macOS Sleep/ Wake notifications in golang

While working on my golang chime SDK I ran across the issue of properly reconnecting when macOS wakes up from sleep mode. Apple provides an official example using IOKit, so I had to wrap this with cgo to use it. This post outlines the required steps and provides an example implementation.

1. write a small wrapper to register/ unregister notifications

   # main.h
   
   #include <ctype.h>
   #include <stdlib.h>
   #include <stdio.h>
   
   #include <mach/mach_port.h>
   #include <mach/mach_interface.h>
   #include <mach/mach_init.h>
   
   #include <IOKit/pwr_mgt/IOPMLib.h>
   #include <IOKit/IOMessage.h>
   
   io_connect_t root_port;
   IONotificationPortRef notifyPortRef;
   io_object_t notifierObject;
   void *refCon;
   CFRunLoopRef runLoop;
   
   void MySleepCallBack(void *refCon, io_service_t service, natural_t messageType, void *messageArgument) {
       switch (messageType) {
       case kIOMessageCanSystemSleep:
           if (CanSleep()) {
               IOAllowPowerChange(root_port, (long)messageArgument);
           } else {
               IOCancelPowerChange(root_port, (long)messageArgument);
           }
   
           break;
       case kIOMessageSystemWillSleep:
           WillSleep();
           IOAllowPowerChange(root_port, (long)messageArgument);
           break;
       case kIOMessageSystemWillPowerOn:
           WillWake();
           break;
       case kIOMessageSystemHasPoweredOn:
           break;
       default:
           break;
       }
   }
   
   // registerNotifications is called from go to register wake/sleep notifications
   void registerNotifications() {
       root_port = IORegisterForSystemPower(refCon, &notifyPortRef, MySleepCallBack, &notifierObject);
       if (root_port == 0) {
           printf("IORegisterForSystemPower failed\n");
       }
   
       CFRunLoopAddSource(CFRunLoopGetCurrent(),
                       IONotificationPortGetRunLoopSource(notifyPortRef), kCFRunLoopCommonModes);
   
       runLoop = CFRunLoopGetCurrent();
       CFRunLoopRun();
   }
   
   // unregisterNotifications is called from go to remove wake/sleep notifications
   void unregisterNotifications() {
       CFRunLoopRemoveSource(runLoop,
                           IONotificationPortGetRunLoopSource(notifyPortRef),
                           kCFRunLoopCommonModes);
   
       IODeregisterForSystemPower(&notifierObject);
       IOServiceClose(root_port);
       IONotificationPortDestroy(notifyPortRef);
       CFRunLoopStop(runLoop);
   }
   

2. Expose go functions to cgo, so that we can call into existing go code for network reconnection handling:

   # gofuncs.go
   
   package main
   
   import (
       "C"
       "log"
   )
   
   //export CanSleep
   func CanSleep() C.int {
       return 1
   }
   
   //export WillWake
   func WillWake() {
       log.Printf("Will Wake")
   }
   
   //export WillSleep
   func WillSleep() {
       log.Printf("Will Sleep")
   }
   

3. Use the notification handler:

   package main
   
   // #cgo LDFLAGS: -framework CoreFoundation -framework IOKit
   // int CanSleep();
   // void WillWake();
   // void WillSleep();
   // #include "main.h"
   import "C"
   import (
       "log"
       "time"
   )
   
   func main() {
       go func() {
           C.registerNotifications()
           log.Printf("Go bye")
       }()
   
       log.Printf("Hello, World")
       time.Sleep(time.Minute)
       C.unregisterNotifications()
       time.Sleep(time.Minute)
   }
   

that’s it - actually quite simple. The trickiest part was getting the LDFLAGS right. Hopefully I won’t need to look this up the next time I need it :)