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Introduction to CaptainHook

CaptainHook is a generic hooking framework for the Objective-C 2.0 runtime designed to make hooking methods simple.

Basic Setup

#import <CaptainHook/CaptainHook.h>

Initializes CaptainHook so the fun can begin.

Declaring Classes

Classes must be declared and loaded before they can be used with CaptainHook. CHConstructor blocks denote code that will be run as soon as the binary is loaded.

#import <CaptainHook/CaptainHook.h>
CHDeclareClass(NSString);
CHConstructor {
  CHLoadLateClass(NSString);
}

Method Hooking

Standard Method

Methods are hooked by first declaring a method using CHMethod, and then registering it in a constructor using CHHook:

#import <CaptainHook/CaptainHook.h>
CHDeclareClass(NSString);
CHMethod(2, void, NSString, writeToFile, NSString *, path, atomically, BOOL, flag)
{
    NSLog(@"Writing string to %@: %@", path, self);
    CHSuper(2, NSString, writeToFile, path, atomically, flag);
}

CHConstructor
{
    CHLoadClass(NSString);
    CHHook(2, NSString, writeToFile, atomically);
}

Simpler Method

A simpler syntax may be used, but it is slightly less efficient and offers no control over when the hooks get registered:

#import <CaptainHook/CaptainHook.h>
CHDeclareClass(NSString);
CHDeclareMethod(2, void, NSString, writeToFile, NSString *, path, atomically, BOOL, flag)
{
    NSLog(@"Writing string to %@: %@", path, self);
    CHSuper(2, NSString, writeToFile, path, atomically, flag);
}

New Classes at Runtime

New Classes may be created at runtime by using the CHRegisterClass macro:

#import <CaptainHook/CaptainHook.h>
CHDeclareClass(NSObject);
CHDeclareClass(MyNewClass);
CHMethod(0, id, MyNewClass, init)
{
    if ((self = CHSuper(0, MyNewClass, init))) {
        NSLog(@"Initted MyNewClass");
    }
    return self;
}

CHConstructor
{
    CHAutoreleasePoolForScope();
    CHLoadClass(NSObject);
    CHRegisterClass(MyNewClass, NSObject) {
        CHHook(0, MyNewClass, init);
    }
    [CHAlloc(MyNewClass) autorelease];
}

This works even for classes that can’t be linked