Adding upstream version 1.19.8.upstream/1.19.8upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1573 insertions, 0 deletions

diff --git a/src/crypto/tls/conn.go b/src/crypto/tls/conn.go
new file mode 100644
index 0000000..73f0c17
--- /dev/null
+++ b/src/crypto/tls/conn.go
@@ -0,0 +1,1573 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TLS low level connection and record layer
+
+package tls
+
+import (
+	"bytes"
+	"context"
+	"crypto/cipher"
+	"crypto/subtle"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"hash"
+	"io"
+	"net"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// A Conn represents a secured connection.
+// It implements the net.Conn interface.
+type Conn struct {
+	// constant
+	conn        net.Conn
+	isClient    bool
+	handshakeFn func(context.Context) error // (*Conn).clientHandshake or serverHandshake
+
+	// handshakeStatus is 1 if the connection is currently transferring
+	// application data (i.e. is not currently processing a handshake).
+	// handshakeStatus == 1 implies handshakeErr == nil.
+	// This field is only to be accessed with sync/atomic.
+	handshakeStatus uint32
+	// constant after handshake; protected by handshakeMutex
+	handshakeMutex sync.Mutex
+	handshakeErr   error   // error resulting from handshake
+	vers           uint16  // TLS version
+	haveVers       bool    // version has been negotiated
+	config         *Config // configuration passed to constructor
+	// handshakes counts the number of handshakes performed on the
+	// connection so far. If renegotiation is disabled then this is either
+	// zero or one.
+	handshakes       int
+	didResume        bool // whether this connection was a session resumption
+	cipherSuite      uint16
+	ocspResponse     []byte   // stapled OCSP response
+	scts             [][]byte // signed certificate timestamps from server
+	peerCertificates []*x509.Certificate
+	// verifiedChains contains the certificate chains that we built, as
+	// opposed to the ones presented by the server.
+	verifiedChains [][]*x509.Certificate
+	// serverName contains the server name indicated by the client, if any.
+	serverName string
+	// secureRenegotiation is true if the server echoed the secure
+	// renegotiation extension. (This is meaningless as a server because
+	// renegotiation is not supported in that case.)
+	secureRenegotiation bool
+	// ekm is a closure for exporting keying material.
+	ekm func(label string, context []byte, length int) ([]byte, error)
+	// resumptionSecret is the resumption_master_secret for handling
+	// NewSessionTicket messages. nil if config.SessionTicketsDisabled.
+	resumptionSecret []byte
+
+	// ticketKeys is the set of active session ticket keys for this
+	// connection. The first one is used to encrypt new tickets and
+	// all are tried to decrypt tickets.
+	ticketKeys []ticketKey
+
+	// clientFinishedIsFirst is true if the client sent the first Finished
+	// message during the most recent handshake. This is recorded because
+	// the first transmitted Finished message is the tls-unique
+	// channel-binding value.
+	clientFinishedIsFirst bool
+
+	// closeNotifyErr is any error from sending the alertCloseNotify record.
+	closeNotifyErr error
+	// closeNotifySent is true if the Conn attempted to send an
+	// alertCloseNotify record.
+	closeNotifySent bool
+
+	// clientFinished and serverFinished contain the Finished message sent
+	// by the client or server in the most recent handshake. This is
+	// retained to support the renegotiation extension and tls-unique
+	// channel-binding.
+	clientFinished [12]byte
+	serverFinished [12]byte
+
+	// clientProtocol is the negotiated ALPN protocol.
+	clientProtocol string
+
+	// input/output
+	in, out   halfConn
+	rawInput  bytes.Buffer // raw input, starting with a record header
+	input     bytes.Reader // application data waiting to be read, from rawInput.Next
+	hand      bytes.Buffer // handshake data waiting to be read
+	buffering bool         // whether records are buffered in sendBuf
+	sendBuf   []byte       // a buffer of records waiting to be sent
+
+	// bytesSent counts the bytes of application data sent.
+	// packetsSent counts packets.
+	bytesSent   int64
+	packetsSent int64
+
+	// retryCount counts the number of consecutive non-advancing records
+	// received by Conn.readRecord. That is, records that neither advance the
+	// handshake, nor deliver application data. Protected by in.Mutex.
+	retryCount int
+
+	// activeCall is an atomic int32; the low bit is whether Close has
+	// been called. the rest of the bits are the number of goroutines
+	// in Conn.Write.
+	activeCall int32
+
+	tmp [16]byte
+}
+
+// Access to net.Conn methods.
+// Cannot just embed net.Conn because that would
+// export the struct field too.
+
+// LocalAddr returns the local network address.
+func (c *Conn) LocalAddr() net.Addr {
+	return c.conn.LocalAddr()
+}
+
+// RemoteAddr returns the remote network address.
+func (c *Conn) RemoteAddr() net.Addr {
+	return c.conn.RemoteAddr()
+}
+
+// SetDeadline sets the read and write deadlines associated with the connection.
+// A zero value for t means Read and Write will not time out.
+// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
+func (c *Conn) SetDeadline(t time.Time) error {
+	return c.conn.SetDeadline(t)
+}
+
+// SetReadDeadline sets the read deadline on the underlying connection.
+// A zero value for t means Read will not time out.
+func (c *Conn) SetReadDeadline(t time.Time) error {
+	return c.conn.SetReadDeadline(t)
+}
+
+// SetWriteDeadline sets the write deadline on the underlying connection.
+// A zero value for t means Write will not time out.
+// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
+func (c *Conn) SetWriteDeadline(t time.Time) error {
+	return c.conn.SetWriteDeadline(t)
+}
+
+// NetConn returns the underlying connection that is wrapped by c.
+// Note that writing to or reading from this connection directly will corrupt the
+// TLS session.
+func (c *Conn) NetConn() net.Conn {
+	return c.conn
+}
+
+// A halfConn represents one direction of the record layer
+// connection, either sending or receiving.
+type halfConn struct {
+	sync.Mutex
+
+	err     error  // first permanent error
+	version uint16 // protocol version
+	cipher  any    // cipher algorithm
+	mac     hash.Hash
+	seq     [8]byte // 64-bit sequence number
+
+	scratchBuf [13]byte // to avoid allocs; interface method args escape
+
+	nextCipher any       // next encryption state
+	nextMac    hash.Hash // next MAC algorithm
+
+	trafficSecret []byte // current TLS 1.3 traffic secret
+}
+
+type permanentError struct {
+	err net.Error
+}
+
+func (e *permanentError) Error() string   { return e.err.Error() }
+func (e *permanentError) Unwrap() error   { return e.err }
+func (e *permanentError) Timeout() bool   { return e.err.Timeout() }
+func (e *permanentError) Temporary() bool { return false }
+
+func (hc *halfConn) setErrorLocked(err error) error {
+	if e, ok := err.(net.Error); ok {
+		hc.err = &permanentError{err: e}
+	} else {
+		hc.err = err
+	}
+	return hc.err
+}
+
+// prepareCipherSpec sets the encryption and MAC states
+// that a subsequent changeCipherSpec will use.
+func (hc *halfConn) prepareCipherSpec(version uint16, cipher any, mac hash.Hash) {
+	hc.version = version
+	hc.nextCipher = cipher
+	hc.nextMac = mac
+}
+
+// changeCipherSpec changes the encryption and MAC states
+// to the ones previously passed to prepareCipherSpec.
+func (hc *halfConn) changeCipherSpec() error {
+	if hc.nextCipher == nil || hc.version == VersionTLS13 {
+		return alertInternalError
+	}
+	hc.cipher = hc.nextCipher
+	hc.mac = hc.nextMac
+	hc.nextCipher = nil
+	hc.nextMac = nil
+	for i := range hc.seq {
+		hc.seq[i] = 0
+	}
+	return nil
+}
+
+func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, secret []byte) {
+	hc.trafficSecret = secret
+	key, iv := suite.trafficKey(secret)
+	hc.cipher = suite.aead(key, iv)
+	for i := range hc.seq {
+		hc.seq[i] = 0
+	}
+}
+
+// incSeq increments the sequence number.
+func (hc *halfConn) incSeq() {
+	for i := 7; i >= 0; i-- {
+		hc.seq[i]++
+		if hc.seq[i] != 0 {
+			return
+		}
+	}
+
+	// Not allowed to let sequence number wrap.
+	// Instead, must renegotiate before it does.
+	// Not likely enough to bother.
+	panic("TLS: sequence number wraparound")
+}
+
+// explicitNonceLen returns the number of bytes of explicit nonce or IV included
+// in each record. Explicit nonces are present only in CBC modes after TLS 1.0
+// and in certain AEAD modes in TLS 1.2.
+func (hc *halfConn) explicitNonceLen() int {
+	if hc.cipher == nil {
+		return 0
+	}
+
+	switch c := hc.cipher.(type) {
+	case cipher.Stream:
+		return 0
+	case aead:
+		return c.explicitNonceLen()
+	case cbcMode:
+		// TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack.
+		if hc.version >= VersionTLS11 {
+			return c.BlockSize()
+		}
+		return 0
+	default:
+		panic("unknown cipher type")
+	}
+}
+
+// extractPadding returns, in constant time, the length of the padding to remove
+// from the end of payload. It also returns a byte which is equal to 255 if the
+// padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
+func extractPadding(payload []byte) (toRemove int, good byte) {
+	if len(payload) < 1 {
+		return 0, 0
+	}
+
+	paddingLen := payload[len(payload)-1]
+	t := uint(len(payload)-1) - uint(paddingLen)
+	// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
+	good = byte(int32(^t) >> 31)
+
+	// The maximum possible padding length plus the actual length field
+	toCheck := 256
+	// The length of the padded data is public, so we can use an if here
+	if toCheck > len(payload) {
+		toCheck = len(payload)
+	}
+
+	for i := 0; i < toCheck; i++ {
+		t := uint(paddingLen) - uint(i)
+		// if i <= paddingLen then the MSB of t is zero
+		mask := byte(int32(^t) >> 31)
+		b := payload[len(payload)-1-i]
+		good &^= mask&paddingLen ^ mask&b
+	}
+
+	// We AND together the bits of good and replicate the result across
+	// all the bits.
+	good &= good << 4
+	good &= good << 2
+	good &= good << 1
+	good = uint8(int8(good) >> 7)
+
+	// Zero the padding length on error. This ensures any unchecked bytes
+	// are included in the MAC. Otherwise, an attacker that could
+	// distinguish MAC failures from padding failures could mount an attack
+	// similar to POODLE in SSL 3.0: given a good ciphertext that uses a
+	// full block's worth of padding, replace the final block with another
+	// block. If the MAC check passed but the padding check failed, the
+	// last byte of that block decrypted to the block size.
+	//
+	// See also macAndPaddingGood logic below.
+	paddingLen &= good
+
+	toRemove = int(paddingLen) + 1
+	return
+}
+
+func roundUp(a, b int) int {
+	return a + (b-a%b)%b
+}
+
+// cbcMode is an interface for block ciphers using cipher block chaining.
+type cbcMode interface {
+	cipher.BlockMode
+	SetIV([]byte)
+}
+
+// decrypt authenticates and decrypts the record if protection is active at
+// this stage. The returned plaintext might overlap with the input.
+func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) {
+	var plaintext []byte
+	typ := recordType(record[0])
+	payload := record[recordHeaderLen:]
+
+	// In TLS 1.3, change_cipher_spec messages are to be ignored without being
+	// decrypted. See RFC 8446, Appendix D.4.
+	if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec {
+		return payload, typ, nil
+	}
+
+	paddingGood := byte(255)
+	paddingLen := 0
+
+	explicitNonceLen := hc.explicitNonceLen()
+
+	if hc.cipher != nil {
+		switch c := hc.cipher.(type) {
+		case cipher.Stream:
+			c.XORKeyStream(payload, payload)
+		case aead:
+			if len(payload) < explicitNonceLen {
+				return nil, 0, alertBadRecordMAC
+			}
+			nonce := payload[:explicitNonceLen]
+			if len(nonce) == 0 {
+				nonce = hc.seq[:]
+			}
+			payload = payload[explicitNonceLen:]
+
+			var additionalData []byte
+			if hc.version == VersionTLS13 {
+				additionalData = record[:recordHeaderLen]
+			} else {
+				additionalData = append(hc.scratchBuf[:0], hc.seq[:]...)
+				additionalData = append(additionalData, record[:3]...)
+				n := len(payload) - c.Overhead()
+				additionalData = append(additionalData, byte(n>>8), byte(n))
+			}
+
+			var err error
+			plaintext, err = c.Open(payload[:0], nonce, payload, additionalData)
+			if err != nil {
+				return nil, 0, alertBadRecordMAC
+			}
+		case cbcMode:
+			blockSize := c.BlockSize()
+			minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize)
+			if len(payload)%blockSize != 0 || len(payload) < minPayload {
+				return nil, 0, alertBadRecordMAC
+			}
+
+			if explicitNonceLen > 0 {
+				c.SetIV(payload[:explicitNonceLen])
+				payload = payload[explicitNonceLen:]
+			}
+			c.CryptBlocks(payload, payload)
+
+			// In a limited attempt to protect against CBC padding oracles like
+			// Lucky13, the data past paddingLen (which is secret) is passed to
+			// the MAC function as extra data, to be fed into the HMAC after
+			// computing the digest. This makes the MAC roughly constant time as
+			// long as the digest computation is constant time and does not
+			// affect the subsequent write, modulo cache effects.
+			paddingLen, paddingGood = extractPadding(payload)
+		default:
+			panic("unknown cipher type")
+		}
+
+		if hc.version == VersionTLS13 {
+			if typ != recordTypeApplicationData {
+				return nil, 0, alertUnexpectedMessage
+			}
+			if len(plaintext) > maxPlaintext+1 {
+				return nil, 0, alertRecordOverflow
+			}
+			// Remove padding and find the ContentType scanning from the end.
+			for i := len(plaintext) - 1; i >= 0; i-- {
+				if plaintext[i] != 0 {
+					typ = recordType(plaintext[i])
+					plaintext = plaintext[:i]
+					break
+				}
+				if i == 0 {
+					return nil, 0, alertUnexpectedMessage
+				}
+			}
+		}
+	} else {
+		plaintext = payload
+	}
+
+	if hc.mac != nil {
+		macSize := hc.mac.Size()
+		if len(payload) < macSize {
+			return nil, 0, alertBadRecordMAC
+		}
+
+		n := len(payload) - macSize - paddingLen
+		n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 }
+		record[3] = byte(n >> 8)
+		record[4] = byte(n)
+		remoteMAC := payload[n : n+macSize]
+		localMAC := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload[:n], payload[n+macSize:])
+
+		// This is equivalent to checking the MACs and paddingGood
+		// separately, but in constant-time to prevent distinguishing
+		// padding failures from MAC failures. Depending on what value
+		// of paddingLen was returned on bad padding, distinguishing
+		// bad MAC from bad padding can lead to an attack.
+		//
+		// See also the logic at the end of extractPadding.
+		macAndPaddingGood := subtle.ConstantTimeCompare(localMAC, remoteMAC) & int(paddingGood)
+		if macAndPaddingGood != 1 {
+			return nil, 0, alertBadRecordMAC
+		}
+
+		plaintext = payload[:n]
+	}
+
+	hc.incSeq()
+	return plaintext, typ, nil
+}
+
+// sliceForAppend extends the input slice by n bytes. head is the full extended
+// slice, while tail is the appended part. If the original slice has sufficient
+// capacity no allocation is performed.
+func sliceForAppend(in []byte, n int) (head, tail []byte) {
+	if total := len(in) + n; cap(in) >= total {
+		head = in[:total]
+	} else {
+		head = make([]byte, total)
+		copy(head, in)
+	}
+	tail = head[len(in):]
+	return
+}
+
+// encrypt encrypts payload, adding the appropriate nonce and/or MAC, and
+// appends it to record, which must already contain the record header.
+func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) {
+	if hc.cipher == nil {
+		return append(record, payload...), nil
+	}
+
+	var explicitNonce []byte
+	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
+		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
+		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
+			// The AES-GCM construction in TLS has an explicit nonce so that the
+			// nonce can be random. However, the nonce is only 8 bytes which is
+			// too small for a secure, random nonce. Therefore we use the
+			// sequence number as the nonce. The 3DES-CBC construction also has
+			// an 8 bytes nonce but its nonces must be unpredictable (see RFC
+			// 5246, Appendix F.3), forcing us to use randomness. That's not
+			// 3DES' biggest problem anyway because the birthday bound on block
+			// collision is reached first due to its similarly small block size
+			// (see the Sweet32 attack).
+			copy(explicitNonce, hc.seq[:])
+		} else {
+			if _, err := io.ReadFull(rand, explicitNonce); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	var dst []byte
+	switch c := hc.cipher.(type) {
+	case cipher.Stream:
+		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
+		record, dst = sliceForAppend(record, len(payload)+len(mac))
+		c.XORKeyStream(dst[:len(payload)], payload)
+		c.XORKeyStream(dst[len(payload):], mac)
+	case aead:
+		nonce := explicitNonce
+		if len(nonce) == 0 {
+			nonce = hc.seq[:]
+		}
+
+		if hc.version == VersionTLS13 {
+			record = append(record, payload...)
+
+			// Encrypt the actual ContentType and replace the plaintext one.
+			record = append(record, record[0])
+			record[0] = byte(recordTypeApplicationData)
+
+			n := len(payload) + 1 + c.Overhead()
+			record[3] = byte(n >> 8)
+			record[4] = byte(n)
+
+			record = c.Seal(record[:recordHeaderLen],
+				nonce, record[recordHeaderLen:], record[:recordHeaderLen])
+		} else {
+			additionalData := append(hc.scratchBuf[:0], hc.seq[:]...)
+			additionalData = append(additionalData, record[:recordHeaderLen]...)
+			record = c.Seal(record, nonce, payload, additionalData)
+		}
+	case cbcMode:
+		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
+		blockSize := c.BlockSize()
+		plaintextLen := len(payload) + len(mac)
+		paddingLen := blockSize - plaintextLen%blockSize
+		record, dst = sliceForAppend(record, plaintextLen+paddingLen)
+		copy(dst, payload)
+		copy(dst[len(payload):], mac)
+		for i := plaintextLen; i < len(dst); i++ {
+			dst[i] = byte(paddingLen - 1)
+		}
+		if len(explicitNonce) > 0 {
+			c.SetIV(explicitNonce)
+		}
+		c.CryptBlocks(dst, dst)
+	default:
+		panic("unknown cipher type")
+	}
+
+	// Update length to include nonce, MAC and any block padding needed.
+	n := len(record) - recordHeaderLen
+	record[3] = byte(n >> 8)
+	record[4] = byte(n)
+	hc.incSeq()
+
+	return record, nil
+}
+
+// RecordHeaderError is returned when a TLS record header is invalid.
+type RecordHeaderError struct {
+	// Msg contains a human readable string that describes the error.
+	Msg string
+	// RecordHeader contains the five bytes of TLS record header that
+	// triggered the error.
+	RecordHeader [5]byte
+	// Conn provides the underlying net.Conn in the case that a client
+	// sent an initial handshake that didn't look like TLS.
+	// It is nil if there's already been a handshake or a TLS alert has
+	// been written to the connection.
+	Conn net.Conn
+}
+
+func (e RecordHeaderError) Error() string { return "tls: " + e.Msg }
+
+func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) {
+	err.Msg = msg
+	err.Conn = conn
+	copy(err.RecordHeader[:], c.rawInput.Bytes())
+	return err
+}
+
+func (c *Conn) readRecord() error {
+	return c.readRecordOrCCS(false)
+}
+
+func (c *Conn) readChangeCipherSpec() error {
+	return c.readRecordOrCCS(true)
+}
+
+// readRecordOrCCS reads one or more TLS records from the connection and
+// updates the record layer state. Some invariants:
+//   - c.in must be locked
+//   - c.input must be empty
+//
+// During the handshake one and only one of the following will happen:
+//   - c.hand grows
+//   - c.in.changeCipherSpec is called
+//   - an error is returned
+//
+// After the handshake one and only one of the following will happen:
+//   - c.hand grows
+//   - c.input is set
+//   - an error is returned
+func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
+	if c.in.err != nil {
+		return c.in.err
+	}
+	handshakeComplete := c.handshakeComplete()
+
+	// This function modifies c.rawInput, which owns the c.input memory.
+	if c.input.Len() != 0 {
+		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
+	}
+	c.input.Reset(nil)
+
+	// Read header, payload.
+	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
+		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
+		// is an error, but popular web sites seem to do this, so we accept it
+		// if and only if at the record boundary.
+		if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 {
+			err = io.EOF
+		}
+		if e, ok := err.(net.Error); !ok || !e.Temporary() {
+			c.in.setErrorLocked(err)
+		}
+		return err
+	}
+	hdr := c.rawInput.Bytes()[:recordHeaderLen]
+	typ := recordType(hdr[0])
+
+	// No valid TLS record has a type of 0x80, however SSLv2 handshakes
+	// start with a uint16 length where the MSB is set and the first record
+	// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
+	// an SSLv2 client.
+	if !handshakeComplete && typ == 0x80 {
+		c.sendAlert(alertProtocolVersion)
+		return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received"))
+	}
+
+	vers := uint16(hdr[1])<<8 | uint16(hdr[2])
+	n := int(hdr[3])<<8 | int(hdr[4])
+	if c.haveVers && c.vers != VersionTLS13 && vers != c.vers {
+		c.sendAlert(alertProtocolVersion)
+		msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, c.vers)
+		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
+	}
+	if !c.haveVers {
+		// First message, be extra suspicious: this might not be a TLS
+		// client. Bail out before reading a full 'body', if possible.
+		// The current max version is 3.3 so if the version is >= 16.0,
+		// it's probably not real.
+		if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 {
+			return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake"))
+		}
+	}
+	if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext {
+		c.sendAlert(alertRecordOverflow)
+		msg := fmt.Sprintf("oversized record received with length %d", n)
+		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
+	}
+	if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
+		if e, ok := err.(net.Error); !ok || !e.Temporary() {
+			c.in.setErrorLocked(err)
+		}
+		return err
+	}
+
+	// Process message.
+	record := c.rawInput.Next(recordHeaderLen + n)
+	data, typ, err := c.in.decrypt(record)
+	if err != nil {
+		return c.in.setErrorLocked(c.sendAlert(err.(alert)))
+	}
+	if len(data) > maxPlaintext {
+		return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow))
+	}
+
+	// Application Data messages are always protected.
+	if c.in.cipher == nil && typ == recordTypeApplicationData {
+		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+	}
+
+	if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 {
+		// This is a state-advancing message: reset the retry count.
+		c.retryCount = 0
+	}
+
+	// Handshake messages MUST NOT be interleaved with other record types in TLS 1.3.
+	if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 {
+		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+	}
+
+	switch typ {
+	default:
+		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+
+	case recordTypeAlert:
+		if len(data) != 2 {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+		if alert(data[1]) == alertCloseNotify {
+			return c.in.setErrorLocked(io.EOF)
+		}
+		if c.vers == VersionTLS13 {
+			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
+		}
+		switch data[0] {
+		case alertLevelWarning:
+			// Drop the record on the floor and retry.
+			return c.retryReadRecord(expectChangeCipherSpec)
+		case alertLevelError:
+			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
+		default:
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+
+	case recordTypeChangeCipherSpec:
+		if len(data) != 1 || data[0] != 1 {
+			return c.in.setErrorLocked(c.sendAlert(alertDecodeError))
+		}
+		// Handshake messages are not allowed to fragment across the CCS.
+		if c.hand.Len() > 0 {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+		// In TLS 1.3, change_cipher_spec records are ignored until the
+		// Finished. See RFC 8446, Appendix D.4. Note that according to Section
+		// 5, a server can send a ChangeCipherSpec before its ServerHello, when
+		// c.vers is still unset. That's not useful though and suspicious if the
+		// server then selects a lower protocol version, so don't allow that.
+		if c.vers == VersionTLS13 {
+			return c.retryReadRecord(expectChangeCipherSpec)
+		}
+		if !expectChangeCipherSpec {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+		if err := c.in.changeCipherSpec(); err != nil {
+			return c.in.setErrorLocked(c.sendAlert(err.(alert)))
+		}
+
+	case recordTypeApplicationData:
+		if !handshakeComplete || expectChangeCipherSpec {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+		// Some OpenSSL servers send empty records in order to randomize the
+		// CBC IV. Ignore a limited number of empty records.
+		if len(data) == 0 {
+			return c.retryReadRecord(expectChangeCipherSpec)
+		}
+		// Note that data is owned by c.rawInput, following the Next call above,
+		// to avoid copying the plaintext. This is safe because c.rawInput is
+		// not read from or written to until c.input is drained.
+		c.input.Reset(data)
+
+	case recordTypeHandshake:
+		if len(data) == 0 || expectChangeCipherSpec {
+			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+		}
+		c.hand.Write(data)
+	}
+
+	return nil
+}
+
+// retryReadRecord recurs into readRecordOrCCS to drop a non-advancing record, like
+// a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3.
+func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error {
+	c.retryCount++
+	if c.retryCount > maxUselessRecords {
+		c.sendAlert(alertUnexpectedMessage)
+		return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
+	}
+	return c.readRecordOrCCS(expectChangeCipherSpec)
+}
+
+// atLeastReader reads from R, stopping with EOF once at least N bytes have been
+// read. It is different from an io.LimitedReader in that it doesn't cut short
+// the last Read call, and in that it considers an early EOF an error.
+type atLeastReader struct {
+	R io.Reader
+	N int64
+}
+
+func (r *atLeastReader) Read(p []byte) (int, error) {
+	if r.N <= 0 {
+		return 0, io.EOF
+	}
+	n, err := r.R.Read(p)
+	r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809
+	if r.N > 0 && err == io.EOF {
+		return n, io.ErrUnexpectedEOF
+	}
+	if r.N <= 0 && err == nil {
+		return n, io.EOF
+	}
+	return n, err
+}
+
+// readFromUntil reads from r into c.rawInput until c.rawInput contains
+// at least n bytes or else returns an error.
+func (c *Conn) readFromUntil(r io.Reader, n int) error {
+	if c.rawInput.Len() >= n {
+		return nil
+	}
+	needs := n - c.rawInput.Len()
+	// There might be extra input waiting on the wire. Make a best effort
+	// attempt to fetch it so that it can be used in (*Conn).Read to
+	// "predict" closeNotify alerts.
+	c.rawInput.Grow(needs + bytes.MinRead)
+	_, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)})
+	return err
+}
+
+// sendAlert sends a TLS alert message.
+func (c *Conn) sendAlertLocked(err alert) error {
+	switch err {
+	case alertNoRenegotiation, alertCloseNotify:
+		c.tmp[0] = alertLevelWarning
+	default:
+		c.tmp[0] = alertLevelError
+	}
+	c.tmp[1] = byte(err)
+
+	_, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2])
+	if err == alertCloseNotify {
+		// closeNotify is a special case in that it isn't an error.
+		return writeErr
+	}
+
+	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
+}
+
+// sendAlert sends a TLS alert message.
+func (c *Conn) sendAlert(err alert) error {
+	c.out.Lock()
+	defer c.out.Unlock()
+	return c.sendAlertLocked(err)
+}
+
+const (
+	// tcpMSSEstimate is a conservative estimate of the TCP maximum segment
+	// size (MSS). A constant is used, rather than querying the kernel for
+	// the actual MSS, to avoid complexity. The value here is the IPv6
+	// minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40
+	// bytes) and a TCP header with timestamps (32 bytes).
+	tcpMSSEstimate = 1208
+
+	// recordSizeBoostThreshold is the number of bytes of application data
+	// sent after which the TLS record size will be increased to the
+	// maximum.
+	recordSizeBoostThreshold = 128 * 1024
+)
+
+// maxPayloadSizeForWrite returns the maximum TLS payload size to use for the
+// next application data record. There is the following trade-off:
+//
+//   - For latency-sensitive applications, such as web browsing, each TLS
+//     record should fit in one TCP segment.
+//   - For throughput-sensitive applications, such as large file transfers,
+//     larger TLS records better amortize framing and encryption overheads.
+//
+// A simple heuristic that works well in practice is to use small records for
+// the first 1MB of data, then use larger records for subsequent data, and
+// reset back to smaller records after the connection becomes idle. See "High
+// Performance Web Networking", Chapter 4, or:
+// https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/
+//
+// In the interests of simplicity and determinism, this code does not attempt
+// to reset the record size once the connection is idle, however.
+func (c *Conn) maxPayloadSizeForWrite(typ recordType) int {
+	if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData {
+		return maxPlaintext
+	}
+
+	if c.bytesSent >= recordSizeBoostThreshold {
+		return maxPlaintext
+	}
+
+	// Subtract TLS overheads to get the maximum payload size.
+	payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen()
+	if c.out.cipher != nil {
+		switch ciph := c.out.cipher.(type) {
+		case cipher.Stream:
+			payloadBytes -= c.out.mac.Size()
+		case cipher.AEAD:
+			payloadBytes -= ciph.Overhead()
+		case cbcMode:
+			blockSize := ciph.BlockSize()
+			// The payload must fit in a multiple of blockSize, with
+			// room for at least one padding byte.
+			payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1
+			// The MAC is appended before padding so affects the
+			// payload size directly.
+			payloadBytes -= c.out.mac.Size()
+		default:
+			panic("unknown cipher type")
+		}
+	}
+	if c.vers == VersionTLS13 {
+		payloadBytes-- // encrypted ContentType
+	}
+
+	// Allow packet growth in arithmetic progression up to max.
+	pkt := c.packetsSent
+	c.packetsSent++
+	if pkt > 1000 {
+		return maxPlaintext // avoid overflow in multiply below
+	}
+
+	n := payloadBytes * int(pkt+1)
+	if n > maxPlaintext {
+		n = maxPlaintext
+	}
+	return n
+}
+
+func (c *Conn) write(data []byte) (int, error) {
+	if c.buffering {
+		c.sendBuf = append(c.sendBuf, data...)
+		return len(data), nil
+	}
+
+	n, err := c.conn.Write(data)
+	c.bytesSent += int64(n)
+	return n, err
+}
+
+func (c *Conn) flush() (int, error) {
+	if len(c.sendBuf) == 0 {
+		return 0, nil
+	}
+
+	n, err := c.conn.Write(c.sendBuf)
+	c.bytesSent += int64(n)
+	c.sendBuf = nil
+	c.buffering = false
+	return n, err
+}
+
+// outBufPool pools the record-sized scratch buffers used by writeRecordLocked.
+var outBufPool = sync.Pool{
+	New: func() any {
+		return new([]byte)
+	},
+}
+
+// writeRecordLocked writes a TLS record with the given type and payload to the
+// connection and updates the record layer state.
+func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
+	outBufPtr := outBufPool.Get().(*[]byte)
+	outBuf := *outBufPtr
+	defer func() {
+		// You might be tempted to simplify this by just passing &outBuf to Put,
+		// but that would make the local copy of the outBuf slice header escape
+		// to the heap, causing an allocation. Instead, we keep around the
+		// pointer to the slice header returned by Get, which is already on the
+		// heap, and overwrite and return that.
+		*outBufPtr = outBuf
+		outBufPool.Put(outBufPtr)
+	}()
+
+	var n int
+	for len(data) > 0 {
+		m := len(data)
+		if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload {
+			m = maxPayload
+		}
+
+		_, outBuf = sliceForAppend(outBuf[:0], recordHeaderLen)
+		outBuf[0] = byte(typ)
+		vers := c.vers
+		if vers == 0 {
+			// Some TLS servers fail if the record version is
+			// greater than TLS 1.0 for the initial ClientHello.
+			vers = VersionTLS10
+		} else if vers == VersionTLS13 {
+			// TLS 1.3 froze the record layer version to 1.2.
+			// See RFC 8446, Section 5.1.
+			vers = VersionTLS12
+		}
+		outBuf[1] = byte(vers >> 8)
+		outBuf[2] = byte(vers)
+		outBuf[3] = byte(m >> 8)
+		outBuf[4] = byte(m)
+
+		var err error
+		outBuf, err = c.out.encrypt(outBuf, data[:m], c.config.rand())
+		if err != nil {
+			return n, err
+		}
+		if _, err := c.write(outBuf); err != nil {
+			return n, err
+		}
+		n += m
+		data = data[m:]
+	}
+
+	if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 {
+		if err := c.out.changeCipherSpec(); err != nil {
+			return n, c.sendAlertLocked(err.(alert))
+		}
+	}
+
+	return n, nil
+}
+
+// writeHandshakeRecord writes a handshake message to the connection and updates
+// the record layer state. If transcript is non-nil the marshalled message is
+// written to it.
+func (c *Conn) writeHandshakeRecord(msg handshakeMessage, transcript transcriptHash) (int, error) {
+	c.out.Lock()
+	defer c.out.Unlock()
+
+	data, err := msg.marshal()
+	if err != nil {
+		return 0, err
+	}
+	if transcript != nil {
+		transcript.Write(data)
+	}
+
+	return c.writeRecordLocked(recordTypeHandshake, data)
+}
+
+// writeChangeCipherRecord writes a ChangeCipherSpec message to the connection and
+// updates the record layer state.
+func (c *Conn) writeChangeCipherRecord() error {
+	c.out.Lock()
+	defer c.out.Unlock()
+	_, err := c.writeRecordLocked(recordTypeChangeCipherSpec, []byte{1})
+	return err
+}
+
+// readHandshake reads the next handshake message from
+// the record layer. If transcript is non-nil, the message
+// is written to the passed transcriptHash.
+func (c *Conn) readHandshake(transcript transcriptHash) (any, error) {
+	for c.hand.Len() < 4 {
+		if err := c.readRecord(); err != nil {
+			return nil, err
+		}
+	}
+
+	data := c.hand.Bytes()
+	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
+	if n > maxHandshake {
+		c.sendAlertLocked(alertInternalError)
+		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
+	}
+	for c.hand.Len() < 4+n {
+		if err := c.readRecord(); err != nil {
+			return nil, err
+		}
+	}
+	data = c.hand.Next(4 + n)
+	var m handshakeMessage
+	switch data[0] {
+	case typeHelloRequest:
+		m = new(helloRequestMsg)
+	case typeClientHello:
+		m = new(clientHelloMsg)
+	case typeServerHello:
+		m = new(serverHelloMsg)
+	case typeNewSessionTicket:
+		if c.vers == VersionTLS13 {
+			m = new(newSessionTicketMsgTLS13)
+		} else {
+			m = new(newSessionTicketMsg)
+		}
+	case typeCertificate:
+		if c.vers == VersionTLS13 {
+			m = new(certificateMsgTLS13)
+		} else {
+			m = new(certificateMsg)
+		}
+	case typeCertificateRequest:
+		if c.vers == VersionTLS13 {
+			m = new(certificateRequestMsgTLS13)
+		} else {
+			m = &certificateRequestMsg{
+				hasSignatureAlgorithm: c.vers >= VersionTLS12,
+			}
+		}
+	case typeCertificateStatus:
+		m = new(certificateStatusMsg)
+	case typeServerKeyExchange:
+		m = new(serverKeyExchangeMsg)
+	case typeServerHelloDone:
+		m = new(serverHelloDoneMsg)
+	case typeClientKeyExchange:
+		m = new(clientKeyExchangeMsg)
+	case typeCertificateVerify:
+		m = &certificateVerifyMsg{
+			hasSignatureAlgorithm: c.vers >= VersionTLS12,
+		}
+	case typeFinished:
+		m = new(finishedMsg)
+	case typeEncryptedExtensions:
+		m = new(encryptedExtensionsMsg)
+	case typeEndOfEarlyData:
+		m = new(endOfEarlyDataMsg)
+	case typeKeyUpdate:
+		m = new(keyUpdateMsg)
+	default:
+		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+	}
+
+	// The handshake message unmarshalers
+	// expect to be able to keep references to data,
+	// so pass in a fresh copy that won't be overwritten.
+	data = append([]byte(nil), data...)
+
+	if !m.unmarshal(data) {
+		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+	}
+
+	if transcript != nil {
+		transcript.Write(data)
+	}
+
+	return m, nil
+}
+
+var (
+	errShutdown = errors.New("tls: protocol is shutdown")
+)
+
+// Write writes data to the connection.
+//
+// As Write calls Handshake, in order to prevent indefinite blocking a deadline
+// must be set for both Read and Write before Write is called when the handshake
+// has not yet completed. See SetDeadline, SetReadDeadline, and
+// SetWriteDeadline.
+func (c *Conn) Write(b []byte) (int, error) {
+	// interlock with Close below
+	for {
+		x := atomic.LoadInt32(&c.activeCall)
+		if x&1 != 0 {
+			return 0, net.ErrClosed
+		}
+		if atomic.CompareAndSwapInt32(&c.activeCall, x, x+2) {
+			break
+		}
+	}
+	defer atomic.AddInt32(&c.activeCall, -2)
+
+	if err := c.Handshake(); err != nil {
+		return 0, err
+	}
+
+	c.out.Lock()
+	defer c.out.Unlock()
+
+	if err := c.out.err; err != nil {
+		return 0, err
+	}
+
+	if !c.handshakeComplete() {
+		return 0, alertInternalError
+	}
+
+	if c.closeNotifySent {
+		return 0, errShutdown
+	}
+
+	// TLS 1.0 is susceptible to a chosen-plaintext
+	// attack when using block mode ciphers due to predictable IVs.
+	// This can be prevented by splitting each Application Data
+	// record into two records, effectively randomizing the IV.
+	//
+	// https://www.openssl.org/~bodo/tls-cbc.txt
+	// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
+	// https://www.imperialviolet.org/2012/01/15/beastfollowup.html
+
+	var m int
+	if len(b) > 1 && c.vers == VersionTLS10 {
+		if _, ok := c.out.cipher.(cipher.BlockMode); ok {
+			n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1])
+			if err != nil {
+				return n, c.out.setErrorLocked(err)
+			}
+			m, b = 1, b[1:]
+		}
+	}
+
+	n, err := c.writeRecordLocked(recordTypeApplicationData, b)
+	return n + m, c.out.setErrorLocked(err)
+}
+
+// handleRenegotiation processes a HelloRequest handshake message.
+func (c *Conn) handleRenegotiation() error {
+	if c.vers == VersionTLS13 {
+		return errors.New("tls: internal error: unexpected renegotiation")
+	}
+
+	msg, err := c.readHandshake(nil)
+	if err != nil {
+		return err
+	}
+
+	helloReq, ok := msg.(*helloRequestMsg)
+	if !ok {
+		c.sendAlert(alertUnexpectedMessage)
+		return unexpectedMessageError(helloReq, msg)
+	}
+
+	if !c.isClient {
+		return c.sendAlert(alertNoRenegotiation)
+	}
+
+	switch c.config.Renegotiation {
+	case RenegotiateNever:
+		return c.sendAlert(alertNoRenegotiation)
+	case RenegotiateOnceAsClient:
+		if c.handshakes > 1 {
+			return c.sendAlert(alertNoRenegotiation)
+		}
+	case RenegotiateFreelyAsClient:
+		// Ok.
+	default:
+		c.sendAlert(alertInternalError)
+		return errors.New("tls: unknown Renegotiation value")
+	}
+
+	c.handshakeMutex.Lock()
+	defer c.handshakeMutex.Unlock()
+
+	atomic.StoreUint32(&c.handshakeStatus, 0)
+	if c.handshakeErr = c.clientHandshake(context.Background()); c.handshakeErr == nil {
+		c.handshakes++
+	}
+	return c.handshakeErr
+}
+
+// handlePostHandshakeMessage processes a handshake message arrived after the
+// handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation.
+func (c *Conn) handlePostHandshakeMessage() error {
+	if c.vers != VersionTLS13 {
+		return c.handleRenegotiation()
+	}
+
+	msg, err := c.readHandshake(nil)
+	if err != nil {
+		return err
+	}
+
+	c.retryCount++
+	if c.retryCount > maxUselessRecords {
+		c.sendAlert(alertUnexpectedMessage)
+		return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
+	}
+
+	switch msg := msg.(type) {
+	case *newSessionTicketMsgTLS13:
+		return c.handleNewSessionTicket(msg)
+	case *keyUpdateMsg:
+		return c.handleKeyUpdate(msg)
+	default:
+		c.sendAlert(alertUnexpectedMessage)
+		return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
+	}
+}
+
+func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
+	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
+	if cipherSuite == nil {
+		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
+	}
+
+	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
+	c.in.setTrafficSecret(cipherSuite, newSecret)
+
+	if keyUpdate.updateRequested {
+		c.out.Lock()
+		defer c.out.Unlock()
+
+		msg := &keyUpdateMsg{}
+		msgBytes, err := msg.marshal()
+		if err != nil {
+			return err
+		}
+		_, err = c.writeRecordLocked(recordTypeHandshake, msgBytes)
+		if err != nil {
+			// Surface the error at the next write.
+			c.out.setErrorLocked(err)
+			return nil
+		}
+
+		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
+		c.out.setTrafficSecret(cipherSuite, newSecret)
+	}
+
+	return nil
+}
+
+// Read reads data from the connection.
+//
+// As Read calls Handshake, in order to prevent indefinite blocking a deadline
+// must be set for both Read and Write before Read is called when the handshake
+// has not yet completed. See SetDeadline, SetReadDeadline, and
+// SetWriteDeadline.
+func (c *Conn) Read(b []byte) (int, error) {
+	if err := c.Handshake(); err != nil {
+		return 0, err
+	}
+	if len(b) == 0 {
+		// Put this after Handshake, in case people were calling
+		// Read(nil) for the side effect of the Handshake.
+		return 0, nil
+	}
+
+	c.in.Lock()
+	defer c.in.Unlock()
+
+	for c.input.Len() == 0 {
+		if err := c.readRecord(); err != nil {
+			return 0, err
+		}
+		for c.hand.Len() > 0 {
+			if err := c.handlePostHandshakeMessage(); err != nil {
+				return 0, err
+			}
+		}
+	}
+
+	n, _ := c.input.Read(b)
+
+	// If a close-notify alert is waiting, read it so that we can return (n,
+	// EOF) instead of (n, nil), to signal to the HTTP response reading
+	// goroutine that the connection is now closed. This eliminates a race
+	// where the HTTP response reading goroutine would otherwise not observe
+	// the EOF until its next read, by which time a client goroutine might
+	// have already tried to reuse the HTTP connection for a new request.
+	// See https://golang.org/cl/76400046 and https://golang.org/issue/3514
+	if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 &&
+		recordType(c.rawInput.Bytes()[0]) == recordTypeAlert {
+		if err := c.readRecord(); err != nil {
+			return n, err // will be io.EOF on closeNotify
+		}
+	}
+
+	return n, nil
+}
+
+// Close closes the connection.
+func (c *Conn) Close() error {
+	// Interlock with Conn.Write above.
+	var x int32
+	for {
+		x = atomic.LoadInt32(&c.activeCall)
+		if x&1 != 0 {
+			return net.ErrClosed
+		}
+		if atomic.CompareAndSwapInt32(&c.activeCall, x, x|1) {
+			break
+		}
+	}
+	if x != 0 {
+		// io.Writer and io.Closer should not be used concurrently.
+		// If Close is called while a Write is currently in-flight,
+		// interpret that as a sign that this Close is really just
+		// being used to break the Write and/or clean up resources and
+		// avoid sending the alertCloseNotify, which may block
+		// waiting on handshakeMutex or the c.out mutex.
+		return c.conn.Close()
+	}
+
+	var alertErr error
+	if c.handshakeComplete() {
+		if err := c.closeNotify(); err != nil {
+			alertErr = fmt.Errorf("tls: failed to send closeNotify alert (but connection was closed anyway): %w", err)
+		}
+	}
+
+	if err := c.conn.Close(); err != nil {
+		return err
+	}
+	return alertErr
+}
+
+var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
+
+// CloseWrite shuts down the writing side of the connection. It should only be
+// called once the handshake has completed and does not call CloseWrite on the
+// underlying connection. Most callers should just use Close.
+func (c *Conn) CloseWrite() error {
+	if !c.handshakeComplete() {
+		return errEarlyCloseWrite
+	}
+
+	return c.closeNotify()
+}
+
+func (c *Conn) closeNotify() error {
+	c.out.Lock()
+	defer c.out.Unlock()
+
+	if !c.closeNotifySent {
+		// Set a Write Deadline to prevent possibly blocking forever.
+		c.SetWriteDeadline(time.Now().Add(time.Second * 5))
+		c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify)
+		c.closeNotifySent = true
+		// Any subsequent writes will fail.
+		c.SetWriteDeadline(time.Now())
+	}
+	return c.closeNotifyErr
+}
+
+// Handshake runs the client or server handshake
+// protocol if it has not yet been run.
+//
+// Most uses of this package need not call Handshake explicitly: the
+// first Read or Write will call it automatically.
+//
+// For control over canceling or setting a timeout on a handshake, use
+// HandshakeContext or the Dialer's DialContext method instead.
+func (c *Conn) Handshake() error {
+	return c.HandshakeContext(context.Background())
+}
+
+// HandshakeContext runs the client or server handshake
+// protocol if it has not yet been run.
+//
+// The provided Context must be non-nil. If the context is canceled before
+// the handshake is complete, the handshake is interrupted and an error is returned.
+// Once the handshake has completed, cancellation of the context will not affect the
+// connection.
+//
+// Most uses of this package need not call HandshakeContext explicitly: the
+// first Read or Write will call it automatically.
+func (c *Conn) HandshakeContext(ctx context.Context) error {
+	// Delegate to unexported method for named return
+	// without confusing documented signature.
+	return c.handshakeContext(ctx)
+}
+
+func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
+	// Fast sync/atomic-based exit if there is no handshake in flight and the
+	// last one succeeded without an error. Avoids the expensive context setup
+	// and mutex for most Read and Write calls.
+	if c.handshakeComplete() {
+		return nil
+	}
+
+	handshakeCtx, cancel := context.WithCancel(ctx)
+	// Note: defer this before starting the "interrupter" goroutine
+	// so that we can tell the difference between the input being canceled and
+	// this cancellation. In the former case, we need to close the connection.
+	defer cancel()
+
+	// Start the "interrupter" goroutine, if this context might be canceled.
+	// (The background context cannot).
+	//
+	// The interrupter goroutine waits for the input context to be done and
+	// closes the connection if this happens before the function returns.
+	if ctx.Done() != nil {
+		done := make(chan struct{})
+		interruptRes := make(chan error, 1)
+		defer func() {
+			close(done)
+			if ctxErr := <-interruptRes; ctxErr != nil {
+				// Return context error to user.
+				ret = ctxErr
+			}
+		}()
+		go func() {
+			select {
+			case <-handshakeCtx.Done():
+				// Close the connection, discarding the error
+				_ = c.conn.Close()
+				interruptRes <- handshakeCtx.Err()
+			case <-done:
+				interruptRes <- nil
+			}
+		}()
+	}
+
+	c.handshakeMutex.Lock()
+	defer c.handshakeMutex.Unlock()
+
+	if err := c.handshakeErr; err != nil {
+		return err
+	}
+	if c.handshakeComplete() {
+		return nil
+	}
+
+	c.in.Lock()
+	defer c.in.Unlock()
+
+	c.handshakeErr = c.handshakeFn(handshakeCtx)
+	if c.handshakeErr == nil {
+		c.handshakes++
+	} else {
+		// If an error occurred during the handshake try to flush the
+		// alert that might be left in the buffer.
+		c.flush()
+	}
+
+	if c.handshakeErr == nil && !c.handshakeComplete() {
+		c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
+	}
+	if c.handshakeErr != nil && c.handshakeComplete() {
+		panic("tls: internal error: handshake returned an error but is marked successful")
+	}
+
+	return c.handshakeErr
+}
+
+// ConnectionState returns basic TLS details about the connection.
+func (c *Conn) ConnectionState() ConnectionState {
+	c.handshakeMutex.Lock()
+	defer c.handshakeMutex.Unlock()
+	return c.connectionStateLocked()
+}
+
+func (c *Conn) connectionStateLocked() ConnectionState {
+	var state ConnectionState
+	state.HandshakeComplete = c.handshakeComplete()
+	state.Version = c.vers
+	state.NegotiatedProtocol = c.clientProtocol
+	state.DidResume = c.didResume
+	state.NegotiatedProtocolIsMutual = true
+	state.ServerName = c.serverName
+	state.CipherSuite = c.cipherSuite
+	state.PeerCertificates = c.peerCertificates
+	state.VerifiedChains = c.verifiedChains
+	state.SignedCertificateTimestamps = c.scts
+	state.OCSPResponse = c.ocspResponse
+	if !c.didResume && c.vers != VersionTLS13 {
+		if c.clientFinishedIsFirst {
+			state.TLSUnique = c.clientFinished[:]
+		} else {
+			state.TLSUnique = c.serverFinished[:]
+		}
+	}
+	if c.config.Renegotiation != RenegotiateNever {
+		state.ekm = noExportedKeyingMaterial
+	} else {
+		state.ekm = c.ekm
+	}
+	return state
+}
+
+// OCSPResponse returns the stapled OCSP response from the TLS server, if
+// any. (Only valid for client connections.)
+func (c *Conn) OCSPResponse() []byte {
+	c.handshakeMutex.Lock()
+	defer c.handshakeMutex.Unlock()
+
+	return c.ocspResponse
+}
+
+// VerifyHostname checks that the peer certificate chain is valid for
+// connecting to host. If so, it returns nil; if not, it returns an error
+// describing the problem.
+func (c *Conn) VerifyHostname(host string) error {
+	c.handshakeMutex.Lock()
+	defer c.handshakeMutex.Unlock()
+	if !c.isClient {
+		return errors.New("tls: VerifyHostname called on TLS server connection")
+	}
+	if !c.handshakeComplete() {
+		return errors.New("tls: handshake has not yet been performed")
+	}
+	if len(c.verifiedChains) == 0 {
+		return errors.New("tls: handshake did not verify certificate chain")
+	}
+	return c.peerCertificates[0].VerifyHostname(host)
+}
+
+func (c *Conn) handshakeComplete() bool {
+	return atomic.LoadUint32(&c.handshakeStatus) == 1
+}