SecKeychainAddCallback and command-line program

Question

kithrup OP

Created May ’22

Replies 4

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Participants 2

I was trying to figure out how to monitor keychain events, and wrote:

        dispatch_async(dispatch_get_main_queue(), ^{
            OSStatus kr = SecKeychainAddCallback(MyKeychainEventCallback, kSecEveryEventMask, NULL);
            printf("Got result %d\n", kr);
        });
        dispatch_main();

However, the callback never gets called.

I put the same code into a simple GUI app (invoked from the didFinishLaunching method), and it does work. So presumably this is something run-loop related. But I can't seem to figure it out -- so what am I doing wrong?

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Answer 1

DTS Engineer OP

Apple

May ’22

Given the age of this API it’s likely to be run loop based, so you’ll need to park the main thread is NSRunLoop rather than ‘parking’ [1] it in dispatch_main.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] dispatch_main actually terminates the main thread, which is kinda neat. The kernel will then start a worker thread in your process to service any Dispatch sources.

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Answer 2

kithrup OP

May ’22

siiiiiiiiiiigh. The rest of the daemon I'd like to put this in is, of course, dispatch-based. I assume I can mix them both in, but I'll have to create a run loop just for this?

It's been a long time since I've had to do run loop stuff.

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Answer 3

DTS Engineer OP

Apple

May ’22

Looking at the code I believe that SecKeychainAddCallback schedules its run loop source on the current thead’s run loop rather than the main thread’s run loop. If I’m right, you should be able to start a thread to run this run loop source. So something like:

Thread {
    let err = SecKeychainAddCallback(…)
    … do something with err …
    RunLoop.current.run()
}

The rest of the daemon

Why are you registering this callback in a daemon? Most of the events it delivers aren’t relevant in that context.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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Answer 4

kithrup OP

May ’22

As usual, I probably WAY overthought it, and did:

        dispatch_async(dispatch_get_main_queue(), ^{
            NSRunLoop *myLoop = NSRunLoop.currentRunLoop;
            OSStatus kr = SecKeychainAddCallback(MyKeychainEventCallback, kSecEveryEventMask, NULL);
            while (1) {
                // Keep running, restarting every 10 minutes. We could make
                // this a lot longer, though.
                [myLoop runUntilDate:[NSDate dateWithTimeIntervalSinceNow:600]];
            }
        });

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