I had no problems hijacking function with Detours for a long time... When I tried to hijack class methods (in my case IHTMLDocument2::write from mshtml.dll) I encountered endless problems (mainly type mismatching). As I didn't find any relevant example on the net I began doubting this can be done.
My question is: is it possible to hijack class methods with Detours? Can I have an example, please? If not, is it possible to hijack class methods in a simpler way with another hooking library?
Thanks in advance guys!
IHTMLDocument2::write is not just a class method; it's a COM method. That implies a whole lot more. For instance, there's also an equivalent C declaration. You can use that C signature when detouring the method; it's still the same function.
http://pastebin.com/f6559d448
Yeah!
Related
In this example...
http://www.sqlite.org/quickstart.html
...I see how to use sqlite3_exec() with a callback class method or function in order to get a recordset and iterate through it.
Well, what if I want to create a class DB and have a static class method
static void * getRS(void *hDB,std::string sSQL) ?
I'm kind of new with C++ but getting the hang of it extremely rapidly. Is there a way in C++ to create like a Lambda function, get the results from that, and pass them back? Or, is there another technique to return a std::map, std::multimap, etc. that I can iterate through each row?
(Note, I'm using XCode and calling C++ from a db.static.mm file in my Objective C project, if that matters.)
This question is not a duplicate of sqlite3_exec() Callback function Clarification. In that question, the author asks essentially how the callback is used in sqlite3_exec(). In my question, I'm asking how to do a top-down approach of SQLite3 code instead of using a callback. It just so happens that someone left an answer (not the approved answer, mind you) that solves my problem, not that author's problem.
The best solution to do this in a top-down (rather than callback) manner is to not use sqlite3_exec(). Instead, do it with sqlite3_prepare_v2(), sqlite3_step(), and then sqlite3_finalize(). Optionally, one can inject/bind query parameters with various sqlite3_bind_*() calls.
Here's an example of the proper code for that.
In this code headerTable and rowsTable are Java Objects. Here the same method with the same argument is being called on them:
(.setHorizontalAlignment headerTable Element/ALIGN_LEFT)
(.setHorizontalAlignment rowsTable Element/ALIGN_LEFT)
Is there a better way of doing this? I would think there must be a way to combine the two calls into one somehow. But since this is 'side effecting' code, perhaps not??
I'm thinking of an answer without writing a custom function or macro, something like "just use juxt or comp", but then maybe I'm being a bit too prescriptive...
Edit Type hinting was mentioned by Leonid Beschastny, so just in case it helps, here's the Java method signature:
public void setHorizontalAlignment(int horizontalAlignment)
And the class is PdfPTable, from iText. (This code is being used to create PDF files).
There are many possible refactorings, one would be
(run! #(.setHorizontalAlignment ^PdfPTable % Element/ALIGN_LEFT)
[headerTable rowsTable])
So I've decided to investigate using seams in PHPUnit, but I came across a problem
I rearranged my class in a way that I broke the dependencies to database class
db_Class::getMyData($vars);
became
self::getMyData($vars);
and I added functions to my code
protected static function getMyData($vars) {
return db_Class::getMyData($vars);
}
This was done so I can make a class that inherits this class and overloads the getMyData function. To be able to alter it when I run my test cases.
So for example in the seam class that extends the class above and overloads that function:
protected static function getMyData($vars) {
return array('id'=>1, 'name'=>"My Name");
}
This would be very useful, as I can alter the data as I like. However when using PHPUnit you have the possibility to run mocks using $this->getMock and similar. Would I ever be able to achieve this inside the seam class.
I'm trying to look for a solution where I am not using a dependency injector, which would be my other alternative, not so bad at all, just want to evaluate both alternatives.
Michael C. Feathers expressed a seam to be the following:
A seam is a place where you can alter behavior in your program without editing in that place.
So I might not get the full picture, and I've been trying to get it for a while now, and I just cant get my head around it. Please comment if you have any ideas or questions.
What I ask for is a way to work with mocks easy in different scenarios. I dont always want to return the same value in the seam, sometimes I want to return null to get an error, and sometimes an array with correct data, and sometimes something else probably.
Thanks
Because you must reference the class directly when calling static methods, you cannot override them as you can non-static methods. Static methods make testing difficult. I won't bother repeating what's written there, and I highly recommend following the links in the answers.
In any case, why is that method static? Being protected, you can call it only from the same class or its subclasses. Can you post more of the context here? How do you intend to use it, and where will you test it? Can you change it to non-static?
I found an answer to my question here:
http://sebastian-bergmann.de/archives/885-Stubbing-Hard-Coded-Dependencies.html
The idea here is that you can prepare testable version of X where only thing overriden will be getMyData:
protected static function getMyData($vars) {
return $some_dummy_data;
}
You write tests for X indirectly trough TestX.
Now lets assume that you change something in original X that breaks it. TestX does inherit that broken code, thus its tests fail. Exactly what we wanted!
I have a function (actually from ATL, it is ATL::CSoapMSXMLInetClient::SendRequest(LPCTSTR)) whose behaviour should slightly be modified. That is, I just have to add one function call somewhere in the middle of the function.
Taking into consideration that this is not a template method, what is the best practice of changing its behaviour? Do I have to re-write the whole function?
Thanks in advance.
EDIT: Deriving from the class ATL::CSoapMSXMLInetClient and copy-pasting whole function code with a slight modification in subclass function definition does not work because most of the members used in ATL::CSoapMSXMLInetClient::SendRequest are "private" and accessing them in subclass is a compile time error.
Rather than best practice I am looking for a way to do it now, if there is any. :(
Yes you will. If it's in the middle of the function there is no way of getting around it.
There are some refactoring methods you can use. But I cannot think of any pretty ones, and all depend heavily on the code within the class, although for you case it might be tough to find any that works.
Like if you have a line:
do_frobnicate();
dingbat->pling();
And you need to call somefunc() after the dingbat plings. You can, if the dingbat is an interface that you provide, make a new dingbat that also do somefunc() when it plings. Given that the only place this dingbat plings is in this function.
Also, if do_frobnicate() is a free function and you want to add the somefunc() after this, you could create a function within the class, or within its namespace that is called the same. That way you make your own do_frobnicate() that also does somefunc().
in C++, I can easily create a function pointer by taking the address of a member function. However, is it possible to change the address of that local function?
I.e. say I have funcA() and funcB() in the same class, defined differently. I'm looking to change the address of funcA() to that of funcB(), such that at run time calling funcA() actually results in a call to funcB(). I know this is ugly, but I need to do this, thanks!
EDIT----------
Background on what I'm trying to do:
I'm hoping to implement unit tests for an existing code base, some of the methods in the base class which all of my modules are inheriting from are non-virtual. I'm not allowed to edit any production code. I can fiddle with the build process and substitute in a base class with the relevant methods set to virtual but I thought I'd rather use a hack like this (which I thought was possible).
Also, I'm interested in the topic out of technical curiosity, as through the process of trying to hack around this problem I'm learning quite a bit about how things such as code generation & function look-up work under the hood, which I haven't had a chance to learn in school having just finished 2nd year of university. I'm not sure as to I'll ever be taught such things in school as I'm in a computer engineering program rather than CS.
Back on topic
The the method funcA() and funcB() do indeed have the same signature, so the problem is that I can only get the address of a function using the & operator? Would I be correct in saying that I can't change the address of the function, or swap out the contents at that address without corrupting portions of memory? Would DLL injection be a good approach for a situation like this if the functions are exported to a dll?
No. Functions are compiled into the executable, and their address is fixed throughout the life-time of the program.
The closest thing is virtual functions. Give us an example of what you're trying to accomplish, I promise there's a better way.
It cannot be done the way you describe it. The only way to change the target for a statically bound call is by modifying the actual executable code of your program. C++ language has no features that could accomplish that.
If you want function calls to be resolved at run-time you have to either use explicitly indirect calls (call through function pointers), or use language features that are based on run-time call resolution (like virtual functions), or you can use plain branching with good-old if or switch. Which is more appropriate in your case depends on your specific problem.
Technically it might be possible for virtual functions by modifying the vtable of the type, but you most certainly cannot do it without violating the standard (causing Undefined Behavior) and it would require knowledge of how your specific compiler handles vtables.
For other functions it is not possible because the addresses of the functions are directly written to program code, which is generally on a read-only memory area.
I am fairly sure this is impossible in pure C++. C++ is not a dynamic language.
What you want is a pointer to a function, you can point it to FuncA or FuncB assuming that they have the same signature.
You cannot do what you want to do directly. However, you can achieve a similar result with some slightly different criteria, using something you are already familiar with -- function pointers. Consider:
// This type could be whatever you need, including a member function pointer type.
typedef void (*FunctionPointer)();
struct T {
FunctionPointer Function;
};
Now you can set the Function member on any given T instance, and call it. This is about as close as you can reasonably get, and I presume that since you are already aware of function pointers you're already aware of this solution.
Why don't you edit your question with a more complete description of the problem you're trying to solve? As it stands it really sounds like you're trying to do something horrible.
Its simple!
For
at run time calling funcA() actually results in a call to funcB().
write funcA() similar to following:
int funcA( int a, int b) {
return funcB( a, b );
}
:-)