TdsSslHandler incompatible with Netty 4.2 AdaptivePoolingAllocator (Spring Boot 4)

[kevin-nca]

Versions

• Driver: r2dbc-mssql 1.0.4.RELEASE
• Database: Microsoft SQL Server 2019
• Java: 21
• OS: Linux (Kubernetes container)
• Netty: 4.2.9 (Spring Boot 4.0.2)

Current Behavior

All connections fail during TLS handshake. Netty 4.2 changed the default allocator to AdaptivePoolingAllocator (migration guide). TdsSslHandler.channelRead() calls alloc() on a released ByteBuf, which the new allocator rejects. This breaks every connection, including with sslMode=disable, since TDS always does a TLS handshake for login credentials (?).

Workaround: -Dio.netty.allocator.type=pooled

Stack trace

io.netty.util.IllegalReferenceCountException: null
    at i.n.b.AdaptivePoolingAllocator$AdaptiveByteBuf.rootParent(AdaptivePoolingAllocator.java:1427)
    at i.n.b.AdaptivePoolingAllocator$AdaptiveByteBuf.alloc(AdaptivePoolingAllocator.java:1481)
    at io.r2dbc.mssql.client.ssl.TdsSslHandler.channelRead(TdsSslHandler.java:346)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:354)
    at i.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1429)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:918)

Table schema

N/A, it fails during connection establishment.

Steps to reproduce

1. Spring Boot 4.0.x + r2dbc-mssql + any SQL Server instance
2. Every connection attempt fails