feat(scheduler): Support multiple receivers

The scheduler now also accepts the `:from` field in the events sent from the
executor to either be a single `string?` or a collection of `string?` which
represents a broadcast.

src/scheduler/src/scheduler/pure.clj

@@ -258,6 +258,19 @@
 
 (def entries? (s/coll-of entry? :kind vector?))
 
+
+(s/def :ext/to
+  (s/or :singleton string?
+        :set (s/coll-of string? :kind vector?)))
+
+(def ext-entry?
+  (s/and (s/keys :req-un [::kind
+                          ::event
+                          ::args
+                          :ext/to
+                          ::from])
+         #(not (#{"timer"} (:kind %)))))
+
 (def timer?
   (s/and (s/keys :req-un [::kind
                           ::args
@@ -269,8 +282,22 @@
   (s/or :entry entry?
         :timer timer?))
 
+(def ext-event?
+  (s/or :entry ext-entry?
+        :timer timer?))
+
 (def events? (s/coll-of event? :kind vector?))
 
+(>defn expand-events
+       [events]
+       [(s/coll-of ext-event?) => (s/coll-of event? :kind vector?)]
+       (let [up (fn [event]
+                  (case (:kind event)
+                    "timer" [event]
+                    (if (string? (:to event))
+                      [event]
+                      (mapv #(assoc event :to %) (:to event)))))]
+         (vec (mapcat up events))))
 (s/def ::events events?)
 
 (defn error-state?
@@ -368,7 +395,8 @@
                     [events (-> (client/post (str url (if (= (:kind body) "timer") "timer" "event"))
                                              {:body (json/write body) :content-type "application/json; charset=utf-8"})
                                 :body
-                                json/read)]
+                                json/read
+                                (update :events expand-events))]
                   ;; TODO(stevan): go into error state if response body is of form {"error": ...}
                   ;; (if (:error events) true false)
 
@@ -583,7 +611,8 @@
                      (-> (client/get (str executor-id "/inits"))
                          :body
                          json/read
-                         :events))
+                         :events
+                         expand-events))
         _ (log/debug :get-initial-events executor-id events (:state data))
         [data' timestamped-entries] (timestamp-entries data events (:clock data))
         [data'' queue-size] (enqueue-timestamped-entries data' timestamped-entries)]
@@ -639,7 +668,8 @@
                                                       :component component})
                                    :content-type "application/json; charset=utf-8"})
                       :body
-                      json/read)]
+                      json/read
+                      (update :events expand-events))]
        (assert (= (keys events) '(:events))
                (str "execute!: unexpected response body: " events))
        (doseq [event (:events events)]