Client headers are parsed into the context before coprocessor hook

[smyrick]

EDIT: The initial use case can now be solved with a work-around, see below, but there still exists the issue, even if non-urgent that there is not some external hook mechanism before the Router reads HTTP request data

Describe the bug In 1.40.2 the populate_context function, which is called in the SupergraphService lifecycle, looks up the client_name_header and stores it in the context.

In 1.45.1, it no longer looks up that header in that function. Glancing through, it looks like this occurred in this commit, "Remove Legacy Validation".

So, it looks like the client name is now extracted in an Apollo-owned Router Service plugin. To my knowledge, this will run before any plugin lifecycle we can possibly create - Router Service is the earliest lifecycle, and Apollo space ones will always run before user space plugins I think. So, in the current state I don't think modifications to the client name header are possible from our code. Is this intended, or is there a workaround to ensure we can update headers prior to the header being collected for telemetry?

To Reproduce

• Start Router with the following YAML

telemetry:
  apollo:
    client_name_header: x-caller-id
    client_version_header: x-caller-version

• Add a rhai script or coprocessor that mutates the headers and copies the value from one header to the client one

x-foobar-name -> x-caller-id x-foobar-version -> x-caller-version

• The operations in GraphOS still appear as Unidentified client because the Apollo code runs before any custom plugin

Expected behavior I can use Rust, Rhai, or Coprocessor plugins at some stage to mutate the headers before Apollo uses them

Desktop (please complete the following information):

• OS: MacOS 14.5

• Version Router 1.45.1

  I sent the header shane-1-40 on Router 1.40.0 and shane-1-47 on Router 1.47.0 and I only see the old name in Studio

[smyrick]

I was able to reproduce the bug here: https://github.com/apollosolutions/router-playground/pull/25

[Geal]

Could a router level rhai script fix it? Here would be the order of operations:

• query comes in
• telemetry plugin runs at the router service level, extracts data from headers and puts it in the apollo_telemetry::client_name and apollo_telemetry::client_version context keys
• the rhai router plugin updates the context key by looking the corect values from the different headers
• on the way out, when looking at responses, the telemetry plugin gets the name and versions from the context

[smyrick]

@Geal That works! I modified the coprocessor to manually set the context value from the header

payload.context.entries['apollo_telemetry::client_name'] = headerValue;

If this is our recommended way to set the client reporting values then that works for this, but we still have the issue that we can't mutate any other headers before Router reads them. Shouldn't the coprocessor be the first call out in the the RouterRequest lifecycle?

[Geal]

for various reasons, telemetry has to be called before everything else. We're planning changes to the pipeline that might help here