fix(translator): Fix panic with request mirror + grpcroute

[AndyMoreland]

What this PR does / why we need it:

This fixes an unconditional panic when the RequestMirror filter is used with GRPCRoutes

Which issue(s) this PR fixes:

Fixes #6874

Release Notes: No

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.08%. Comparing base (c181d47) to head (c502048).
⚠️ Report is 200 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6875      +/-   ##
==========================================
- Coverage   71.10%   71.08%   -0.03%     
==========================================
  Files         225      225              
  Lines       39859    39868       +9     
==========================================
- Hits        28343    28340       -3     
- Misses       9848     9857       +9     
- Partials     1668     1671       +3     

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[arkodg]

can we eliminate this ?
validateBackendRef already accepts a backend interface

gateway/internal/gatewayapi/validate.go

Line 29 in c181d47

func (t *Translator) validateBackendRef(backendRefContext BackendRefContext, route RouteContext,

[AndyMoreland]

@arkodg I think we need some kind of split in the concrete type of the iface approximately here, because validateBackendRefFilters needs GRPCRoutes to have a GRPCRouteFilter-containing-backendref, and HTTPRoutes to have an HTTPRouteFilter-containing-backendref -- the panic was caused by the existing unification causing the downstream cast to fail.

[AndyMoreland]

(I'm not a go expert or familiar with the types in play, but this was the smallest code diff way I found to avoid the unchecked cast panic)

[kkk777-7]

@AndyMoreland
thanks for raising the issue and working on the fix!
If we just want to switch the type of BackendRef, how about retrieving the RouteType from filterContext and converting it to the appropriate type?

e.g.

	var mirrorBackendRef BackendRefContext
	routeType := GetRouteType(filterContext.Route)
	if routeType == resource.KindGRPCRoute {
		mirrorBackendRef = gwapiv1.GRPCBackendRef{
			BackendRef: gwapiv1.BackendRef{
				BackendObjectReference: mirrorBackend,
				Weight:                 &weight,
			},
		}
	} else {
		mirrorBackendRef = gwapiv1.HTTPBackendRef{
			BackendRef: gwapiv1.BackendRef{
				BackendObjectReference: mirrorBackend,
				Weight:                 &weight,
			},
		}
	}

	// This sets the status on the HTTPRoute, should the usage be changed so that the status message reflects that the backendRef is from the filter?
	filterNs := filterContext.Route.GetNamespace()
	serviceNamespace := NamespaceDerefOr(mirrorBackend.Namespace, filterNs)
	err = t.validateBackendRef(mirrorBackendRef, filterContext.Route,
		resources, serviceNamespace, routeType)

[arkodg]

+1 to #6875 (comment)

[AndyMoreland]

I've applied the suggested change

[arkodg]

thanks for addressing the comments @AndyMoreland, added one minor comment

[AndyMoreland]

I've merged your suggestion

[arkodg]

LGTM thanks