Add maximum columns per table limit

Author: mtopolnik

core/src/main/java/io/questdb/client/cutlass/qwp/protocol/QwpConstants.java

@@ -69,6 +69,12 @@ public final class QwpConstants {
      * Magic bytes for QWP v1 message: "QWP1" (ASCII).
      */
     public static final int MAGIC_MESSAGE = 0x31505751; // "QWP1" in little-endian
+    /**
+     * Maximum columns per table. Must match the server-side constant of
+     * the same name so the client can produce an error before sending to
+     * the server and finding out.
+     */
+    public static final int MAX_COLUMNS_PER_TABLE = 2048;
     /**
      * Schema mode: Full schema included.
      */

core/src/main/java/io/questdb/client/cutlass/qwp/protocol/QwpTableBuffer.java

@@ -371,6 +371,11 @@ private static void assertColumnType(CharSequence name, byte type, ColumnBuffer
     }
 
     private ColumnBuffer createColumn(CharSequence name, byte type, boolean useNullBitmap) {
+        if (columns.size() >= MAX_COLUMNS_PER_TABLE) {
+            throw new LineSenderException("column count exceeds maximum: " + (columns.size() + 1) +
+                    " (max " + MAX_COLUMNS_PER_TABLE + ")"
+            );
+        }
         ColumnBuffer col = new ColumnBuffer(Chars.toString(name), type, useNullBitmap);
         try {
             col.sender = sender;
@@ -1533,6 +1538,13 @@ private static int checkedElementCount(long product) {
             return (int) product;
         }
 
+        private static int checkedStringOffset(long offset) {
+            if (offset > Integer.MAX_VALUE) {
+                throw new LineSenderException("string column data exceeds 2 GiB per batch, flush more frequently");
+            }
+            return (int) offset;
+        }
+
         private void allocateStorage(byte type) {
             switch (type) {
                 case TYPE_BOOLEAN:
@@ -1737,13 +1749,6 @@ private int getOrAddLocalSymbol(CharSequence value) {
             return idx;
         }
 
-        private static int checkedStringOffset(long offset) {
-            if (offset > Integer.MAX_VALUE) {
-                throw new LineSenderException("string column data exceeds 2 GiB per batch, flush more frequently");
-            }
-            return (int) offset;
-        }
-
         private void markNull(int index) {
             long longAddr = nullBufPtr + ((long) (index >>> 6)) * 8;
             int bitIndex = index & 63;

core/src/test/java/io/questdb/client/test/cutlass/qwp/protocol/QwpConstantsTest.java

@@ -158,4 +158,9 @@ public void testMagicBytesValue() {
         Assert.assertEquals((byte) ((MAGIC_MESSAGE >> 16) & 0xFF), expected[2]);
         Assert.assertEquals((byte) ((MAGIC_MESSAGE >> 24) & 0xFF), expected[3]);
     }
+
+    @Test
+    public void testMaxColumnsPerTable() {
+        Assert.assertEquals(2048, MAX_COLUMNS_PER_TABLE);
+    }
 }

core/src/test/java/io/questdb/client/test/cutlass/qwp/protocol/QwpTableBufferTest.java

@@ -980,6 +980,29 @@ public void testGetOrCreateColumnConflictingTypeSlowPath() throws Exception {
         });
     }
 
+    @Test
+    public void testGetOrCreateColumnThrowsWhenExceedingMaxColumnCount() throws Exception {
+        assertMemoryLeak(() -> {
+            try (QwpTableBuffer table = new QwpTableBuffer("test")) {
+                for (int i = 0; i < QwpConstants.MAX_COLUMNS_PER_TABLE; i++) {
+                    table.getOrCreateColumn("c" + i, QwpConstants.TYPE_LONG, false);
+                }
+                assertEquals(QwpConstants.MAX_COLUMNS_PER_TABLE, table.getColumnCount());
+                try {
+                    table.getOrCreateColumn("overflow", QwpConstants.TYPE_LONG, false);
+                    fail("Expected LineSenderException for exceeding max column count");
+                } catch (LineSenderException e) {
+                    assertEquals(
+                            "column count exceeds maximum: " + (QwpConstants.MAX_COLUMNS_PER_TABLE + 1)
+                                    + " (max " + QwpConstants.MAX_COLUMNS_PER_TABLE + ")",
+                            e.getMessage()
+                    );
+                }
+                assertEquals(QwpConstants.MAX_COLUMNS_PER_TABLE, table.getColumnCount());
+            }
+        });
+    }
+
     @Test
     public void testLongArrayMultipleRows() throws Exception {
         assertMemoryLeak(() -> {