Method Write

conn.go:1269–1323

Write writes data to the connection. As Write calls [Conn.Handshake], in order to prevent indefinite blocking a deadline must be set for both [Conn.Read] and Write before Write is called when the handshake has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and [Conn.SetWriteDead

(b []byte)

// has not yet completed. See [Conn.SetDeadline], [Conn.SetReadDeadline], and
// [Conn.SetWriteDeadline].
func (c *Conn) Write(b []byte) (int, error) {
	// interlock with Close below
	for {
		x := c.activeCall.Load()
		if x&1 != 0 {
			return 0, net.ErrClosed
		}
		if c.activeCall.CompareAndSwap(x, x+2) {
			break
		}
	}
	defer c.activeCall.Add(-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.isHandshakeComplete.Load() {
		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 {