The following contents are taken from iOS App Reverse Engineering
Create tweak project “iOSREMadridMessenger”
snakeninnys-MacBook:Code snakeninny$ /opt/theos/bin/nic.pl
NIC 2.0 - New Instance Creator
------------------------------
[1.] iphone/application
[2.] iphone/cydget
[3.] iphone/framework
[4.] iphone/library
[5.] iphone/notification_center_widget
[6.] iphone/preference_bundle
[7.] iphone/sbsettingstoggle
[8.] iphone/tool
[9.] iphone/tweak
[10.] iphone/xpc_service
Choose a Template (required): 9
Project Name (required): iOSREMadridMessenger
Package Name [com.yourcompany.iosremadridmessenger]: com.iosre.iosremadridmessenger
Author/Maintainer Name [snakeninny]: snakeninny
[iphone/tweak] MobileSubstrate Bundle filter [com.apple.springboard]: com.apple.MobileSMS
[iphone/tweak] List of applications to terminate upon installation (space-separated, '-' for none) [SpringBoard]: MobileSMS
Instantiating iphone/tweak in iosremadridmessenger/...
Done.
Compose iOSREMadridMessenger.h
@interface IDSIDQueryController
+ (instancetype)sharedInstance;
- (NSDictionary *)_currentIDStatusForDestinations:(NSArray *)arg1 service:(NSString *)arg2 listenerID:(NSString *)arg3;
@end
@interface IMServiceImpl : NSObject
+ (instancetype)iMessageService;
@end
@class IMHandle;
@interface IMAccount : NSObject
- (IMHandle *)imHandleWithID:(NSString *)arg1 alreadyCanonical:(BOOL)arg2;
@end
@interface IMAccountController : NSObject
+ (instancetype)sharedInstance;
- (IMAccount *)__ck_defaultAccountForService:(IMServiceImpl *)arg1;
@end
@interface IMMessage : NSObject
+ (instancetype)instantMessageWithText:(NSAttributedString *)arg1 flags:(unsigned long long)arg2;
@end
@interface IMChat : NSObject
- (void)sendMessage:(IMMessage *)arg1;
@end
@interface IMChatRegistry : NSObject
+ (instancetype)sharedInstance;
- (IMChat *)chatForIMHandle:(IMHandle *)arg1;
@end
Edit Tweak.xm
#import "iOSREMadridMessenger.h"
%hook SMSApplication
%new
- (int)madridStatusForAddress:(NSString *)address
{
NSString *formattedAddress = nil;
if ([address rangeOfString:@"@"].location != NSNotFound) formattedAddress = [@"mailto:" stringByAppendingString:address];
else formattedAddress = [@"tel:" stringByAppendingString:address];
NSDictionary *status = [[IDSIDQueryController sharedInstance] _currentIDStatusForDestinations:@[formattedAddress] service:@"com.apple.madrid" listenerID:@"__kIMChatServiceForSendingIDSQueryControllerListenerID"];
return [status[formattedAddress] intValue];
}
%new
- (void)sendMadridMessageToAddress:(NSString *)address withText:(NSString *)text
{
IMServiceImpl *service = [IMServiceImpl iMessageService];
IMAccount *account = [[IMAccountController sharedInstance] __ck_defaultAccountForService:service];
IMHandle *handle = [account imHandleWithID:address alreadyCanonical:NO];
IMChat *chat = [[IMChatRegistry sharedInstance] chatForIMHandle:handle];
NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:text];
IMMessage *message = [IMMessage instantMessageWithText:attributedString flags:1048581];
[chat sendMessage:message];
[attributedString release];
}
%end
Edit Makefile
THEOS_DEVICE_IP = iOSIP
ARCHS = armv7 arm64
TARGET = iphone:latest:8.0
include theos/makefiles/common.mk
TWEAK_NAME = iOSREMadridMessenger
iOSREMadridMessenger_FILES = Tweak.xm
iOSREMadridMessenger_PRIVATE_FRAMEWORKS = IDS ChatKit IMCore
include $(THEOS_MAKE_PATH)/tweak.mk
after-install::
install.exec "killall -9 MobileSMS"
Edit control
Package: com.iosre.iosremadridmessenger
Name: iOSREMadridMessenger
Depends: mobilesubstrate, firmware (>= 8.0)
Version: 1.0
Architecture: iphoneos-arm
Description: Detect and send iMessage example
Maintainer: snakeninny
Author: snakeninny
Section: Tweaks
Homepage: http://bbs.iosre.com
You know how to compile and install the tweak. After that test if with Cycript:
FunMaker-5:~ root# cycript -p MobileSMS
cy# [UIApp madridStatusForAddress:@"snakeninny@icloud.com"]
1
cy# [UIApp sendMadridMessageToAddress:@"snakeninny@icloud.com" withText:@"Sent from iOSREMadridMessenger"]
And we’re done 
Here’s how it looks:
The book explains everything in details, please stay tuned and check it out! Cheers!