Reject non-12-byte inputs in BINARY_AS_INT96_TIMESTAMP_COMPARATOR

Without the guard, a malformed Binary throws IndexOutOfBoundsException
from inside the stats-pruning path (for length < 12) or silently
mis-compares by reading only the first 12 bytes (for length > 12).
Throw IllegalArgumentException with a clear message instead, matching
the precedent set by Binary.get2BytesLittleEndian for FLOAT16.

Author: rahulketch

parquet-column/src/main/java/org/apache/parquet/schema/PrimitiveComparator.java

@@ -215,6 +215,10 @@ public String toString() {
   static final PrimitiveComparator<Binary> BINARY_AS_INT96_TIMESTAMP_COMPARATOR = new BinaryComparator() {
     @Override
     int compareBinary(Binary b1, Binary b2) {
+      if (b1.length() != 12 || b2.length() != 12) {
+        throw new IllegalArgumentException(
+            "INT96 binary length must be 12, got " + b1.length() + " and " + b2.length());
+      }
       ByteBuffer bb1 = b1.toByteBuffer().slice();
       ByteBuffer bb2 = b2.toByteBuffer().slice();
       bb1.order(java.nio.ByteOrder.LITTLE_ENDIAN);

parquet-column/src/test/java/org/apache/parquet/schema/TestPrimitiveComparator.java

@@ -355,6 +355,27 @@ public void testInt96Comparator() {
     }
   }
 
+  @Test
+  public void testInt96ComparatorRejectsInvalidLengths() {
+    Binary valid = timestampToInt96("2020-01-01T00:00:00.000");
+    int[] invalidLengths = {0, 4, 8, 11, 13, 16};
+    for (int len : invalidLengths) {
+      Binary wrongLength = Binary.fromConstantByteArray(new byte[len]);
+      try {
+        BINARY_AS_INT96_TIMESTAMP_COMPARATOR.compare(wrongLength, valid);
+        fail("Expected IllegalArgumentException when left operand has length " + len);
+      } catch (IllegalArgumentException expected) {
+        // ok
+      }
+      try {
+        BINARY_AS_INT96_TIMESTAMP_COMPARATOR.compare(valid, wrongLength);
+        fail("Expected IllegalArgumentException when right operand has length " + len);
+      } catch (IllegalArgumentException expected) {
+        // ok
+      }
+    }
+  }
+
   @Test
   public void testFloat16Comparator() {
     Binary[] valuesInAscendingOrder = {