Http服务器-Netty FileRegions是否可重用？

Question

I am currently working on an http server and some things are behaving kind of strange. I want to generate dynamic content and also just provide static files. Serving dynamic generated content works without problems. Since I want to profit from zero copy I use FileRegions to serve static files. My channel pipline contains the following handlers (in this order):

1. HttpRequestDecoder
2. HttpResponseEncoder
3. HttpObjectAggregator
4. ApiMapper

The ApiMapper is sharable and derived from the SimpleInboundHandler. On creation the ApiMapper creates a FileRegion from a static file. Now everytime the "/" uri is requested this happens:

1. A DefaultHttpReponse is written to the ChannelHandlerContext. The DefaultHttpReponse is not reused and contains headers for Content-Type and Content-Length
2. The ReferenceCount of the FileRegion is increased using its retain method. Then writeAndFlush is called on the ChannelHandlerContext with the FileRegion as parameter. To the returned ChannelFuture a ChannelFutureListener is added which prints "DONE".

The first response works as expected, the browser gets the full file and displays it correctly and "DONE" gets printed. But if the "/" uri is called again the browser doesn't show anything and just loads forever BUT "DONE" gets printed. Then after I restarted the server I used telnet to make the calls manually. The first response is correct, but then I noticed that the second call only returns a header, but no content. "DONE" still gets printed.

So my question: Can the same FileRegion object be used multiple times? Am I doing anything other wrong?

Answer 1

No you can not write the same FileRegion multiple times this way as the transferred state is updated on the DefaultFileRegion object. You will need to create a new DefaultFileRegion instance for each write here.

Also you need to ensure you send a LastHttpContent after your FileRegion as otherwise the state-machine in HttpResponseEncoder will not be in the correct state when you write the second HttpResponse .