Method beginMessage

conn.go:475–508

beginMessage prepares a connection and message writer for a new message.

(mw *messageWriter, messageType int)

// beginMessage prepares a connection and message writer for a new message.
func (c *Conn) beginMessage(mw *messageWriter, messageType int) error {
	// Close previous writer if not already closed by the application. It's
	// probably better to return an error in this situation, but we cannot
	// change this without breaking existing applications.
	if c.writer != nil {
		c.writer.Close()
		c.writer = nil
	}

	if !isControl(messageType) && !isData(messageType) {
		return errBadWriteOpCode
	}

	c.writeErrMu.Lock()
	err := c.writeErr
	c.writeErrMu.Unlock()
	if err != nil {
		return err
	}

	mw.c = c
	mw.frameType = messageType
	mw.pos = maxFrameHeaderSize

	if c.writeBuf == nil {
		wpd, ok := c.writePool.Get().(writePoolData)
		if ok {
			c.writeBuf = wpd.buf
		} else {
			c.writeBuf = make([]byte, c.writeBufSize)
		}
	}
	return nil
}

// NextWriter returns a writer for the next message to send. The writer's Close
// method flushes the complete message to the network.