// network.cc //	Routines to simulate a network interface, using UNIX sockets//	to deliver packets between multiple invocations of nachos.////  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.#include "copyright.h"#include "system.h"// Dummy functions because C++ can't call member functions indirectly static void NetworkReadPoll(int arg){ Network *net = (Network *)arg; net->CheckPktAvail(); }static void NetworkSendDone(int arg){ Network *net = (Network *)arg; net->SendDone(); }// Initialize the network emulation//   addr is used to generate the socket name//   reliability says whether we drop packets to emulate unreliable links//   readAvail, writeDone, callArg -- analogous to consoleNetwork::Network(NetworkAddress addr, double reliability,	VoidFunctionPtr readAvail, VoidFunctionPtr writeDone, int callArg){    ident = addr;    if (reliability < 0) chanceToWork = 0;    else if (reliability > 1) chanceToWork = 1;    else chanceToWork = reliability;    // set up the stuff to emulate asynchronous interrupts    writeHandler = writeDone;    readHandler = readAvail;    handlerArg = callArg;    sendBusy = FALSE;    inHdr.length = 0;        sock = OpenSocket();    sprintf(sockName, "SOCKET_%d", (int)addr);    AssignNameToSocket(sockName, sock);		 // Bind socket to a filename 						 // in the current directory.    // start polling for incoming packets    interrupt->Schedule(NetworkReadPoll, (int)this, NetworkTime, NetworkRecvInt);}Network::~Network(){    CloseSocket(sock);    DeAssignNameToSocket(sockName);}// if a packet is already buffered, we simply delay reading // the incoming packet.  In real life, the incoming // packet might be dropped if we can't read it in time.voidNetwork::CheckPktAvail(){    // schedule the next time to poll for a packet    interrupt->Schedule(NetworkReadPoll, (int)this, NetworkTime, NetworkRecvInt);    if (inHdr.length != 0) 	// do nothing if packet is already buffered	return;		    if (!PollSocket(sock)) 	// do nothing if no packet to be read	return;    // otherwise, read packet in    char *buffer = new char[MaxWireSize];    ReadFromSocket(sock, buffer, MaxWireSize);    // divide packet into header and data    inHdr = *(PacketHeader *)buffer;    ASSERT((inHdr.to == ident) && (inHdr.length <= MaxPacketSize));    bcopy(buffer + sizeof(PacketHeader), inbox, inHdr.length);    delete []buffer ;    DEBUG('n', "Network received packet from %d, length %d...\n",	  				(int) inHdr.from, inHdr.length);    stats->numPacketsRecvd++;    // tell post office that the packet has arrived    (*readHandler)(handlerArg);	}// notify user that another packet can be sentvoidNetwork::SendDone(){    sendBusy = FALSE;    stats->numPacketsSent++;    (*writeHandler)(handlerArg);}// send a packet by concatenating hdr and data, and schedule// an interrupt to tell the user when the next packet can be sent //// Note we always pad out a packet to MaxWireSize before putting it into// the socket, because it's simpler at the receive end.voidNetwork::Send(PacketHeader hdr, char* data){    char toName[32];    sprintf(toName, "SOCKET_%d", (int)hdr.to);        ASSERT((sendBusy == FALSE) && (hdr.length > 0) 		&& (hdr.length <= MaxPacketSize) && (hdr.from == ident));    DEBUG('n', "Sending to addr %d, %d bytes... ", hdr.to, hdr.length);    interrupt->Schedule(NetworkSendDone, (int)this, NetworkTime, NetworkSendInt);    if (Random() % 100 >= chanceToWork * 100) { // emulate a lost packet	DEBUG('n', "oops, lost it!\n");	return;    }    // concatenate hdr and data into a single buffer, and send it out    char *buffer = new char[MaxWireSize];    *(PacketHeader *)buffer = hdr;    bcopy(data, buffer + sizeof(PacketHeader), hdr.length);    SendToSocket(sock, buffer, MaxWireSize, toName);    delete []buffer;}// read a packet, if one is bufferedPacketHeaderNetwork::Receive(char* data){    PacketHeader hdr = inHdr;    inHdr.length = 0;    if (hdr.length != 0)    	bcopy(inbox, data, hdr.length);    return hdr;}