How do I include internal redirect response headers in the subsequent request?

[majames]

How do I include internal redirect response headers in the subsequent request?

Description

I posted this question on Stack Overflow, but I also see that GitHub issues can be used for questions so I'm asking it here as well 🙂

Is it currently possible to include a subset of the 302 redirect response headers in the subsequent request Envoy sends when the redirect is handled internally? If not, does anyone have a good suggestion for a workaround for doing this?

[junr03]

Per my reading of the redirect docs:

The altered request headers will then have a new route selected, be sent through a new filter chain, and then shipped upstream with all of the normal Envoy request sanitization taking place.

Filters would have access to modify the redirected request headers. However, as far as I can read the chain would not have access to the redirect response headers.

cc @alyssawilk do you have any suggestions here?

[alyssawilk]

There's no way to do this with Envoy's redirect utils.
We could potentially add this as config and code to the Envoy code or you could handle the redirect in a custom filter.

[majames]

@alyssawilk thanks for the response! It'd be great if Envoy supported adding the redirect response headers to the subsequent request!

you could handle the redirect in a custom filter

Do you mind adding a little bit more detail to this please? From my understanding you're suggesting:

1. I remove the internal redirect handling configuration from my Envoy config
2. And, instead, use a Lua response handler instead. The response handler would check if the response is a 302 and, if it is, initiate a response_handle:httpCall() to the targeted upstream which includes the headers of interest from the original response. The response from this httpCall() would then be passed through to the downstream service via the response_handle:headers() and response_handle:body():setBytes() APIs

[alyssawilk]

ah, I was thinking more of a C++ filter which called recreateStream much as the router filter does today for internal redirects. sorry I'm not terribly familiar with Envoy's lua fitler so I can't speak to how well that option would work.

[majames]

Gotcha. I've never heard of a C++ filter or recreateStream... do you have docs you could link me about these please? 🙏

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