public final class EmbeddedChannel : Channel

EmbeddedChannel is a Channel implementation that does neither any actual IO nor has a proper eventing mechanism. The prime use-case for EmbeddedChannel is in unit tests when you want to feed the inbound events and check the outbound events manually.

To feed events through an EmbeddedChannel‘s ChannelPipeline use EmbeddedChannel.writeInbound which accepts data of any type. It will then forward that data through the ChannelPipeline and the subsequent ChannelInboundHandler will receive it through the usual channelRead event. The user is responsible for making sure the first ChannelInboundHandler expects data of that type.

EmbeddedChannel automatically collects arriving outbound data and makes it available one-by-one through readOutbound.


Due to #243 EmbeddedChannel expects outbound data to be of IOData type. This is an incorrect and unfortunate assumption that will be fixed with the next major NIO release when we can change the public API again. If you do need to collect outbound data that is not IOData you can create a custom ChannelOutboundHandler, insert it at the very beginning of the ChannelPipeline and collect the outbound data there. Just don’t forward it using context.write.


EmbeddedChannel is currently only compatible with EmbeddedEventLoops and cannot be used with SelectableEventLoops from for example MultiThreadedEventLoopGroup.


Unlike other Channels, EmbeddedChannel is not thread-safe. This is because it is intended to be run in the thread that instantiated it. Users are responsible for ensuring they never call into an EmbeddedChannel in an unsynchronized fashion. EmbeddedEventLoops notes also apply as EmbeddedChannel uses an EmbeddedEventLoop as its EventLoop.