其实最重要的就是拿到block的方法签名
block的本质也是一个对象，其结构就是LD_Block_literal_1这种，LD_Block_literal_1来源见Block-ABI链接
LD_Block_literal_1就是编译后block的真实结构

/**
 Type Encodings:
 https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html#//apple_ref/doc/uid/TP40008048-CH100
 
 Block-ABI:
 http://clang.llvm.org/docs/Block-ABI-Apple.html
 */
enum {
    // Set to true on blocks that have captures (and thus are not true
    // global blocks) but are known not to escape for various other
    // reasons. For backward compatibility with old runtimes, whenever
    // BLOCK_IS_NOESCAPE is set, BLOCK_IS_GLOBAL is set too. Copying a
    // non-escaping block returns the original block and releasing such a
    // block is a no-op, which is exactly how global blocks are handled.
    LD_BLOCK_IS_NOESCAPE      =  (1 << 23),

    LD_BLOCK_HAS_COPY_DISPOSE =  (1 << 25),
    LD_BLOCK_HAS_CTOR =          (1 << 26), // helpers have C++ code
    LD_BLOCK_IS_GLOBAL =         (1 << 28),
    LD_BLOCK_HAS_STRET =         (1 << 29), // IFF BLOCK_HAS_SIGNATURE
    LD_BLOCK_HAS_SIGNATURE =     (1 << 30),
};

struct LD_Block_literal_1 {
    void *isa; // initialized to &_NSConcreteStackBlock or &_NSConcreteGlobalBlock
    int flags;
    int reserved;
    void (*invoke)(void *, ...);
    struct LD_Block_descriptor_1 {
        unsigned long int reserved;         // NULL
        unsigned long int size;         // sizeof(struct Block_literal_1)
        // optional helper functions
        void (*copy_helper)(void *dst, void *src);     // IFF (1<<25)
        void (*dispose_helper)(void *src);             // IFF (1<<25)
        // required ABI.2010.3.16
        const char *signature;                         // IFF (1<<30)
    } *descriptor;
    // imported variables
};

NSMethodSignature *ld_blockMethodSignature(id block) {
    if (!block) {
        return nil;
    }
    struct LD_Block_literal_1 *_block = (__bridge void *)block;
    if (_block->flags & LD_BLOCK_HAS_SIGNATURE) {
        void *_descriptor = _block->descriptor;
        _descriptor += (2*sizeof(unsigned long int)); // 地址偏移（针对reserved和size）
        if (_block->flags & LD_BLOCK_HAS_COPY_DISPOSE) { // 是否有copy_helper以及dispose_helper这两个函数
            _descriptor += (2*sizeof(void *)); // 地址偏移（针对copy_helper和dispose_helper）
        }
        // 此时_descriptor存储的地址就是signature的地址
        const char *_signature = (const char *)(*(int64_t *)_descriptor);
        // const char *_signature = (*(const char **)_descriptor); //跟上面一句作用相同
        NSLog(@"%s", _signature);
        return [NSMethodSignature signatureWithObjCTypes:_signature];
    }
    return nil;
}

void * _Nullable ld_invokeBlock(id _Nullable block, NSArray * _Nullable arguments) {
    // 调用者自己保证arguments的数量和block中参数的数量相等即可
    NSMethodSignature *_signature = ld_blockMethodSignature(block);
    NSLog(@"%@", _signature);
    NSInvocation *_invocation = [NSInvocation invocationWithMethodSignature:_signature];
    _invocation.target = block;
    NSUInteger numberOfArguments = _signature.numberOfArguments;
    for (int i = 0; i < numberOfArguments - 1; i++) {
        id argument = arguments[i];
        [_invocation setArgument:&argument atIndex:i + 1];
    }
    [_invocation invoke];
    
    const char *type = _signature.methodReturnType;
    if (strcmp(type, "v") == 0) {
        return nil;
    }
    
    void *result = NULL;
    [_invocation getReturnValue:&result];
    return result;
}

//调用示例
int res = ld_invokeBlock(^int(id obj, NSNumber *num) {
        NSLog(@"%p, %@", obj, num);
        return 88;
    }, @[[NSObject new], @66]);