From 40d13169f969462dd65e812f94d9df3e304eb336 Mon Sep 17 00:00:00 2001
From: Christian Nautze <christian.nautze@exoscale.ch>
Date: Mon, 26 Aug 2024 21:08:28 +0200
Subject: [PATCH] Cursor: fix apply with stateful transducer

---
 src/exoscale/vinyl/cursor.clj       | 25 ++++++++++-------
 test/exoscale/vinyl/cursor_test.clj | 43 +++++++++++++++++++++++++++--
 2 files changed, 55 insertions(+), 13 deletions(-)

diff --git a/src/exoscale/vinyl/cursor.clj b/src/exoscale/vinyl/cursor.clj
index cc96821..37d502d 100644
--- a/src/exoscale/vinyl/cursor.clj
+++ b/src/exoscale/vinyl/cursor.clj
@@ -32,16 +32,21 @@
       (AsyncUtil/whileTrue
        (reify Supplier
          (get [_]
-           (-> cursor
-               .onNext
-               (.thenApply
-                (fn/make-fun
-                 (fn [^RecordCursorResult result]
-                   (when (ifn? cont-fn)
-                     (-> result .getContinuation .toBytes cont-fn))
-                   (let [next?   (.hasNext result)
-                         new-acc (when next? (swap! acc reducer (.get result)))]
-                     (and (not (reduced? new-acc)) next?))))))))
+           (try
+             (-> cursor
+                 .onNext
+                 (.thenApply
+                  (fn/make-fun
+                   (fn [^RecordCursorResult result]
+                     (when (ifn? cont-fn)
+                       (-> result .getContinuation .toBytes cont-fn))
+                     (let [next?   (.hasNext result)
+                           new-acc (when next? (swap! acc reducer (.get result)))]
+                       (and (not (reduced? new-acc)) next?))))))
+             (catch Exception e
+               (when (some? xform)
+                 (reducer @acc))
+               (throw e)))))
        (.getExecutor cursor))
       (fn/make-fun (fn [_]
                      (unreduced
diff --git a/test/exoscale/vinyl/cursor_test.clj b/test/exoscale/vinyl/cursor_test.clj
index 8bf5740..80183cc 100644
--- a/test/exoscale/vinyl/cursor_test.clj
+++ b/test/exoscale/vinyl/cursor_test.clj
@@ -1,14 +1,39 @@
 (ns exoscale.vinyl.cursor-test
-  (:require [clojure.test          :refer [deftest are]]
+  (:require [clojure.test :refer [deftest are is]]
             [exoscale.vinyl.cursor :refer [apply-transforms]]
-            [exoscale.vinyl.store  :as    store])
-  (:import com.apple.foundationdb.record.RecordCursor))
+            [exoscale.vinyl.demostore :as ds :refer [*db*]]
+            [exoscale.vinyl.store :as store])
+  (:import [com.apple.foundationdb.record RecordCursor]
+           [com.apple.foundationdb FDBException]
+           [java.util Iterator]))
 
 (defn from-list
   "Transform a list of items to a `RecordCursor` instance"
   [items]
   (RecordCursor/fromList (seq items)))
 
+(defn from-iterator
+  [iterator]
+  (RecordCursor/fromIterator iterator))
+
+(defrecord FaultyIterator [items pos error-index]
+  Iterator
+  (forEachRemaining [_ _action])
+  (hasNext [_]
+    (< @pos (count items)))
+  (next [_]
+    (if (= @pos @error-index)
+      (do
+        (vreset! error-index -1)
+        (throw (FDBException. "Retryable error" 1007)))
+      (let [result (nth items @pos)]
+        (vswap! pos inc)
+        result)))
+  (remove [_]))
+
+(defn make-faulty-iterator [items error-index]
+  (->FaultyIterator items (volatile! 0) (volatile! error-index)))
+
 (defn reduce-plus
   [x y]
   (let [acc (+ x y)]
@@ -30,3 +55,15 @@
                                      ::store/reduce-init init}))
     [0 1 2 3 4 5 6] +           0 28
     [0 1 2 3 4 5 6] (completing reduce-plus) 0 15))
+
+(deftest stateful-transducer-test
+  (let [processed (atom [])]
+    (is (= [[1 2 3] [4 5] [6 7 8] [9]]
+           (ds/with-build-fdb
+             (fn [] (let [cursor (from-iterator (make-faulty-iterator [1 2 3 4 5 6 7 8 9] 5))]
+                      @(store/run-async *db* (fn [_store] (apply-transforms
+                                                            cursor
+                                                            {::store/reducer     (completing (fn [_acc items] (swap! processed conj items)))
+                                                             ::store/reduce-init []
+                                                             ::store/transducer  (partition-all 3)})))
+                      @processed)))))))