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  	"context"
    12  	"crypto/cipher"
    13  	"crypto/subtle"
    14  	"crypto/x509"
    15  	"errors"
    16  	"fmt"
    17  	"hash"
    18  	"internal/godebug"
    19  	"io"
    20  	"net"
    21  	"sync"
    22  	"sync/atomic"
    23  	"time"
    24  )
    25  
    26  // A Conn represents a secured connection.
    27  // It implements the net.Conn interface.
    28  type Conn struct {
    29  	// constant
    30  	conn        net.Conn
    31  	isClient    bool
    32  	handshakeFn func(context.Context) error // (*Conn).clientHandshake or serverHandshake
    33  	quic        *quicState                  // nil for non-QUIC connections
    34  
    35  	// isHandshakeComplete is true if the connection is currently transferring
    36  	// application data (i.e. is not currently processing a handshake).
    37  	// isHandshakeComplete is true implies handshakeErr == nil.
    38  	isHandshakeComplete atomic.Bool
    39  	// constant after handshake; protected by handshakeMutex
    40  	handshakeMutex sync.Mutex
    41  	handshakeErr   error   // error resulting from handshake
    42  	vers           uint16  // TLS version
    43  	haveVers       bool    // version has been negotiated
    44  	config         *Config // configuration passed to constructor
    45  	// handshakes counts the number of handshakes performed on the
    46  	// connection so far. If renegotiation is disabled then this is either
    47  	// zero or one.
    48  	handshakes       int
    49  	extMasterSecret  bool
    50  	didResume        bool // whether this connection was a session resumption
    51  	cipherSuite      uint16
    52  	ocspResponse     []byte   // stapled OCSP response
    53  	scts             [][]byte // signed certificate timestamps from server
    54  	peerCertificates []*x509.Certificate
    55  	// activeCertHandles contains the cache handles to certificates in
    56  	// peerCertificates that are used to track active references.
    57  	activeCertHandles []*activeCert
    58  	// verifiedChains contains the certificate chains that we built, as
    59  	// opposed to the ones presented by the server.
    60  	verifiedChains [][]*x509.Certificate
    61  	// serverName contains the server name indicated by the client, if any.
    62  	serverName string
    63  	// secureRenegotiation is true if the server echoed the secure
    64  	// renegotiation extension. (This is meaningless as a server because
    65  	// renegotiation is not supported in that case.)
    66  	secureRenegotiation bool
    67  	// ekm is a closure for exporting keying material.
    68  	ekm func(label string, context []byte, length int) ([]byte, error)
    69  	// resumptionSecret is the resumption_master_secret for handling
    70  	// or sending NewSessionTicket messages.
    71  	resumptionSecret []byte
    72  
    73  	// ticketKeys is the set of active session ticket keys for this
    74  	// connection. The first one is used to encrypt new tickets and
    75  	// all are tried to decrypt tickets.
    76  	ticketKeys []ticketKey
    77  
    78  	// clientFinishedIsFirst is true if the client sent the first Finished
    79  	// message during the most recent handshake. This is recorded because
    80  	// the first transmitted Finished message is the tls-unique
    81  	// channel-binding value.
    82  	clientFinishedIsFirst bool
    83  
    84  	// closeNotifyErr is any error from sending the alertCloseNotify record.
    85  	closeNotifyErr error
    86  	// closeNotifySent is true if the Conn attempted to send an
    87  	// alertCloseNotify record.
    88  	closeNotifySent bool
    89  
    90  	// clientFinished and serverFinished contain the Finished message sent
    91  	// by the client or server in the most recent handshake. This is
    92  	// retained to support the renegotiation extension and tls-unique
    93  	// channel-binding.
    94  	clientFinished [12]byte
    95  	serverFinished [12]byte
    96  
    97  	// clientProtocol is the negotiated ALPN protocol.
    98  	clientProtocol string
    99  
   100  	// input/output
   101  	in, out   halfConn
   102  	rawInput  bytes.Buffer // raw input, starting with a record header
   103  	input     bytes.Reader // application data waiting to be read, from rawInput.Next
   104  	hand      bytes.Buffer // handshake data waiting to be read
   105  	buffering bool         // whether records are buffered in sendBuf
   106  	sendBuf   []byte       // a buffer of records waiting to be sent
   107  
   108  	// bytesSent counts the bytes of application data sent.
   109  	// packetsSent counts packets.
   110  	bytesSent   int64
   111  	packetsSent int64
   112  
   113  	// retryCount counts the number of consecutive non-advancing records
   114  	// received by Conn.readRecord. That is, records that neither advance the
   115  	// handshake, nor deliver application data. Protected by in.Mutex.
   116  	retryCount int
   117  
   118  	// activeCall indicates whether Close has been call in the low bit.
   119  	// the rest of the bits are the number of goroutines in Conn.Write.
   120  	activeCall atomic.Int32
   121  
   122  	tmp [16]byte
   123  }
   124  
   125  // Access to net.Conn methods.
   126  // Cannot just embed net.Conn because that would
   127  // export the struct field too.
   128  
   129  // LocalAddr returns the local network address.
   130  func (c *Conn) LocalAddr() net.Addr {
   131  	return c.conn.LocalAddr()
   132  }
   133  
   134  // RemoteAddr returns the remote network address.
   135  func (c *Conn) RemoteAddr() net.Addr {
   136  	return c.conn.RemoteAddr()
   137  }
   138  
   139  // SetDeadline sets the read and write deadlines associated with the connection.
   140  // A zero value for t means [Conn.Read] and [Conn.Write] will not time out.
   141  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   142  func (c *Conn) SetDeadline(t time.Time) error {
   143  	return c.conn.SetDeadline(t)
   144  }
   145  
   146  // SetReadDeadline sets the read deadline on the underlying connection.
   147  // A zero value for t means [Conn.Read] will not time out.
   148  func (c *Conn) SetReadDeadline(t time.Time) error {
   149  	return c.conn.SetReadDeadline(t)
   150  }
   151  
   152  // SetWriteDeadline sets the write deadline on the underlying connection.
   153  // A zero value for t means [Conn.Write] will not time out.
   154  // After a [Conn.Write] has timed out, the TLS state is corrupt and all future writes will return the same error.
   155  func (c *Conn) SetWriteDeadline(t time.Time) error {
   156  	return c.conn.SetWriteDeadline(t)
   157  }
   158  
   159  // NetConn returns the underlying connection that is wrapped by c.
   160  // Note that writing to or reading from this connection directly will corrupt the
   161  // TLS session.
   162  func (c *Conn) NetConn() net.Conn {
   163  	return c.conn
   164  }
   165  
   166  // A halfConn represents one direction of the record layer
   167  // connection, either sending or receiving.
   168  type halfConn struct {
   169  	sync.Mutex
   170  
   171  	err     error  // first permanent error
   172  	version uint16 // protocol version
   173  	cipher  any    // cipher algorithm
   174  	mac     hash.Hash
   175  	seq     [8]byte // 64-bit sequence number
   176  
   177  	scratchBuf [13]byte // to avoid allocs; interface method args escape
   178  
   179  	nextCipher any       // next encryption state
   180  	nextMac    hash.Hash // next MAC algorithm
   181  
   182  	level         QUICEncryptionLevel // current QUIC encryption level
   183  	trafficSecret []byte              // current TLS 1.3 traffic secret
   184  }
   185  
   186  type permanentError struct {
   187  	err net.Error
   188  }
   189  
   190  func (e *permanentError) Error() string   { return e.err.Error() }
   191  func (e *permanentError) Unwrap() error   { return e.err }
   192  func (e *permanentError) Timeout() bool   { return e.err.Timeout() }
   193  func (e *permanentError) Temporary() bool { return false }
   194  
   195  func (hc *halfConn) setErrorLocked(err error) error {
   196  	if e, ok := err.(net.Error); ok {
   197  		hc.err = &permanentError{err: e}
   198  	} else {
   199  		hc.err = err
   200  	}
   201  	return hc.err
   202  }
   203  
   204  // prepareCipherSpec sets the encryption and MAC states
   205  // that a subsequent changeCipherSpec will use.
   206  func (hc *halfConn) prepareCipherSpec(version uint16, cipher any, mac hash.Hash) {
   207  	hc.version = version
   208  	hc.nextCipher = cipher
   209  	hc.nextMac = mac
   210  }
   211  
   212  // changeCipherSpec changes the encryption and MAC states
   213  // to the ones previously passed to prepareCipherSpec.
   214  func (hc *halfConn) changeCipherSpec() error {
   215  	if hc.nextCipher == nil || hc.version == VersionTLS13 {
   216  		return alertInternalError
   217  	}
   218  	hc.cipher = hc.nextCipher
   219  	hc.mac = hc.nextMac
   220  	hc.nextCipher = nil
   221  	hc.nextMac = nil
   222  	for i := range hc.seq {
   223  		hc.seq[i] = 0
   224  	}
   225  	return nil
   226  }
   227  
   228  func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, level QUICEncryptionLevel, secret []byte) {
   229  	hc.trafficSecret = secret
   230  	hc.level = level
   231  	key, iv := suite.trafficKey(secret)
   232  	hc.cipher = suite.aead(key, iv)
   233  	for i := range hc.seq {
   234  		hc.seq[i] = 0
   235  	}
   236  }
   237  
   238  // incSeq increments the sequence number.
   239  func (hc *halfConn) incSeq() {
   240  	for i := 7; i >= 0; i-- {
   241  		hc.seq[i]++
   242  		if hc.seq[i] != 0 {
   243  			return
   244  		}
   245  	}
   246  
   247  	// Not allowed to let sequence number wrap.
   248  	// Instead, must renegotiate before it does.
   249  	// Not likely enough to bother.
   250  	panic("TLS: sequence number wraparound")
   251  }
   252  
   253  // explicitNonceLen returns the number of bytes of explicit nonce or IV included
   254  // in each record. Explicit nonces are present only in CBC modes after TLS 1.0
   255  // and in certain AEAD modes in TLS 1.2.
   256  func (hc *halfConn) explicitNonceLen() int {
   257  	if hc.cipher == nil {
   258  		return 0
   259  	}
   260  
   261  	switch c := hc.cipher.(type) {
   262  	case cipher.Stream:
   263  		return 0
   264  	case aead:
   265  		return c.explicitNonceLen()
   266  	case cbcMode:
   267  		// TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack.
   268  		if hc.version >= VersionTLS11 {
   269  			return c.BlockSize()
   270  		}
   271  		return 0
   272  	default:
   273  		panic("unknown cipher type")
   274  	}
   275  }
   276  
   277  // extractPadding returns, in constant time, the length of the padding to remove
   278  // from the end of payload. It also returns a byte which is equal to 255 if the
   279  // padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
   280  func extractPadding(payload []byte) (toRemove int, good byte) {
   281  	if len(payload) < 1 {
   282  		return 0, 0
   283  	}
   284  
   285  	paddingLen := payload[len(payload)-1]
   286  	t := uint(len(payload)-1) - uint(paddingLen)
   287  	// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
   288  	good = byte(int32(^t) >> 31)
   289  
   290  	// The maximum possible padding length plus the actual length field
   291  	toCheck := 256
   292  	// The length of the padded data is public, so we can use an if here
   293  	if toCheck > len(payload) {
   294  		toCheck = len(payload)
   295  	}
   296  
   297  	for i := 0; i < toCheck; i++ {
   298  		t := uint(paddingLen) - uint(i)
   299  		// if i <= paddingLen then the MSB of t is zero
   300  		mask := byte(int32(^t) >> 31)
   301  		b := payload[len(payload)-1-i]
   302  		good &^= mask&paddingLen ^ mask&b
   303  	}
   304  
   305  	// We AND together the bits of good and replicate the result across
   306  	// all the bits.
   307  	good &= good << 4
   308  	good &= good << 2
   309  	good &= good << 1
   310  	good = uint8(int8(good) >> 7)
   311  
   312  	// Zero the padding length on error. This ensures any unchecked bytes
   313  	// are included in the MAC. Otherwise, an attacker that could
   314  	// distinguish MAC failures from padding failures could mount an attack
   315  	// similar to POODLE in SSL 3.0: given a good ciphertext that uses a
   316  	// full block's worth of padding, replace the final block with another
   317  	// block. If the MAC check passed but the padding check failed, the
   318  	// last byte of that block decrypted to the block size.
   319  	//
   320  	// See also macAndPaddingGood logic below.
   321  	paddingLen &= good
   322  
   323  	toRemove = int(paddingLen) + 1
   324  	return
   325  }
   326  
   327  func roundUp(a, b int) int {
   328  	return a + (b-a%b)%b
   329  }
   330  
   331  // cbcMode is an interface for block ciphers using cipher block chaining.
   332  type cbcMode interface {
   333  	cipher.BlockMode
   334  	SetIV([]byte)
   335  }
   336  
   337  // decrypt authenticates and decrypts the record if protection is active at
   338  // this stage. The returned plaintext might overlap with the input.
   339  func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) {
   340  	var plaintext []byte
   341  	typ := recordType(record[0])
   342  	payload := record[recordHeaderLen:]
   343  
   344  	// In TLS 1.3, change_cipher_spec messages are to be ignored without being
   345  	// decrypted. See RFC 8446, Appendix D.4.
   346  	if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec {
   347  		return payload, typ, nil
   348  	}
   349  
   350  	paddingGood := byte(255)
   351  	paddingLen := 0
   352  
   353  	explicitNonceLen := hc.explicitNonceLen()
   354  
   355  	if hc.cipher != nil {
   356  		switch c := hc.cipher.(type) {
   357  		case cipher.Stream:
   358  			c.XORKeyStream(payload, payload)
   359  		case aead:
   360  			if len(payload) < explicitNonceLen {
   361  				return nil, 0, alertBadRecordMAC
   362  			}
   363  			nonce := payload[:explicitNonceLen]
   364  			if len(nonce) == 0 {
   365  				nonce = hc.seq[:]
   366  			}
   367  			payload = payload[explicitNonceLen:]
   368  
   369  			var additionalData []byte
   370  			if hc.version == VersionTLS13 {
   371  				additionalData = record[:recordHeaderLen]
   372  			} else {
   373  				additionalData = append(hc.scratchBuf[:0], hc.seq[:]...)
   374  				additionalData = append(additionalData, record[:3]...)
   375  				n := len(payload) - c.Overhead()
   376  				additionalData = append(additionalData, byte(n>>8), byte(n))
   377  			}
   378  
   379  			var err error
   380  			plaintext, err = c.Open(payload[:0], nonce, payload, additionalData)
   381  			if err != nil {
   382  				return nil, 0, alertBadRecordMAC
   383  			}
   384  		case cbcMode:
   385  			blockSize := c.BlockSize()
   386  			minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize)
   387  			if len(payload)%blockSize != 0 || len(payload) < minPayload {
   388  				return nil, 0, alertBadRecordMAC
   389  			}
   390  
   391  			if explicitNonceLen > 0 {
   392  				c.SetIV(payload[:explicitNonceLen])
   393  				payload = payload[explicitNonceLen:]
   394  			}
   395  			c.CryptBlocks(payload, payload)
   396  
   397  			// In a limited attempt to protect against CBC padding oracles like
   398  			// Lucky13, the data past paddingLen (which is secret) is passed to
   399  			// the MAC function as extra data, to be fed into the HMAC after
   400  			// computing the digest. This makes the MAC roughly constant time as
   401  			// long as the digest computation is constant time and does not
   402  			// affect the subsequent write, modulo cache effects.
   403  			paddingLen, paddingGood = extractPadding(payload)
   404  		default:
   405  			panic("unknown cipher type")
   406  		}
   407  
   408  		if hc.version == VersionTLS13 {
   409  			if typ != recordTypeApplicationData {
   410  				return nil, 0, alertUnexpectedMessage
   411  			}
   412  			if len(plaintext) > maxPlaintext+1 {
   413  				return nil, 0, alertRecordOverflow
   414  			}
   415  			// Remove padding and find the ContentType scanning from the end.
   416  			for i := len(plaintext) - 1; i >= 0; i-- {
   417  				if plaintext[i] != 0 {
   418  					typ = recordType(plaintext[i])
   419  					plaintext = plaintext[:i]
   420  					break
   421  				}
   422  				if i == 0 {
   423  					return nil, 0, alertUnexpectedMessage
   424  				}
   425  			}
   426  		}
   427  	} else {
   428  		plaintext = payload
   429  	}
   430  
   431  	if hc.mac != nil {
   432  		macSize := hc.mac.Size()
   433  		if len(payload) < macSize {
   434  			return nil, 0, alertBadRecordMAC
   435  		}
   436  
   437  		n := len(payload) - macSize - paddingLen
   438  		n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 }
   439  		record[3] = byte(n >> 8)
   440  		record[4] = byte(n)
   441  		remoteMAC := payload[n : n+macSize]
   442  		localMAC := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload[:n], payload[n+macSize:])
   443  
   444  		// This is equivalent to checking the MACs and paddingGood
   445  		// separately, but in constant-time to prevent distinguishing
   446  		// padding failures from MAC failures. Depending on what value
   447  		// of paddingLen was returned on bad padding, distinguishing
   448  		// bad MAC from bad padding can lead to an attack.
   449  		//
   450  		// See also the logic at the end of extractPadding.
   451  		macAndPaddingGood := subtle.ConstantTimeCompare(localMAC, remoteMAC) & int(paddingGood)
   452  		if macAndPaddingGood != 1 {
   453  			return nil, 0, alertBadRecordMAC
   454  		}
   455  
   456  		plaintext = payload[:n]
   457  	}
   458  
   459  	hc.incSeq()
   460  	return plaintext, typ, nil
   461  }
   462  
   463  // sliceForAppend extends the input slice by n bytes. head is the full extended
   464  // slice, while tail is the appended part. If the original slice has sufficient
   465  // capacity no allocation is performed.
   466  func sliceForAppend(in []byte, n int) (head, tail []byte) {
   467  	if total := len(in) + n; cap(in) >= total {
   468  		head = in[:total]
   469  	} else {
   470  		head = make([]byte, total)
   471  		copy(head, in)
   472  	}
   473  	tail = head[len(in):]
   474  	return
   475  }
   476  
   477  // encrypt encrypts payload, adding the appropriate nonce and/or MAC, and
   478  // appends it to record, which must already contain the record header.
   479  func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) {
   480  	if hc.cipher == nil {
   481  		return append(record, payload...), nil
   482  	}
   483  
   484  	var explicitNonce []byte
   485  	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
   486  		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
   487  		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
   488  			// The AES-GCM construction in TLS has an explicit nonce so that the
   489  			// nonce can be random. However, the nonce is only 8 bytes which is
   490  			// too small for a secure, random nonce. Therefore we use the
   491  			// sequence number as the nonce. The 3DES-CBC construction also has
   492  			// an 8 bytes nonce but its nonces must be unpredictable (see RFC
   493  			// 5246, Appendix F.3), forcing us to use randomness. That's not
   494  			// 3DES' biggest problem anyway because the birthday bound on block
   495  			// collision is reached first due to its similarly small block size
   496  			// (see the Sweet32 attack).
   497  			copy(explicitNonce, hc.seq[:])
   498  		} else {
   499  			if _, err := io.ReadFull(rand, explicitNonce); err != nil {
   500  				return nil, err
   501  			}
   502  		}
   503  	}
   504  
   505  	var dst []byte
   506  	switch c := hc.cipher.(type) {
   507  	case cipher.Stream:
   508  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   509  		record, dst = sliceForAppend(record, len(payload)+len(mac))
   510  		c.XORKeyStream(dst[:len(payload)], payload)
   511  		c.XORKeyStream(dst[len(payload):], mac)
   512  	case aead:
   513  		nonce := explicitNonce
   514  		if len(nonce) == 0 {
   515  			nonce = hc.seq[:]
   516  		}
   517  
   518  		if hc.version == VersionTLS13 {
   519  			record = append(record, payload...)
   520  
   521  			// Encrypt the actual ContentType and replace the plaintext one.
   522  			record = append(record, record[0])
   523  			record[0] = byte(recordTypeApplicationData)
   524  
   525  			n := len(payload) + 1 + c.Overhead()
   526  			record[3] = byte(n >> 8)
   527  			record[4] = byte(n)
   528  
   529  			record = c.Seal(record[:recordHeaderLen],
   530  				nonce, record[recordHeaderLen:], record[:recordHeaderLen])
   531  		} else {
   532  			additionalData := append(hc.scratchBuf[:0], hc.seq[:]...)
   533  			additionalData = append(additionalData, record[:recordHeaderLen]...)
   534  			record = c.Seal(record, nonce, payload, additionalData)
   535  		}
   536  	case cbcMode:
   537  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   538  		blockSize := c.BlockSize()
   539  		plaintextLen := len(payload) + len(mac)
   540  		paddingLen := blockSize - plaintextLen%blockSize
   541  		record, dst = sliceForAppend(record, plaintextLen+paddingLen)
   542  		copy(dst, payload)
   543  		copy(dst[len(payload):], mac)
   544  		for i := plaintextLen; i < len(dst); i++ {
   545  			dst[i] = byte(paddingLen - 1)
   546  		}
   547  		if len(explicitNonce) > 0 {
   548  			c.SetIV(explicitNonce)
   549  		}
   550  		c.CryptBlocks(dst, dst)
   551  	default:
   552  		panic("unknown cipher type")
   553  	}
   554  
   555  	// Update length to include nonce, MAC and any block padding needed.
   556  	n := len(record) - recordHeaderLen
   557  	record[3] = byte(n >> 8)
   558  	record[4] = byte(n)
   559  	hc.incSeq()
   560  
   561  	return record, nil
   562  }
   563  
   564  // RecordHeaderError is returned when a TLS record header is invalid.
   565  type RecordHeaderError struct {
   566  	// Msg contains a human readable string that describes the error.
   567  	Msg string
   568  	// RecordHeader contains the five bytes of TLS record header that
   569  	// triggered the error.
   570  	RecordHeader [5]byte
   571  	// Conn provides the underlying net.Conn in the case that a client
   572  	// sent an initial handshake that didn't look like TLS.
   573  	// It is nil if there's already been a handshake or a TLS alert has
   574  	// been written to the connection.
   575  	Conn net.Conn
   576  }
   577  
   578  func (e RecordHeaderError) Error() string { return "tls: " + e.Msg }
   579  
   580  func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) {
   581  	err.Msg = msg
   582  	err.Conn = conn
   583  	copy(err.RecordHeader[:], c.rawInput.Bytes())
   584  	return err
   585  }
   586  
   587  func (c *Conn) readRecord() error {
   588  	return c.readRecordOrCCS(false)
   589  }
   590  
   591  func (c *Conn) readChangeCipherSpec() error {
   592  	return c.readRecordOrCCS(true)
   593  }
   594  
   595  // readRecordOrCCS reads one or more TLS records from the connection and
   596  // updates the record layer state. Some invariants:
   597  //   - c.in must be locked
   598  //   - c.input must be empty
   599  //
   600  // During the handshake one and only one of the following will happen:
   601  //   - c.hand grows
   602  //   - c.in.changeCipherSpec is called
   603  //   - an error is returned
   604  //
   605  // After the handshake one and only one of the following will happen:
   606  //   - c.hand grows
   607  //   - c.input is set
   608  //   - an error is returned
   609  func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
   610  	if c.in.err != nil {
   611  		return c.in.err
   612  	}
   613  	handshakeComplete := c.isHandshakeComplete.Load()
   614  
   615  	// This function modifies c.rawInput, which owns the c.input memory.
   616  	if c.input.Len() != 0 {
   617  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
   618  	}
   619  	c.input.Reset(nil)
   620  
   621  	if c.quic != nil {
   622  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with QUIC transport"))
   623  	}
   624  
   625  	// Read header, payload.
   626  	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
   627  		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
   628  		// is an error, but popular web sites seem to do this, so we accept it
   629  		// if and only if at the record boundary.
   630  		if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 {
   631  			err = io.EOF
   632  		}
   633  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   634  			c.in.setErrorLocked(err)
   635  		}
   636  		return err
   637  	}
   638  	hdr := c.rawInput.Bytes()[:recordHeaderLen]
   639  	typ := recordType(hdr[0])
   640  
   641  	// No valid TLS record has a type of 0x80, however SSLv2 handshakes
   642  	// start with a uint16 length where the MSB is set and the first record
   643  	// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
   644  	// an SSLv2 client.
   645  	if !handshakeComplete && typ == 0x80 {
   646  		c.sendAlert(alertProtocolVersion)
   647  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received"))
   648  	}
   649  
   650  	vers := uint16(hdr[1])<<8 | uint16(hdr[2])
   651  	expectedVers := c.vers
   652  	if expectedVers == VersionTLS13 {
   653  		// All TLS 1.3 records are expected to have 0x0303 (1.2) after
   654  		// the initial hello (RFC 8446 Section 5.1).
   655  		expectedVers = VersionTLS12
   656  	}
   657  	n := int(hdr[3])<<8 | int(hdr[4])
   658  	if c.haveVers && vers != expectedVers {
   659  		c.sendAlert(alertProtocolVersion)
   660  		msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, expectedVers)
   661  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   662  	}
   663  	if !c.haveVers {
   664  		// First message, be extra suspicious: this might not be a TLS
   665  		// client. Bail out before reading a full 'body', if possible.
   666  		// The current max version is 3.3 so if the version is >= 16.0,
   667  		// it's probably not real.
   668  		if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 {
   669  			return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake"))
   670  		}
   671  	}
   672  	if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext {
   673  		c.sendAlert(alertRecordOverflow)
   674  		msg := fmt.Sprintf("oversized record received with length %d", n)
   675  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   676  	}
   677  	if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
   678  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   679  			c.in.setErrorLocked(err)
   680  		}
   681  		return err
   682  	}
   683  
   684  	// Process message.
   685  	record := c.rawInput.Next(recordHeaderLen + n)
   686  	data, typ, err := c.in.decrypt(record)
   687  	if err != nil {
   688  		return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   689  	}
   690  	if len(data) > maxPlaintext {
   691  		return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow))
   692  	}
   693  
   694  	// Application Data messages are always protected.
   695  	if c.in.cipher == nil && typ == recordTypeApplicationData {
   696  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   697  	}
   698  
   699  	if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 {
   700  		// This is a state-advancing message: reset the retry count.
   701  		c.retryCount = 0
   702  	}
   703  
   704  	// Handshake messages MUST NOT be interleaved with other record types in TLS 1.3.
   705  	if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 {
   706  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   707  	}
   708  
   709  	switch typ {
   710  	default:
   711  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   712  
   713  	case recordTypeAlert:
   714  		if c.quic != nil {
   715  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   716  		}
   717  		if len(data) != 2 {
   718  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   719  		}
   720  		if alert(data[1]) == alertCloseNotify {
   721  			return c.in.setErrorLocked(io.EOF)
   722  		}
   723  		if c.vers == VersionTLS13 {
   724  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   725  		}
   726  		switch data[0] {
   727  		case alertLevelWarning:
   728  			// Drop the record on the floor and retry.
   729  			return c.retryReadRecord(expectChangeCipherSpec)
   730  		case alertLevelError:
   731  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   732  		default:
   733  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   734  		}
   735  
   736  	case recordTypeChangeCipherSpec:
   737  		if len(data) != 1 || data[0] != 1 {
   738  			return c.in.setErrorLocked(c.sendAlert(alertDecodeError))
   739  		}
   740  		// Handshake messages are not allowed to fragment across the CCS.
   741  		if c.hand.Len() > 0 {
   742  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   743  		}
   744  		// In TLS 1.3, change_cipher_spec records are ignored until the
   745  		// Finished. See RFC 8446, Appendix D.4. Note that according to Section
   746  		// 5, a server can send a ChangeCipherSpec before its ServerHello, when
   747  		// c.vers is still unset. That's not useful though and suspicious if the
   748  		// server then selects a lower protocol version, so don't allow that.
   749  		if c.vers == VersionTLS13 {
   750  			return c.retryReadRecord(expectChangeCipherSpec)
   751  		}
   752  		if !expectChangeCipherSpec {
   753  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   754  		}
   755  		if err := c.in.changeCipherSpec(); err != nil {
   756  			return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   757  		}
   758  
   759  	case recordTypeApplicationData:
   760  		if !handshakeComplete || expectChangeCipherSpec {
   761  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   762  		}
   763  		// Some OpenSSL servers send empty records in order to randomize the
   764  		// CBC IV. Ignore a limited number of empty records.
   765  		if len(data) == 0 {
   766  			return c.retryReadRecord(expectChangeCipherSpec)
   767  		}
   768  		// Note that data is owned by c.rawInput, following the Next call above,
   769  		// to avoid copying the plaintext. This is safe because c.rawInput is
   770  		// not read from or written to until c.input is drained.
   771  		c.input.Reset(data)
   772  
   773  	case recordTypeHandshake:
   774  		if len(data) == 0 || expectChangeCipherSpec {
   775  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   776  		}
   777  		c.hand.Write(data)
   778  	}
   779  
   780  	return nil
   781  }
   782  
   783  // retryReadRecord recurs into readRecordOrCCS to drop a non-advancing record, like
   784  // a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3.
   785  func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error {
   786  	c.retryCount++
   787  	if c.retryCount > maxUselessRecords {
   788  		c.sendAlert(alertUnexpectedMessage)
   789  		return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
   790  	}
   791  	return c.readRecordOrCCS(expectChangeCipherSpec)
   792  }
   793  
   794  // atLeastReader reads from R, stopping with EOF once at least N bytes have been
   795  // read. It is different from an io.LimitedReader in that it doesn't cut short
   796  // the last Read call, and in that it considers an early EOF an error.
   797  type atLeastReader struct {
   798  	R io.Reader
   799  	N int64
   800  }
   801  
   802  func (r *atLeastReader) Read(p []byte) (int, error) {
   803  	if r.N <= 0 {
   804  		return 0, io.EOF
   805  	}
   806  	n, err := r.R.Read(p)
   807  	r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809
   808  	if r.N > 0 && err == io.EOF {
   809  		return n, io.ErrUnexpectedEOF
   810  	}
   811  	if r.N <= 0 && err == nil {
   812  		return n, io.EOF
   813  	}
   814  	return n, err
   815  }
   816  
   817  // readFromUntil reads from r into c.rawInput until c.rawInput contains
   818  // at least n bytes or else returns an error.
   819  func (c *Conn) readFromUntil(r io.Reader, n int) error {
   820  	if c.rawInput.Len() >= n {
   821  		return nil
   822  	}
   823  	needs := n - c.rawInput.Len()
   824  	// There might be extra input waiting on the wire. Make a best effort
   825  	// attempt to fetch it so that it can be used in (*Conn).Read to
   826  	// "predict" closeNotify alerts.
   827  	c.rawInput.Grow(needs + bytes.MinRead)
   828  	_, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)})
   829  	return err
   830  }
   831  
   832  // sendAlertLocked sends a TLS alert message.
   833  func (c *Conn) sendAlertLocked(err alert) error {
   834  	if c.quic != nil {
   835  		return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   836  	}
   837  
   838  	switch err {
   839  	case alertNoRenegotiation, alertCloseNotify:
   840  		c.tmp[0] = alertLevelWarning
   841  	default:
   842  		c.tmp[0] = alertLevelError
   843  	}
   844  	c.tmp[1] = byte(err)
   845  
   846  	_, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2])
   847  	if err == alertCloseNotify {
   848  		// closeNotify is a special case in that it isn't an error.
   849  		return writeErr
   850  	}
   851  
   852  	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   853  }
   854  
   855  // sendAlert sends a TLS alert message.
   856  func (c *Conn) sendAlert(err alert) error {
   857  	c.out.Lock()
   858  	defer c.out.Unlock()
   859  	return c.sendAlertLocked(err)
   860  }
   861  
   862  const (
   863  	// tcpMSSEstimate is a conservative estimate of the TCP maximum segment
   864  	// size (MSS). A constant is used, rather than querying the kernel for
   865  	// the actual MSS, to avoid complexity. The value here is the IPv6
   866  	// minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40
   867  	// bytes) and a TCP header with timestamps (32 bytes).
   868  	tcpMSSEstimate = 1208
   869  
   870  	// recordSizeBoostThreshold is the number of bytes of application data
   871  	// sent after which the TLS record size will be increased to the
   872  	// maximum.
   873  	recordSizeBoostThreshold = 128 * 1024
   874  )
   875  
   876  // maxPayloadSizeForWrite returns the maximum TLS payload size to use for the
   877  // next application data record. There is the following trade-off:
   878  //
   879  //   - For latency-sensitive applications, such as web browsing, each TLS
   880  //     record should fit in one TCP segment.
   881  //   - For throughput-sensitive applications, such as large file transfers,
   882  //     larger TLS records better amortize framing and encryption overheads.
   883  //
   884  // A simple heuristic that works well in practice is to use small records for
   885  // the first 1MB of data, then use larger records for subsequent data, and
   886  // reset back to smaller records after the connection becomes idle. See "High
   887  // Performance Web Networking", Chapter 4, or:
   888  // https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/
   889  //
   890  // In the interests of simplicity and determinism, this code does not attempt
   891  // to reset the record size once the connection is idle, however.
   892  func (c *Conn) maxPayloadSizeForWrite(typ recordType) int {
   893  	if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData {
   894  		return maxPlaintext
   895  	}
   896  
   897  	if c.bytesSent >= recordSizeBoostThreshold {
   898  		return maxPlaintext
   899  	}
   900  
   901  	// Subtract TLS overheads to get the maximum payload size.
   902  	payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen()
   903  	if c.out.cipher != nil {
   904  		switch ciph := c.out.cipher.(type) {
   905  		case cipher.Stream:
   906  			payloadBytes -= c.out.mac.Size()
   907  		case cipher.AEAD:
   908  			payloadBytes -= ciph.Overhead()
   909  		case cbcMode:
   910  			blockSize := ciph.BlockSize()
   911  			// The payload must fit in a multiple of blockSize, with
   912  			// room for at least one padding byte.
   913  			payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1
   914  			// The MAC is appended before padding so affects the
   915  			// payload size directly.
   916  			payloadBytes -= c.out.mac.Size()
   917  		default:
   918  			panic("unknown cipher type")
   919  		}
   920  	}
   921  	if c.vers == VersionTLS13 {
   922  		payloadBytes-- // encrypted ContentType
   923  	}
   924  
   925  	// Allow packet growth in arithmetic progression up to max.
   926  	pkt := c.packetsSent
   927  	c.packetsSent++
   928  	if pkt > 1000 {
   929  		return maxPlaintext // avoid overflow in multiply below
   930  	}
   931  
   932  	n := payloadBytes * int(pkt+1)
   933  	if n > maxPlaintext {
   934  		n = maxPlaintext
   935  	}
   936  	return n
   937  }
   938  
   939  func (c *Conn) write(data []byte) (int, error) {
   940  	if c.buffering {
   941  		c.sendBuf = append(c.sendBuf, data...)
   942  		return len(data), nil
   943  	}
   944  
   945  	n, err := c.conn.Write(data)
   946  	c.bytesSent += int64(n)
   947  	return n, err
   948  }
   949  
   950  func (c *Conn) flush() (int, error) {
   951  	if len(c.sendBuf) == 0 {
   952  		return 0, nil
   953  	}
   954  
   955  	n, err := c.conn.Write(c.sendBuf)
   956  	c.bytesSent += int64(n)
   957  	c.sendBuf = nil
   958  	c.buffering = false
   959  	return n, err
   960  }
   961  
   962  // outBufPool pools the record-sized scratch buffers used by writeRecordLocked.
   963  var outBufPool = sync.Pool{
   964  	New: func() any {
   965  		return new([]byte)
   966  	},
   967  }
   968  
   969  // writeRecordLocked writes a TLS record with the given type and payload to the
   970  // connection and updates the record layer state.
   971  func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
   972  	if c.quic != nil {
   973  		if typ != recordTypeHandshake {
   974  			return 0, errors.New("tls: internal error: sending non-handshake message to QUIC transport")
   975  		}
   976  		c.quicWriteCryptoData(c.out.level, data)
   977  		if !c.buffering {
   978  			if _, err := c.flush(); err != nil {
   979  				return 0, err
   980  			}
   981  		}
   982  		return len(data), nil
   983  	}
   984  
   985  	outBufPtr := outBufPool.Get().(*[]byte)
   986  	outBuf := *outBufPtr
   987  	defer func() {
   988  		// You might be tempted to simplify this by just passing &outBuf to Put,
   989  		// but that would make the local copy of the outBuf slice header escape
   990  		// to the heap, causing an allocation. Instead, we keep around the
   991  		// pointer to the slice header returned by Get, which is already on the
   992  		// heap, and overwrite and return that.
   993  		*outBufPtr = outBuf
   994  		outBufPool.Put(outBufPtr)
   995  	}()
   996  
   997  	var n int
   998  	for len(data) > 0 {
   999  		m := len(data)
  1000  		if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload {
  1001  			m = maxPayload
  1002  		}
  1003  
  1004  		_, outBuf = sliceForAppend(outBuf[:0], recordHeaderLen)
  1005  		outBuf[0] = byte(typ)
  1006  		vers := c.vers
  1007  		if vers == 0 {
  1008  			// Some TLS servers fail if the record version is
  1009  			// greater than TLS 1.0 for the initial ClientHello.
  1010  			vers = VersionTLS10
  1011  		} else if vers == VersionTLS13 {
  1012  			// TLS 1.3 froze the record layer version to 1.2.
  1013  			// See RFC 8446, Section 5.1.
  1014  			vers = VersionTLS12
  1015  		}
  1016  		outBuf[1] = byte(vers >> 8)
  1017  		outBuf[2] = byte(vers)
  1018  		outBuf[3] = byte(m >> 8)
  1019  		outBuf[4] = byte(m)
  1020  
  1021  		var err error
  1022  		outBuf, err = c.out.encrypt(outBuf, data[:m], c.config.rand())
  1023  		if err != nil {
  1024  			return n, err
  1025  		}
  1026  		if _, err := c.write(outBuf); err != nil {
  1027  			return n, err
  1028  		}
  1029  		n += m
  1030  		data = data[m:]
  1031  	}
  1032  
  1033  	if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 {
  1034  		if err := c.out.changeCipherSpec(); err != nil {
  1035  			return n, c.sendAlertLocked(err.(alert))
  1036  		}
  1037  	}
  1038  
  1039  	return n, nil
  1040  }
  1041  
  1042  // writeHandshakeRecord writes a handshake message to the connection and updates
  1043  // the record layer state. If transcript is non-nil the marshalled message is
  1044  // written to it.
  1045  func (c *Conn) writeHandshakeRecord(msg handshakeMessage, transcript transcriptHash) (int, error) {
  1046  	c.out.Lock()
  1047  	defer c.out.Unlock()
  1048  
  1049  	data, err := msg.marshal()
  1050  	if err != nil {
  1051  		return 0, err
  1052  	}
  1053  	if transcript != nil {
  1054  		transcript.Write(data)
  1055  	}
  1056  
  1057  	return c.writeRecordLocked(recordTypeHandshake, data)
  1058  }
  1059  
  1060  // writeChangeCipherRecord writes a ChangeCipherSpec message to the connection and
  1061  // updates the record layer state.
  1062  func (c *Conn) writeChangeCipherRecord() error {
  1063  	c.out.Lock()
  1064  	defer c.out.Unlock()
  1065  	_, err := c.writeRecordLocked(recordTypeChangeCipherSpec, []byte{1})
  1066  	return err
  1067  }
  1068  
  1069  // readHandshakeBytes reads handshake data until c.hand contains at least n bytes.
  1070  func (c *Conn) readHandshakeBytes(n int) error {
  1071  	if c.quic != nil {
  1072  		return c.quicReadHandshakeBytes(n)
  1073  	}
  1074  	for c.hand.Len() < n {
  1075  		if err := c.readRecord(); err != nil {
  1076  			return err
  1077  		}
  1078  	}
  1079  	return nil
  1080  }
  1081  
  1082  // readHandshake reads the next handshake message from
  1083  // the record layer. If transcript is non-nil, the message
  1084  // is written to the passed transcriptHash.
  1085  func (c *Conn) readHandshake(transcript transcriptHash) (any, error) {
  1086  	if err := c.readHandshakeBytes(4); err != nil {
  1087  		return nil, err
  1088  	}
  1089  	data := c.hand.Bytes()
  1090  	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
  1091  	if n > maxHandshake {
  1092  		c.sendAlertLocked(alertInternalError)
  1093  		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
  1094  	}
  1095  	if err := c.readHandshakeBytes(4 + n); err != nil {
  1096  		return nil, err
  1097  	}
  1098  	data = c.hand.Next(4 + n)
  1099  	return c.unmarshalHandshakeMessage(data, transcript)
  1100  }
  1101  
  1102  func (c *Conn) unmarshalHandshakeMessage(data []byte, transcript transcriptHash) (handshakeMessage, error) {
  1103  	var m handshakeMessage
  1104  	switch data[0] {
  1105  	case typeHelloRequest:
  1106  		m = new(helloRequestMsg)
  1107  	case typeClientHello:
  1108  		m = new(clientHelloMsg)
  1109  	case typeServerHello:
  1110  		m = new(serverHelloMsg)
  1111  	case typeNewSessionTicket:
  1112  		if c.vers == VersionTLS13 {
  1113  			m = new(newSessionTicketMsgTLS13)
  1114  		} else {
  1115  			m = new(newSessionTicketMsg)
  1116  		}
  1117  	case typeCertificate:
  1118  		if c.vers == VersionTLS13 {
  1119  			m = new(certificateMsgTLS13)
  1120  		} else {
  1121  			m = new(certificateMsg)
  1122  		}
  1123  	case typeCertificateRequest:
  1124  		if c.vers == VersionTLS13 {
  1125  			m = new(certificateRequestMsgTLS13)
  1126  		} else {
  1127  			m = &certificateRequestMsg{
  1128  				hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1129  			}
  1130  		}
  1131  	case typeCertificateStatus:
  1132  		m = new(certificateStatusMsg)
  1133  	case typeServerKeyExchange:
  1134  		m = new(serverKeyExchangeMsg)
  1135  	case typeServerHelloDone:
  1136  		m = new(serverHelloDoneMsg)
  1137  	case typeClientKeyExchange:
  1138  		m = new(clientKeyExchangeMsg)
  1139  	case typeCertificateVerify:
  1140  		m = &certificateVerifyMsg{
  1141  			hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1142  		}
  1143  	case typeFinished:
  1144  		m = new(finishedMsg)
  1145  	case typeEncryptedExtensions:
  1146  		m = new(encryptedExtensionsMsg)
  1147  	case typeEndOfEarlyData:
  1148  		m = new(endOfEarlyDataMsg)
  1149  	case typeKeyUpdate:
  1150  		m = new(keyUpdateMsg)
  1151  	default:
  1152  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1153  	}
  1154  
  1155  	// The handshake message unmarshalers
  1156  	// expect to be able to keep references to data,
  1157  	// so pass in a fresh copy that won't be overwritten.
  1158  	data = append([]byte(nil), data...)
  1159  
  1160  	if !m.unmarshal(data) {
  1161  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1162  	}
  1163  
  1164  	if transcript != nil {
  1165  		transcript.Write(data)
  1166  	}
  1167  
  1168  	return m, nil
  1169  }
  1170  
  1171  var (
  1172  	errShutdown = errors.New("tls: protocol is shutdown")
  1173  )
  1174  
  1175  // Write writes data to the connection.
  1176  //
  1177  // As Write calls [Conn.Handshake], in order to prevent indefinite blocking a deadline
  1178  // must be set for both [Conn.Read] and Write before Write is called when the handshake
  1179  // has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and
  1180  // [Conn.SetWriteDeadline].
  1181  func (c *Conn) Write(b []byte) (int, error) {
  1182  	// interlock with Close below
  1183  	for {
  1184  		x := c.activeCall.Load()
  1185  		if x&1 != 0 {
  1186  			return 0, net.ErrClosed
  1187  		}
  1188  		if c.activeCall.CompareAndSwap(x, x+2) {
  1189  			break
  1190  		}
  1191  	}
  1192  	defer c.activeCall.Add(-2)
  1193  
  1194  	if err := c.Handshake(); err != nil {
  1195  		return 0, err
  1196  	}
  1197  
  1198  	c.out.Lock()
  1199  	defer c.out.Unlock()
  1200  
  1201  	if err := c.out.err; err != nil {
  1202  		return 0, err
  1203  	}
  1204  
  1205  	if !c.isHandshakeComplete.Load() {
  1206  		return 0, alertInternalError
  1207  	}
  1208  
  1209  	if c.closeNotifySent {
  1210  		return 0, errShutdown
  1211  	}
  1212  
  1213  	// TLS 1.0 is susceptible to a chosen-plaintext
  1214  	// attack when using block mode ciphers due to predictable IVs.
  1215  	// This can be prevented by splitting each Application Data
  1216  	// record into two records, effectively randomizing the IV.
  1217  	//
  1218  	// https://www.openssl.org/~bodo/tls-cbc.txt
  1219  	// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
  1220  	// https://www.imperialviolet.org/2012/01/15/beastfollowup.html
  1221  
  1222  	var m int
  1223  	if len(b) > 1 && c.vers == VersionTLS10 {
  1224  		if _, ok := c.out.cipher.(cipher.BlockMode); ok {
  1225  			n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1])
  1226  			if err != nil {
  1227  				return n, c.out.setErrorLocked(err)
  1228  			}
  1229  			m, b = 1, b[1:]
  1230  		}
  1231  	}
  1232  
  1233  	n, err := c.writeRecordLocked(recordTypeApplicationData, b)
  1234  	return n + m, c.out.setErrorLocked(err)
  1235  }
  1236  
  1237  // handleRenegotiation processes a HelloRequest handshake message.
  1238  func (c *Conn) handleRenegotiation() error {
  1239  	if c.vers == VersionTLS13 {
  1240  		return errors.New("tls: internal error: unexpected renegotiation")
  1241  	}
  1242  
  1243  	msg, err := c.readHandshake(nil)
  1244  	if err != nil {
  1245  		return err
  1246  	}
  1247  
  1248  	helloReq, ok := msg.(*helloRequestMsg)
  1249  	if !ok {
  1250  		c.sendAlert(alertUnexpectedMessage)
  1251  		return unexpectedMessageError(helloReq, msg)
  1252  	}
  1253  
  1254  	if !c.isClient {
  1255  		return c.sendAlert(alertNoRenegotiation)
  1256  	}
  1257  
  1258  	switch c.config.Renegotiation {
  1259  	case RenegotiateNever:
  1260  		return c.sendAlert(alertNoRenegotiation)
  1261  	case RenegotiateOnceAsClient:
  1262  		if c.handshakes > 1 {
  1263  			return c.sendAlert(alertNoRenegotiation)
  1264  		}
  1265  	case RenegotiateFreelyAsClient:
  1266  		// Ok.
  1267  	default:
  1268  		c.sendAlert(alertInternalError)
  1269  		return errors.New("tls: unknown Renegotiation value")
  1270  	}
  1271  
  1272  	c.handshakeMutex.Lock()
  1273  	defer c.handshakeMutex.Unlock()
  1274  
  1275  	c.isHandshakeComplete.Store(false)
  1276  	if c.handshakeErr = c.clientHandshake(context.Background()); c.handshakeErr == nil {
  1277  		c.handshakes++
  1278  	}
  1279  	return c.handshakeErr
  1280  }
  1281  
  1282  // handlePostHandshakeMessage processes a handshake message arrived after the
  1283  // handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation.
  1284  func (c *Conn) handlePostHandshakeMessage() error {
  1285  	if c.vers != VersionTLS13 {
  1286  		return c.handleRenegotiation()
  1287  	}
  1288  
  1289  	msg, err := c.readHandshake(nil)
  1290  	if err != nil {
  1291  		return err
  1292  	}
  1293  	c.retryCount++
  1294  	if c.retryCount > maxUselessRecords {
  1295  		c.sendAlert(alertUnexpectedMessage)
  1296  		return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
  1297  	}
  1298  
  1299  	switch msg := msg.(type) {
  1300  	case *newSessionTicketMsgTLS13:
  1301  		return c.handleNewSessionTicket(msg)
  1302  	case *keyUpdateMsg:
  1303  		return c.handleKeyUpdate(msg)
  1304  	}
  1305  	// The QUIC layer is supposed to treat an unexpected post-handshake CertificateRequest
  1306  	// as a QUIC-level PROTOCOL_VIOLATION error (RFC 9001, Section 4.4). Returning an
  1307  	// unexpected_message alert here doesn't provide it with enough information to distinguish
  1308  	// this condition from other unexpected messages. This is probably fine.
  1309  	c.sendAlert(alertUnexpectedMessage)
  1310  	return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
  1311  }
  1312  
  1313  func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
  1314  	if c.quic != nil {
  1315  		c.sendAlert(alertUnexpectedMessage)
  1316  		return c.in.setErrorLocked(errors.New("tls: received unexpected key update message"))
  1317  	}
  1318  
  1319  	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
  1320  	if cipherSuite == nil {
  1321  		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
  1322  	}
  1323  
  1324  	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
  1325  	c.in.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
  1326  
  1327  	if keyUpdate.updateRequested {
  1328  		c.out.Lock()
  1329  		defer c.out.Unlock()
  1330  
  1331  		msg := &keyUpdateMsg{}
  1332  		msgBytes, err := msg.marshal()
  1333  		if err != nil {
  1334  			return err
  1335  		}
  1336  		_, err = c.writeRecordLocked(recordTypeHandshake, msgBytes)
  1337  		if err != nil {
  1338  			// Surface the error at the next write.
  1339  			c.out.setErrorLocked(err)
  1340  			return nil
  1341  		}
  1342  
  1343  		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
  1344  		c.out.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
  1345  	}
  1346  
  1347  	return nil
  1348  }
  1349  
  1350  // Read reads data from the connection.
  1351  //
  1352  // As Read calls [Conn.Handshake], in order to prevent indefinite blocking a deadline
  1353  // must be set for both Read and [Conn.Write] before Read is called when the handshake
  1354  // has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and
  1355  // [Conn.SetWriteDeadline].
  1356  func (c *Conn) Read(b []byte) (int, error) {
  1357  	if err := c.Handshake(); err != nil {
  1358  		return 0, err
  1359  	}
  1360  	if len(b) == 0 {
  1361  		// Put this after Handshake, in case people were calling
  1362  		// Read(nil) for the side effect of the Handshake.
  1363  		return 0, nil
  1364  	}
  1365  
  1366  	c.in.Lock()
  1367  	defer c.in.Unlock()
  1368  
  1369  	for c.input.Len() == 0 {
  1370  		if err := c.readRecord(); err != nil {
  1371  			return 0, err
  1372  		}
  1373  		for c.hand.Len() > 0 {
  1374  			if err := c.handlePostHandshakeMessage(); err != nil {
  1375  				return 0, err
  1376  			}
  1377  		}
  1378  	}
  1379  
  1380  	n, _ := c.input.Read(b)
  1381  
  1382  	// If a close-notify alert is waiting, read it so that we can return (n,
  1383  	// EOF) instead of (n, nil), to signal to the HTTP response reading
  1384  	// goroutine that the connection is now closed. This eliminates a race
  1385  	// where the HTTP response reading goroutine would otherwise not observe
  1386  	// the EOF until its next read, by which time a client goroutine might
  1387  	// have already tried to reuse the HTTP connection for a new request.
  1388  	// See https://golang.org/cl/76400046 and https://golang.org/issue/3514
  1389  	if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 &&
  1390  		recordType(c.rawInput.Bytes()[0]) == recordTypeAlert {
  1391  		if err := c.readRecord(); err != nil {
  1392  			return n, err // will be io.EOF on closeNotify
  1393  		}
  1394  	}
  1395  
  1396  	return n, nil
  1397  }
  1398  
  1399  // Close closes the connection.
  1400  func (c *Conn) Close() error {
  1401  	// Interlock with Conn.Write above.
  1402  	var x int32
  1403  	for {
  1404  		x = c.activeCall.Load()
  1405  		if x&1 != 0 {
  1406  			return net.ErrClosed
  1407  		}
  1408  		if c.activeCall.CompareAndSwap(x, x|1) {
  1409  			break
  1410  		}
  1411  	}
  1412  	if x != 0 {
  1413  		// io.Writer and io.Closer should not be used concurrently.
  1414  		// If Close is called while a Write is currently in-flight,
  1415  		// interpret that as a sign that this Close is really just
  1416  		// being used to break the Write and/or clean up resources and
  1417  		// avoid sending the alertCloseNotify, which may block
  1418  		// waiting on handshakeMutex or the c.out mutex.
  1419  		return c.conn.Close()
  1420  	}
  1421  
  1422  	var alertErr error
  1423  	if c.isHandshakeComplete.Load() {
  1424  		if err := c.closeNotify(); err != nil {
  1425  			alertErr = fmt.Errorf("tls: failed to send closeNotify alert (but connection was closed anyway): %w", err)
  1426  		}
  1427  	}
  1428  
  1429  	if err := c.conn.Close(); err != nil {
  1430  		return err
  1431  	}
  1432  	return alertErr
  1433  }
  1434  
  1435  var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
  1436  
  1437  // CloseWrite shuts down the writing side of the connection. It should only be
  1438  // called once the handshake has completed and does not call CloseWrite on the
  1439  // underlying connection. Most callers should just use [Conn.Close].
  1440  func (c *Conn) CloseWrite() error {
  1441  	if !c.isHandshakeComplete.Load() {
  1442  		return errEarlyCloseWrite
  1443  	}
  1444  
  1445  	return c.closeNotify()
  1446  }
  1447  
  1448  func (c *Conn) closeNotify() error {
  1449  	c.out.Lock()
  1450  	defer c.out.Unlock()
  1451  
  1452  	if !c.closeNotifySent {
  1453  		// Set a Write Deadline to prevent possibly blocking forever.
  1454  		c.SetWriteDeadline(time.Now().Add(time.Second * 5))
  1455  		c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify)
  1456  		c.closeNotifySent = true
  1457  		// Any subsequent writes will fail.
  1458  		c.SetWriteDeadline(time.Now())
  1459  	}
  1460  	return c.closeNotifyErr
  1461  }
  1462  
  1463  // Handshake runs the client or server handshake
  1464  // protocol if it has not yet been run.
  1465  //
  1466  // Most uses of this package need not call Handshake explicitly: the
  1467  // first [Conn.Read] or [Conn.Write] will call it automatically.
  1468  //
  1469  // For control over canceling or setting a timeout on a handshake, use
  1470  // [Conn.HandshakeContext] or the [Dialer]'s DialContext method instead.
  1471  //
  1472  // In order to avoid denial of service attacks, the maximum RSA key size allowed
  1473  // in certificates sent by either the TLS server or client is limited to 8192
  1474  // bits. This limit can be overridden by setting tlsmaxrsasize in the GODEBUG
  1475  // environment variable (e.g. GODEBUG=tlsmaxrsasize=4096).
  1476  func (c *Conn) Handshake() error {
  1477  	return c.HandshakeContext(context.Background())
  1478  }
  1479  
  1480  // HandshakeContext runs the client or server handshake
  1481  // protocol if it has not yet been run.
  1482  //
  1483  // The provided Context must be non-nil. If the context is canceled before
  1484  // the handshake is complete, the handshake is interrupted and an error is returned.
  1485  // Once the handshake has completed, cancellation of the context will not affect the
  1486  // connection.
  1487  //
  1488  // Most uses of this package need not call HandshakeContext explicitly: the
  1489  // first [Conn.Read] or [Conn.Write] will call it automatically.
  1490  func (c *Conn) HandshakeContext(ctx context.Context) error {
  1491  	// Delegate to unexported method for named return
  1492  	// without confusing documented signature.
  1493  	return c.handshakeContext(ctx)
  1494  }
  1495  
  1496  func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
  1497  	// Fast sync/atomic-based exit if there is no handshake in flight and the
  1498  	// last one succeeded without an error. Avoids the expensive context setup
  1499  	// and mutex for most Read and Write calls.
  1500  	if c.isHandshakeComplete.Load() {
  1501  		return nil
  1502  	}
  1503  
  1504  	handshakeCtx, cancel := context.WithCancel(ctx)
  1505  	// Note: defer this before starting the "interrupter" goroutine
  1506  	// so that we can tell the difference between the input being canceled and
  1507  	// this cancellation. In the former case, we need to close the connection.
  1508  	defer cancel()
  1509  
  1510  	if c.quic != nil {
  1511  		c.quic.cancelc = handshakeCtx.Done()
  1512  		c.quic.cancel = cancel
  1513  	} else if ctx.Done() != nil {
  1514  		// Start the "interrupter" goroutine, if this context might be canceled.
  1515  		// (The background context cannot).
  1516  		//
  1517  		// The interrupter goroutine waits for the input context to be done and
  1518  		// closes the connection if this happens before the function returns.
  1519  		done := make(chan struct{})
  1520  		interruptRes := make(chan error, 1)
  1521  		defer func() {
  1522  			close(done)
  1523  			if ctxErr := <-interruptRes; ctxErr != nil {
  1524  				// Return context error to user.
  1525  				ret = ctxErr
  1526  			}
  1527  		}()
  1528  		go func() {
  1529  			select {
  1530  			case <-handshakeCtx.Done():
  1531  				// Close the connection, discarding the error
  1532  				_ = c.conn.Close()
  1533  				interruptRes <- handshakeCtx.Err()
  1534  			case <-done:
  1535  				interruptRes <- nil
  1536  			}
  1537  		}()
  1538  	}
  1539  
  1540  	c.handshakeMutex.Lock()
  1541  	defer c.handshakeMutex.Unlock()
  1542  
  1543  	if err := c.handshakeErr; err != nil {
  1544  		return err
  1545  	}
  1546  	if c.isHandshakeComplete.Load() {
  1547  		return nil
  1548  	}
  1549  
  1550  	c.in.Lock()
  1551  	defer c.in.Unlock()
  1552  
  1553  	c.handshakeErr = c.handshakeFn(handshakeCtx)
  1554  	if c.handshakeErr == nil {
  1555  		c.handshakes++
  1556  	} else {
  1557  		// If an error occurred during the handshake try to flush the
  1558  		// alert that might be left in the buffer.
  1559  		c.flush()
  1560  	}
  1561  
  1562  	if c.handshakeErr == nil && !c.isHandshakeComplete.Load() {
  1563  		c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
  1564  	}
  1565  	if c.handshakeErr != nil && c.isHandshakeComplete.Load() {
  1566  		panic("tls: internal error: handshake returned an error but is marked successful")
  1567  	}
  1568  
  1569  	if c.quic != nil {
  1570  		if c.handshakeErr == nil {
  1571  			c.quicHandshakeComplete()
  1572  			// Provide the 1-RTT read secret now that the handshake is complete.
  1573  			// The QUIC layer MUST NOT decrypt 1-RTT packets prior to completing
  1574  			// the handshake (RFC 9001, Section 5.7).
  1575  			c.quicSetReadSecret(QUICEncryptionLevelApplication, c.cipherSuite, c.in.trafficSecret)
  1576  		} else {
  1577  			var a alert
  1578  			c.out.Lock()
  1579  			if !errors.As(c.out.err, &a) {
  1580  				a = alertInternalError
  1581  			}
  1582  			c.out.Unlock()
  1583  			// Return an error which wraps both the handshake error and
  1584  			// any alert error we may have sent, or alertInternalError
  1585  			// if we didn't send an alert.
  1586  			// Truncate the text of the alert to 0 characters.
  1587  			c.handshakeErr = fmt.Errorf("%w%.0w", c.handshakeErr, AlertError(a))
  1588  		}
  1589  		close(c.quic.blockedc)
  1590  		close(c.quic.signalc)
  1591  	}
  1592  
  1593  	return c.handshakeErr
  1594  }
  1595  
  1596  // ConnectionState returns basic TLS details about the connection.
  1597  func (c *Conn) ConnectionState() ConnectionState {
  1598  	c.handshakeMutex.Lock()
  1599  	defer c.handshakeMutex.Unlock()
  1600  	return c.connectionStateLocked()
  1601  }
  1602  
  1603  var tlsunsafeekm = godebug.New("tlsunsafeekm")
  1604  
  1605  func (c *Conn) connectionStateLocked() ConnectionState {
  1606  	var state ConnectionState
  1607  	state.HandshakeComplete = c.isHandshakeComplete.Load()
  1608  	state.Version = c.vers
  1609  	state.NegotiatedProtocol = c.clientProtocol
  1610  	state.DidResume = c.didResume
  1611  	state.NegotiatedProtocolIsMutual = true
  1612  	state.ServerName = c.serverName
  1613  	state.CipherSuite = c.cipherSuite
  1614  	state.PeerCertificates = c.peerCertificates
  1615  	state.VerifiedChains = c.verifiedChains
  1616  	state.SignedCertificateTimestamps = c.scts
  1617  	state.OCSPResponse = c.ocspResponse
  1618  	if (!c.didResume || c.extMasterSecret) && c.vers != VersionTLS13 {
  1619  		if c.clientFinishedIsFirst {
  1620  			state.TLSUnique = c.clientFinished[:]
  1621  		} else {
  1622  			state.TLSUnique = c.serverFinished[:]
  1623  		}
  1624  	}
  1625  	if c.config.Renegotiation != RenegotiateNever {
  1626  		state.ekm = noEKMBecauseRenegotiation
  1627  	} else if c.vers != VersionTLS13 && !c.extMasterSecret {
  1628  		state.ekm = func(label string, context []byte, length int) ([]byte, error) {
  1629  			if tlsunsafeekm.Value() == "1" {
  1630  				tlsunsafeekm.IncNonDefault()
  1631  				return c.ekm(label, context, length)
  1632  			}
  1633  			return noEKMBecauseNoEMS(label, context, length)
  1634  		}
  1635  	} else {
  1636  		state.ekm = c.ekm
  1637  	}
  1638  	return state
  1639  }
  1640  
  1641  // OCSPResponse returns the stapled OCSP response from the TLS server, if
  1642  // any. (Only valid for client connections.)
  1643  func (c *Conn) OCSPResponse() []byte {
  1644  	c.handshakeMutex.Lock()
  1645  	defer c.handshakeMutex.Unlock()
  1646  
  1647  	return c.ocspResponse
  1648  }
  1649  
  1650  // VerifyHostname checks that the peer certificate chain is valid for
  1651  // connecting to host. If so, it returns nil; if not, it returns an error
  1652  // describing the problem.
  1653  func (c *Conn) VerifyHostname(host string) error {
  1654  	c.handshakeMutex.Lock()
  1655  	defer c.handshakeMutex.Unlock()
  1656  	if !c.isClient {
  1657  		return errors.New("tls: VerifyHostname called on TLS server connection")
  1658  	}
  1659  	if !c.isHandshakeComplete.Load() {
  1660  		return errors.New("tls: handshake has not yet been performed")
  1661  	}
  1662  	if len(c.verifiedChains) == 0 {
  1663  		return errors.New("tls: handshake did not verify certificate chain")
  1664  	}
  1665  	return c.peerCertificates[0].VerifyHostname(host)
  1666  }
  1667  

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