Does `send!` block if it needs to exert backpressure? If so, the `go-loop`
seems dangerous. If not, how does backpressure work?
On Wed, Dec 17, 2014 at 8:07 AM, Malcolm Sparks <malc...@juxt.pro> wrote:
>
> Here is a solution for SSE over http-kit channels
>
> (defn server-event-source [ch] ;; Adding a mult here is dangerous because
> it bleeds the underlying ;; channel dry. We should provide the mult via
> modular.async (let [m (async/mult ch)] (fn [req] (let [ch (async/chan 16)]
> (async/tap m ch) (with-channel req net-ch (on-close net-ch (fn [_]
> (async/untap m ch) (async/close! ch))) (send! net-ch {:headers headers}
> false) (go-loop [] (when-let [data (<! ch)] (println "Got data! " data)
> (send! net-ch (->message data) false) (recur))))))))
>
>
> https://github.com/juxt/modular/blob/master/modules/http-kit-events/src/modular/http_kit/events.clj
>
>
> On Saturday, 6 December 2014 17:03:41 UTC, Lars Ole Avery Simonsen wrote:
>>
>> Hi guys
>>
>> I am trying to implement Server Sent Event support in a small hobby
>> project based on the http-kit server framework and compojure.
>>
>> I am still quite new to clojure in general, so it may very well be that I
>> am missing something obvious, but this SSE detail has me stumped.
>>
>> What I have tried is to take inspiration from the Eventual
>> <https://github.com/ninjudd/eventual> library for the SSE implementation
>> (which is aimed at jetty). I have changed the Eventual implementation so
>> that it uses the http-kit async-channel implementation for data
>> transmission. What I am seeing is that everything seems to run without
>> errors except for the fact that no data is being received at the
>> EventSource in the browser.
>>
>> If I allow the sse channel to close immediately after opening (which is
>> pretty useless), the initial message is received at the browser side, but
>> if I keep the connection open, nothing gets received.
>>
>> Having had a look at the http-kit internals, my suspicion is that the
>> socket doesn't get flushed and so all my attempts at communication are
>> sitting in some buffer somewhere.
>>
>> All SSE implementations I have looked at for other platforms have
>> explicit calls to flush the socket buffers on the long lived connection
>> after each message transmission.
>>
>> Does anyone have any suggestions as to a better way to achieve SSE
>> support in a http-kit based server? Or maybe ideas as to what I might be
>> doing wrong?
>>
>> Thanks in advance.
>>
>> LOAS
>>
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