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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ByteBuf.nioBuffer() returns a buffer with all zeros","articleBody":"Hi,\r\n\r\nI'm running into a weird issue where calling `nioBuffer` on a `ByteBuf` received from `lmdb-java` results in a `NIO ByteBuffer` with the desired size but a value of all zeros.\r\n\r\nI'm on `Netty 4.1.90.Final` and `lmdbjava 0.8.3` and JDK 19 . The repro is as follows:\r\n\r\n```\r\npackage foo;\r\n\r\nimport io.netty.buffer.ByteBufUtil;\r\nimport io.netty.buffer.PooledByteBufAllocator;\r\nimport io.netty.buffer.Unpooled;\r\nimport org.junit.jupiter.api.Test;\r\nimport org.junit.jupiter.api.io.TempDir;\r\nimport org.lmdbjava.ByteBufProxy;\r\nimport org.lmdbjava.DbiFlags;\r\nimport org.lmdbjava.Env;\r\n\r\nimport java.io.File;\r\n\r\nimport static java.nio.charset.StandardCharsets.UTF_8;\r\nimport static org.junit.jupiter.api.Assertions.assertNotNull;\r\n\r\npublic class ByteBufMinimalReproTest {\r\n    @TempDir\r\n    File tmp;\r\n\r\n    @Test\r\n    void minimalRepro() {\r\n        var env = Env.create(ByteBufProxy.PROXY_NETTY)\r\n                .setMapSize(10_485_760)\r\n                .setMaxDbs(1)\r\n                .open(tmp);\r\n        var db = env.openDbi(\"testdb\", DbiFlags.MDB_CREATE);\r\n        var alloc = PooledByteBufAllocator.DEFAULT;\r\n\r\n        var key = alloc.directBuffer(env.getMaxKeySize());\r\n        var value = alloc.directBuffer(700);\r\n\r\n        key.writeCharSequence(\"greeting\", UTF_8);\r\n        value.writeCharSequence(\"Hello World\", UTF_8);\r\n\r\n        System.out.println(\"Sanity -- Key\");\r\n        System.out.println(ByteBufUtil.prettyHexDump(key));\r\n        System.out.println(\"Sanity -- Key NIO\");\r\n        System.out.println(ByteBufUtil.prettyHexDump(Unpooled.wrappedBuffer(key.nioBuffer())));\r\n\r\n        System.out.println(\"Sanity -- Value\");\r\n        System.out.println(ByteBufUtil.prettyHexDump(value));\r\n        System.out.println(\"Sanity -- Value NIO\");\r\n        System.out.println(ByteBufUtil.prettyHexDump(Unpooled.wrappedBuffer(value.nioBuffer())));\r\n\r\n\r\n        db.put(key, value);\r\n        // need a transaction to read values.\r\n        try (var txn = env.txnRead()) {\r\n            var found = db.get(txn, key);\r\n            assertNotNull(found);\r\n\r\n            System.out.println(\"Found Value\");\r\n            System.out.println(ByteBufUtil.prettyHexDump(found));\r\n            System.out.println(\"Found Value - NIO (Bad: all zeros)\");\r\n            System.out.println(ByteBufUtil.prettyHexDump(Unpooled.wrappedBuffer(\r\n                    found.nioBuffer())));\r\n\r\n            var fetchedVal = txn.val();\r\n            System.out.println(\"val via txn\");\r\n            System.out.println(ByteBufUtil.prettyHexDump(fetchedVal));\r\n            System.out.println(\"val via txn - NIO (Bad: all zeros)\");\r\n            System.out.println(ByteBufUtil.prettyHexDump(Unpooled.wrappedBuffer(\r\n                    txn.val().nioBuffer())));\r\n        }\r\n        env.close();\r\n    }\r\n}\r\n```\r\n\r\nWhich prints:\r\n\r\n```\r\nSanity -- Key\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 67 72 65 65 74 69 6e 67                         |greeting        |\r\n+--------+-------------------------------------------------+----------------+\r\nSanity -- Key NIO\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 67 72 65 65 74 69 6e 67                         |greeting        |\r\n+--------+-------------------------------------------------+----------------+\r\nSanity -- Value\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64                |Hello World     |\r\n+--------+-------------------------------------------------+----------------+\r\nSanity -- Value NIO\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64                |Hello World     |\r\n+--------+-------------------------------------------------+----------------+\r\nFound Value\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64                |Hello World     |\r\n+--------+-------------------------------------------------+----------------+\r\nFound Value - NIO (Bad: all zeros)\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 00 00 00 00 00 00 00 00 00 00 00                |...........     |\r\n+--------+-------------------------------------------------+----------------+\r\nval via txn\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 48 65 6c 6c 6f 20 57 6f 72 6c 64                |Hello World     |\r\n+--------+-------------------------------------------------+----------------+\r\nval via txn - NIO (Bad: all zeros)\r\n         +-------------------------------------------------+\r\n         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |\r\n+--------+-------------------------------------------------+----------------+\r\n|00000000| 00 00 00 00 00 00 00 00 00 00 00                |...........     |\r\n+--------+-------------------------------------------------+----------------+\r\n```\r\n\r\nMy repro is using the prettyHexDump from ByteBuf, which is why i need to re-wrap nioBuffer.  I'm pretty sure this isn't causing any problems because when I write the bytebuf to file, I see all zeros.\r\n\r\nThe reason I'm doing nioBuffer on this netty buffer is because I need to pass it to Zstd java for decompression.\r\n\r\nI'm new to both lmdb java and netty, and it's possible i'm doing something wrong, but I'd appreciate your help with this.","author":{"url":"https://github.com/kanak","@type":"Person","name":"kanak"},"datePublished":"2023-04-02T17:55:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/215/lmdbjava/issues/215"}