launchk VS rust-block

I wondered if there was something similar to LaunchControl that could run in a terminal. I've used chkservice on Linux, but there seems to be no macOS equivalent. I've been dying for an excuse to learn a little bit of Rust (loved n+1 years in a row by the SO developer survey2) -- so this was my chance. Several months later I ended up with launchk. The rest of this post will go over: getting started, interfacing with launchd, a lot of macOS IPC bits, getting stuck, and a bunch of probably questionable Rust FFI stuff.

let block = ConcreteBlock::new(move |key: *const c_char, value: xpc_object_t| { unsafe { xpc_retain(value) }; let str_key = unsafe { CStr::from_ptr(key).to_string_lossy().to_string() }; let xpc_object: XPCObject = value.into(); map_refcell .borrow_mut() .insert(str_key, xpc_object.into()); true }); // https://github.com/SSheldon/rust-block#creating-blocks let block = block.copy(); let ok = unsafe { xpc_dictionary_apply(object.as_ptr(), &*block as *const _ as *mut _) };