I am trying to use Clojure manifold library, and in order to understand it, I need wanted to convert a core.async channel into a manifold stream.
I would like to create the equivalent the following using a core.async channel :
(require '[manifold.stream :as s])
(s/periodically 100 #(str " ok "))
;; Here is what I tried, it fails with an error 500
(let [ch (chan)]
(go-loop []
(>! ch " ok ")
(<! (timeout 100))
(recur))
(s/->source ch))
I am trying to feed a core.async channel into yada. The first code sample, using manifold.stream/periodic works, not the others using core.async. I tried on yada 1.0.0 and 1.1.0-SNAPSHOT.
Using manifold.stream/periodic works :
(def get-stream
(yada (fn [ctx]
(-> (:response ctx)
(assoc :status 202)
(assoc :body (s/periodically 1000 #(str (System/currentTimeMillis) " ")))))
{:representations [{:media-type "application/json"
:charset "UTF-8"}
{:media-type "application/edn"
:charset "UTF-8"}]}))
Using manifold.stream/->source returns an error 500 :
(def get-stream
(yada (fn [ctx]
(-> (:response ctx)
(assoc :status 202)
;; Similar to this : https://github.com/juxt/yada/blob/94f3ee93de155a8513b27e0508608691ed556a55/dev/src/yada/dev/async.clj
(assoc :body (let [ch (chan)]
(go-loop []
(>! ch " ok ")
(<! (timeout 100))
(recur))
(s/->source ch)))))
{:representations [{:media-type "application/json"
:charset "UTF-8"}
{:media-type "application/edn"
:charset "UTF-8"}]}))
;; Error on the page :
;; 500: Unknown
;; Error on GET
;; #error {
;; :cause "No implementation of method: :to-body of protocol: #'yada.body/MessageBody found for class: manifold.stream.async.CoreAsyncSource"
;; :via
;; [{:type clojure.lang.ExceptionInfo
;; :message "Error on GET"
;; :data {:response #yada.response.Response{:representation {:media-type #yada.media-type[application/json;q=1.0], :charset #yada.charset.CharsetMap{:alias "UTF-8", :quality 1.0}}, :vary #{:media-type}}, :resource #function[backend.routes.examples.ts/fn--57734]}
;; :at [clojure.core$ex_info invoke "core.clj" 4593]}
;; {:type java.lang.IllegalArgumentException
;; :message "No implementation of method: :to-body of protocol: #'yada.body/MessageBody found for class: manifold.stream.async.CoreAsyncSource"
;; :at [clojure.core$_cache_protocol_fn invoke "core_deftype.clj" 554]}]
;; :trace
Third attempt, with a core.async channel (different error 500) :
(def get-stream
(yada (fn [ctx]
(-> (:response ctx)
(assoc :status 202)
(assoc :body (chan)))
{:representations [{:media-type "application/json"
:charset "UTF-8"}
{:media-type "application/edn"
:charset "UTF-8"}]}))
;; Error on the page :
;; 500: Unknown
;; Error on GET
;; #error {
;; :cause "No implementation of method: :to-body of protocol: #'yada.body/MessageBody found for class: clojure.core.async.impl.channels.ManyToManyChannel"
;; :via
;; [{:type clojure.lang.ExceptionInfo
;; :message "Error on GET"
;; :data {:response #yada.response.Response{:representation {:media-type #yada.media-type[application/json;q=1.0], :charset #yada.charset.CharsetMap{:alias "UTF-8", :quality 1.0}}, :vary #{:media-type}}, :resource #function[backend.routes.api.subscribe/subscribe$fn--64130]}
;; :at [clojure.core$ex_info invoke "core.clj" 4593]}
;; {:type java.lang.IllegalArgumentException
;; :message "No implementation of method: :to-body of protocol: #'yada.body/MessageBody found for class: clojure.core.async.impl.channels.ManyToManyChannel"
;; :at [clojure.core$_cache_protocol_fn invoke "core_deftype.clj" 554]}]
;; :trace
The key error is this:
"No implementation of method: :to-body of protocol:
#'yada.body/MessageBody
found for class: manifold.stream.async.CoreAsyncSource"
It reveals that the yada version you are using is trying to coerce a body type it doesn't understand. More recent versions of yada are more permissive about what you can send through to the web-server, and allow anything through that it doesn't know how to transform.