AsyncMiddleManServlet removes content-length header if the client doesn't send Expect: 100-Continue

[mtheos]

Jetty version
10.0.15
Java version
17.0.3
Question

Hi Jetty,

The AsyncMiddleManServlet.ProxyReader removes the content-length header and switches to chunked encoding when proxying.

I initially thought this was because you don't know the length of the transformed request, but I noticed that it only does this when the client doesn't send Expect: 100-Continue and otherwise keeps the content length header.

Do you know why this difference in behaviour exists? It would be possible to change the headers in copyRequestHeaders myself if the content length is unknown without enforcing it in the reader.

I can extend the ProxyReader impl to change this behaviour, but it's a significant amount of code that needs to be copied to make a very small behaviour change.

[sbordet]

It is a bug that we keep the Content-Length header when the client request has Expect: 100-Continue because we do not know the size of the transformed request content.

With that fixed, the behavior will be the same: if the proxy can read the whole client request content in one read, then the proxy request to the server will have Content-Length, otherwise it will be chunked.

Would that solve this issue?
I ask because I'm not sure I understand what you are asking in the last part of your comment above.

[mtheos]

Hi Simone,

In our use case, we know the size of the transformed request up front since we're only adding metadata to the body, so we can add the content-length header before we've read the client request.

The issue we faced is that the downstream expects the content-length header so it can adjust how it handles the request based on the size.

We worked around the issue by copying the code and modifying it.

[sbordet]

Can you detail what code you have modified?
It may be that we can add an overridable method that will make your life simpler rather than copying large chunks of code.

[mtheos]

I copied the AsyncMiddleManServlet and removed that line. That was the only change needed.

We were looking at the middle man servlet as an option, but we've since moved to reactor netty with webflux so I wouldn't worry about changing this for us unless you think it's the right change.

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