CoreFoundation/examples/CFLocalServer/Protocol.h

/*
 *    Copyright (c) 2009 Grant Erickson <gerickson@nuovations.com>
 *    All rights reserved.
 *
 * This source code is a modified version of the CoreFoundation sources released by Apple Inc. under
 * the terms of the BSD-style license (see below).
 *
 * For information about changes from the original Apple source release can be found by reviewing the
 * source control system for the project at https://sourceforge.net/svn/?group_id=246198.
 *
 */

/*
    File:       Protocol.h

    Contains:   Definition of the communication protocol between client and server.

    Written by: DTS

    Copyright:  Copyright (c) 2005 by Apple Computer, Inc., All Rights Reserved.

    Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple Computer, Inc.
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                please do not use, install, modify or redistribute this Apple software.

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    Change History (most recent first):

$Log: Protocol.h,v $
Revision 1.1  2005/05/17 12:19:23         
First checked in.


*/

#ifndef _PROTOCOL_H
#define _PROTOCOL_H

/////////////////////////////////////////////////////////////////

// System interfaces

#include <CoreFoundation/CoreFoundation.h>


/////////////////////////////////////////////////////////////////

// Packet types

enum {
    kPacketTypeGoodbye = 'GDBY',            // sent by client to server before signing off
    kPacketTypeNOP     = 'NOOP',            // no operation, test for client/server RPC
    kPacketTypeReply   = 'RPLY',            // all RPC replies are of this type
    kPacketTypeWhisper = 'WSPR',            // client/server RPC to print message on server
    kPacketTypeShout   = 'SHOU',            // sent by client to server, which echoes it to all listening clients
    kPacketTypeListen  = 'LSTN',            // client/server RPC to register for shouts
    kPacketTypeQuit    = 'QUIT'             // client/server RPC to tell server to quit
};

// Well known packet IDs (for the fID field of the packet header).
// kPacketIDFirst is just a suggestion.  The server doesn't require 
// that the client use sequential IDs starting from 1; the IDs are 
// for the client to choose.  However, the use of kPacketIDNone for 
// some packets (those that don't have a reply) is a hard requirement 
// in the server.  

enum {
    kPacketIDNone  = 0,
    kPacketIDFirst = 1
};

// kPacketMagic is first four bytes of every packet.  If the packet stream 
// gets out of sync, this will quickly detect the problem.

enum {
    kPacketMagic = 'LSPM'               // for Local Server Packet Magic
};

// kPacketMaximumSize is an arbitrary limit, chosen so that we can detect 
// if the packet streams get out of sync or if a client goes mad.

enum {  
    kPacketMaximumSize = 100 * 1024     // just basic sanity checks
};

// IMPORTANT:
// The following structures define the packets sent between the client and 
// the server.  For a network protocol you'd need to worry about byte ordering, 
// but this isn't a network protocol (it always stays on the same machine) so 
// I don't have to worry.  However, I do need to worry about having 
// size invariant types (so that 32- and 64-bit clients and servers are 
// all compatible) and structure alignment (so that code compiled by different 
// compilers is compatible).  Size invariant types is easy, and represented 
// by the structures below.  Alignment is trickier, and I'm mostly just 
// glossing over the issue right now.

// PacketHeader is the header at the front of every packet.

typedef uint32_t FourCharCode;
typedef FourCharCode OSType;

struct PacketHeader {
    OSType          fMagic;             // must be kPacketMagic
    OSType          fType;              // kPacketTypeGoodbye etc 
    int32_t         fID;                // kPacketIDNone or some other value
    uint32_t        fSize;              // includes size of header itself
};
typedef struct PacketHeader PacketHeader;

struct PacketGoodbye {                  // reply: n/a
    PacketHeader    fHeader;            // fType is kPacketTypeGoodbye, fID must be kPacketIDNone
    char            fMessage[32];       // Just for fun.
};
typedef struct PacketGoodbye PacketGoodbye;

struct PacketNOP {                      // reply: PacketReply
    PacketHeader    fHeader;            // fType is kPacketTypeNOP, fID echoed
};
typedef struct PacketNOP PacketNOP;

struct PacketReply {                    // reply: n/a
    PacketHeader    fHeader;            // fType is kPacketTypeReply, fID is ID of request
    int32_t         fErr;               // result of operation, errno-style
};
typedef struct PacketReply PacketReply;

struct PacketWhisper {                  // reply: PacketReply
    PacketHeader    fHeader;            // fType is kPacketTypeWhisper, fID echoed
    char            fMessage[32];       // message to print
};
typedef struct PacketWhisper PacketWhisper;

struct PacketShout {                    // reply: none
    PacketHeader    fHeader;            // fType is kPacketTypeShout, fID must be kPacketIDNone
    char            fMessage[32];       // message for each of the clients
};
typedef struct PacketShout PacketShout;

// Shouts are echoed to anyone who listens, including sender.

struct PacketListen {                   // reply: PacketReply
    PacketHeader    fHeader;            // fType is kPacketTypeListen, fID echoed
};
typedef struct PacketListen PacketListen;

struct PacketQuit {                     // reply: PacketReply
    PacketHeader    fHeader;            // fType is kPacketTypeQuit, fID echoed
};
typedef struct PacketQuit PacketQuit;

// IMPORTANT:
// The location of the kServerAddress socket file is intimately tied to the 
// security of the server.  The file should be placed in a directory that's 
// read access to everyone who needs access to the service, but only write 
// accessible to the UID that's running the server.  Failure to follow this  
// guideline may make your server subject to security exploits.
//
// To prevent this sort of silliness I require that the socket be created 
// in a directory owned by the server's user ("com.apple.dts.CFLocalServer") 
// within a directory that's sticky ("/var/tmp", not "/tmp" because that's 
// periodically cleaned up). See SafeBindUnixDomainSocket (in "Server.c") for 
// the details about how I achieve this.

#define kServerSocketPath "/var/tmp/com.apple.dts.CFLocalServer/Socket"

#endif