KeyValue atomic delete and purge methods.

src/main/java/io/nats/client/KeyValue.java

@@ -138,6 +138,16 @@ public interface KeyValue {
      */
     void delete(String key) throws IOException, JetStreamApiException;
 
+    /**
+     * Soft deletes the key by placing a delete marker iff the key exists and its last revision matches the expected
+     * @param key the key
+     * @param expectedRevision the expected last revision
+     * @throws IOException covers various communication issues with the NATS
+     *         server such as timeout or interruption
+     * @throws JetStreamApiException the request had an error related to the data
+     */
+    void delete(String key, long expectedRevision) throws IOException, JetStreamApiException;
+
     /**
      * Purge all values/history from the specific key
      * @param key the key
@@ -147,6 +157,16 @@ public interface KeyValue {
      */
     void purge(String key) throws IOException, JetStreamApiException;
 
+    /**
+     * Purge all values/history from the specific key iff the key exists and its last revision matches the expected
+     * @param key the key
+     * @param expectedRevision the expected last revision
+     * @throws IOException covers various communication issues with the NATS
+     *         server such as timeout or interruption
+     * @throws JetStreamApiException the request had an error related to the data
+     */
+    void purge(String key, long expectedRevision) throws IOException, JetStreamApiException;
+
     /**
      * Watch updates for a specific key.
      * @param key the key

src/main/java/io/nats/client/impl/NatsKeyValue.java

@@ -203,6 +203,16 @@ public void delete(String key) throws IOException, JetStreamApiException {
         _write(key, null, getDeleteHeaders());
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void delete(String key, long expectedRevision) throws IOException, JetStreamApiException {
+        validateNonWildcardKvKeyRequired(key);
+        Headers h = getDeleteHeaders().put(EXPECTED_LAST_SUB_SEQ_HDR, Long.toString(expectedRevision));
+        _write(key, null, h).getSeqno();
+    }
+
     /**
      * {@inheritDoc}
      */
@@ -211,6 +221,15 @@ public void purge(String key) throws IOException, JetStreamApiException {
         _write(key, null, getPurgeHeaders());
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public void purge(String key, long expectedRevision) throws IOException, JetStreamApiException {
+        Headers h = getPurgeHeaders().put(EXPECTED_LAST_SUB_SEQ_HDR, Long.toString(expectedRevision));
+        _write(key, null, h);
+    }
+
     private PublishAck _write(String key, byte[] data, Headers h) throws IOException, JetStreamApiException {
         validateNonWildcardKvKeyRequired(key);
         return js.publish(NatsMessage.builder().subject(writeSubject(key)).data(data).headers(h).build());

src/test/java/io/nats/client/impl/KeyValueTests.java

@@ -547,6 +547,63 @@ public void testHistoryDeletePurge() throws Exception {
         });
     }
 
+    @Test
+    public void testAtomicDeleteAtomicPurge() throws Exception {
+        jsServer.run(nc -> {
+            KeyValueManagement kvm = nc.keyValueManagement();
+
+            // create bucket
+            String bucket = bucket();
+            kvm.create(KeyValueConfiguration.builder()
+                    .name(bucket)
+                    .storageType(StorageType.Memory)
+                    .maxHistoryPerKey(64)
+                    .build());
+
+            KeyValue kv = nc.keyValue(bucket);
+            String key = key();
+            kv.put(key, "a");
+            kv.put(key, "b");
+            kv.put(key, "c");
+            assertEquals(3, kv.get(key).getRevision());
+
+            // Delete wrong revision rejected
+            assertThrows(JetStreamApiException.class, () -> kv.delete(key, 1));
+
+            // Correct revision writes tombstone and bumps revision
+            kv.delete(key, 3);
+
+            assertHistory(Arrays.asList(
+                    kv.get(key, 1L),
+                    kv.get(key, 2L),
+                    kv.get(key, 3L),
+                    KeyValueOperation.DELETE),
+                    kv.history(key));
+
+            // Wrong revision rejected again
+            assertThrows(JetStreamApiException.class, () -> kv.delete(key, 3));
+
+            // Delete is idempotent: two consecutive tombstones
+            kv.delete(key, 4);
+
+            assertHistory(Arrays.asList(
+                    kv.get(key, 1L),
+                    kv.get(key, 2L),
+                    kv.get(key, 3L),
+                    KeyValueOperation.DELETE,
+                    KeyValueOperation.DELETE),
+                    kv.history(key));
+
+            // Purge wrong revision rejected
+            assertThrows(JetStreamApiException.class, () -> kv.purge(key, 1));
+
+            // Correct revision writes roll-up purge tombstone
+            kv.purge(key, 5);
+
+            assertHistory(Arrays.asList(KeyValueOperation.PURGE), kv.history(key));
+        });
+    }
+
     @Test
     public void testPurgeDeletes() throws Exception {
         jsServer.run(nc -> {