Problem :
I know the ClientWebSocket class of .Net 4.5 is not supported on Windows 7, but is it possible to create a WebSocket server running on Windows 7 using the .Net 4.5 API?
To make myself clearer, according to both here and here, it looks like the server side part of the .Net 4.5 WebSocket implementation should be supported even on Windows 7, yet running a HttpListener and trying to access it using an open-source WebSocket implementation got me a “Portocol not supported” error
Solution :
The OS-level HTTP.SYS support for websockets is limited to Win8 / Windows Server 2012 – which I agree is silly (it should be part of a windows-update, or a service-pack at most, IMO).
This means that you can’t use the framework support for WebSockets from HttpListener or ASP.NET directly.
But: as for “is it possible to create a WebSocket server” – sure… but only if you handle the TCP/IP comms yourself, or use a 3rd-party library for the same. This is a little annoying, but is not as bad as it might sound.
Edit: after some checking, I can confirm that the server-side components for this do not work on Windows 7 (etc); the IsWebSocketRequest returns false even though it is a web-socket request with Connection: Upgrade and Upgrade: websocket (etc) headers (from a Chrome session, as it helps).
I am, however, very surprised to find that the client-side pieces don’t work, because: that is simpler and doesn’t (or at least, doesn’t need to) involve HTTP.SYS. Trying to use them throws a PlatformNotSupportedException.
As Marc says, the Microsoft APIs do not work on Windows 7. However there are several open source libraries that support WebSockets on Windows 7, and in some cases even cross platform via Mono.
To quote from the System.Net.WebSockets documentation:
Some of the classes in the System.Net.WebSockets namespace are
supported on Windows 7, Windows Vista SP2, and Windows Server 2008.
However, the only public implementations of client and server
WebSockets are supported on Windows 8 and Windows Server 2012. The
classes and class elements in the System.Net.WebSockets namespace that
are supported on Windows 7, Windows Vista SP2, and Windows Server 2008
are abstract classes. This allows an application developer to inherit
and extend these abstract classes with an actual implementation of
client WebSockets.
In other words: DIY the actual implementation.