return db value length from db.Get(key, buffer, ...), fixing #45

Author: warrenfalk

RocksDbSharp/RocksDb.cs

@@ -129,8 +129,8 @@ public long Get(byte[] key, long keyLength, byte[] buffer, long offset, long len
             unsafe
             {
                 var ptr = Native.Instance.rocksdb_get(Handle, (readOptions ?? DefaultReadOptions).Handle, key, keyLength, out long valLength, cf);
-                valLength = Math.Min(length, valLength);
-                Marshal.Copy(ptr, buffer, (int)offset, (int)valLength);
+                var copyLength = Math.Min(length, valLength);
+                Marshal.Copy(ptr, buffer, (int)offset, (int)copyLength);
                 Native.Instance.rocksdb_free(ptr);
                 return valLength;
             }

tests/RocksDbSharpTest/FunctionalTests.cs

@@ -56,6 +56,11 @@ public void FunctionalTest()
                 Assert.Equal(8, length);
                 Assert.Equal(new byte[] { 0, 1, 2, 3, 4, 5, 6, 7 }, buffer.Take((int)length).ToList());
 
+                buffer = new byte[5];
+                length = db.Get(Encoding.UTF8.GetBytes("key"), buffer, 0, buffer.Length);
+                Assert.Equal(8, length);
+                Assert.Equal(new byte[] { 0, 1, 2, 3, 4 }, buffer.Take((int)Math.Min(buffer.Length, length)));
+
                 // Write batches
                 // With strings
                 using (WriteBatch batch = new WriteBatch()