Fix stale OutOfMemoryError reference in XXHashJNI

src/java/net/jpountz/xxhash/StreamingXXHash32JNI.java

@@ -55,8 +55,10 @@ private void checkState() {
   @Override
   public synchronized void reset() {
     checkState();
+    // create the new state first so that a failed init leaves this instance usable
+    final long newState = XXHashJNI.XXH32_init(seed);
     XXHashJNI.XXH32_free(state);
-    state = XXHashJNI.XXH32_init(seed);
+    state = newState;
   }
 
   @Override

src/java/net/jpountz/xxhash/StreamingXXHash64JNI.java

@@ -56,8 +56,10 @@ private void checkState() {
   @Override
   public synchronized void reset() {
     checkState();
+    // create the new state first so that a failed init leaves this instance usable
+    final long newState = XXHashJNI.XXH64_init(seed);
     XXHashJNI.XXH64_free(state);
-    state = XXHashJNI.XXH64_init(seed);
+    state = newState;
   }
 
   @Override

src/jni/net_jpountz_xxhash_XXHashJNI.c

@@ -20,14 +20,28 @@
 
 static jclass OutOfMemoryError;
 
+/* Stand-in input for empty direct buffers whose address is NULL. */
+static const char empty_input[1] = { 0 };
+
+static int init_class_ref(JNIEnv *env, jclass *target, const char *className) {
+  jclass localClass = (*env)->FindClass(env, className);
+  if (localClass == NULL) {
+    return 0;
+  }
+
+  *target = (jclass) (*env)->NewGlobalRef(env, localClass);
+  (*env)->DeleteLocalRef(env, localClass);
+  return *target != NULL;
+}
+
 /*
  * Class:     net_jpountz_xxhash_XXHashJNI
  * Method:    init
  * Signature: ()V
  */
 JNIEXPORT void JNICALL Java_net_jpountz_xxhash_XXHashJNI_init
   (JNIEnv *env, jclass cls) {
-  OutOfMemoryError = (*env)->FindClass(env, "java/lang/OutOfMemoryError");
+  init_class_ref(env, &OutOfMemoryError, "java/lang/OutOfMemoryError");
 }
 
 static void throw_OOM(JNIEnv *env) {
@@ -71,8 +85,13 @@ JNIEXPORT jint JNICALL Java_net_jpountz_xxhash_XXHashJNI_XXH32BB
 
   in = (char*) (*env)->GetDirectBufferAddress(env, buf);
   if (in == NULL) {
-    throw_OOM(env);
-    return 0;
+    if (len != 0) {
+      throw_OOM(env);
+      return 0;
+    }
+    /* e.g. a zero-length mapped buffer: hash the empty input */
+    in = (char*) empty_input;
+    off = 0;
   }
 
   h32 = XXH32(in + off, len, seed);
@@ -90,6 +109,11 @@ JNIEXPORT jlong JNICALL Java_net_jpountz_xxhash_XXHashJNI_XXH32_1init
   (JNIEnv *env, jclass cls, jint seed) {
 
   XXH32_state_t *state = XXH32_createState();
+  if (state == NULL) {
+    throw_OOM(env);
+    return 0;
+  }
+
   if (XXH32_reset(state, seed) != XXH_OK) {
     XXH32_freeState(state);
     throw_OOM(env);
@@ -181,8 +205,13 @@ JNIEXPORT jlong JNICALL Java_net_jpountz_xxhash_XXHashJNI_XXH64BB
 
   in = (char*) (*env)->GetDirectBufferAddress(env, buf);
   if (in == NULL) {
-    throw_OOM(env);
-    return 0;
+    if (len != 0) {
+      throw_OOM(env);
+      return 0;
+    }
+    /* e.g. a zero-length mapped buffer: hash the empty input */
+    in = (char*) empty_input;
+    off = 0;
   }
 
   h64 = XXH64(in + off, len, seed);
@@ -200,6 +229,11 @@ JNIEXPORT jlong JNICALL Java_net_jpountz_xxhash_XXHashJNI_XXH64_1init
   (JNIEnv *env, jclass cls, jlong seed) {
 
   XXH64_state_t *state = XXH64_createState();
+  if (state == NULL) {
+    throw_OOM(env);
+    return 0;
+  }
+
   if (XXH64_reset(state, seed) != XXH_OK) {
     XXH64_freeState(state);
     throw_OOM(env);

src/test/net/jpountz/xxhash/XXHash32Test.java

@@ -16,7 +16,12 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
 
 import net.jpountz.lz4.AbstractLZ4Test;
 import net.jpountz.util.SafeUtils;
@@ -104,6 +109,22 @@ public void testEmpty() {
     }
   }
 
+  @Test
+  public void testEmptyMappedBuffer() throws IOException {
+    // a zero-length mapping is a direct buffer with a NULL address
+    final Path file = Files.createTempFile("xxhash", ".dat");
+    try (FileChannel channel = FileChannel.open(file, StandardOpenOption.READ, StandardOpenOption.WRITE)) {
+      final ByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, 0);
+      final int seed = randomInt();
+      final int expected = XXHashFactory.safeInstance().hash32().hash(buf, 0, 0, seed);
+      for (int i = 0; i < 2; ++i) {
+        assertEquals(expected, XXHashFactory.nativeInstance().hash32().hash(buf, 0, 0, seed));
+      }
+    } finally {
+      Files.delete(file);
+    }
+  }
+
   @Test
   public void testSafeUtilsRejectsNullEmptyRange() {
     assertThrows(NullPointerException.class, () -> SafeUtils.checkRange(null, 0, 0));

src/test/net/jpountz/xxhash/XXHash64Test.java

@@ -16,7 +16,12 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
 
 import net.jpountz.lz4.AbstractLZ4Test;
 import net.jpountz.util.SafeUtils;
@@ -104,6 +109,22 @@ public void testEmpty() {
     }
   }
 
+  @Test
+  public void testEmptyMappedBuffer() throws IOException {
+    // a zero-length mapping is a direct buffer with a NULL address
+    final Path file = Files.createTempFile("xxhash", ".dat");
+    try (FileChannel channel = FileChannel.open(file, StandardOpenOption.READ, StandardOpenOption.WRITE)) {
+      final ByteBuffer buf = channel.map(FileChannel.MapMode.READ_WRITE, 0, 0);
+      final long seed = randomLong();
+      final long expected = XXHashFactory.safeInstance().hash64().hash(buf, 0, 0, seed);
+      for (int i = 0; i < 2; ++i) {
+        assertEquals(expected, XXHashFactory.nativeInstance().hash64().hash(buf, 0, 0, seed));
+      }
+    } finally {
+      Files.delete(file);
+    }
+  }
+
   @Test
   public void testSafeUtilsRejectsNullEmptyRange() {
     assertThrows(NullPointerException.class, () -> SafeUtils.checkRange(null, 0, 0));