Trailer header field included with 304

Including the Trailer header field with responses that don't have Transfer-Encoding: chunked causes some (overly strict?) proxies to drop the response e.g. IBM Bluemix sends back a 502 instead of the response generated by Express.

I think a possible solution here would be to remove the Trailer header field for 304, in addition to the fields currently removed. Here is where that code lives: https://github.com/strongloop/express/blob/f73ff9243006ea010fffdaa748f06df3a5b986e7/lib/response.js#L192

Would it make sense to also move trailer values to the header of the 304 response here-ish?

[dougwilson]

Would it make sense to also move trailer values to the header of the 304 response here-ish?

By their nature, the trailing values won't even be available until after the application has finished sending the response body (since, for example, they may be calculating a MD5 hash).

Right now, the fact that you can write a body in a 304 and it doesn't actually get sent is all handled by Node.js core HTTP. Perhaps that may be the better place to add this functionality?

Thanks! You're of course right and the trailer won't be known until the response finishes streaming, which defeats the purpose.

I'll open an issue for Node about Trailer.

[hacksparrow]

@dougwilson @wprl so can we close this?

[dougwilson]

This is actually a bug. Changing the labels.

[tunniclm]

Is sounds like the spec allows a response to have a Trailer: ... header without the matching trailer.
It sounds to me like the proxy should be allowing this valid response through.

The user (ie app/middleware author) could also prevent this issue by not adding a Trailer: ... header to responses that are not chunked (including 304s which shouldn't be chunked).

Is there really a bug in Express to fix here?

EDIT: Prematurely hit "Comment", added the rest in via an edit.

[dougwilson]

Yea, @tunniclm, I sort of agree :) You see, by default Node.js will send responses chunked, but the Express helpers actually force them to non-chunked, which is a more efficient data transfer mechanism and easier to parse for a lot of clients. Ideally Express needs to be a lot smarter around this and how it decides to send the response out according to the headers that were built up before writing them.

[tunniclm]

Do you still think this is a bug, or is it something that can be addressed as an enhancement?
And what are you proposing we do? If we can define the goal of a change more explicitly, I'm happy to have a go at making it.