XPC What I Did There?

A whirlwind tour of the XPC API wrapped in a story of learning.

Transcript

1. XPC What I Did There? Mikey Ward / Big Nerd Ranch
3. The best-laid plans of mice. Goal: Mac-native HTTP Proxy like Charles.app • Hijack/inspect HTTP connections • Add itself as the global HTTP proxy • Allow scripting of modifications to requests/responses
4. SystemConfiguration.framework The audience for this document comprises two main groups: •Developers of network configuration or dialer software. •Developers of applications that need to request and use network connections. + (Reachability*) reachabilityWithHostName: (NSString*) hostName; { Reachability* retVal = NULL; SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithName(NULL, [hostName UTF8String]); if(reachability!= NULL) { retVal= [[[self alloc] init] autorelease]; if(retVal!= NULL) { retVal->reachabilityRef = reachability; retVal->localWiFiRef = NO; } } return retVal; }
5. SystemConfiguration.h //     //  Dear  developer:   //     //  Once  you  are  done  trying  to  utilize     //  SystemConfiguration.framework,   //  and  have  realized  what  a  terrible  mistake  that  was,   //  please  increment  the  following  counter  as  a  warning   //  to  the  next  developer:   //     const  NSInteger  totalHoursWasted  =  42;   *Stolen from http://stackoverflow.com/questions/184618/
6. A better way:
7. A better way:
8. NSTask Malcolm.app networksetup
9. Using networksetup with NSTask: + (NSString *)outputOfTaskWithPath:(NSString *)path arguments:(NSArray *)args { NSPipe *pipe = [[NSPipe alloc] init]; NSPipe *resultPipe = [[NSPipe alloc] init]; NSTask *task = [[NSTask alloc] init]; [task setLaunchPath:path]; [task setStandardInput:pipe]; [task setStandardOutput:resultPipe]; [task setArguments:args]; [task launch]; NSData *result = [[resultPipe fileHandleForReading] readDataToEndOfFile]; NSString *resultString = [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding]; return resultString; }
10. GODF%*^&@MMIT
11. sudo make me a proxy NSTask Malcolm.app networksetup
12. A better way?
13. AuthorizationExecuteWithPrivileges() // Create authorization reference AuthorizationRef authorizationRef; OSStatus status; status = AuthorizationCreate( NULL, kAuthorizationEmptyEnvironment, kAuthorizationFlagDefaults, &authorizationRef); // Run the tool using the authorization reference char *tool = "/sbin/dmesg"; char *args[] = {NULL}; FILE *pipe = NULL; status = AuthorizationExecuteWithPrivileges( authorizationRef, tool, kAuthorizationFlagDefaults, args, &pipe); sauce: http://www.michaelvobrien.com/blog/2009/07/authorizationexecutewithprivileges-a-simple-example/
14. LOL AuthorizationExecute WithPrivileges() NSTask Malcolm.app networksetup
15. Authorization Services C Reference
16. A better prayer:
17. Daemons and Services Programming Guide Creating XPC Services The XPC Services API, part of libSystem, provides a lightweight mechanism for basic interprocess communication integrated with Grand Central Dispatch (GCD) and launchd. The XPC Services API allows you to create lightweight helper tools, called XPC services, that perform work on behalf of your application. There are two main reasons to use XPC services: privilege separation and stability.
18. Daemons and Services Programming Guide Other mechanisms for dividing an application into smaller parts, such as NSTask and posix_spawn(2) OS X Developer Tools Manual Page, do not let you put each part of the application in its own sandbox, so it is not possible to use them to implement privilege separation. An XPC service can inherit the sandbox of the main application, or it can have its own sandbox. Putting the XPC service in its own sandbox allows you to implement privilege separation.
19. XPC Malcolm.app [XPC] NSTask networksetup com.malcolm.proxifier
20. XPC Malcolm.app [XPC] NSTask networksetup com.malcolm.proxifier
21. XPC in a Nutshell
22. XPSee and net-service
23. New Target
24. Build Phases
25. Capabilities
26. Fetching an image // In the window controller implementation - (void)loadURL:(NSURL *)url { NSURLSession *session = [NSURLSession sharedSession]; NSURLSessionTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSImage *image = [[NSImage alloc] initWithData:data]; dispatch_async(dispatch_get_main_queue(), ^{ self.imageView.layer.contents = image; }); }]; [task resume]; }
27. Fetching an image
28. Fetching an image // In the window controller implementation - (void)loadURL:(NSURL *)url { NSString *serviceName = @"com.bignerdranch.net-service"; NSXPCConnection *connection = [[NSXPCConnection alloc] initWithServiceName:serviceName]; connection.remoteObjectInterface = [NSXPCInterface interfaceWithProtocol:@protocol(BNRDownload)]; [connection resume]; id downloader = connection.remoteObjectProxy; [downloader downloadImageAtURL:url withReply:^(BNRDownloadedImage *dl, NSError *error) { dispatch_async(dispatch_get_main_queue(), ^{ self.imageView.layer.contents = dl.image; }); }]; }
29. NSSecureCoding / BNRDownloadedImage + (BOOL)supportsSecureCoding { return YES; } - (instancetype)initWithCoder:(NSCoder *)coder { self = [super init]; if (self) { self.sourceURL = [coder decodeObjectOfClass:[NSURL class] forKey:@"sourceURL"]; NSData *data = [coder decodeObjectOfClass:[NSData class] forKey:@"imageData"]; self.image = [NSKeyedUnarchiver unarchiveObjectWithData:data]; } return self; } - (void)encodeWithCoder:(NSCoder *)coder { NSData *data = [NSKeyedArchiver archivedDataWithRootObject:self.image]; [coder encodeObject:data forKey:@"imageData"]; [coder encodeObject:self.sourceURL forKey:@"sourceURL"]; }
30. NSXPCInterface
31. BNRDownload.h @protocol BNRDownload <NSObject> - (void)downloadImageAtURL:(NSURL *)url withReply:(void (^)(BNRDownloadedImage *img, NSError *error))replyBlock; @end
32. net-service’s main()
33. net-service’s main.m int main(int argc, const char *argv[]) { NSXPCListener *listener = [NSXPCListener serviceListener]; BNRConnectionHandler *handler = [[BNRConnectionHandler alloc] init]; listener.delegate = handler; [listener resume]; return 0; }
34. net-service’s BNRConnectionHandler
35. net-service’s BNRConnectionHandler #pragma mark - NSXPCListenerDelegate - (BOOL)listener:(NSXPCListener *)listener shouldAcceptNewConnection:(NSXPCConnection *)newConnection { newConnection.exportedInterface = [NSXPCInterface interfaceWithProtocol:@protocol(BNRDownload)]; newConnection.exportedObject = [[BNRDownloader alloc] init]; [newConnection resume]; return YES; }
36. net-service’s BNRDownloader
37. net-service’s BNRDownloader #pragma mark - BNRDownload Protocol - (void)downloadImageAtURL:(NSURL *)url withReply:(void (^)(BNRDownloadedImage *, NSError *))replyBlock { NSURLSession *session = [NSURLSession sharedSession]; NSURLSessionTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSImage *image = [[NSImage alloc] initWithData:data]; BNRDownloadedImage *dl = [BNRDownloadedImage new]; dl.image = image; dl.sourceURL = url; dispatch_async(dispatch_get_main_queue(), ^{ if (replyBlock) { replyBlock(dl, error); } }); }]; [task resume]; }
38. XPC, folks.
39. ...meanwhile...
40. Understanding the Structure and Behavior XPC services are managed by launchd, which launches them on demand, restarts them if they crash, and terminates them (by sending SIGKILL) when they are idle. This is transparent to the application using the service, except for the case of a service that crashes while processing a message that requires a response. In that case, the application can see that its XPC connection has become invalid until the service is restarted by launchd. Because an XPC service can be terminated suddenly at any time, it must be designed to hold on to minimal state—ideally, your service should be completely stateless, although this is not always possible. By default, XPC services are run in the most restricted environment possible—sandboxed with minimal filesystem access, network access, and so on. Elevating a service’s privileges to root is not supported. Further, an XPC service is private, and is available only to the main application that contains it. Privelege separation
41. Understanding the Structure and Behavior XPC services are managed by launchd, which launches them on demand, restarts them if they crash, and terminates them (by sending SIGKILL) when they are idle. This is transparent to the application using the service, except for the case of a service that crashes while processing a message that requires a response. In that case, the application can see that its XPC connection has become invalid until the service is restarted by launchd. Because an XPC service can be terminated suddenly at any time, it must be designed to hold on to minimal state—ideally, your service should be completely stateless, although this is not always possible. By default, XPC services are run in the most restricted environment possible—sandboxed with minimal filesystem access, network access, and so on. Elevating a service’s privileges to root is not supported. Further, an XPC service is private, and is available only to the main application that contains it. Privelege separation
42. XPC Malcolm.app [XPC] NSTask networksetup com.malcolm.proxifier LOLNOPE
43. A better… you know what? Fudge it.
45. ServiceManagement.h Reference
46. ServiceManagement.h Reference /Library/PrivilegedHelperTools/com.xpsee.net-service
47. Fetching an image
48. - (BOOL)blessTheChild { BOOL result = NO; AuthorizationItem authItem = { kSMRightBlessPrivilegedHelper, 0, NULL, 0 }; AuthorizationRights authRights = { 1, &authItem }; AuthorizationFlags flags = (kAuthorizationFlagDefaults | kAuthorizationFlagInteractionAllowed | kAuthorizationFlagPreAuthorize | kAuthorizationFlagExtendRights); AuthorizationRef authRef = NULL; OSStatus status = AuthorizationCreate( &authRights, kAuthorizationEmptyEnvironment, flags, &authRef); if (status == errAuthorizationSuccess){ result = SMJobBless( kSMDomainSystemLaunchd, “com.bignerdranch.net-service”, authRef, NULL); } return result; } Using SMJobBless() #import <ServiceManagement/ServiceManagement.h>
49. Fetching an image with an XPC service // In the window controller implementation - (void)loadURL:(NSURL *)url { NSString *serviceName = @"com.bignerdranch.net-service"; NSXPCConnection *connection = [[NSXPCConnection alloc] initWithServiceName:serviceName]; connection.remoteObjectInterface = [NSXPCInterface interfaceWithProtocol:@protocol(BNRDownload)]; [connection resume]; id downloader = connection.remoteObjectProxy; [downloader downloadImageAtURL:url withReply:^(BNRDownloadedImage *dl, NSError *error) { dispatch_async(dispatch_get_main_queue(), ^{ self.imageView.layer.contents = dl.image; }); }]; }
50. Fetching an image with a mach service // In the window controller implementation - (void)loadURL:(NSURL *)url { [self blessTheChild]; NSString *serviceName = @"com.bignerdranch.net-service"; NSXPCConnection *connection = [[NSXPCConnection alloc] initWithMachServiceName:serviceName options:NSXPCConnectionPrivileged]; connection.remoteObjectInterface = [NSXPCInterface interfaceWithProtocol:@protocol(BNRDownload)]; [connection resume]; id downloader = connection.remoteObjectProxy; [downloader downloadImageAtURL:url withReply:^(BNRDownloadedImage *dl, NSError *error) { dispatch_async(dispatch_get_main_queue(), ^{ self.imageView.layer.contents = dl.image; }); }]; }
51. Creating a mach service for XPC
52. Main app’s info.plist
53. Helper’s info.plist
54. Helper’s Launchd.plist
55. Main app’s build phases
56. XPC Malcolm.app [XPC] NSTask networksetup com.malcolm.proxifier
57. XPC What I Did There? Mikey Ward / Big Nerd Ranch (or, “How I Learned to Stop Worrying and Love the Docs”) @wookiee / ward@bignerdranch.com