Do we need to close the System.Net.WebRequest's ResponseStream?

Question

I was wondering will I end up having any unclosed streams from this code:

   Public Function [Get](ByVal url As String) As String
        Using reader = New System.IO.StreamReader(System.Net.WebRequest.Create(url).GetResponse.GetResponseStream)
            Return reader.ReadToEnd
        End Using
    End Function

What about this:

  Public Function Get2(ByVal url As String) As String
        Using stream = System.Net.WebRequest.Create(url).GetResponse.GetResponseStream
            Using reader = New System.IO.StreamReader(stream)
                Return reader.ReadToEnd
            End Using
        End Using
    End Function

Basically, do we need to close the System.Net.WebRequest's ResponseStream ?

No you don't need to close it, using is a wrapper for try{ Stream stream; ... }catch {..} finally { if (stream != null) { stream.Close(); } } — Alan Turing, Sep 12 '11 at 10:54
@Artur: I think you've misunderstood the question - it's not about whether you need to explicitly call Close, it's whether closing the StreamReader (via a using statement) is enough to close the stream and the WebResponse. — Jon Skeet, Sep 12 '11 at 11:08
@Artur: `using` finally calls `Dispose()` on the object, not `Close()`. Disposing an object should close open resources, but `using` doesn't do so directly. — Suncat2000, May 09 '19 at 11:44

Jon Skeet · Accepted Answer · 2011-09-12T11:03:35.493

You either need to close the response stream or you need to close the response. Note that closing a StreamReader wrapping a Stream will close the stream anyway, so the first version should be okay. (Note that I'm deeming "dispose with a Using statement" to be semantically equal to "close in a finally block" - there's no benefit in explicitly calling Close instead of just disposing of the stream or response.)

I believe that closing the stream is good enough - that you don't need to close the response as well - and indeed that's what MSDN states, but personally I'd do so for clarity:

Public Function [Get](ByVal url As String) As String
    Using response = WebRequest.Create(url).GetResponse
        Using reader = New System.IO.StreamReader(response.GetResponseStream)
            Return reader.ReadToEnd
        End Using
    End Using
End Function

(There's a theoretical benefit here that it will close the response if GetResponse returns successfully but either GetResponseStream or the StreamReader constructor throws an exception. I don't expect that to have any practical implications.)

If you don't close anything, you could very easily run into timeouts in future requests to the same host - the "open" response will essentially hog the connection to that host, and by default there's a limit of two open connections per host. This is a very common cause of timeouts - there are lots of SO questions where folks are getting timeouts due to not closing anything.

@Artur: Which bit? I'm very well aware of what a Using statement means in IL - which bit of my answer goes against that? — Jon Skeet, Sep 12 '11 at 11:06

score 2 · Answer 2 · answered Sep 12 '11 at 10:52

2

It is not necessary to call the Close method on the WebResponse, but doing so is not harmful

http://msdn.microsoft.com/en-us/library/debx8sh9.aspx

answered Sep 12 '11 at 10:52

Massimiliano Peluso

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Doing this will show up the bad knowledge of C# language specification, ECMA standart. Again, using statement is a syntax shugar wrapper for try { Stream stream; ... } catch {..} finally { if (stream != null) { stream.Close(); } } block. – Alan Turing Sep 12 '11 at 10:59
I agree you but I was just reporting what MSDN says about that – Massimiliano Peluso Sep 12 '11 at 11:53

Do we need to close the System.Net.WebRequest's ResponseStream?

2 Answers2