Restart btcdata when its fenced database session closes

test/clj/pmagnus/btcdata/web/controllers/health_test.clj

@@ -4,8 +4,18 @@
 
 (def disabled-stream {:state (atom {:enabled? false}) :latest-price (atom nil)})
 
-(deftest healthcheck-is-process-only
-  (is (= 200 (:status (health/healthcheck! {})))))
+(deftest liveness-check-is-local-and-detects-lost-writer
+  (let [closed? (atom false)
+        connection (proxy [java.sql.Connection] []
+                     (isClosed [] @closed?))
+        query-fn (with-meta (fn [& _] (throw (Exception. "Must not query database")))
+                   {:connection connection})]
+    (is (= 200 (:status (health/healthcheck! query-fn {}))))
+    (reset! closed? true)
+    (is (= 503 (:status (health/healthcheck! query-fn {}))))
+    (is (= "writer session closed"
+           (get-in (health/healthcheck! query-fn {}) [:body :reason]))))
+  (is (= 503 (:status (health/healthcheck! (fn [& _]) {})))))
 
 (deftest readiness-check-tests-database
   (let [called (atom nil)

test/clj/pmagnus/btcdata/writer_test.clj

@@ -13,6 +13,13 @@
     (is (= :result (query :insert-price {:price 1})))
     (is (= [connection :insert-price {:price 1}] @seen))))
 
+(deftest session-liveness-fails-closed
+  (is (false? (writer/session-live? (fn [& _]))))
+  (let [connection (proxy [java.sql.Connection] []
+                     (isClosed [] (throw (java.sql.SQLException. "broken"))))]
+    (is (false? (writer/session-live? (with-meta (fn [& _])
+                                       {:connection connection}))))))
+
 (deftest server-session-has-bounded-dead-peer-detection
   (let [connection (Object.)
         calls (atom [])]
@@ -44,7 +51,9 @@
         (is (thrown-with-msg? clojure.lang.ExceptionInfo #"Another btcdata writer"
               (ig/init-key :writer/query-fn opts)))
         ;; Closing the owning session cannot transparently reconnect for writes.
+        (is (writer/session-live? first-writer))
         (.close (:connection (meta first-writer)))
+        (is (false? (writer/session-live? first-writer)))
         (is (thrown? Exception (first-writer :check {})))
         (let [replacement (ig/init-key :writer/query-fn opts)]
           (try