Allow timestamp-only rows in QWP UDP sender

Author: mtopolnik

core/src/main/java/io/questdb/client/cutlass/qwp/client/QwpUdpSender.java

@@ -719,9 +719,6 @@ private void appendLongArrayValue(QwpTableBuffer.ColumnBuffer column, Object val
     }
 
     private void atMicros(long timestampMicros) {
-        if (inProgressRowValueCount == 0) {
-            throw new LineSenderException("no columns were provided");
-        }
         try {
             stageDesignatedTimestampValue(timestampMicros, false);
             commitCurrentRow();
@@ -732,9 +729,6 @@ private void atMicros(long timestampMicros) {
     }
 
     private void atNanos(long timestampNanos) {
-        if (inProgressRowValueCount == 0) {
-            throw new LineSenderException("no columns were provided");
-        }
         try {
             stageDesignatedTimestampValue(timestampNanos, true);
             commitCurrentRow();
@@ -817,10 +811,6 @@ private void clearTransientRowState() {
     }
 
     private void commitCurrentRow() {
-        if (inProgressRowValueCount == 0) {
-            throw new LineSenderException("no columns were provided");
-        }
-
         long estimate = 0;
         long committedEstimateBeforeRow = 0;
         int targetRows = currentTableBuffer.getRowCount() + 1;

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/QwpUdpSenderTest.java

@@ -1580,6 +1580,27 @@ public void testSymbolPrefixFlushKeepsSingleRetainedDictionaryEntry() throws Exc
         });
     }
 
+    @Test
+    public void testTimestampOnlyRows() throws Exception {
+        assertMemoryLeak(() -> {
+            CapturingNetworkFacade nf = new CapturingNetworkFacade();
+            try (QwpUdpSender sender = new QwpUdpSender(nf, 0, 0, 9000, 1)) {
+                // at() with no other columns: designated timestamp is staged
+                sender.table("t").at(1_000L, ChronoUnit.MICROS);
+                // atNow() with no other columns: server assigns the timestamp
+                sender.table("t").atNow();
+                sender.flush();
+            }
+
+            List<DecodedRow> rows = decodeRows(nf.packets);
+            Assert.assertEquals("expected 2 timestamp-only rows", 2, rows.size());
+            assertRowsEqual(Arrays.asList(
+                    decodedRow("t", "", 1_000L),
+                    decodedRow("t", "", null)
+            ), rows);
+        });
+    }
+
     @Test
     public void testUnboundedSenderOmittedNullableAndNonNullableColumnsPreservesRows() throws Exception {
         assertMemoryLeak(() -> {
@@ -1712,20 +1733,6 @@ public void testUtf8StringAndSymbolStagingSupportsCancelAndPacketSizing() throws
         });
     }
 
-    @Test
-    public void testZeroColumnRowsThrow() throws Exception {
-        assertMemoryLeak(() -> {
-            CapturingNetworkFacade nf = new CapturingNetworkFacade();
-            try (QwpUdpSender sender = new QwpUdpSender(nf, 0, 0, 9000, 1, 1024 * 1024)) {
-                sender.table("t");
-
-                assertThrowsContains("no columns were provided", sender::atNow);
-                assertThrowsContains("no columns were provided", () -> sender.at(1, ChronoUnit.MICROS));
-                assertThrowsContains("no columns were provided", () -> sender.at(1, ChronoUnit.NANOS));
-            }
-        });
-    }
-
     private static void assertEstimateAtLeastActual(List<ScenarioRow> rows) throws Exception {
         CapturingNetworkFacade nf = new CapturingNetworkFacade();
         try (QwpUdpSender sender = new QwpUdpSender(nf, 0, 0, 9000, 1, 1024 * 1024)) {

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/QwpWebSocketSenderStateTest.java

@@ -218,6 +218,34 @@ public void testResetClearsAllTableBuffersAndPendingRowCount() throws Exception
         });
     }
 
+    @Test
+    public void testTimestampOnlyRows() throws Exception {
+        assertMemoryLeak(() -> {
+            // autoFlushRows=10_000 prevents auto-flush; bytes and interval disabled
+            QwpWebSocketSender sender = QwpWebSocketSender.createForTesting(
+                    "localhost", 0, 10_000, 0, 0L, 1
+            );
+            try {
+                setField(sender, "connected", true);
+                setField(sender, "inFlightWindow", new InFlightWindow(1, InFlightWindow.DEFAULT_TIMEOUT_MS));
+
+                // at(micros) with no other columns
+                sender.table("t").at(1_000L, ChronoUnit.MICROS);
+                // atNow() with no other columns
+                sender.table("t").atNow();
+
+                QwpTableBuffer tb = sender.getTableBuffer("t");
+                Assert.assertEquals(
+                        "at() and atNow() with no other columns must each buffer a row",
+                        2, tb.getRowCount()
+                );
+            } finally {
+                setField(sender, "connected", false);
+                sender.close();
+            }
+        });
+    }
+
     private static void setField(Object target, String fieldName, Object value) throws Exception {
         Field f = target.getClass().getDeclaredField(fieldName);
         f.setAccessible(true);