// 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 tls

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"io"
	"strings"
	"sync"
	"time"
)

const (
	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)

	versionSSL30 = 0x0300
	versionTLS10 = 0x0301

	minVersion = versionSSL30
	maxVersion = versionTLS10
)

// 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
	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
var (
	extensionServerName      uint16 = 0
	extensionStatusRequest   uint16 = 5
	extensionSupportedCurves uint16 = 10
	extensionSupportedPoints uint16 = 11
	extensionNextProtoNeg    uint16 = 13172 // not IANA assigned
)

// TLS Elliptic Curves
// http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-8
var (
	curveP256 uint16 = 23
	curveP384 uint16 = 24
	curveP521 uint16 = 25
)

// TLS Elliptic Curve Point Formats
// http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-9
var (
	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
	// Rest of these are reserved by the TLS spec
)

// ConnectionState records basic TLS details about the connection.
type ConnectionState struct {
	HandshakeComplete          bool
	CipherSuite                uint16
	NegotiatedProtocol         string
	NegotiatedProtocolIsMutual bool

	// ServerName contains the server name indicated by the client, if any.
	// (Only valid for server connections.)
	ServerName string

	// the certificate chain that was presented by the other side
	PeerCertificates []*x509.Certificate
	// the verified certificate chains built from PeerCertificates.
	VerifiedChains [][]*x509.Certificate
}

// 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.
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.
	Rand io.Reader

	// Time returns the current time as the number of seconds since the epoch.
	// If Time is nil, TLS uses the system time.Seconds.
	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

	// 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 included in the client's handshake to support virtual
	// hosting.
	ServerName string

	// AuthenticateClient controls whether a server will request a certificate
	// from the client. It does not require that the client send a
	// certificate nor does it require that the certificate sent be
	// anything more than self-signed.
	AuthenticateClient bool

	// 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
}

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) rootCAs() *x509.CertPool {
	s := c.RootCAs
	if s == nil {
		s = defaultRoots()
	}
	return s
}

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

// 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  *rsa.PrivateKey
	// OCSPStaple contains an optional OCSP response which will be served
	// to clients that request it.
	OCSPStaple []byte
}

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

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

// mutualVersion returns the protocol version to use given the advertised
// version of the peer.
func mutualVersion(vers uint16) (uint16, bool) {
	if vers < minVersion {
		return 0, false
	}
	if vers > maxVersion {
		vers = maxVersion
	}
	return vers, true
}

var emptyConfig Config

func defaultConfig() *Config {
	return &emptyConfig
}

var once sync.Once

func defaultRoots() *x509.CertPool {
	once.Do(initDefaults)
	return varDefaultRoots
}

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

func initDefaults() {
	initDefaultRoots()
	initDefaultCipherSuites()
}

var (
	varDefaultRoots        *x509.CertPool
	varDefaultCipherSuites []uint16
)

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