[REQ] option to disable protocol upgrade for Apache client

[gnarroway]

Is your feature request related to a problem? Please describe.

Recent versions of Apache httpclient default to trying to upgrade TLS. This is incompatible with certain middleware such as envoy/istio as documented at istio/istio#53239

The suggested workaround is to disable that behaviour in the client by using setProtocolUpgradeEnabled

Describe the solution you'd like

Add support for setting this on the client for all requests. Note that the method only exists on recent versions so will have to be graceful (do nothing if the client version is below 5.4)

Describe alternatives you've considered

• use a non Apache client
• force the Apache version to remain outdated, but this can conflict with other deps

Additional context

As per the attached issue, this will start to become a more prevalent issue as spring etc update their dependency version, resulting in mysterious errors in run time whenever envoy is used. Providing an option around it is the best path forward.

[martin-mfg]

Hi @gnarroway, thanks for bringing up this problem!

If users are affected by this problem they should be able to customize the apache http client via Configuration.setDefaultApiClient or Configuration.setApiClientFactory. (Which is similar to what Spring Boot suggests to its users here.) It also seems that envoy and istio are working on a fix on their side. And finally, we're currently using version 5.2.1 of apache httpclient, so the problem doesn't affect our users yet.

So all in all I think we don't need to do anything on OpenAPI Generator side, especially because users can customize the http client already. If you have a use case in mind where this customization doesn't help, please let me know.