code: func (msg *MsgGetHeaders) MaxPayloadLength(pver uint32) uint32 {
  	// Version 4 bytes + num block locator hashes (varInt) + max allowed block
  	// locators + hash stop.
  	return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg *
  		chainhash.HashSize) + chainhash.HashSize
  }
docs: // MaxPayloadLength returns the maximum length the payload can be for the
  // receiver.  This is part of the Message interface implementation.