// network.h //	Data structures to emulate a physical network connection.//	The network provides the abstraction of ordered, unreliable,//	fixed-size packet delivery to other machines on the network.////	You may note that the interface to the network is similar to //	the console device -- both are full duplex channels.////  DO NOT CHANGE -- part of the machine emulation//// Copyright (c) 1992-1993 The Regents of the University of California.// All rights reserved.  See copyright.h for copyright notice and limitation // of liability and disclaimer of warranty provisions.#ifndef NETWORK_H#define NETWORK_H#include "copyright.h"#include "utility.h"// Network address -- uniquely identifies a machine.  This machine's ID //  is given on the command line.typedef int NetworkAddress;	 // The following class defines the network packet header.// The packet header is prepended to the data payload by the Network driver, // before the packet is sent over the wire.  The format on the wire is:  //	packet header (PacketHeader)//	data (containing MailHeader from the PostOffice!)class PacketHeader {  public:    NetworkAddress to;		// Destination machine ID    NetworkAddress from;	// source machine ID    unsigned length;	 	// bytes of packet data, excluding the 				// packet header (but including the 				// MailHeader prepended by the post office)};#define MaxWireSize 	64	// largest packet that can go out on the wire#define MaxPacketSize 	(MaxWireSize - sizeof(struct PacketHeader))					// data "payload" of the largest packet// The following class defines a physical network device.  The network// is capable of delivering fixed sized packets, in order but unreliably, // to other machines connected to the network.//// The "reliability" of the network can be specified to the constructor.// This number, between 0 and 1, is the chance that the network will lose // a packet.  Note that you can change the seed for the random number // generator, by changing the arguments to RandomInit() in Initialize().// The random number generator is used to choose which packets to drop.class Network {  public:    Network(NetworkAddress addr, double reliability,  	  VoidFunctionPtr readAvail, VoidFunctionPtr writeDone, int callArg);				// Allocate and initialize network driver    ~Network();			// De-allocate the network driver data        void Send(PacketHeader hdr, char* data);    				// Send the packet data to a remote machine,				// specified by "hdr".  Returns immediately.    				// "writeHandler" is invoked once the next 				// packet can be sent.  Note that writeHandler 				// is called whether or not the packet is 				// dropped, and note that the "from" field of 				// the PacketHeader is filled in automatically 				// by Send().    PacketHeader Receive(char* data);    				// Poll the network for incoming messages.  				// If there is a packet waiting, copy the 				// packet into "data" and return the header.				// If no packet is waiting, return a header 				// with length 0.    void SendDone();		// Interrupt handler, called when message is 				// sent    void CheckPktAvail();	// Check if there is an incoming packet  private:    NetworkAddress ident;	// This machine's network address    double chanceToWork;	// Likelihood packet will be dropped    int sock;			// UNIX socket number for incoming packets    char sockName[32];		// File name corresponding to UNIX socket    VoidFunctionPtr writeHandler; // Interrupt handler, signalling next packet 				//      can be sent.      VoidFunctionPtr readHandler;  // Interrupt handler, signalling packet has 				// 	arrived.    int handlerArg;		// Argument to be passed to interrupt handler				//   (pointer to post office)    bool sendBusy;		// Packet is being sent.    bool packetAvail;		// Packet has arrived, can be pulled off of				//   network    PacketHeader inHdr;		// Information about arrived packet    char inbox[MaxPacketSize];  // Data for arrived packet};#endif // NETWORK_H