C#: "Using" Statements with HttpWebRequests/HttpWebResponses

Question

Jon Skeet made a comment (via Twitter) on my SOApiDotNet code (a .NET library for the pre-alpha Stack Overflow API):

@maximz2005 One thing I've noticed just from browsing the source quickly: you don't disposed (sic) of WebResponses. "using" statements FTW.

He indicates that I need to wrap these Web sessions in "using" statements. However, I have a question about this: should I wrap the whole thing, starting with the HttpWebRequest, or should I create the WebRequest outside of the "using" statement and then wrap the Response inside? I have a feeling that the difference is that, in the former, both objects would be disposed of - is this correct?

Thanks in advance.

Solution 1

HttpWebRequest itself is not disposable unlike HttpWebResponse. You should wrap disposable resources with using to allow early and determined cleanup. Correctly implemented IDisposable pattern allows multiple calls to Dispose without any issues so even the outer using statement wraps resource that during its own dispose disposes inner using statement resource it is still ok.

Code example

var request = (HttpWebRequest)WebRequest.Create("example.com"); 
using (var response = (HttpWebResponse)request.GetResponse()) 
{ 
    // Code here 
}

Solution 2

Everything wrapped in a using () {} block (that is, inside of the first brackets) is disposed when you leave the scope.

I haven't used your library so far (seems nice though), but I'd argue that you should explicitly dispose every IDisposable you create (= are responsible for) and don't return to a caller.

A sidenote, since I've seen a lot of people struggling with multiple things to dispose: Instead of

using (var foo = SomeIDisposable) {
  using (var bar = SomeOtherIDisposable) {
  }
}

which needs a lot of vertical space you can write

using (var foo = SomeIDisposable)
using (var bar = SomeOtherIDisposable) {
}

Solution 3

In order to prevent memory leaks you should call Dispose on every object that implements IDisposable. You can ensure that the Dispose method in called by using the using keyword (no pun intended) as it is just a syntactic sugar for try-finally block.

Comments

[Maxim Zaslavsky]

So should I declare ..Request outside, or what?

[Benjamin Podszun]

Yes, that means you'd do a var request = (HttpWebRequest)WebRequest.Create("example.com"); using (var response = (HttpWebResponse)request.GetResponse()) { // Code here }

[Jan Jongboom]

@Dzmitry, @Benjamin. I added Benjamin's code example to your answer.

[Tomas]

Your second paragraph (which is correct, I believe) contradicts the first. If everything inside the using-block is disposed, you wouldn't need the inner using statement.

[Benjamin Podszun]

See my updated post: Everything inside of using (...) is disposed when you leave the following block (this part: { ... })