On 3 September 2014 09:35, Laurens Van Houtven <[email protected]> wrote:
>
> > (defn handler [req]
> > (httpkit/with-channel req http-ch
> > (let [resp-ch (async-handler! req)]
> > (httpkit/on-close (fn [_] (a/close! resp-ch)))
> > (a/take! resp-ch (fn [resp] (httpkit/send! http-ch resp)
> (httpkit/close http-ch))))))
>
> That’s what I wanted to do, but then I saw the warning on http-kit’s
> website at http://http-kit.org/server.html#channel , which states:
>
> Data is sent directly to the client, NO RING MIDDLEWARE IS APPLIED.
>
> … which leads me to believe that the send! API just totally sidesteps any
> middleware, and it’s not so much up to the middleware whether or not it
> supports asynchronous operation. Unless of course it actually works fine,
> and that’s simply some stale documentation?
>
It means that any middleware wrapping the handler won't affect the response.
For instance, assume you have an async handler that returns a channel.
(defn async-handler! [req]
(let [ch (a/chan)]
(go (<! ch {:status 200, :headers {}, :body "Hello World"}) (a/close!
ch))
ch))
The normal way of applying middleware is to pass the handler to a
wrap-whatever function:
(def async-handler!
(wrap-foo
(fn [req]
(let [ch (a/chan)]
(go (<! ch {:status 200, :headers {}, :body "Hello World"})
(a/close! ch))
ch))
The middleware function expects the handler to return a map, not a channel,
so this won't work. However, Ring supplies foo-request and foo-response
functions for all the standard middleware, so you can write:
(defn async-handler! [req]
(let [ch (a/chan)]
(go (<! ch (foo-response {:status 200, :headers {}, :body "Hello
World"})) (a/close! ch))
ch))
Using the standard wrap-foo middleware is obviously preferable the vast
majority of the time, as it's less complected.
- James
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