Method processClientHello

handshake_server.go:216–326

()

}

func (hs *serverHandshakeState) processClientHello() error {
	c := hs.c

	hs.hello = new(serverHelloMsg)
	hs.hello.vers = c.vers

	foundCompression := false
	// We only support null compression, so check that the client offered it.
	for _, compression := range hs.clientHello.compressionMethods {
		if compression == compressionNone {
			foundCompression = true
			break
		}
	}

	if !foundCompression {
		c.sendAlert(alertIllegalParameter)
		return errors.New("tls: client does not support uncompressed connections")
	}

	hs.hello.random = make([]byte, 32)
	serverRandom := hs.hello.random
	// Downgrade protection canaries. See RFC 8446, Section 4.1.3.
	maxVers := c.config.maxSupportedVersion(roleServer)
	if maxVers >= VersionTLS12 && c.vers < maxVers || testingOnlyForceDowngradeCanary {
		if c.vers == VersionTLS12 {
			copy(serverRandom[24:], downgradeCanaryTLS12)
		} else {
			copy(serverRandom[24:], downgradeCanaryTLS11)
		}
		serverRandom = serverRandom[:24]
	}
	_, err := io.ReadFull(c.config.rand(), serverRandom)
	if err != nil {
		c.sendAlert(alertInternalError)
		return err
	}

	if len(hs.clientHello.secureRenegotiation) != 0 {
		c.sendAlert(alertHandshakeFailure)
		return errors.New("tls: initial handshake had non-empty renegotiation extension")
	}

	hs.hello.extendedMasterSecret = hs.clientHello.extendedMasterSecret
	hs.hello.secureRenegotiationSupported = hs.clientHello.secureRenegotiationSupported
	hs.hello.compressionMethod = compressionNone
	if len(hs.clientHello.serverName) > 0 {
		c.serverName = hs.clientHello.serverName
	}

	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols, false)
	if err != nil {
		c.sendAlert(alertNoApplicationProtocol)
		return err
	}
	hs.hello.alpnProtocol = selectedProto
	c.clientProtocol = selectedProto