How to set alignment for ByteBuf?

[tisonkun]

This code fails:

        final Path p = Path.of("pom.xml");
        final FileStore fs = Files.getFileStore(p);
        try (FileChannel channel = FileChannel.open(p, ExtendedOpenOption.DIRECT)) {
            final int alignment = (int) fs.getBlockSize();
            final ByteBuf bytes = Unpooled.directBuffer(alignment);
            bytes.writeBytes(channel, 0, alignment);
            System.out.println("bytes: " + bytes.readCharSequence(alignment, StandardCharsets.UTF_8));
        }

Exception in thread "main" java.io.IOException: Current position of the bytebuffer (0) is not a multiple of the block size (4096): alignment offset = 512
	at java.base/sun.nio.ch.Util.checkBufferPositionAligned(Util.java:510)
	at java.base/sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:328)
	at java.base/sun.nio.ch.IOUtil.read(IOUtil.java:294)
	at java.base/sun.nio.ch.IOUtil.read(IOUtil.java:283)
	at java.base/sun.nio.ch.FileChannelImpl.readInternal(FileChannelImpl.java:984)
	at java.base/sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:967)
	at io.netty.buffer.UnpooledDirectByteBuf.setBytes(UnpooledDirectByteBuf.java:582)
	at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1142)

[chrisvest]

The Unpooled allocator cannot specify alignment.
You need to use the PooledByteBufAllocator and construct it with an alignment requirement for direct buffers:

netty/buffer/src/main/java/io/netty/buffer/PooledByteBufAllocator.java

Lines 265 to 267 in 68b0989

	public PooledByteBufAllocator(boolean preferDirect, int nHeapArena, int nDirectArena, int pageSize, int maxOrder,
	int smallCacheSize, int normalCacheSize,
	boolean useCacheForAllThreads, int directMemoryCacheAlignment) {

[tisonkun]

Thank you!