network.h

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// 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

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