[QUESTION]How to write a simple TCP proxy server using muduo?

[yusiwen]

Hi,

Yesterday I found 'muduo' on GitHub when random browsing, and find it very interesting and useful. After a quick browse of your code, I can't help to write some something on 'muduo'.

I want to write a simple TCP socket proxy using it. It will simply transfer what it receives to the back-end TCP server, and send back the response from the back-end server to the client. I'm not very good at C++, so I'm quite confused right now:

Can this be done by using muduo? And can it be done asynchronously? Should I start two EventLoop, one for listening from the client, the other for the back-end server? If so, how can these loops communicate with each other?

Any help would be appreciated.

I know this post is not an issue, sorry for the trouble.

[chenshuo]

Take a look at examples/socks4a/tcprelay.cc

[yusiwen]

@chenshuo Thanks. This example is really a great help for me, and there are so much to learn about muduo and asynchronous socket programming.

In my program, a custom protocol is introduced into the app layer, which contains a 4-bytes message header to indicate the whole message length.

In tcprelay.cc, I find this call buf->readableBytes(); in the callback onClientMessage() and onServerMessage(), does it return the whole message every time? If not, how to check the received message's integrity using my message header? If the buf doesn't contain the whole message, should I wait on a blocked socket recv() routine? Or is there some mechanism to inform me when the message is fully received?

I'm really a newbie in asynchronous socket programming, and find myself lost in the callbacks. Any help would be appreciated. Thanks.

[chenshuo]

You should never issue a blocking call like recv() in an event handler, it may block all connections.
Check LengthHeaderCodec in examples/asio/chat/codec.h for how to decode the protocol correctly.