Source file src/crypto/tls/conn.go

Documentation: crypto/tls

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // TLS low level connection and record layer
     6  
     7  package tls
     8  
     9  import (
    10  	"bytes"
    11  	"crypto/cipher"
    12  	"crypto/subtle"
    13  	"crypto/x509"
    14  	"errors"
    15  	"fmt"
    16  	"io"
    17  	"net"
    18  	"sync"
    19  	"sync/atomic"
    20  	"time"
    21  )
    22  
    23  // A Conn represents a secured connection.
    24  // It implements the net.Conn interface.
    25  type Conn struct {
    26  	// constant
    27  	conn     net.Conn
    28  	isClient bool
    29  
    30  	// handshakeStatus is 1 if the connection is currently transferring
    31  	// application data (i.e. is not currently processing a handshake).
    32  	// This field is only to be accessed with sync/atomic.
    33  	handshakeStatus uint32
    34  	// constant after handshake; protected by handshakeMutex
    35  	handshakeMutex sync.Mutex
    36  	handshakeErr   error   // error resulting from handshake
    37  	vers           uint16  // TLS version
    38  	haveVers       bool    // version has been negotiated
    39  	config         *Config // configuration passed to constructor
    40  	// handshakes counts the number of handshakes performed on the
    41  	// connection so far. If renegotiation is disabled then this is either
    42  	// zero or one.
    43  	handshakes       int
    44  	didResume        bool // whether this connection was a session resumption
    45  	cipherSuite      uint16
    46  	ocspResponse     []byte   // stapled OCSP response
    47  	scts             [][]byte // signed certificate timestamps from server
    48  	peerCertificates []*x509.Certificate
    49  	// verifiedChains contains the certificate chains that we built, as
    50  	// opposed to the ones presented by the server.
    51  	verifiedChains [][]*x509.Certificate
    52  	// serverName contains the server name indicated by the client, if any.
    53  	serverName string
    54  	// secureRenegotiation is true if the server echoed the secure
    55  	// renegotiation extension. (This is meaningless as a server because
    56  	// renegotiation is not supported in that case.)
    57  	secureRenegotiation bool
    58  	// ekm is a closure for exporting keying material.
    59  	ekm func(label string, context []byte, length int) ([]byte, error)
    60  	// resumptionSecret is the resumption_master_secret for handling
    61  	// NewSessionTicket messages. nil if config.SessionTicketsDisabled.
    62  	resumptionSecret []byte
    63  
    64  	// clientFinishedIsFirst is true if the client sent the first Finished
    65  	// message during the most recent handshake. This is recorded because
    66  	// the first transmitted Finished message is the tls-unique
    67  	// channel-binding value.
    68  	clientFinishedIsFirst bool
    69  
    70  	// closeNotifyErr is any error from sending the alertCloseNotify record.
    71  	closeNotifyErr error
    72  	// closeNotifySent is true if the Conn attempted to send an
    73  	// alertCloseNotify record.
    74  	closeNotifySent bool
    75  
    76  	// clientFinished and serverFinished contain the Finished message sent
    77  	// by the client or server in the most recent handshake. This is
    78  	// retained to support the renegotiation extension and tls-unique
    79  	// channel-binding.
    80  	clientFinished [12]byte
    81  	serverFinished [12]byte
    82  
    83  	clientProtocol         string
    84  	clientProtocolFallback bool
    85  
    86  	// input/output
    87  	in, out   halfConn
    88  	rawInput  bytes.Buffer // raw input, starting with a record header
    89  	input     bytes.Reader // application data waiting to be read, from rawInput.Next
    90  	hand      bytes.Buffer // handshake data waiting to be read
    91  	outBuf    []byte       // scratch buffer used by out.encrypt
    92  	buffering bool         // whether records are buffered in sendBuf
    93  	sendBuf   []byte       // a buffer of records waiting to be sent
    94  
    95  	// bytesSent counts the bytes of application data sent.
    96  	// packetsSent counts packets.
    97  	bytesSent   int64
    98  	packetsSent int64
    99  
   100  	// retryCount counts the number of consecutive non-advancing records
   101  	// received by Conn.readRecord. That is, records that neither advance the
   102  	// handshake, nor deliver application data. Protected by in.Mutex.
   103  	retryCount int
   104  
   105  	// activeCall is an atomic int32; the low bit is whether Close has
   106  	// been called. the rest of the bits are the number of goroutines
   107  	// in Conn.Write.
   108  	activeCall int32
   109  
   110  	tmp [16]byte
   111  }
   112  
   113  // Access to net.Conn methods.
   114  // Cannot just embed net.Conn because that would
   115  // export the struct field too.
   116  
   117  // LocalAddr returns the local network address.
   118  func (c *Conn) LocalAddr() net.Addr {
   119  	return c.conn.LocalAddr()
   120  }
   121  
   122  // RemoteAddr returns the remote network address.
   123  func (c *Conn) RemoteAddr() net.Addr {
   124  	return c.conn.RemoteAddr()
   125  }
   126  
   127  // SetDeadline sets the read and write deadlines associated with the connection.
   128  // A zero value for t means Read and Write will not time out.
   129  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   130  func (c *Conn) SetDeadline(t time.Time) error {
   131  	return c.conn.SetDeadline(t)
   132  }
   133  
   134  // SetReadDeadline sets the read deadline on the underlying connection.
   135  // A zero value for t means Read will not time out.
   136  func (c *Conn) SetReadDeadline(t time.Time) error {
   137  	return c.conn.SetReadDeadline(t)
   138  }
   139  
   140  // SetWriteDeadline sets the write deadline on the underlying connection.
   141  // A zero value for t means Write will not time out.
   142  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   143  func (c *Conn) SetWriteDeadline(t time.Time) error {
   144  	return c.conn.SetWriteDeadline(t)
   145  }
   146  
   147  // A halfConn represents one direction of the record layer
   148  // connection, either sending or receiving.
   149  type halfConn struct {
   150  	sync.Mutex
   151  
   152  	err            error       // first permanent error
   153  	version        uint16      // protocol version
   154  	cipher         interface{} // cipher algorithm
   155  	mac            macFunction
   156  	seq            [8]byte  // 64-bit sequence number
   157  	additionalData [13]byte // to avoid allocs; interface method args escape
   158  
   159  	nextCipher interface{} // next encryption state
   160  	nextMac    macFunction // next MAC algorithm
   161  
   162  	trafficSecret []byte // current TLS 1.3 traffic secret
   163  }
   164  
   165  func (hc *halfConn) setErrorLocked(err error) error {
   166  	hc.err = err
   167  	return err
   168  }
   169  
   170  // prepareCipherSpec sets the encryption and MAC states
   171  // that a subsequent changeCipherSpec will use.
   172  func (hc *halfConn) prepareCipherSpec(version uint16, cipher interface{}, mac macFunction) {
   173  	hc.version = version
   174  	hc.nextCipher = cipher
   175  	hc.nextMac = mac
   176  }
   177  
   178  // changeCipherSpec changes the encryption and MAC states
   179  // to the ones previously passed to prepareCipherSpec.
   180  func (hc *halfConn) changeCipherSpec() error {
   181  	if hc.nextCipher == nil || hc.version == VersionTLS13 {
   182  		return alertInternalError
   183  	}
   184  	hc.cipher = hc.nextCipher
   185  	hc.mac = hc.nextMac
   186  	hc.nextCipher = nil
   187  	hc.nextMac = nil
   188  	for i := range hc.seq {
   189  		hc.seq[i] = 0
   190  	}
   191  	return nil
   192  }
   193  
   194  func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, secret []byte) {
   195  	hc.trafficSecret = secret
   196  	key, iv := suite.trafficKey(secret)
   197  	hc.cipher = suite.aead(key, iv)
   198  	for i := range hc.seq {
   199  		hc.seq[i] = 0
   200  	}
   201  }
   202  
   203  // incSeq increments the sequence number.
   204  func (hc *halfConn) incSeq() {
   205  	for i := 7; i >= 0; i-- {
   206  		hc.seq[i]++
   207  		if hc.seq[i] != 0 {
   208  			return
   209  		}
   210  	}
   211  
   212  	// Not allowed to let sequence number wrap.
   213  	// Instead, must renegotiate before it does.
   214  	// Not likely enough to bother.
   215  	panic("TLS: sequence number wraparound")
   216  }
   217  
   218  // explicitNonceLen returns the number of bytes of explicit nonce or IV included
   219  // in each record. Explicit nonces are present only in CBC modes after TLS 1.0
   220  // and in certain AEAD modes in TLS 1.2.
   221  func (hc *halfConn) explicitNonceLen() int {
   222  	if hc.cipher == nil {
   223  		return 0
   224  	}
   225  
   226  	switch c := hc.cipher.(type) {
   227  	case cipher.Stream:
   228  		return 0
   229  	case aead:
   230  		return c.explicitNonceLen()
   231  	case cbcMode:
   232  		// TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack.
   233  		if hc.version >= VersionTLS11 {
   234  			return c.BlockSize()
   235  		}
   236  		return 0
   237  	default:
   238  		panic("unknown cipher type")
   239  	}
   240  }
   241  
   242  // extractPadding returns, in constant time, the length of the padding to remove
   243  // from the end of payload. It also returns a byte which is equal to 255 if the
   244  // padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
   245  func extractPadding(payload []byte) (toRemove int, good byte) {
   246  	if len(payload) < 1 {
   247  		return 0, 0
   248  	}
   249  
   250  	paddingLen := payload[len(payload)-1]
   251  	t := uint(len(payload)-1) - uint(paddingLen)
   252  	// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
   253  	good = byte(int32(^t) >> 31)
   254  
   255  	// The maximum possible padding length plus the actual length field
   256  	toCheck := 256
   257  	// The length of the padded data is public, so we can use an if here
   258  	if toCheck > len(payload) {
   259  		toCheck = len(payload)
   260  	}
   261  
   262  	for i := 0; i < toCheck; i++ {
   263  		t := uint(paddingLen) - uint(i)
   264  		// if i <= paddingLen then the MSB of t is zero
   265  		mask := byte(int32(^t) >> 31)
   266  		b := payload[len(payload)-1-i]
   267  		good &^= mask&paddingLen ^ mask&b
   268  	}
   269  
   270  	// We AND together the bits of good and replicate the result across
   271  	// all the bits.
   272  	good &= good << 4
   273  	good &= good << 2
   274  	good &= good << 1
   275  	good = uint8(int8(good) >> 7)
   276  
   277  	// Zero the padding length on error. This ensures any unchecked bytes
   278  	// are included in the MAC. Otherwise, an attacker that could
   279  	// distinguish MAC failures from padding failures could mount an attack
   280  	// similar to POODLE in SSL 3.0: given a good ciphertext that uses a
   281  	// full block's worth of padding, replace the final block with another
   282  	// block. If the MAC check passed but the padding check failed, the
   283  	// last byte of that block decrypted to the block size.
   284  	//
   285  	// See also macAndPaddingGood logic below.
   286  	paddingLen &= good
   287  
   288  	toRemove = int(paddingLen) + 1
   289  	return
   290  }
   291  
   292  // extractPaddingSSL30 is a replacement for extractPadding in the case that the
   293  // protocol version is SSLv3. In this version, the contents of the padding
   294  // are random and cannot be checked.
   295  func extractPaddingSSL30(payload []byte) (toRemove int, good byte) {
   296  	if len(payload) < 1 {
   297  		return 0, 0
   298  	}
   299  
   300  	paddingLen := int(payload[len(payload)-1]) + 1
   301  	if paddingLen > len(payload) {
   302  		return 0, 0
   303  	}
   304  
   305  	return paddingLen, 255
   306  }
   307  
   308  func roundUp(a, b int) int {
   309  	return a + (b-a%b)%b
   310  }
   311  
   312  // cbcMode is an interface for block ciphers using cipher block chaining.
   313  type cbcMode interface {
   314  	cipher.BlockMode
   315  	SetIV([]byte)
   316  }
   317  
   318  // decrypt authenticates and decrypts the record if protection is active at
   319  // this stage. The returned plaintext might overlap with the input.
   320  func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) {
   321  	var plaintext []byte
   322  	typ := recordType(record[0])
   323  	payload := record[recordHeaderLen:]
   324  
   325  	// In TLS 1.3, change_cipher_spec messages are to be ignored without being
   326  	// decrypted. See RFC 8446, Appendix D.4.
   327  	if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec {
   328  		return payload, typ, nil
   329  	}
   330  
   331  	paddingGood := byte(255)
   332  	paddingLen := 0
   333  
   334  	explicitNonceLen := hc.explicitNonceLen()
   335  
   336  	if hc.cipher != nil {
   337  		switch c := hc.cipher.(type) {
   338  		case cipher.Stream:
   339  			c.XORKeyStream(payload, payload)
   340  		case aead:
   341  			if len(payload) < explicitNonceLen {
   342  				return nil, 0, alertBadRecordMAC
   343  			}
   344  			nonce := payload[:explicitNonceLen]
   345  			if len(nonce) == 0 {
   346  				nonce = hc.seq[:]
   347  			}
   348  			payload = payload[explicitNonceLen:]
   349  
   350  			additionalData := hc.additionalData[:]
   351  			if hc.version == VersionTLS13 {
   352  				additionalData = record[:recordHeaderLen]
   353  			} else {
   354  				copy(additionalData, hc.seq[:])
   355  				copy(additionalData[8:], record[:3])
   356  				n := len(payload) - c.Overhead()
   357  				additionalData[11] = byte(n >> 8)
   358  				additionalData[12] = byte(n)
   359  			}
   360  
   361  			var err error
   362  			plaintext, err = c.Open(payload[:0], nonce, payload, additionalData)
   363  			if err != nil {
   364  				return nil, 0, alertBadRecordMAC
   365  			}
   366  		case cbcMode:
   367  			blockSize := c.BlockSize()
   368  			minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize)
   369  			if len(payload)%blockSize != 0 || len(payload) < minPayload {
   370  				return nil, 0, alertBadRecordMAC
   371  			}
   372  
   373  			if explicitNonceLen > 0 {
   374  				c.SetIV(payload[:explicitNonceLen])
   375  				payload = payload[explicitNonceLen:]
   376  			}
   377  			c.CryptBlocks(payload, payload)
   378  
   379  			// In a limited attempt to protect against CBC padding oracles like
   380  			// Lucky13, the data past paddingLen (which is secret) is passed to
   381  			// the MAC function as extra data, to be fed into the HMAC after
   382  			// computing the digest. This makes the MAC roughly constant time as
   383  			// long as the digest computation is constant time and does not
   384  			// affect the subsequent write, modulo cache effects.
   385  			if hc.version == VersionSSL30 {
   386  				paddingLen, paddingGood = extractPaddingSSL30(payload)
   387  			} else {
   388  				paddingLen, paddingGood = extractPadding(payload)
   389  			}
   390  		default:
   391  			panic("unknown cipher type")
   392  		}
   393  
   394  		if hc.version == VersionTLS13 {
   395  			if typ != recordTypeApplicationData {
   396  				return nil, 0, alertUnexpectedMessage
   397  			}
   398  			if len(plaintext) > maxPlaintext+1 {
   399  				return nil, 0, alertRecordOverflow
   400  			}
   401  			// Remove padding and find the ContentType scanning from the end.
   402  			for i := len(plaintext) - 1; i >= 0; i-- {
   403  				if plaintext[i] != 0 {
   404  					typ = recordType(plaintext[i])
   405  					plaintext = plaintext[:i]
   406  					break
   407  				}
   408  				if i == 0 {
   409  					return nil, 0, alertUnexpectedMessage
   410  				}
   411  			}
   412  		}
   413  	} else {
   414  		plaintext = payload
   415  	}
   416  
   417  	if hc.mac != nil {
   418  		macSize := hc.mac.Size()
   419  		if len(payload) < macSize {
   420  			return nil, 0, alertBadRecordMAC
   421  		}
   422  
   423  		n := len(payload) - macSize - paddingLen
   424  		n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 }
   425  		record[3] = byte(n >> 8)
   426  		record[4] = byte(n)
   427  		remoteMAC := payload[n : n+macSize]
   428  		localMAC := hc.mac.MAC(hc.seq[0:], record[:recordHeaderLen], payload[:n], payload[n+macSize:])
   429  
   430  		// This is equivalent to checking the MACs and paddingGood
   431  		// separately, but in constant-time to prevent distinguishing
   432  		// padding failures from MAC failures. Depending on what value
   433  		// of paddingLen was returned on bad padding, distinguishing
   434  		// bad MAC from bad padding can lead to an attack.
   435  		//
   436  		// See also the logic at the end of extractPadding.
   437  		macAndPaddingGood := subtle.ConstantTimeCompare(localMAC, remoteMAC) & int(paddingGood)
   438  		if macAndPaddingGood != 1 {
   439  			return nil, 0, alertBadRecordMAC
   440  		}
   441  
   442  		plaintext = payload[:n]
   443  	}
   444  
   445  	hc.incSeq()
   446  	return plaintext, typ, nil
   447  }
   448  
   449  // sliceForAppend extends the input slice by n bytes. head is the full extended
   450  // slice, while tail is the appended part. If the original slice has sufficient
   451  // capacity no allocation is performed.
   452  func sliceForAppend(in []byte, n int) (head, tail []byte) {
   453  	if total := len(in) + n; cap(in) >= total {
   454  		head = in[:total]
   455  	} else {
   456  		head = make([]byte, total)
   457  		copy(head, in)
   458  	}
   459  	tail = head[len(in):]
   460  	return
   461  }
   462  
   463  // encrypt encrypts payload, adding the appropriate nonce and/or MAC, and
   464  // appends it to record, which contains the record header.
   465  func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) {
   466  	if hc.cipher == nil {
   467  		return append(record, payload...), nil
   468  	}
   469  
   470  	var explicitNonce []byte
   471  	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
   472  		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
   473  		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
   474  			// The AES-GCM construction in TLS has an explicit nonce so that the
   475  			// nonce can be random. However, the nonce is only 8 bytes which is
   476  			// too small for a secure, random nonce. Therefore we use the
   477  			// sequence number as the nonce. The 3DES-CBC construction also has
   478  			// an 8 bytes nonce but its nonces must be unpredictable (see RFC
   479  			// 5246, Appendix F.3), forcing us to use randomness. That's not
   480  			// 3DES' biggest problem anyway because the birthday bound on block
   481  			// collision is reached first due to its simlarly small block size
   482  			// (see the Sweet32 attack).
   483  			copy(explicitNonce, hc.seq[:])
   484  		} else {
   485  			if _, err := io.ReadFull(rand, explicitNonce); err != nil {
   486  				return nil, err
   487  			}
   488  		}
   489  	}
   490  
   491  	var mac []byte
   492  	if hc.mac != nil {
   493  		mac = hc.mac.MAC(hc.seq[:], record[:recordHeaderLen], payload, nil)
   494  	}
   495  
   496  	var dst []byte
   497  	switch c := hc.cipher.(type) {
   498  	case cipher.Stream:
   499  		record, dst = sliceForAppend(record, len(payload)+len(mac))
   500  		c.XORKeyStream(dst[:len(payload)], payload)
   501  		c.XORKeyStream(dst[len(payload):], mac)
   502  	case aead:
   503  		nonce := explicitNonce
   504  		if len(nonce) == 0 {
   505  			nonce = hc.seq[:]
   506  		}
   507  
   508  		if hc.version == VersionTLS13 {
   509  			record = append(record, payload...)
   510  
   511  			// Encrypt the actual ContentType and replace the plaintext one.
   512  			record = append(record, record[0])
   513  			record[0] = byte(recordTypeApplicationData)
   514  
   515  			n := len(payload) + 1 + c.Overhead()
   516  			record[3] = byte(n >> 8)
   517  			record[4] = byte(n)
   518  
   519  			record = c.Seal(record[:recordHeaderLen],
   520  				nonce, record[recordHeaderLen:], record[:recordHeaderLen])
   521  		} else {
   522  			copy(hc.additionalData[:], hc.seq[:])
   523  			copy(hc.additionalData[8:], record)
   524  			record = c.Seal(record, nonce, payload, hc.additionalData[:])
   525  		}
   526  	case cbcMode:
   527  		blockSize := c.BlockSize()
   528  		plaintextLen := len(payload) + len(mac)
   529  		paddingLen := blockSize - plaintextLen%blockSize
   530  		record, dst = sliceForAppend(record, plaintextLen+paddingLen)
   531  		copy(dst, payload)
   532  		copy(dst[len(payload):], mac)
   533  		for i := plaintextLen; i < len(dst); i++ {
   534  			dst[i] = byte(paddingLen - 1)
   535  		}
   536  		if len(explicitNonce) > 0 {
   537  			c.SetIV(explicitNonce)
   538  		}
   539  		c.CryptBlocks(dst, dst)
   540  	default:
   541  		panic("unknown cipher type")
   542  	}
   543  
   544  	// Update length to include nonce, MAC and any block padding needed.
   545  	n := len(record) - recordHeaderLen
   546  	record[3] = byte(n >> 8)
   547  	record[4] = byte(n)
   548  	hc.incSeq()
   549  
   550  	return record, nil
   551  }
   552  
   553  // RecordHeaderError is returned when a TLS record header is invalid.
   554  type RecordHeaderError struct {
   555  	// Msg contains a human readable string that describes the error.
   556  	Msg string
   557  	// RecordHeader contains the five bytes of TLS record header that
   558  	// triggered the error.
   559  	RecordHeader [5]byte
   560  	// Conn provides the underlying net.Conn in the case that a client
   561  	// sent an initial handshake that didn't look like TLS.
   562  	// It is nil if there's already been a handshake or a TLS alert has
   563  	// been written to the connection.
   564  	Conn net.Conn
   565  }
   566  
   567  func (e RecordHeaderError) Error() string { return "tls: " + e.Msg }
   568  
   569  func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) {
   570  	err.Msg = msg
   571  	err.Conn = conn
   572  	copy(err.RecordHeader[:], c.rawInput.Bytes())
   573  	return err
   574  }
   575  
   576  func (c *Conn) readRecord() error {
   577  	return c.readRecordOrCCS(false)
   578  }
   579  
   580  func (c *Conn) readChangeCipherSpec() error {
   581  	return c.readRecordOrCCS(true)
   582  }
   583  
   584  // readRecordOrCCS reads one or more TLS records from the connection and
   585  // updates the record layer state. Some invariants:
   586  //   * c.in must be locked
   587  //   * c.input must be empty
   588  // During the handshake one and only one of the following will happen:
   589  //   - c.hand grows
   590  //   - c.in.changeCipherSpec is called
   591  //   - an error is returned
   592  // After the handshake one and only one of the following will happen:
   593  //   - c.hand grows
   594  //   - c.input is set
   595  //   - an error is returned
   596  func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
   597  	if c.in.err != nil {
   598  		return c.in.err
   599  	}
   600  	handshakeComplete := c.handshakeComplete()
   601  
   602  	// This function modifies c.rawInput, which owns the c.input memory.
   603  	if c.input.Len() != 0 {
   604  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
   605  	}
   606  	c.input.Reset(nil)
   607  
   608  	// Read header, payload.
   609  	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
   610  		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
   611  		// is an error, but popular web sites seem to do this, so we accept it
   612  		// if and only if at the record boundary.
   613  		if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 {
   614  			err = io.EOF
   615  		}
   616  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   617  			c.in.setErrorLocked(err)
   618  		}
   619  		return err
   620  	}
   621  	hdr := c.rawInput.Bytes()[:recordHeaderLen]
   622  	typ := recordType(hdr[0])
   623  
   624  	// No valid TLS record has a type of 0x80, however SSLv2 handshakes
   625  	// start with a uint16 length where the MSB is set and the first record
   626  	// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
   627  	// an SSLv2 client.
   628  	if !handshakeComplete && typ == 0x80 {
   629  		c.sendAlert(alertProtocolVersion)
   630  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received"))
   631  	}
   632  
   633  	vers := uint16(hdr[1])<<8 | uint16(hdr[2])
   634  	n := int(hdr[3])<<8 | int(hdr[4])
   635  	if c.haveVers && c.vers != VersionTLS13 && vers != c.vers {
   636  		c.sendAlert(alertProtocolVersion)
   637  		msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, c.vers)
   638  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   639  	}
   640  	if !c.haveVers {
   641  		// First message, be extra suspicious: this might not be a TLS
   642  		// client. Bail out before reading a full 'body', if possible.
   643  		// The current max version is 3.3 so if the version is >= 16.0,
   644  		// it's probably not real.
   645  		if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 {
   646  			return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake"))
   647  		}
   648  	}
   649  	if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext {
   650  		c.sendAlert(alertRecordOverflow)
   651  		msg := fmt.Sprintf("oversized record received with length %d", n)
   652  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   653  	}
   654  	if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
   655  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   656  			c.in.setErrorLocked(err)
   657  		}
   658  		return err
   659  	}
   660  
   661  	// Process message.
   662  	record := c.rawInput.Next(recordHeaderLen + n)
   663  	data, typ, err := c.in.decrypt(record)
   664  	if err != nil {
   665  		return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   666  	}
   667  	if len(data) > maxPlaintext {
   668  		return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow))
   669  	}
   670  
   671  	// Application Data messages are always protected.
   672  	if c.in.cipher == nil && typ == recordTypeApplicationData {
   673  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   674  	}
   675  
   676  	if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 {
   677  		// This is a state-advancing message: reset the retry count.
   678  		c.retryCount = 0
   679  	}
   680  
   681  	// Handshake messages MUST NOT be interleaved with other record types in TLS 1.3.
   682  	if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 {
   683  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   684  	}
   685  
   686  	switch typ {
   687  	default:
   688  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   689  
   690  	case recordTypeAlert:
   691  		if len(data) != 2 {
   692  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   693  		}
   694  		if alert(data[1]) == alertCloseNotify {
   695  			return c.in.setErrorLocked(io.EOF)
   696  		}
   697  		if c.vers == VersionTLS13 {
   698  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   699  		}
   700  		switch data[0] {
   701  		case alertLevelWarning:
   702  			// Drop the record on the floor and retry.
   703  			return c.retryReadRecord(expectChangeCipherSpec)
   704  		case alertLevelError:
   705  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   706  		default:
   707  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   708  		}
   709  
   710  	case recordTypeChangeCipherSpec:
   711  		if len(data) != 1 || data[0] != 1 {
   712  			return c.in.setErrorLocked(c.sendAlert(alertDecodeError))
   713  		}
   714  		// Handshake messages are not allowed to fragment across the CCS.
   715  		if c.hand.Len() > 0 {
   716  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   717  		}
   718  		// In TLS 1.3, change_cipher_spec records are ignored until the
   719  		// Finished. See RFC 8446, Appendix D.4. Note that according to Section
   720  		// 5, a server can send a ChangeCipherSpec before its ServerHello, when
   721  		// c.vers is still unset. That's not useful though and suspicious if the
   722  		// server then selects a lower protocol version, so don't allow that.
   723  		if c.vers == VersionTLS13 {
   724  			return c.retryReadRecord(expectChangeCipherSpec)
   725  		}
   726  		if !expectChangeCipherSpec {
   727  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   728  		}
   729  		if err := c.in.changeCipherSpec(); err != nil {
   730  			return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   731  		}
   732  
   733  	case recordTypeApplicationData:
   734  		if !handshakeComplete || expectChangeCipherSpec {
   735  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   736  		}
   737  		// Some OpenSSL servers send empty records in order to randomize the
   738  		// CBC IV. Ignore a limited number of empty records.
   739  		if len(data) == 0 {
   740  			return c.retryReadRecord(expectChangeCipherSpec)
   741  		}
   742  		// Note that data is owned by c.rawInput, following the Next call above,
   743  		// to avoid copying the plaintext. This is safe because c.rawInput is
   744  		// not read from or written to until c.input is drained.
   745  		c.input.Reset(data)
   746  
   747  	case recordTypeHandshake:
   748  		if len(data) == 0 || expectChangeCipherSpec {
   749  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   750  		}
   751  		c.hand.Write(data)
   752  	}
   753  
   754  	return nil
   755  }
   756  
   757  // retryReadRecord recurses into readRecordOrCCS to drop a non-advancing record, like
   758  // a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3.
   759  func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error {
   760  	c.retryCount++
   761  	if c.retryCount > maxUselessRecords {
   762  		c.sendAlert(alertUnexpectedMessage)
   763  		return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
   764  	}
   765  	return c.readRecordOrCCS(expectChangeCipherSpec)
   766  }
   767  
   768  // atLeastReader reads from R, stopping with EOF once at least N bytes have been
   769  // read. It is different from an io.LimitedReader in that it doesn't cut short
   770  // the last Read call, and in that it considers an early EOF an error.
   771  type atLeastReader struct {
   772  	R io.Reader
   773  	N int64
   774  }
   775  
   776  func (r *atLeastReader) Read(p []byte) (int, error) {
   777  	if r.N <= 0 {
   778  		return 0, io.EOF
   779  	}
   780  	n, err := r.R.Read(p)
   781  	r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809
   782  	if r.N > 0 && err == io.EOF {
   783  		return n, io.ErrUnexpectedEOF
   784  	}
   785  	if r.N <= 0 && err == nil {
   786  		return n, io.EOF
   787  	}
   788  	return n, err
   789  }
   790  
   791  // readFromUntil reads from r into c.rawInput until c.rawInput contains
   792  // at least n bytes or else returns an error.
   793  func (c *Conn) readFromUntil(r io.Reader, n int) error {
   794  	if c.rawInput.Len() >= n {
   795  		return nil
   796  	}
   797  	needs := n - c.rawInput.Len()
   798  	// There might be extra input waiting on the wire. Make a best effort
   799  	// attempt to fetch it so that it can be used in (*Conn).Read to
   800  	// "predict" closeNotify alerts.
   801  	c.rawInput.Grow(needs + bytes.MinRead)
   802  	_, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)})
   803  	return err
   804  }
   805  
   806  // sendAlert sends a TLS alert message.
   807  func (c *Conn) sendAlertLocked(err alert) error {
   808  	switch err {
   809  	case alertNoRenegotiation, alertCloseNotify:
   810  		c.tmp[0] = alertLevelWarning
   811  	default:
   812  		c.tmp[0] = alertLevelError
   813  	}
   814  	c.tmp[1] = byte(err)
   815  
   816  	_, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2])
   817  	if err == alertCloseNotify {
   818  		// closeNotify is a special case in that it isn't an error.
   819  		return writeErr
   820  	}
   821  
   822  	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   823  }
   824  
   825  // sendAlert sends a TLS alert message.
   826  func (c *Conn) sendAlert(err alert) error {
   827  	c.out.Lock()
   828  	defer c.out.Unlock()
   829  	return c.sendAlertLocked(err)
   830  }
   831  
   832  const (
   833  	// tcpMSSEstimate is a conservative estimate of the TCP maximum segment
   834  	// size (MSS). A constant is used, rather than querying the kernel for
   835  	// the actual MSS, to avoid complexity. The value here is the IPv6
   836  	// minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40
   837  	// bytes) and a TCP header with timestamps (32 bytes).
   838  	tcpMSSEstimate = 1208
   839  
   840  	// recordSizeBoostThreshold is the number of bytes of application data
   841  	// sent after which the TLS record size will be increased to the
   842  	// maximum.
   843  	recordSizeBoostThreshold = 128 * 1024
   844  )
   845  
   846  // maxPayloadSizeForWrite returns the maximum TLS payload size to use for the
   847  // next application data record. There is the following trade-off:
   848  //
   849  //   - For latency-sensitive applications, such as web browsing, each TLS
   850  //     record should fit in one TCP segment.
   851  //   - For throughput-sensitive applications, such as large file transfers,
   852  //     larger TLS records better amortize framing and encryption overheads.
   853  //
   854  // A simple heuristic that works well in practice is to use small records for
   855  // the first 1MB of data, then use larger records for subsequent data, and
   856  // reset back to smaller records after the connection becomes idle. See "High
   857  // Performance Web Networking", Chapter 4, or:
   858  // https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/
   859  //
   860  // In the interests of simplicity and determinism, this code does not attempt
   861  // to reset the record size once the connection is idle, however.
   862  func (c *Conn) maxPayloadSizeForWrite(typ recordType) int {
   863  	if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData {
   864  		return maxPlaintext
   865  	}
   866  
   867  	if c.bytesSent >= recordSizeBoostThreshold {
   868  		return maxPlaintext
   869  	}
   870  
   871  	// Subtract TLS overheads to get the maximum payload size.
   872  	payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen()
   873  	if c.out.cipher != nil {
   874  		switch ciph := c.out.cipher.(type) {
   875  		case cipher.Stream:
   876  			payloadBytes -= c.out.mac.Size()
   877  		case cipher.AEAD:
   878  			payloadBytes -= ciph.Overhead()
   879  		case cbcMode:
   880  			blockSize := ciph.BlockSize()
   881  			// The payload must fit in a multiple of blockSize, with
   882  			// room for at least one padding byte.
   883  			payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1
   884  			// The MAC is appended before padding so affects the
   885  			// payload size directly.
   886  			payloadBytes -= c.out.mac.Size()
   887  		default:
   888  			panic("unknown cipher type")
   889  		}
   890  	}
   891  	if c.vers == VersionTLS13 {
   892  		payloadBytes-- // encrypted ContentType
   893  	}
   894  
   895  	// Allow packet growth in arithmetic progression up to max.
   896  	pkt := c.packetsSent
   897  	c.packetsSent++
   898  	if pkt > 1000 {
   899  		return maxPlaintext // avoid overflow in multiply below
   900  	}
   901  
   902  	n := payloadBytes * int(pkt+1)
   903  	if n > maxPlaintext {
   904  		n = maxPlaintext
   905  	}
   906  	return n
   907  }
   908  
   909  func (c *Conn) write(data []byte) (int, error) {
   910  	if c.buffering {
   911  		c.sendBuf = append(c.sendBuf, data...)
   912  		return len(data), nil
   913  	}
   914  
   915  	n, err := c.conn.Write(data)
   916  	c.bytesSent += int64(n)
   917  	return n, err
   918  }
   919  
   920  func (c *Conn) flush() (int, error) {
   921  	if len(c.sendBuf) == 0 {
   922  		return 0, nil
   923  	}
   924  
   925  	n, err := c.conn.Write(c.sendBuf)
   926  	c.bytesSent += int64(n)
   927  	c.sendBuf = nil
   928  	c.buffering = false
   929  	return n, err
   930  }
   931  
   932  // writeRecordLocked writes a TLS record with the given type and payload to the
   933  // connection and updates the record layer state.
   934  func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
   935  	var n int
   936  	for len(data) > 0 {
   937  		m := len(data)
   938  		if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload {
   939  			m = maxPayload
   940  		}
   941  
   942  		_, c.outBuf = sliceForAppend(c.outBuf[:0], recordHeaderLen)
   943  		c.outBuf[0] = byte(typ)
   944  		vers := c.vers
   945  		if vers == 0 {
   946  			// Some TLS servers fail if the record version is
   947  			// greater than TLS 1.0 for the initial ClientHello.
   948  			vers = VersionTLS10
   949  		} else if vers == VersionTLS13 {
   950  			// TLS 1.3 froze the record layer version to 1.2.
   951  			// See RFC 8446, Section 5.1.
   952  			vers = VersionTLS12
   953  		}
   954  		c.outBuf[1] = byte(vers >> 8)
   955  		c.outBuf[2] = byte(vers)
   956  		c.outBuf[3] = byte(m >> 8)
   957  		c.outBuf[4] = byte(m)
   958  
   959  		var err error
   960  		c.outBuf, err = c.out.encrypt(c.outBuf, data[:m], c.config.rand())
   961  		if err != nil {
   962  			return n, err
   963  		}
   964  		if _, err := c.write(c.outBuf); err != nil {
   965  			return n, err
   966  		}
   967  		n += m
   968  		data = data[m:]
   969  	}
   970  
   971  	if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 {
   972  		if err := c.out.changeCipherSpec(); err != nil {
   973  			return n, c.sendAlertLocked(err.(alert))
   974  		}
   975  	}
   976  
   977  	return n, nil
   978  }
   979  
   980  // writeRecord writes a TLS record with the given type and payload to the
   981  // connection and updates the record layer state.
   982  func (c *Conn) writeRecord(typ recordType, data []byte) (int, error) {
   983  	c.out.Lock()
   984  	defer c.out.Unlock()
   985  
   986  	return c.writeRecordLocked(typ, data)
   987  }
   988  
   989  // readHandshake reads the next handshake message from
   990  // the record layer.
   991  func (c *Conn) readHandshake() (interface{}, error) {
   992  	for c.hand.Len() < 4 {
   993  		if err := c.readRecord(); err != nil {
   994  			return nil, err
   995  		}
   996  	}
   997  
   998  	data := c.hand.Bytes()
   999  	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
  1000  	if n > maxHandshake {
  1001  		c.sendAlertLocked(alertInternalError)
  1002  		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
  1003  	}
  1004  	for c.hand.Len() < 4+n {
  1005  		if err := c.readRecord(); err != nil {
  1006  			return nil, err
  1007  		}
  1008  	}
  1009  	data = c.hand.Next(4 + n)
  1010  	var m handshakeMessage
  1011  	switch data[0] {
  1012  	case typeHelloRequest:
  1013  		m = new(helloRequestMsg)
  1014  	case typeClientHello:
  1015  		m = new(clientHelloMsg)
  1016  	case typeServerHello:
  1017  		m = new(serverHelloMsg)
  1018  	case typeNewSessionTicket:
  1019  		if c.vers == VersionTLS13 {
  1020  			m = new(newSessionTicketMsgTLS13)
  1021  		} else {
  1022  			m = new(newSessionTicketMsg)
  1023  		}
  1024  	case typeCertificate:
  1025  		if c.vers == VersionTLS13 {
  1026  			m = new(certificateMsgTLS13)
  1027  		} else {
  1028  			m = new(certificateMsg)
  1029  		}
  1030  	case typeCertificateRequest:
  1031  		if c.vers == VersionTLS13 {
  1032  			m = new(certificateRequestMsgTLS13)
  1033  		} else {
  1034  			m = &certificateRequestMsg{
  1035  				hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1036  			}
  1037  		}
  1038  	case typeCertificateStatus:
  1039  		m = new(certificateStatusMsg)
  1040  	case typeServerKeyExchange:
  1041  		m = new(serverKeyExchangeMsg)
  1042  	case typeServerHelloDone:
  1043  		m = new(serverHelloDoneMsg)
  1044  	case typeClientKeyExchange:
  1045  		m = new(clientKeyExchangeMsg)
  1046  	case typeCertificateVerify:
  1047  		m = &certificateVerifyMsg{
  1048  			hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1049  		}
  1050  	case typeNextProtocol:
  1051  		m = new(nextProtoMsg)
  1052  	case typeFinished:
  1053  		m = new(finishedMsg)
  1054  	case typeEncryptedExtensions:
  1055  		m = new(encryptedExtensionsMsg)
  1056  	case typeEndOfEarlyData:
  1057  		m = new(endOfEarlyDataMsg)
  1058  	case typeKeyUpdate:
  1059  		m = new(keyUpdateMsg)
  1060  	default:
  1061  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1062  	}
  1063  
  1064  	// The handshake message unmarshalers
  1065  	// expect to be able to keep references to data,
  1066  	// so pass in a fresh copy that won't be overwritten.
  1067  	data = append([]byte(nil), data...)
  1068  
  1069  	if !m.unmarshal(data) {
  1070  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1071  	}
  1072  	return m, nil
  1073  }
  1074  
  1075  var (
  1076  	errClosed   = errors.New("tls: use of closed connection")
  1077  	errShutdown = errors.New("tls: protocol is shutdown")
  1078  )
  1079  
  1080  // Write writes data to the connection.
  1081  func (c *Conn) Write(b []byte) (int, error) {
  1082  	// interlock with Close below
  1083  	for {
  1084  		x := atomic.LoadInt32(&c.activeCall)
  1085  		if x&1 != 0 {
  1086  			return 0, errClosed
  1087  		}
  1088  		if atomic.CompareAndSwapInt32(&c.activeCall, x, x+2) {
  1089  			defer atomic.AddInt32(&c.activeCall, -2)
  1090  			break
  1091  		}
  1092  	}
  1093  
  1094  	if err := c.Handshake(); err != nil {
  1095  		return 0, err
  1096  	}
  1097  
  1098  	c.out.Lock()
  1099  	defer c.out.Unlock()
  1100  
  1101  	if err := c.out.err; err != nil {
  1102  		return 0, err
  1103  	}
  1104  
  1105  	if !c.handshakeComplete() {
  1106  		return 0, alertInternalError
  1107  	}
  1108  
  1109  	if c.closeNotifySent {
  1110  		return 0, errShutdown
  1111  	}
  1112  
  1113  	// SSL 3.0 and TLS 1.0 are susceptible to a chosen-plaintext
  1114  	// attack when using block mode ciphers due to predictable IVs.
  1115  	// This can be prevented by splitting each Application Data
  1116  	// record into two records, effectively randomizing the IV.
  1117  	//
  1118  	// https://www.openssl.org/~bodo/tls-cbc.txt
  1119  	// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
  1120  	// https://www.imperialviolet.org/2012/01/15/beastfollowup.html
  1121  
  1122  	var m int
  1123  	if len(b) > 1 && c.vers <= VersionTLS10 {
  1124  		if _, ok := c.out.cipher.(cipher.BlockMode); ok {
  1125  			n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1])
  1126  			if err != nil {
  1127  				return n, c.out.setErrorLocked(err)
  1128  			}
  1129  			m, b = 1, b[1:]
  1130  		}
  1131  	}
  1132  
  1133  	n, err := c.writeRecordLocked(recordTypeApplicationData, b)
  1134  	return n + m, c.out.setErrorLocked(err)
  1135  }
  1136  
  1137  // handleRenegotiation processes a HelloRequest handshake message.
  1138  func (c *Conn) handleRenegotiation() error {
  1139  	if c.vers == VersionTLS13 {
  1140  		return errors.New("tls: internal error: unexpected renegotiation")
  1141  	}
  1142  
  1143  	msg, err := c.readHandshake()
  1144  	if err != nil {
  1145  		return err
  1146  	}
  1147  
  1148  	helloReq, ok := msg.(*helloRequestMsg)
  1149  	if !ok {
  1150  		c.sendAlert(alertUnexpectedMessage)
  1151  		return unexpectedMessageError(helloReq, msg)
  1152  	}
  1153  
  1154  	if !c.isClient {
  1155  		return c.sendAlert(alertNoRenegotiation)
  1156  	}
  1157  
  1158  	switch c.config.Renegotiation {
  1159  	case RenegotiateNever:
  1160  		return c.sendAlert(alertNoRenegotiation)
  1161  	case RenegotiateOnceAsClient:
  1162  		if c.handshakes > 1 {
  1163  			return c.sendAlert(alertNoRenegotiation)
  1164  		}
  1165  	case RenegotiateFreelyAsClient:
  1166  		// Ok.
  1167  	default:
  1168  		c.sendAlert(alertInternalError)
  1169  		return errors.New("tls: unknown Renegotiation value")
  1170  	}
  1171  
  1172  	c.handshakeMutex.Lock()
  1173  	defer c.handshakeMutex.Unlock()
  1174  
  1175  	atomic.StoreUint32(&c.handshakeStatus, 0)
  1176  	if c.handshakeErr = c.clientHandshake(); c.handshakeErr == nil {
  1177  		c.handshakes++
  1178  	}
  1179  	return c.handshakeErr
  1180  }
  1181  
  1182  // handlePostHandshakeMessage processes a handshake message arrived after the
  1183  // handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation.
  1184  func (c *Conn) handlePostHandshakeMessage() error {
  1185  	if c.vers != VersionTLS13 {
  1186  		return c.handleRenegotiation()
  1187  	}
  1188  
  1189  	msg, err := c.readHandshake()
  1190  	if err != nil {
  1191  		return err
  1192  	}
  1193  
  1194  	c.retryCount++
  1195  	if c.retryCount > maxUselessRecords {
  1196  		c.sendAlert(alertUnexpectedMessage)
  1197  		return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
  1198  	}
  1199  
  1200  	switch msg := msg.(type) {
  1201  	case *newSessionTicketMsgTLS13:
  1202  		return c.handleNewSessionTicket(msg)
  1203  	case *keyUpdateMsg:
  1204  		return c.handleKeyUpdate(msg)
  1205  	default:
  1206  		c.sendAlert(alertUnexpectedMessage)
  1207  		return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
  1208  	}
  1209  }
  1210  
  1211  func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
  1212  	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
  1213  	if cipherSuite == nil {
  1214  		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
  1215  	}
  1216  
  1217  	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
  1218  	c.in.setTrafficSecret(cipherSuite, newSecret)
  1219  
  1220  	if keyUpdate.updateRequested {
  1221  		c.out.Lock()
  1222  		defer c.out.Unlock()
  1223  
  1224  		msg := &keyUpdateMsg{}
  1225  		_, err := c.writeRecordLocked(recordTypeHandshake, msg.marshal())
  1226  		if err != nil {
  1227  			// Surface the error at the next write.
  1228  			c.out.setErrorLocked(err)
  1229  			return nil
  1230  		}
  1231  
  1232  		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
  1233  		c.out.setTrafficSecret(cipherSuite, newSecret)
  1234  	}
  1235  
  1236  	return nil
  1237  }
  1238  
  1239  // Read can be made to time out and return a net.Error with Timeout() == true
  1240  // after a fixed time limit; see SetDeadline and SetReadDeadline.
  1241  func (c *Conn) Read(b []byte) (int, error) {
  1242  	if err := c.Handshake(); err != nil {
  1243  		return 0, err
  1244  	}
  1245  	if len(b) == 0 {
  1246  		// Put this after Handshake, in case people were calling
  1247  		// Read(nil) for the side effect of the Handshake.
  1248  		return 0, nil
  1249  	}
  1250  
  1251  	c.in.Lock()
  1252  	defer c.in.Unlock()
  1253  
  1254  	for c.input.Len() == 0 {
  1255  		if err := c.readRecord(); err != nil {
  1256  			return 0, err
  1257  		}
  1258  		for c.hand.Len() > 0 {
  1259  			if err := c.handlePostHandshakeMessage(); err != nil {
  1260  				return 0, err
  1261  			}
  1262  		}
  1263  	}
  1264  
  1265  	n, _ := c.input.Read(b)
  1266  
  1267  	// If a close-notify alert is waiting, read it so that we can return (n,
  1268  	// EOF) instead of (n, nil), to signal to the HTTP response reading
  1269  	// goroutine that the connection is now closed. This eliminates a race
  1270  	// where the HTTP response reading goroutine would otherwise not observe
  1271  	// the EOF until its next read, by which time a client goroutine might
  1272  	// have already tried to reuse the HTTP connection for a new request.
  1273  	// See https://golang.org/cl/76400046 and https://golang.org/issue/3514
  1274  	if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 &&
  1275  		recordType(c.rawInput.Bytes()[0]) == recordTypeAlert {
  1276  		if err := c.readRecord(); err != nil {
  1277  			return n, err // will be io.EOF on closeNotify
  1278  		}
  1279  	}
  1280  
  1281  	return n, nil
  1282  }
  1283  
  1284  // Close closes the connection.
  1285  func (c *Conn) Close() error {
  1286  	// Interlock with Conn.Write above.
  1287  	var x int32
  1288  	for {
  1289  		x = atomic.LoadInt32(&c.activeCall)
  1290  		if x&1 != 0 {
  1291  			return errClosed
  1292  		}
  1293  		if atomic.CompareAndSwapInt32(&c.activeCall, x, x|1) {
  1294  			break
  1295  		}
  1296  	}
  1297  	if x != 0 {
  1298  		// io.Writer and io.Closer should not be used concurrently.
  1299  		// If Close is called while a Write is currently in-flight,
  1300  		// interpret that as a sign that this Close is really just
  1301  		// being used to break the Write and/or clean up resources and
  1302  		// avoid sending the alertCloseNotify, which may block
  1303  		// waiting on handshakeMutex or the c.out mutex.
  1304  		return c.conn.Close()
  1305  	}
  1306  
  1307  	var alertErr error
  1308  
  1309  	if c.handshakeComplete() {
  1310  		alertErr = c.closeNotify()
  1311  	}
  1312  
  1313  	if err := c.conn.Close(); err != nil {
  1314  		return err
  1315  	}
  1316  	return alertErr
  1317  }
  1318  
  1319  var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
  1320  
  1321  // CloseWrite shuts down the writing side of the connection. It should only be
  1322  // called once the handshake has completed and does not call CloseWrite on the
  1323  // underlying connection. Most callers should just use Close.
  1324  func (c *Conn) CloseWrite() error {
  1325  	if !c.handshakeComplete() {
  1326  		return errEarlyCloseWrite
  1327  	}
  1328  
  1329  	return c.closeNotify()
  1330  }
  1331  
  1332  func (c *Conn) closeNotify() error {
  1333  	c.out.Lock()
  1334  	defer c.out.Unlock()
  1335  
  1336  	if !c.closeNotifySent {
  1337  		c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify)
  1338  		c.closeNotifySent = true
  1339  	}
  1340  	return c.closeNotifyErr
  1341  }
  1342  
  1343  // Handshake runs the client or server handshake
  1344  // protocol if it has not yet been run.
  1345  // Most uses of this package need not call Handshake
  1346  // explicitly: the first Read or Write will call it automatically.
  1347  func (c *Conn) Handshake() error {
  1348  	c.handshakeMutex.Lock()
  1349  	defer c.handshakeMutex.Unlock()
  1350  
  1351  	if err := c.handshakeErr; err != nil {
  1352  		return err
  1353  	}
  1354  	if c.handshakeComplete() {
  1355  		return nil
  1356  	}
  1357  
  1358  	c.in.Lock()
  1359  	defer c.in.Unlock()
  1360  
  1361  	if c.isClient {
  1362  		c.handshakeErr = c.clientHandshake()
  1363  	} else {
  1364  		c.handshakeErr = c.serverHandshake()
  1365  	}
  1366  	if c.handshakeErr == nil {
  1367  		c.handshakes++
  1368  	} else {
  1369  		// If an error occurred during the hadshake try to flush the
  1370  		// alert that might be left in the buffer.
  1371  		c.flush()
  1372  	}
  1373  
  1374  	if c.handshakeErr == nil && !c.handshakeComplete() {
  1375  		c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
  1376  	}
  1377  
  1378  	return c.handshakeErr
  1379  }
  1380  
  1381  // ConnectionState returns basic TLS details about the connection.
  1382  func (c *Conn) ConnectionState() ConnectionState {
  1383  	c.handshakeMutex.Lock()
  1384  	defer c.handshakeMutex.Unlock()
  1385  
  1386  	var state ConnectionState
  1387  	state.HandshakeComplete = c.handshakeComplete()
  1388  	state.ServerName = c.serverName
  1389  
  1390  	if state.HandshakeComplete {
  1391  		state.Version = c.vers
  1392  		state.NegotiatedProtocol = c.clientProtocol
  1393  		state.DidResume = c.didResume
  1394  		state.NegotiatedProtocolIsMutual = !c.clientProtocolFallback
  1395  		state.CipherSuite = c.cipherSuite
  1396  		state.PeerCertificates = c.peerCertificates
  1397  		state.VerifiedChains = c.verifiedChains
  1398  		state.SignedCertificateTimestamps = c.scts
  1399  		state.OCSPResponse = c.ocspResponse
  1400  		if !c.didResume && c.vers != VersionTLS13 {
  1401  			if c.clientFinishedIsFirst {
  1402  				state.TLSUnique = c.clientFinished[:]
  1403  			} else {
  1404  				state.TLSUnique = c.serverFinished[:]
  1405  			}
  1406  		}
  1407  		if c.config.Renegotiation != RenegotiateNever {
  1408  			state.ekm = noExportedKeyingMaterial
  1409  		} else {
  1410  			state.ekm = c.ekm
  1411  		}
  1412  	}
  1413  
  1414  	return state
  1415  }
  1416  
  1417  // OCSPResponse returns the stapled OCSP response from the TLS server, if
  1418  // any. (Only valid for client connections.)
  1419  func (c *Conn) OCSPResponse() []byte {
  1420  	c.handshakeMutex.Lock()
  1421  	defer c.handshakeMutex.Unlock()
  1422  
  1423  	return c.ocspResponse
  1424  }
  1425  
  1426  // VerifyHostname checks that the peer certificate chain is valid for
  1427  // connecting to host. If so, it returns nil; if not, it returns an error
  1428  // describing the problem.
  1429  func (c *Conn) VerifyHostname(host string) error {
  1430  	c.handshakeMutex.Lock()
  1431  	defer c.handshakeMutex.Unlock()
  1432  	if !c.isClient {
  1433  		return errors.New("tls: VerifyHostname called on TLS server connection")
  1434  	}
  1435  	if !c.handshakeComplete() {
  1436  		return errors.New("tls: handshake has not yet been performed")
  1437  	}
  1438  	if len(c.verifiedChains) == 0 {
  1439  		return errors.New("tls: handshake did not verify certificate chain")
  1440  	}
  1441  	return c.peerCertificates[0].VerifyHostname(host)
  1442  }
  1443  
  1444  func (c *Conn) handshakeComplete() bool {
  1445  	return atomic.LoadUint32(&c.handshakeStatus) == 1
  1446  }
  1447  

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