Envoy: Accessing request headers in envoy_on_response (lua HTTP filter).

[ashwinphatak]

I'm trying to use a lua HTTP filter to set a response header whose value depends on a request header.

As a simple example, suppose we want to copy a header from the request to the response. How can we do this using a lua filter?

Maybe we can store the request header in a "global" table during envoy_on_request and read it later when envoy_on_response is called. However, even if this approach makes sense, how can we correlate responses with requests to be able to do this?

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This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or other activity occurs. Thank you for your contributions.

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[mderazon]

This will be very helpful.
One use case for this:
datawire/ambassador#1847

[Stono]

Could we please reopen this as it's an excellent use case?
For example; we wish to write a response handler which logs information about the request in error scenarios!

[vbuciuc]

see the example here:

https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/lua_filter#set

it stores headers in dynamic metadata in the request handler which are then available in the response handler

[vbuciuc]

see the example here:

https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/lua_filter#set

it stores headers in dynamic metadata in the request handler which are then available in the response handler

[ErikXu]

@vbuciuc Works for me. But the filterName in dynamicMetadata:set(filterName, key, value) confuses me. I have my own http filter named my-filter. Which name should I use, my-filter, my-filter.lua or envoy.filters.http.lua? In addition, is the data stored in a lua file?

[dio]

@ErikXu sorry for confusing docs and late reply. So the filterName can be anything, think about a namespace (we need to update the docs).

As an example:

          - name: envoy.filters.http.lua
            typed_config:
              "@type": type.googleapis.com/envoy.config.filter.http.lua.v2.Lua
              inline_code: |
                function envoy_on_request(request_handle)
                  request_handle:streamInfo():dynamicMetadata():set("context", "foo", "bar")
                end
                function envoy_on_response(response_handle)
                  local foo = response_handle:streamInfo():dynamicMetadata():get("context")["foo"]
                  response_handle:logInfo(foo)
                end