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59 lines
2.0 KiB
TeX
59 lines
2.0 KiB
TeX
% WAI-MW.tex
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\begin{hcarentry}{WAI}
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\label{wai}
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\report{Kazu Yamamoto}%05/16
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\participants{Michael Snoyman, Greg Weber}
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\status{stable}
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\makeheader
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WAI (Web Application Interface) is an application interface
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between web applications and handlers in Haskell.
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The \texttt{Application} data type is defined as follows:
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\begin{verbatim}
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type Application = Request -> (Response -> IO ResponseReceived) -> IO ResponseReceived
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\end{verbatim}
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That is, a WAI application takes two arguments: a \texttt{Request} and
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a function to send a \texttt{Response}.
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So, the typical behavior of WAI application is
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processing a request,
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generating a response and
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passing the response to the function.
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Historically speaking, this interface made possible to develop handlers
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other than HTTP.
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The WAI applications can run through FastCGI (wai-handler-fastcgi),
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run as stand-alone (wai-handler-webkit), etc.
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But the most popular handler is based on HTTP, of course.
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The major HTTP handler for WAI is Warp which now provides
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both HTTP/1.1 and HTTP/2. TLS (warp-tls) is also available.
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New transports such as
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WebSocket (wai-websocket) and Event Source (wai-extra)
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can be implemented, too.
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It is possible to develop WAI applications directly.
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For instance, Hoogle and Mighttpd2~\cref{mighttpd2} take this way.
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However, you may want to use web application frameworks
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such as Apiary, MFlow~\cref{mflow}, rest, Servant, Scotty~\cref{scotty}, Spock,
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Yesod~\cref{yesod}, etc.
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WAI also provides \texttt{Middleware}:
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\begin{verbatim}
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type Middleware = Application -> Application
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\end{verbatim}
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WAI middleware can inspect and transform a request, for example by automatically gzipping a response or logging a request (wai-extra).
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Since the last HCAR, WAI has successfully released version 3.2,
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which removes the experimental HTTP/2 module and some APIs.
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We bumped the version from 3.0 to 3.2 for consistency with
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Warp 3.2.
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\FurtherReading
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\begin{compactitem}
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\item\url{https://groups.google.com/d/forum/haskell-wai}
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\end{compactitem}
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\end{hcarentry}
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