add isValidCompressedBuffer()

src/main/java/org/xerial/snappy/Snappy.java

@@ -40,12 +40,14 @@ public class Snappy
     }
 
     /**
-     * Compress the content of the given input buffer
+     * Compress the content in the given input buffer. After the compression,
+     * you can retrieve the compressed data from the output buffer [pos() ...
+     * limit()) (compressed data size = limit() - pos() = remaining())
      * 
      * @param uncompressed
-     *            input is at buffer[pos() ... limit())
+     *            buffer[pos() ... limit()) containing the input data
      * @param compressed
-     *            output compressed data to buffer[pos()..]
+     *            output of the compressed data. Uses range [pos()..].
      * @return byte size of the compressed data.
      * 
      * @throws SnappyError
@@ -72,13 +74,13 @@ public class Snappy
     }
 
     /**
-     * Uncompress the content of the input buffer. The result is dumped to the
+     * Uncompress the content in the input buffer. The result is dumped to the
      * specified output buffer
      * 
      * @param compressed
-     *            input is at buffer[pos() ... limit())
+     *            buffer[pos() ... limit()) containing the input data
      * @param uncompressed
-     *            output the uncompressed data to buffer[pot())
+     *            output of the the uncompressed data. It uses buffer[pot()..]
      * @return uncompressed data size
      * 
      * @throws SnappyException
@@ -106,7 +108,7 @@ public class Snappy
     }
 
     /**
-     * Get the uncompressed size of the given compressed input
+     * Get the uncompressed byte size of the given compressed input.
      * 
      * @param compressed
      *            input data [pos() ... limit())
@@ -124,7 +126,8 @@ public class Snappy
     }
 
     /**
-     * Get the maximum size of the compressed data of a given byte size
+     * Get the maximum byte size needed for compressing a data of the given byte
+     * size.
      * 
      * @param byteSize
      *            byte size of the data to compress
@@ -134,4 +137,14 @@ public class Snappy
         return SnappyNative.maxCompressedLength(byteSize);
     }
 
+    /**
+     * Returns true iff the contents of compressed buffer [pos() ... limit())
+     * can be uncompressed successfully. Does not return the uncompressed data.
+     * Takes time proportional to compressed_length, but is usually at least a
+     * factor of four faster than actual decompression.
+     */
+    public static boolean isValidCompressedBuffer(ByteBuffer compressed) {
+        return SnappyNative.isValidCompressedBuffer(compressed, compressed.position(), compressed.remaining());
+    }
+
 }

src/main/java/org/xerial/snappy/SnappyNative.cpp

@@ -102,4 +102,12 @@ JNIEXPORT jint JNICALL Java_org_xerial_snappy_SnappyNative_uncompressedLength
 	return (jint) result;
 }
 
+JNIEXPORT jboolean JNICALL Java_org_xerial_snappy_SnappyNative_isValidCompressedBuffer
+  (JNIEnv * env, jclass self, jobject compressed, jint cpos, jint clen)
+{
+	char* compressedBuffer = (char*) env->GetDirectBufferAddress(compressed) + cpos;
+	bool ret = snappy::IsValidCompressedBuffer(compressedBuffer, (size_t) clen);
+	return ret;
+}
+
 

src/main/java/org/xerial/snappy/SnappyNative.h

@@ -47,6 +47,14 @@ JNIEXPORT jint JNICALL Java_org_xerial_snappy_SnappyNative_maxCompressedLength
 JNIEXPORT jint JNICALL Java_org_xerial_snappy_SnappyNative_uncompressedLength
   (JNIEnv *, jclass, jobject, jint, jint);
 
+/*
+ * Class:     org_xerial_snappy_SnappyNative
+ * Method:    isValidCompressedBuffer
+ * Signature: (Ljava/nio/ByteBuffer;II)Z
+ */
+JNIEXPORT jboolean JNICALL Java_org_xerial_snappy_SnappyNative_isValidCompressedBuffer
+  (JNIEnv *, jclass, jobject, jint, jint);
+
 #ifdef __cplusplus
 }
 #endif

src/main/java/org/xerial/snappy/SnappyNative.java

@@ -56,6 +56,8 @@ public class SnappyNative
     // This operation takes O(1) time.
     public native static int uncompressedLength(ByteBuffer compressed, int offset, int len) throws SnappyException;
 
+    public native static boolean isValidCompressedBuffer(ByteBuffer compressed, int offset, int len);
+
     public static void throw_error(int errorCode) throws SnappyException {
         throw new SnappyException(errorCode);
     }

src/test/java/org/xerial/snappy/SnappyTest.java

@@ -82,6 +82,8 @@ public class SnappyTest
         int compressedSize = Snappy.compress(src, compressed);
         _logger.info("compressed length: " + compressedSize);
 
+        assertTrue(Snappy.isValidCompressedBuffer(compressed));
+
         assertEquals(0, src.position());
         assertEquals(orig.length, src.remaining());
         assertEquals(orig.length, src.limit());
@@ -123,6 +125,7 @@ public class SnappyTest
         ByteBuffer compressed = ByteBuffer.allocateDirect(maxCompressedLength + offset2);
         compressed.position(offset2);
         Snappy.compress(input, compressed);
+        assertTrue(Snappy.isValidCompressedBuffer(compressed));
 
         // uncompress
         final int offset3 = 80;