Use SQS long-polling

The intent was to use long-polling, but it wasn't implemented. This
change means we will wait up to 20s on each SQS receive call in
production, instead of it returning immediately.

This will have two benefits:
- We will make fewer SQS receive calls in production, reducing costs
- We won't be spinning on receive calls in dev, reducing CPU usage from
  the repl process and the elasticmq docker instance

Author: tobias

resources/config.edn

@@ -17,14 +17,17 @@
                                            :default    "clojars"}}
  :deletion-backup-dir #profile {:production "/home/clojars/repo-deleted"
                                 :default    "data/test/repo-backup"}
- :event-queue         #profile {:production {:queue-url "https://sqs.us-east-2.amazonaws.com/825662292780/clojars-events"}
+ :event-queue         #profile {:production {:queue-url "https://sqs.us-east-2.amazonaws.com/825662292780/clojars-events"
+                                             :message-wait-timeout 20}
                                 :default    {:credentials {:access-key-id     "fake-access-key"
                                                            :secret-access-key "fake-secret-key"}
                                              :endpoint {:protocol "http"
                                                         :hostname "localhost"
                                                         :port     9324}
                                              :region "us-east-1"
-                                             :queue-url "http://localhost:9324/000000000000/clojars-events"}}
+                                             :queue-url "http://localhost:9324/000000000000/clojars-events"
+                                             :message-wait-timeout #profile {:default 5
+                                                                             :test nil}}}
  :github-oauth        {:client-id     #profile {:production #ssm-parameter "/clojars/production/github_oauth_client_id"
                                                 :default    "testing"}
                        :client-secret #profile {:production #ssm-parameter "/clojars/production/github_oauth_client_secret"

src/clojars/event.clj

@@ -37,12 +37,15 @@
 (defonce ^:private handlers (atom {}))
 
 (defn- sqs-receive-loop
-  [running? error-reporter sqs-client queue-url]
+  [running? error-reporter sqs-client queue-url message-wait-timeout-seconds]
   (while @running?
     (try
-      ;; This will sleep up to 20s waiting on a message
+      ;; This will sleep up to message-wait-timeout-seconds waiting on a message
+      ;; if it is provided
       (let [res (aws-util/invoke sqs-client :ReceiveMessage
-                                 {:QueueUrl queue-url})]
+                                 (cond-> {:QueueUrl queue-url}
+                                   message-wait-timeout-seconds
+                                   (assoc :WaitTimeSeconds message-wait-timeout-seconds)))]
         (doseq [{:keys [Body ReceiptHandle]} (:Messages res)
                 :let [event (edn/read-string Body)]]
           (doseq [handler (vals @handlers)]
@@ -72,7 +75,9 @@
              :running? running?
              :thread (future
                        (sqs-receive-loop running? error-reporter
-                                         (sqs-client config) (:queue-url config))))))
+                                         (sqs-client config)
+                                         (:queue-url config)
+                                         (:message-wait-timeout config))))))
   (stop [this]
     (reset! (:running? this) false)
     (deref (:thread this) 60000 ::timeout)