crypto/tls,regexp: remove always-nil error results

These were harmless, but added unnecessary verbosity to the code.
This can happen as a result of refactors: for example,
the method sessionState used to return errors in some cases.

Change-Id: I4e6dacc01ae6a49b528c672979f95cbb86795a85
Reviewed-on: https://go-review.googlesource.com/c/go/+/528995
Reviewed-by: Leo Isla <islaleo93@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Olivier Mengué <olivier.mengue@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>

handshake_client.go

@@ -915,10 +915,7 @@ func (hs *clientHandshakeState) saveSessionTicket() error {
 		return nil
 	}
 
-	session, err := c.sessionState()
-	if err != nil {
-		return err
-	}
+	session := c.sessionState()
 	session.secret = hs.masterSecret
 
 	cs := &ClientSessionState{ticket: hs.ticket, session: session}

handshake_client_tls13.go

@@ -753,11 +753,7 @@ func (c *Conn) handleNewSessionTicket(msg *newSessionTicketMsgTLS13) error {
 	psk := cipherSuite.expandLabel(c.resumptionSecret, "resumption",
 		msg.nonce, cipherSuite.hash.Size())
 
-	session, err := c.sessionState()
-	if err != nil {
-		c.sendAlert(alertInternalError)
-		return err
-	}
+	session := c.sessionState()
 	session.secret = psk
 	session.useBy = uint64(c.config.time().Add(lifetime).Unix())
 	session.ageAdd = msg.ageAdd

handshake_server.go

@@ -810,10 +810,7 @@ func (hs *serverHandshakeState) sendSessionTicket() error {
 	c := hs.c
 	m := new(newSessionTicketMsg)
 
-	state, err := c.sessionState()
-	if err != nil {
-		return err
-	}
+	state := c.sessionState()
 	state.secret = hs.masterSecret
 	if hs.sessionState != nil {
 		// If this is re-wrapping an old key, then keep
@@ -821,6 +818,7 @@ func (hs *serverHandshakeState) sendSessionTicket() error {
 		state.createdAt = hs.sessionState.createdAt
 	}
 	if c.config.WrapSession != nil {
+		var err error
 		m.ticket, err = c.config.WrapSession(c.connectionStateLocked(), state)
 		if err != nil {
 			return err

handshake_server_tls13.go

@@ -837,13 +837,11 @@ func (c *Conn) sendSessionTicket(earlyData bool) error {
 
 	m := new(newSessionTicketMsgTLS13)
 
-	state, err := c.sessionState()
-	if err != nil {
-		return err
-	}
+	state := c.sessionState()
 	state.secret = psk
 	state.EarlyData = earlyData
 	if c.config.WrapSession != nil {
+		var err error
 		m.label, err = c.config.WrapSession(c.connectionStateLocked(), state)
 		if err != nil {
 			return err
@@ -865,8 +863,7 @@ func (c *Conn) sendSessionTicket(earlyData bool) error {
 	// The value is not stored anywhere; we never need to check the ticket age
 	// because 0-RTT is not supported.
 	ageAdd := make([]byte, 4)
-	_, err = c.config.rand().Read(ageAdd)
-	if err != nil {
+	if _, err := c.config.rand().Read(ageAdd); err != nil {
 		return err
 	}
 	m.ageAdd = binary.LittleEndian.Uint32(ageAdd)

ticket.go

@@ -289,7 +289,7 @@ func ParseSessionState(data []byte) (*SessionState, error) {
 
 // sessionState returns a partially filled-out [SessionState] with information
 // from the current connection.
-func (c *Conn) sessionState() (*SessionState, error) {
+func (c *Conn) sessionState() *SessionState {
 	return &SessionState{
 		version:           c.vers,
 		cipherSuite:       c.cipherSuite,
@@ -302,7 +302,7 @@ func (c *Conn) sessionState() (*SessionState, error) {
 		isClient:          c.isClient,
 		extMasterSecret:   c.extMasterSecret,
 		verifiedChains:    c.verifiedChains,
-	}, nil
+	}
 }
 
 // EncryptTicket encrypts a ticket with the [Config]'s configured (or default)