClientCert or RequireAnyClientCert, then this callback will
	// be considered but the verifiedChains argument will always be nil.
	VerifyPeerCertificate func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error

	// default multiply certificates policy for tls server
	MultiCert MultiCertificate

	// RootCAs defines the set of root certificate authorities
	// that clients use when verifying server certificates.
	// If RootCAs is nil, TLS uses the host's root CA set.
	RootCAs *x509.CertPool

	// NextProtos is a list of supported, application level protocols.
	NextProtos []string

	// ServerName is used to verify the hostname on the returned
	// certificates unless InsecureSkipVerify is given. It is also included
	// in the client's handshake to support virtual hosting.
	ServerName string

	// ClientAuth determines the server's global policy for
	// TLS Client Authentication. The default is NoClientCert.
	ClientAuth ClientAuthType

	// ClientCAs defines the set of root certificate authorities
	// that servers use if required to verify a client certificate
	// by the policy in ClientAuth.
	ClientCAs *x509.CertPool

	// InsecureSkipVerify controls whether a client verifies the
	// server's certificate chain and host name.
	// If InsecureSkipVerify is true, TLS accepts any certificate
	// presented by the server and any host name in that certificate.
	// In this mode, TLS is susceptible to man-in-the-middle attacks.
	// This should be used only for testing.
	InsecureSkipVerify bool

	// CipherSuites is a list of supported cipher suites. If CipherSuites
	// is nil, TLS uses a list of suites supported by the implementation.
	CipherSuites []uint16

	// Priority of cipher suites in server side. If PreferServerCipherSuites
	// is false, CipherSuitesPriority should be ignored during cipher suite
	// negotiation
	CipherSuitesPriority []uint16

	// PreferServerCipherSuites controls whether the server selects the
	// client's most preferred ciphersuite, or the server's most preferred
	// ciphersuite. If true then the server's preference, as expressed in
	// the order of elements in CipherSuites, is used.
	PreferServerCipherSuites bool

	// here prohibit poodle attack by allow RC4 cipher only used with ssl3.0
	Ssl3PoodleProofed bool

	// SessionTicketsDisabled may be set to true to disable session ticket
	// (resumption) support.
	SessionTicketsDisabled bool

	// SessionTicketKey is used by TLS servers to provide session
	// resumption. See RFC 5077. If zero, it will be filled with
	// random data before the first server handshake.
	//
	// If multiple servers are terminating connections for the same host
	// they should all have the same SessionTicketKey. If the
	// SessionTicketKey leaks, previously recorded and future TLS
	// connections using that key are compromised.
	SessionTicketKey [32]byte

	// SessionTicketKeyName is used as an identifier for SessionTicketKey
	// in SessionTicket
	SessionTicketKeyName [16]byte

	// SessionCache is a cache of ClientSessionState entries for TLS session
	// resumption.
	ClientSessionCache ClientSessionCache

	// SessionCache is a cache of sessionState entries for TLS session
	// resumption.
	ServerSessionCache ServerSessionCache

	// SessionCacheDisabled may be set to true to disable session cache
	// (resumption) support.
	SessionCacheDisabled bool

	// MinVersion contains the minimum SSL/TLS version that is acceptable.
	// If zero, then SSLv3 is taken as the minimum.
	MinVersion uint16

	// MaxVersion contains the maximum SSL/TLS version that is acceptable.
	// If zero, then the maximum version supported by this package is used,
	// which is currently TLS 1.2.
	MaxVersion uint16

	// CurvePreferences contains the elliptic curves that will be used in
	// an ECDHE handshake, in preference order. If empty, the default will
	// be used.
	CurvePreferences []CurveID

	// Support SSLv2 ClientHello for backward compatibility with ancient
	// TLS-capable clients.
	EnableSslv2ClientHello bool

	// customized config for server side
	ServerRule ServerRule

	serverInitOnce sync.Once // guards calling (*Config).serverInit
}

// Clone returns a shallow clone of c. It is safe to clone a Config that is
// being used concurrently by a TLS client or server.
func (c *Config) Clone() *Config {
	// Running serverInit ensures that it's safe to read
	// SessionTicketsDisabled.
	c.serverInitOnce.Do(func() { c.serverInit() })

	return &Config{
		Rand:                     c.Rand,
		Time:                     c.Time,
		Certificates:             c.Certificates,
		NameToCertificate:        c.NameToCertificate,
		VerifyPeerCertificate:    c.VerifyPeerCertificate,
		MultiCert:                c.MultiCert,
		RootCAs:                  c.RootCAs,
		NextProtos:               c.NextProtos,
		ServerName:               c.ServerName,
		ClientAuth:               c.ClientAuth,
		ClientCAs:                c.ClientCAs,
		InsecureSkipVerify:       c.InsecureSkipVerify,
		CipherSuites:             c.CipherSuites,
		CipherSuitesPriority:     c.CipherSuitesPriority,
		PreferServerCipherSuites: c.PreferServerCipherSuites,
		Ssl3PoodleProofed:        c.Ssl3PoodleProofed,
		SessionTicketsDisabled:   c.SessionTicketsDisabled,
		SessionTicketKey:         c.SessionTicketKey,
		SessionTicketKeyName:     c.SessionTicketKeyName,
		ClientSessionCache:       c.ClientSessionCache,
		ServerSessionCache:       c.ServerSessionCache,
		SessionCacheDisabled:     c.SessionCacheDisabled,
		MinVersion:               c.MinVersion,
		MaxVersion:               c.MaxVersion,
		CurvePreferences:         c.CurvePreferences,
		EnableSslv2ClientHello:   c.EnableSslv2ClientHello,
		ServerRule:               c.ServerRule,
	}
}

func (c *Config) serverInit() {
	if c.SessionTicketsDisabled {
		return
	}

	// If the key has already been set then we have nothing to do.
	for _, b := range c.SessionTicketKey {
		if b != 0 {
			return
		}
	}

	if _, err := io.ReadFull(c.rand(), c.SessionTicketKey[:]); err != nil {
		c.SessionTicketsDisabled = true
	}
}

func (c *Config) rand() io.Reader {
	r := c.Rand
	if r == nil {
		return rand.Reader
	}
	return r
}

func (c *Config) time() time.Time {
	t := c.Time
	if t == nil {
		t = time.Now
	}
	return t()
}

func (c *Config) cipherSuites() []uint16 {
	s := c.CipherSuites
	if s == nil {
		s = defaultCipherSuites()
	}
	return s
}

func (c *Config) minVersion() uint16 {
	if c == nil || c.MinVersion == 0 {
		return minVersion
	}
	return c.MinVersion
}

func (c *Config) maxVersion() uint16 {
	if c == nil || c.MaxVersion == 0 {
		return maxVersion
	}
	return c.MaxVersion
}

var defaultCurvePreferences = []CurveID{CurveP256, CurveP384, CurveP521}

func (c *Config) curvePreferences() []CurveID {
	if c == nil || len(c.CurvePreferences) == 0 {
		return defaultCurvePreferences
	}
	return c.CurvePreferences
}

// mutualVersion returns the protocol version to use given the advertised
// version of the peer.
func (c *Config) mutualVersion(vers uint16) (uint16, bool) {
	minVersion := c.minVersion()
	maxVersion := c.maxVersion()

	if vers < minVersion {
		return 0, false
	}
	if vers > maxVersion {
		vers = maxVersion
	}
	return vers, true
}

// followed the rule defined in www.ssllabs.com:
// in Grade "A+", ssl version older than tls1.2 is not allowed
// in Grade "A", ssl version older than tls1.0 is not allowed
func (c *Config) checkVersionGrade(vers uint16, grade string) (uint16, bool) {
	// ssl ver older than tls1.0 is not allowed for Grade A
	if grade == GradeA && vers < VersionTLS10 {
		return 0, false
	} else if grade == GradeAPlus && vers < VersionTLS12 { // ssl version older than tls1.2 is not allowed for Grade A+
		return 0, false
	}

	return vers, true
}

const (
	disableRC4 uint8 = 1
	enableRC4  uint8 = 2
	onlyRC4    uint8 = 3
)

// currently, Grade A+ and Grade A need to exclude some ciphers with "RC4"
// ssl grade rule is defined by www.ssllabs.com:
// Grade A: no ssl3 && no RC4 ciphers
// Grade B: ssl3 is ok only with RC4 cipher, or modern version(>=tls10) with no RC4 cipher
// Grade C: ssl3 is ok only with RC4 cipher
func (c *Config) checkCipherGrade(conn *Conn) (useRC4 uint8) {
	switch conn.grade {
	case GradeAPlus:
		fallthrough
	case GradeA:
		return disableRC4
	case GradeB:
		if conn.vers >= VersionTLS10 {
			return disableRC4
		} else { //ssl3.0
			return onlyRC4
		}
	case GradeC:
		if c.Ssl3PoodleProofed && conn.vers == VersionSSL30 {
			return onlyRC4
		}
		return enableRC4
	default:
		// never go here
		return enableRC4
	}
}

// getCertificateForName returns the best certificate for the given name,
// defaulting to the first element of c.Certificates if there are no good
// options.
func (c *Config) getCertificateForName(name string) *Certificate {
	if len(c.Certificates) == 1 || c.NameToCertificate == nil {
		// There's only one choice, so no point doing any work.
		return &c.Certificates[0]
	}

	name = strings.ToLower(name)
	for len(name) > 0 && name[len(name)-1] == '.' {
		name = name[:len(name)-1]
	}

	if cert, ok := c.NameToCertificate[name]; ok {
		return cert
	}

	// try replacing labels in the name with wildcards until we get a
	// match.
	labels := strings.Split(name, ".")
	for i := range labels {
		labels[i] = "*"
		candidate := strings.Join(labels, ".")
		if cert, ok := c.NameToCertificate[candidate]; ok {
			return cert
		}
	}

	// If nothing matches, return the first certificate.
	return &c.Certificates[0]
}

// BuildNameToCertificate parses c.Certificates and builds c.NameToCertificate
// from the CommonName and SubjectAlternateName fields of each of the leaf
// certificates.
func (c *Config) BuildNameToCertificate() {
	c.NameToCertificate = make(map[string]*Certificate)
	for i := range c.Certificates {
		cert := &c.Certificates[i]
		x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
		if err != nil {
			continue
		}
		if len(x509Cert.Subject.CommonName) > 0 {
			c.NameToCertificate[x509Cert.Subject.CommonName] = cert
		}
		for _, san := range x509Cert.DNSNames {
			c.NameToCertificate[san] = cert
		}
	}
}

// A Certificate is a chain of one or more certificates, leaf first.
type Certificate struct {
	Certificate [][]byte
	PrivateKey  crypto.PrivateKey // supported types: *rsa.PrivateKey, *ecdsa.PrivateKey
	// OCSPStaple contains an optional OCSP response which will be served
	// to clients that request it.
	OCSPStaple []byte
	OCSPParse  *ocsp.Response // OCSPParse specify the details of ocsp response
	// Leaf is the parsed form of the leaf certificate, which may be
	// initialized using x509.ParseCertificate to reduce per-handshake
	// processing for TLS clients doing client authentication. If nil, the
	// leaf certificate will be parsed as needed.
	Leaf *x509.Certificate

	// certificate message for tls handshake, which may be initialized
	// using tls.X509Pair to reduce per-handshake processing for TLS server
	message []byte
}

// Prebuild certificate message for tls handshake
func (c *Certificate) buildCertMsg() {
	certMsg := new(certificateMsg)
	certMsg.certificates = c.Certificate
	c.message = certMsg.marshal()
}

// A TLS record.
type record struct {
	contentType  recordType
	major, minor uint8
	payload      []byte
}

type handshakeMessage interface {
	marshal() []byte
	unmarshal([]byte) bool
}

// lruSessionCache is a ClientSessionCache implementation that uses an LRU
// caching strategy.
type lruSessionCache struct {
	sync.Mutex

	m        map[string]*list.Element
	q        *list.List
	capacity int
}

type lruSessionCacheEntry struct {
	sessionKey string
	state      *ClientSessionState
}

// NewLRUClientSessionCache returns a ClientSessionCache with the given
// capacity that uses an LRU strategy. If capacity is < 1, a default capacity
// is used instead.
func NewLRUClientSessionCache(capacity int) ClientSessionCache {
	const defaultSessionCacheCapacity = 64

	if capacity < 1 {
		capacity = defaultSessionCacheCapacity
	}
	return &lruSessionCache{
		m:        make(map[string]*list.Element),
		q:        list.New(),
		capacity: capacity,
	}
}

// Put adds the provided (sessionKey, cs) pair to the cache.
func (c *lruSessionCache) Put(sessionKey string, cs *ClientSessionState) {
	c.Lock()
	defer c.Unlock()

	if elem, ok := c.m[sessionKey]; ok {
		entry := elem.Value.(*lruSessionCacheEntry)
		entry.state = cs
		c.q.MoveToFront(elem)
		return
	}

	if c.q.Len() < c.capacity {
		entry := &lruSessionCacheEntry{sessionKey, cs}
		c.m[sessionKey] = c.q.PushFront(entry)
		return
	}

	elem := c.q.Back()
	entry := elem.Value.(*lruSessionCacheEntry)
	delete(c.m, entry.sessionKey)
	entry.sessionKey = sessionKey
	entry.state = cs
	c.q.MoveToFront(elem)
	c.m[sessionKey] = elem
}

// Get returns the ClientSessionState value associated with a given key. It
// returns (nil, false) if no value is found.
func (c *lruSessionCache) Get(sessionKey string) (*ClientSessionState, bool) {
	c.Lock()
	defer c.Unlock()

	if elem, ok := c.m[sessionKey]; ok {
		c.q.MoveToFront(elem)
		return elem.Value.(*lruSessionCacheEntry).state, true
	}
	return nil, false
}

// TODO(jsing): Make these available to both crypto/x509 and crypto/tls.
type dsaSignature struct {
	R, S *big.Int
}

type ecdsaSignature dsaSignature

var emptyConfig Config

func defaultConfig() *Config {
	return &emptyConfig
}

var (
	once                   sync.Once
	varDefaultCipherSuites []uint16
)

func defaultCipherSuites() []uint16 {
	once.Do(initDefaultCipherSuites)
	return varDefaultCipherSuites
}

func initDefaultCipherSuites() {
	varDefaultCipherSuites = make([]uint16, len(cipherSuites))
	for i, suite := range cipherSuites {
		varDefaultCipherSuites[i] = suite.id
	}
}

func unexpectedMessageError(wanted, got interface{}) error {
	return fmt.Errorf("tls: received unexpected handshake message of type %T when waiting for %T", got, wanted)
}

var versionTextMap = map[uint16]string{
	VersionSSL30: "TLS_VERSION_SSL30",
	VersionTLS10: "TLS_VERSION_TLS10",
	VersionTLS11: "TLS_VERSION_TLS11",
	VersionTLS12: "TLS_VERSION_TLS12",
}

func VersionText(ver uint16) string {
	if text, ok := versionTextMap[ver]; ok {
		return text
	}
	return fmt.Sprintf("TLS_VERSION_%x", ver)
}

// version text in OpenSSL format
var versionTextMapForOpenSSL = map[uint16]string{
	VersionSSL30: "SSLv3.0",
	VersionTLS10: "TLSv1.0",
	VersionTLS11: "TLSv1.1",
	VersionTLS12: "TLSv1.2",
}

func VersionTextForOpenSSL(ver uint16) string {
	if text, ok := versionTextMapForOpenSSL[ver]; ok {
		return text
	}
	return fmt.Sprintf("TLS_VERSION_%x", ver)
}

var (
	helloRandomMagicNum []byte = []byte{66, 73, 68, 85}
	helloRandomFormat   int
)

func SetHelloRandomFormat(format int) {
	helloRandomFormat = format
}

func generateHelloRandom(rand io.Reader) ([]byte, error) {
	random := make([]byte, 32)
	if _, err := io.ReadFull(rand, random); err != nil {
		return nil, err
	}
	return random, nil
}

// OcspTimeRangeCheck check ocsp time update range
func OcspTimeRangeCheck(parse *ocsp.Response) bool {
	serverTime := time.Now()
	nextUpdate := parse.NextUpdate
	thisUpdate := parse.ThisUpdate

	// default tolerant time, one hour
	deltaTime := time.Duration(3600) * time.Second

	// serverTime should be [thisUpdate+deltaTime, nextUpdate-deltaTime]
	if serverTime.Sub(thisUpdate) < deltaTime || nextUpdate.Sub(serverTime) < deltaTime {
		return false
	}

	return true
}

var keyPairLoader KeyPairLoader

type KeyPairLoader interface {
	LoadX509KeyPair(certFile, keyFile string) (cert Certificate, err error)
}

func SetKeyPairLoader(loader KeyPairLoader) {
	keyPairLoader = loader
}
