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I'm writing an app which uses persistent connections over http - that is, the web server never "finishes" writing to the response stream, and the client app reads data from the response stream as it comes in.

I wrote some .NET 3.5 desktop/winforms apps to confirm that the server & client code works, and then wrote a windows phone app to do the same thing. The only difference between the desktop/phone code was that I set the AllowReadStreamBuffering property to false on the phone.

The phone app worked last night, but today it does not work - when attempting to read the response stream, it hangs until the connection is closed from the server side - which means that the AllowReadStreamBuffering setting is not being honored by HttpWebRequest.

The difference between last night and now is that last night, I was on wifi, whereas today i'm connected over cellular.

My hypothesis is that on the phone, HttpWebRequest only honors AllowReadStreamBuffering = false when the connection is wifi (and perhaps Ethernet), but that it ignores it and buffers when using the cellular network.

So is it true that HttpWebRequest forces read stream buffering when connected over cellular? I haven't been able to find any documentation that confirms this behavior, so I'm wondering if anybody else has experienced this. I'll be able to test this more thoroughly later, but for now I figured i'd ask the question.

UPDATE 5-11-12
Tested and answered my own question (see below)

PhilChuang
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2 Answers2

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AllowReadStreamBuffering = false is honored on cellular connections; otherwise (for example) audio streaming apps wouldn't function properly.

Arktronic
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  • My server sends 1 byte per second, and the client wouldn't open the response stream over cellular until the server closed the stream. Doesn't that imply that there is perhaps a minimum data received size before BeginGetResponse fires? – PhilChuang May 10 '12 at 15:58
  • It's possible that the server isn't flushing properly, or perhaps chunked transfers should be enabled for more "proper" long-lived connection support. – Arktronic May 10 '12 at 16:20
  • I'll experiment with server-side changes but the fact that the app works over wifi but not cellular makes me think that it's a .NET framework issue. – PhilChuang May 10 '12 at 18:46
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I verified that my WP7 app would not initially read the response stream unbuffered when connected via cellular - it only does so when on ethernet or wifi.

So I modified my server httphandler to write an initial chunk of data (8k) to the response stream, at the beginning of the connection. Doing this made the app read the response stream immediately on cellular, just like it did when it was on wifi. After ignoring the initial blast of data, the app processed the individual bytes just fine, and in real-time.

The only conclusion that I can think of is that when connected over cellular, HttpWebRequest initially requires a small amount of data to be buffered before allowing the stream to be read unbuffered.

PhilChuang
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