Daemon - Client IPC with Unix sockets

问题

I have a launch daemon which I want to ask for status information from a user app. I implemented a client-server model (with the daemon as server) using unix sockets as described here: OS X - Communication between launch daemon and launch agent

In fact it works well, when I run the daemon as a user process (for debugging), but it will fail when it is actually launched as root.

I have read the TN on Daemons and Agents and the Daemon & Services Programming Guide. However, I could not find decent information how the socket must be used in a launch daemon.

I am confused by several things:

Must I specify the socket in the launch daemon plist file? And how?
If the socket is specified in the plist, does that change the way I need to create the socket in code?
What path would be good for the unix socket? The Technical Note recommends /var/run but I guess a user process may not write there, or can it?
Is there maybe a easier way to do IPC between daemon and client?
What is the best way to log the daemon output. I tried NSLog but it seems not work...

I am also unsure if my socket code is correct. Maybe someone more experienced can tell me if I'm on the right track here. I have the following code in the daemon to initialize the unix socket:

#define SOCKETNAME  "/var/run/com.company.myApp.socket"

- (void) startServer {
    //remove any prev socket
    unlink(SOCKETNAME);
    CFSocketContext CTX = { 0, (__bridge void *)(self), NULL, NULL, NULL };

    CFSocketRef unixSocket = CFSocketCreate(NULL, PF_UNIX, SOCK_STREAM, 0,
                               kCFSocketAcceptCallBack, (CFSocketCallBack)AcceptCallBack, &CTX);
    if (unixSocket == NULL) {/*log and return*/} 

    struct sockaddr_un addr;
    memset(&addr, 0, sizeof(addr));
    addr.sun_family = AF_UNIX;
    strcpy(addr.sun_path, SOCKETNAME);
    addr.sun_len = strlen(addr.sun_path) + sizeof (addr.sun_family);

    NSData *address = [ NSData dataWithBytes: &addr length: sizeof(addr) ];
    if (CFSocketSetAddress(unixSocket, (__bridge CFDataRef) address) != kCFSocketSuccess) {
        NSLog(@"CFSocketSetAddress() failed\n");
        CFRelease(unixSocket);
    }

    CFRunLoopSourceRef sourceRef = CFSocketCreateRunLoopSource(kCFAllocatorDefault, unixSocket, 0);
    CFRunLoopAddSource(CFRunLoopGetCurrent(), sourceRef, kCFRunLoopCommonModes);
    CFRelease(sourceRef);    
    CFRunLoopRun();
}


void AcceptCallBack(CFSocketRef socket, CFSocketCallBackType type, CFDataRef address, const void *data, void *info) {
    CTServerController* selfServerController = (__bridge CTServerController*) info;
    //NSLog(@"acceptCallBack");   
    //...
}

回答1:

you should not specify the socket in the plist, you know the concrete place, the server knows, the client knows, that should be enought
the socket specified in the plist is for launching the deamon/agent ondemand, you do not need that in a basic case
you can use any path, if your daemon starts first (usually the case) it has all the privilege to set the correct rights on the socket to let anybody (or a given user, group) read, read and write or any given rights you wish, i'm sure you just forgot to let the client write/read the unix socket
i think on OSX the unix socket IPC is a perfect, easy solution (you have many other choices too of course, xpc, mach messages, etc.)
you can define where to go the stdout and stderr of a daemon in it's plist (StandardOutPath, StandardErrorPath keys)

来源：https://stackoverflow.com/questions/13858035/daemon-client-ipc-with-unix-sockets

标签

objective-c

macos

ipc

daemon