Why Netty 4 "proxy" example has to set channel "AUTO_READ" as false

Question

In Netty 4 "proxy" example, the channel auto read option has been disabled:

serverBootStrap.group(bossGroup, workerGroup)
    ...
    .childOption(ChannelOption.AUTO_READ, false)

If commented childOption(ChannelOption.AUTO_READ, false), the proxy example will cannot work. And more detailed, in the method channelRead of the class HexDumpProxyFrontendHandler, the outboundChannel will always be inactive.

And I have researched Netty source code, found that "auto read" will affect like that in methods fireChannelActive and fireChannelReadComplete of the class DefaultChannelPipeline

if (channel.config().isAutoRead()) {
    read();
}

But I still cannot figure out what the relationship between auto read and the proxy example. In my mind, when a data send to the inbound buffer, Netty should fire the channel read event.

So there are two questions:

• Why disable auto read is necessary for "proxy" example?
• Why enable auto read will make outboundChannel always inactive?

Answer 1

If you have not set autoread to false you may get into trouble if one channel writes a lot of data before the other can consume it. As it's all asynchronous you may end up with buffers that have too much data and hit OOME.