Netty UnpooledHeapByteBuf, strange and unjustified IndexOutOfBoundsException

Question

In rare occasion Netty throw this kind of exception:

java.lang.IndexOutOfBoundsException: readerIndex(37) + length(2) exceeds writerIndex(185): UnpooledHeapByteBuf(ridx: 37, widx: 185, cap: 185/185) at io.netty.buffer.AbstractByteBuf.checkReadableBytes0(AbstractByteBuf.java:1405) at io.netty.buffer.AbstractByteBuf.checkReadableBytes(AbstractByteBuf.java:1392) at io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:872) at io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:880)

The code is :

private void checkReadableBytes0(int minimumReadableBytes) {
    ensureAccessible();
    if (readerIndex > writerIndex - minimumReadableBytes) {
        throw new IndexOutOfBoundsException(String.format(
                "readerIndex(%d) + length(%d) exceeds writerIndex(%d): %s",
                readerIndex, minimumReadableBytes, writerIndex, this));
    }
}

(37 > 185 - 2) should be true, how can it raise an exception ??

Answer 1

This looks strange. Are you sure you not share the same ByteBuf with different threads ? If this is not the case please open an issue with more informations or even better a reproducer in the Netty issue tracker:

https://github.com/netty/netty

Answer 2

For me helped answer from maximdim : Spring WebFlux, Security and request body

Main idea then you need to use DataBufferUtils.join(exchange.getRequest().getBody()) , because first, you need to collect the all request body (join).