Enforcing maximum size on BigInteger creation. See #497

convex-core/src/main/java/convex/core/Constants.java

@@ -187,5 +187,7 @@ public class Constants {
 
 	public static final long INITIAL_PEER_TIMESTAMP = -1L;
 
+	public static final int MAX_BIG_INTEGER_LENGTH = 4096;
+
 
 }

convex-core/src/main/java/convex/core/data/prim/CVMBigInteger.java

@@ -2,6 +2,7 @@
 
 import java.math.BigInteger;
 
+import convex.core.Constants;
 import convex.core.data.ABlob;
 import convex.core.data.ACell;
 import convex.core.data.AString;
@@ -29,6 +30,7 @@ public final class CVMBigInteger extends AInteger {
 	public static final BigInteger MIN_NEGATIVE_BIG=new BigInteger("-9223372036854775809");
 
 	protected static final long LONG_BYTELENGTH = 8;
+	protected static final long MAX_BYTELENGTH = Constants.MAX_BIG_INTEGER_LENGTH;
 
 	// We store the Integer as either a blob or Java BigInteger, and convert lazily on demand
 	private ABlob blob;
@@ -43,10 +45,11 @@ private CVMBigInteger(ABlob blob, BigInteger value) {
 	 * Creates a CVMBigInteger
 	 * WARNING: might not be canonical
 	 * @param bs Bytes representing BigInteger value. Highest bit assumed to be sign.
-	 * @return CVMBigInteger instance
+	 * @return CVMBigInteger instance or null if not valid
 	 */
 	public static CVMBigInteger wrap(byte[] bs) {
 		byte[] tbs=Utils.trimBigIntegerLeadingBytes(bs);
+		if (tbs.length>MAX_BYTELENGTH) return null;
 		if (tbs==bs) tbs=tbs.clone(); // Defensive copy just in case
 		return new CVMBigInteger(Blob.wrap(tbs),null);
 	}
@@ -55,9 +58,10 @@ public static CVMBigInteger wrap(byte[] bs) {
 	 * Creates a CVMBigInteger
 	 * WARNING: might not be canonical
 	 * @param value Java BigInteger
-	 * @return CVMBigInteger instance
+	 * @return CVMBigInteger instance or null if not valid
 	 */
 	public static CVMBigInteger wrap(BigInteger value) {
+		if (value.bitLength()>(MAX_BYTELENGTH*8-1)) return null; // note bitLength excludes sign bit
 		return new CVMBigInteger(null,value);
 	}
 
@@ -321,7 +325,9 @@ public AInteger sub(AInteger b) {
 	public AInteger negate() {
 		BigInteger bi=big();
 		bi=bi.negate();
-		return CVMBigInteger.wrap(bi).toCanonical();
+		AInteger neg=CVMBigInteger.wrap(bi);
+		if (neg==null) return null; // can theoretically overflow....
+		return neg.toCanonical();
 	}
 
 	/**

convex-core/src/test/java/convex/core/data/prim/BigIntegerTest.java

@@ -3,6 +3,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -13,6 +14,7 @@
 import org.junit.jupiter.api.Test;
 
 import convex.core.Constants;
+import convex.core.data.ABlob;
 import convex.core.data.AString;
 import convex.core.data.Blob;
 import convex.core.data.Blobs;
@@ -89,6 +91,22 @@ public class BigIntegerTest {
 		ObjectsTest.doAnyValueTests(cb);
 	}
 
+	@Test 
+	public void testMaxSize() {
+		byte [] bs=new byte[Constants.MAX_BIG_INTEGER_LENGTH];
+		bs[0]=-128; // set sign bit for max sized negative number
+		ABlob blob=Blob.wrap(bs);
+		CVMBigInteger b=CVMBigInteger.create(blob);
+		assertTrue(b.isCanonical());
+		assertEquals(Constants.MAX_BIG_INTEGER_LENGTH,b.blob().count());
+		assertNull(b.negate());
+		assertNull(b.dec()); // overflow
+		assertNull(b.multiply(CVMLong.create(2))); // overflow
+		assertNotNull(b.inc().negate());
+
+		doBigTest(b);
+	}
+
 	@Test 
 	public void testByteArrayConstruction() {
 		byte[] bs=new byte[] {-1,-1,-1,-1,-1,-1,-1,-1,-128};