# BlockHook
**Repository Path**: leegithub/BlockHook
## Basic Information
- **Project Name**: BlockHook
- **Description**: Hook Objective-C blocks with libffi. It's a powerful AOP tool for blocks. BlockHook can run your code before/instead/after invoking a block. BlockHook can even notify you when a block dealloc.
- **Primary Language**: Objective-C
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No
## Statistics
- **Stars**: 0
- **Forks**: 0
- **Created**: 2021-07-27
- **Last Updated**: 2022-04-06
## Categories & Tags
**Categories**: Uncategorized
**Tags**: None
## README
[](http://cocoapods.org/pods/BlockHook)
[](https://travis-ci.org/yulingtianxia/BlockHook)
[](http://cocoapods.org/pods/BlockHook)
[](https://github.com/Carthage/Carthage)
[](https://codecov.io/gh/yulingtianxia/BlockHook)
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[](https://github.com/yulingtianxia/BlockHook/releases)
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# BlockHook
Hook Objective-C blocks with libffi. It's a powerful AOP tool for blocks. BlockHook can run your code before/instead/after invoking a block. BlockHook can even notify you when a block dealloc. You can trace the whole lifecycle of a block using BlockHook!
**Want to hook blocks passing to methods? Try [BlockTracker](https://github.com/yulingtianxia/BlockTracker)!**
## 🌟 Features
- [x] Easy to use. Keep your code clear.
- [x] Support 4 hook modes: Before, Instead, After and Dead.
- [x] Let you modify return value and arguments.
- [x] Support invoking original implementation.
- [x] Remove hook at any time.
- [x] Traverse all hook tokens of block.
- [x] Provide block mangle name.
- [x] Self-managed tokens.
- [x] Support custom struct.
- [x] Support Carthage & CocoaPods.
## 🔮 Example
BlockHook needs libffi, which supports iOS, tvOS and macOS.
You can run `BlockHookSample iOS`, `BlockHookSample tvOS` or `BlockHookSample macOS` target.
## 🐒 How to use
### Just Hook
You can hook a block using 4 modes (before/instead/after/dead). This method returns a `BHToken` instance for more control. You can `remove` a `BHToken`, or set custom return value to its `retValue` property. Calling `invokeOriginalBlock` method will invoke original implementation of the block.
```objc
- (BHToken *)block_hookWithMode:(BlockHookMode)mode
usingBlock:(id)block
```
BlockHook is easy to use. Its APIs take example by Aspects. [Here](https://github.com/yulingtianxia/BlockHook/blob/master/BlockHookSampleTests/BlockHookSampleTests.m) is a full set of usage of BlockHook.
This is an example for hooking block in all modes. You can change block return value from 8 to 15. Then remove some hook and check if it is successful. Finally we get callback when block dealloc.
```objc
NSObject *z = NSObject.new;
int(^block)(int x, int y) = ^int(int x, int y) {
int result = x + y;
NSLog(@"%d + %d = %d, z is a NSObject: %@", x, y, result, z);
return result;
};
BHToken *token = [block block_hookWithMode:BlockHookModeDead|BlockHookModeBefore|BlockHookModeInstead|BlockHookModeAfter usingBlock:^(BHInvocation *invocation, int x, int y) {
int ret = 0;
[invocation getReturnValue:&ret];
switch (invocation.mode) {
case BlockHookModeBefore:
// BHInvocation has to be the first arg.
NSLog(@"hook before block! invocation:%@", invocation);
break;
case BlockHookModeInstead:
[invocation invokeOriginalBlock];
NSLog(@"let me see original result: %d", ret);
// change the block imp and result
ret = x * y;
[invocation setReturnValue:&ret];
NSLog(@"hook instead: '+' -> '*'");
break;
case BlockHookModeAfter:
// print args and result
NSLog(@"hook after block! %d * %d = %d", x, y, ret);
break;
case BlockHookModeDead:
// BHInvocation is the only arg.
NSLog(@"block dead! token:%@", invocation.token);
break;
default:
break;
}
}];
NSLog(@"hooked block");
int ret = block(3, 5);
NSLog(@"hooked result:%d", ret);
// remove token.
[token remove];
NSLog(@"remove tokens, original block");
ret = block(3, 5);
NSLog(@"original result:%d", ret);
```
Here is the log:
```
hooked block
hook before block! invocation:
3 + 5 = 8, z is a NSObject:
let me see original result: 0
hook instead: '+' -> '*'
hook after block! 3 * 5 = 15
hooked result:15
block dead! token:
remove tokens, original block
3 + 5 = 8, z is a NSObject:
original result:8
```
### Block Interceptor
Sometimes you want user login first before routing to other components. To intercept a block without hacking into code of routers, you can use block interceptor.
```objc
NSObject *testArg = [NSObject new];
NSObject *testArg1 = [NSObject new];
NSObject *(^testblock)(NSObject *) = ^(NSObject *a) {
return [NSObject new];
};
[testblock block_interceptor:^(BHInvocation *invocation, IntercepterCompletion _Nonnull completion) {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSObject * __unsafe_unretained arg;
[invocation getArgument:&arg atIndex:1];
NSLog(@"Original argument:%@", arg);
[invocation setArgument:(void *)&testArg1 atIndex:1];
completion();
});
}];
testblock(testArg);
```
## 📲 Installation
### CocoaPods
[CocoaPods](http://cocoapods.org) is a dependency manager for Cocoa projects. You can install it with the following command:
```bash
$ gem install cocoapods
```
To integrate BlockHook into your Xcode project using CocoaPods, specify it in your `Podfile`:
```
source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'
use_frameworks!
target 'MyApp' do
pod 'BlockHook'
end
```
You need replace "MyApp" with your project's name.
Then, run the following command:
```bash
$ pod install
```
### Carthage
[Carthage](https://github.com/Carthage/Carthage) is a decentralized dependency manager that builds your dependencies and provides you with binary frameworks.
You can install Carthage with [Homebrew](http://brew.sh/) using the following command:
```bash
$ brew update
$ brew install carthage
```
To integrate BlockHook into your Xcode project using Carthage, specify it in your `Cartfile`:
```ogdl
github "yulingtianxia/BlockHook"
```
Run `carthage update` to build the framework and drag the built `BlockHook.framework` into your Xcode project.
### Manual
After importing libffi, just add the two files `BlockHook.h/m` to your project.
## ❤️ Contributed
- If you **need help** or you'd like to **ask a general question**, open an issue.
- If you **found a bug**, open an issue.
- If you **have a feature request**, open an issue.
- If you **want to contribute**, submit a pull request.
## 📚 Article
- [Hook Objective-C Block with Libffi](http://yulingtianxia.com/blog/2018/02/28/Hook-Objective-C-Block-with-Libffi/)
- [BlockHook with Struct](http://yulingtianxia.com/blog/2019/04/27/BlockHook-with-Struct/)
- [BlockHook with Revocation](http://yulingtianxia.com/blog/2019/05/26/BlockHook-with-Revocation/)
- [BlockHook with Private Data](http://yulingtianxia.com/blog/2019/06/19/BlockHook-with-Private-Data/)
- [BlockHook with Invocation(1)](http://yulingtianxia.com/blog/2019/07/27/BlockHook-with-Invocation/)
- [BlockHook with Invocation(2)](http://yulingtianxia.com/blog/2019/08/11/BlockHook-with-Invocation-2/)
- [BlockHook and Memory Safety](http://yulingtianxia.com/blog/2020/05/30/BlockHook-and-Memory-Safety/)
## 👨🏻💻 Author
yulingtianxia, yulingtianxia@gmail.com
## 👮🏻 License
BlockHook is available under the MIT license. See the LICENSE file for more info.
Thanks to MABlockClosure and Aspects!