Why can reflection access protected/private member of class in C#?
Is this not safe for the class, why is reflection given such power? Is this an anti-pattern?
Member accessibility is not a security feature. It is there to protect the programmer against himself or herself. It helps implementing encapsulation but it is by no means a security feature.
Reflection is tedious enough to use so that people normally don't go out of their way to use it to access non-public members. It's also quite slow. Reflection is normally used in special cases only. However, nothing can protect completely against human stupidity, if someone wants to abuse reflection he can easily do it, but even without the reflection API, they can achieve the same thing (if they're running in full trust, that is) if they are determined enough.
This is necessary for scenarios such as remoting, serialization, materialization, etc. You shouldn't use it blindly, but note that these facilities have always been available in any system (essentially, by addressing the memory directly). Reflection simply formalises it, and places controls and checks in the way - which you aren't seeing because you are presumably running at "full trust", so you are already stronger than the system that is being protected.
If you try this in partial trust, you'll see much more control over the internal state.
Is it an anti-pattern?
Only if your code uses it inappropriately. For example, consider the following (valid for a WCF data-contract):
[DataMember]
private int foo;
public int Foo { get {return foo;} set {foo = value;} }
Is it incorrect for WCF to support this? I suspect not... there are multiple scenarios where you want to serialize something that isn't part of the public API, without having a separate DTO. Likewise, LINQ-to-SQL will materialize into private members if you so elect.
Reflection is absolute necessary for a debugger. Imagine that you are stepping through your program and unable to see values of your private variables. That's probably the reason why reflection works in .NET and Java the way it works, to make debugging really easy.
If we wouldn't need debuggers, then I can imagine that reflection would be restricted more in the spirit of OOP.
Related
I ran into, what I thought was a bug is actually, a feature detailed in This post. Can anyone explain to me why this is allowed? It seems like a legacy quirk/bug that became useful.
I'm not sure which part of that you think is a bug, but it has always been possible to access the internals of a class via reflection when you cannot do so at compile time. This is by design. Numerous aspects of the CLR rely on reflection to access fields, such as serialization. The compiled IL needs to be able to access all fields of all objects, or else you couldn't set private fields from within your class.
The access modifiers in C# are not a security mechanism. If you are relying on a field being private to prevent anyone from setting it from the outside, you're doing something wrong. They exist to clearly delineate which parts of your class are it's public contract (and thus, in theory, stable) from those parts that are implementation details (and thus can change without notice.)
If you choose to use reflection to change the internal state of an object, despite all indications that you should leave it alone, you are taking the stability of your application into your own hands, and you get what deserve.
Reflection is allowed only for Full Trust code, so the code already able to do anything (including directly poking in memory of the process). So having supported way of changing values even for private properties does not make code any less secure. It makes reflection API consistent and allows useful scenarios especially for testing.
Is there a reason why I should not be marking everything as public in our intranet reporting app?
No one outside out co will ever have access to this code - we have about 20 projects - mostly small and specific.
Is there really a reason why we should be marking things anything other than public?
I have my own thoughts on this which I'm trying to omit as I want this to be unbiased.
(I have sexed up the title slightly)
Look up Encapsulation and/or "Information Hiding":
In object-oriented programming, information hiding (by way of nesting of types) reduces software development risk by shifting the code's dependency on an uncertain implementation (design decision) onto a well-defined interface. Clients of the interface perform operations purely through it so if the implementation changes, the clients do not have to change.
If you mark the members of every class as public, you're making for a maintenance nightmare where future developers (including yourself) will be unsure on which parts of the class are meant to be permanent (the contract) and which are purely implementation details.
Assuming you mean marking class members/methods as public/private: It is not about security in the sense of someone from outside your organization gaining access to "private" information. It is about teaching the compiler how to detect problems.
For example, say I have a class Account with a member double balance. and member methods Deposit() , Withdraw() and GetBalance() . Calling Deposit() and Withdraw() each does two things: update a table, modify balance
If I leave balance public, a developer (maybe even me) may directly modify the value of balance Now the instance of my class is out of sync with the table. This is a bug. Oh, I'll find the bug eventually - but if balance was private, the compiler would tell me long before run-time.
Using access modifiers correctly really aids the simplicity of your codebase - and its upkeep - as much as code security, which seems to be your concern.
The main reason I can think of would be if you need to perform some checking or other logic when you access variables. This code which you'd normally put into a get or set method would then be by-passable by any developers who make use of the code in the future, but who don't necessarily know the code as well as you?
Also you are making assumptions about the use of the code for which you may not be able to guarantee.
Making the code modular and reusable is always a good goal to aim for, and making everything public could restrict where this code is used?
The word you should look up is "encapsulation". You want to keep the innards of your code private so that other code doesn't depend on how you implemented it.
I assume you are talking about public members in object-oriented programming.
If your apps are small and self-contained, then this probably won't pose much problem. Keep in mind that some things that start small balloon into huge monsters.
For anything of substantial size, the reason to avoid it is that it breaks the object-oriented principles of encapsulation and information hiding. These are important for future maintainability. It is best to keep the interfaces between modules clean and limited. That way you can change the internal implementation without also affecting dozens of dependent modules.
It seems to me that anytime I come across internal calls or types, it's like I hit a road block.
Even if they are accessible in code like open-source, it still feels they are not usable parts of the API code itself. i.e. it's as if they are discouraged to be modified.
Should one keep oneself from using the internal keyword unless it's absolutely necessary?
I am asking this for an open-source API. But still not everyone will want to change the API, but mostly use it to write their own code for the app itself.
There is nothing wrong with having an internal type in your DLL that is not a part of your public API. In fact, if you have anything other than a trivial DLL is more likely a sign of bad design if you don't have an internal type (or at least a non-public type)
Why? Public APIs are a way of exposing the parts of your object model you want a consumer to use. Having an API of entirely public types means that you want the consumer to see literally everything in your DLL.
Think of the versioning issues that come along with that stance. Changing literally anything in your object model is a breaking change. Having internal types allows you great flexibility in your model while avoiding breaking changes to your consumers.
Internal types are types that are explicitly meant to be kept out of the API. You should only mark things internal that you don't want people to see.
My guess is that you're coming across types that are internal, but would have been valuable additions to the public API. I've seen this in quite a few projects. That's a different issue, though - it's really the same issue as whether a private type should have been public.
In general, a good project should have internal or private types. They help implement the required feature set without bloating the public API. Keeping the public API as small as possible to provide the required feature set is part of what makes a library usable.
An API is comprised of its public types and members, anything else is an implementation detail.
That being said, I think that internal types can be very useful especially when you want to return interface types from your API and don't want to expose the concrete types that you have used to implement those interfaces. This gives the API designer a lot of flexibility.
When I attempt to use dotfuscate on my application, I get an application error when I run it.
Dotfuscator (and all obfuscators) are typically safe to run on an application, but they do occasionally cause problems. Without specific details of your problem, it's difficult to diagnose.
However, one common problem with obfuscators is when you mix them with reflection. Since you're changing the type names, but not strings, any time you try to reflect on objects with a specific string name, and use the reflection namespace to construct objects, you'll likely have problems.
Most of the problem I have encountered with obfuscation revolve around types that can't have their name changed, because something needs to reflect on them (your code or the runtime).
for example if you have a class that is being used as a web service proxy, you can't safely obfuscate the class name:
public class MyWebServiceProxy : SoapHttpClientProtocol
{
}
Also some obfuscators can not handle generic methods and classes.
The trick is you need to find these types and prevent the obfuscater from renaming them. This is done with the Obfuscation attribute:
[global::System.Reflection.Obfuscation(Exclude=true, Feature="renaming")]
Another thing that can be a problem with obfuscators is serialization using BinaryFormatter, since it changes the field names. I have some users who use protobuf-net for serialization on their obfuscated code for this reason.
I have wondered about the appropriateness of reflection in C# code. For example I have written a function which iterates through the properties of a given source object and creates a new instance of a specified type, then copies the values of properties with the same name from one to the other. I created this to copy data from one auto-generated LINQ object to another in order to get around the lack of inheritance from multiple tables in LINQ.
However, I can't help but think code like this is really 'cheating', i.e. rather than using using the provided language constructs to achieve a given end it allows you to circumvent them.
To what degree is this sort of code acceptable? What are the risks? What are legitimate uses of this approach?
Sometimes using reflection can be a bit of a hack, but a lot of the time it's simply the most fantastic code tool.
Look at the .Net property grid - anyone who's used Visual Studio will be familiar with it. You can point it at any object and it it will produce a simple property editor. That uses reflection, in fact most of VS's toolbox does.
Look at unit tests - they're loaded by reflection (at least in NUnit and MSTest).
Reflection allows dynamic-style behaviour from static languages.
The one thing it really needs is duck typing - the C# compiler already supports this: you can foreach anything that looks like IEnumerable, whether it implements the interface or not. You can use the C#3 collection syntax on any class that has a method called Add.
Use reflection wherever you need dynamic-style behaviour - for instance you have a collection of objects and you want to check the same property on each.
The risks are similar for dynamic types - compile time exceptions become run time ones. You code is not as 'safe' and you have to react accordingly.
The .Net reflection code is very quick, but not as fast as the explicit call would have been.
I agree, it gives me the it works but it feels like a hack feeling. I try to avoid reflection whenever possible. I have been burned many times after refactoring code which had reflection in it. Code compiles fine, tests even run, but under special circumstances (which the tests didn't cover) the program blows up run-time because of my refactoring in one of the objects the reflection code poked into.
Example 1: Reflection in OR mapper, you change the name or the type of the property in your object model: Blows up run-time.
Example 2: You are in a SOA shop. Web Services are complete decoupled (or so you think). They have their own set of generated proxy classes, but in the mapping you decide to save some time and you do this:
ExternalColor c = (ExternalColor)Enum.Parse(typeof(ExternalColor),
internalColor.ToString());
Under the covers this is also reflection but done by the .net framework itself. Now what happens if you decide to rename InternalColor.Grey to InternalColor.Gray? Everything looks ok, it builds fine, and even runs fine.. until the day some stupid user decides to use the color Gray... at which point the mapper will blow up.
Reflection is a wonderful tool that I could not live without. It can make programming much easier and faster.
For instance, I use reflection in my ORM layer to be able to assign properties with column values from tables. If it wasn't for reflection I have had to create a copy class for each table/class mapping.
As for the external color exception above. The problem is not Enum.Parse, but that the coder didnt not catch the proper exception. Since a string is parsed, the coder should always assume that the string can contain an incorrect value.
The same problem applies to all advanced programming in .Net. "With great power, comes great responsibility". Using reflection gives you much power. But make sure that you know how to use it properly. There are dozens of examples on the web.
It may be just me, but the way I'd get into this is by creating a code generator - using reflection at runtime is a bit costly and untyped. Creating classes that would get generated according to your latest code and copy everything in a strongly typed manner would mean that you will catch these errors at build-time.
For instance, a generated class may look like this:
static class AtoBCopier
{
public static B Copy(A item)
{
return new B() { Prop1 = item.Prop1, Prop2 = item.Prop2 };
}
}
If either class doesn't have the properties or their types change, the code doesn't compile. Plus, there's a huge improvement in times.
I recently used reflection in C# for finding implementations of a specific interface. I had written a simple batch-style interpreter that looked up "actions" for each step of the computation based on the class name. Reflecting the current namespace then pops up the right implementation of my IStep inteface that can be Execute()ed. This way, adding new "actions" is as easy as creating a new derived class - no need to add it to a registry, or even worse: forgetting to add it to a registry...
Reflection makes it very easy to implement plugin architectures where plugin DLLs are automatically loaded at runtime (not explicitly linked at compile time).
These can be scanned for classes that implement/extend relevant interfaces/classes. Reflection can then be used to instantiate instances of these on demand.