How does netty determine when a read is complete?

Question

Below is a ChannelHandler for a echo server.

Netty framework will call channelReadComplete() method to notify the handler that the last call made to channelRead() was the last message in the current batch.

My question is, since data are transferred on wire in trunks, how could Netty know when a batch of message is complete?

Answer 1

channelReadComplete() is triggered once there is no more data to read from the underlying transport. When talking about SocketChannels this would be either of these two cases:

1. read(...) returns 0
2. read(...) got a buffer passed to it that has 1024 bytes to fill, but less than 1024 are filled.