Add support for ResponseHeaderModifier for HTTPRouteRule objects

Problem: Users want to add, set, and remove response headers.

Solution: Use add_header and proxy_hide_header NGINX directives to support ResponseHeaderModifier.

If the action is set, we configure the proxy_hide_header directive to remove the header if exists and add_header directive with the given value in the HTTPRoute spec.
If the action is remove, we configure the proxy_hide_header directive to remove the header.
If the action is add, we simply configure the add_header directive with the given value in the HTTPRoute spec.

Author: kevin85421

internal/mode/static/state/graph/httproute.go

@@ -703,9 +703,9 @@ func validateFilter(
 	case v1.HTTPRouteFilterURLRewrite:
 		return validateFilterRewrite(validator, filter, filterPath)
 	case v1.HTTPRouteFilterRequestHeaderModifier:
-		return validateFilterHeaderModifier(filter.Type, validator, filter.RequestHeaderModifier, filterPath)
+		return validateFilterHeaderModifier(validator, filter.RequestHeaderModifier, filterPath.Child(string(filter.Type)))
 	case v1.HTTPRouteFilterResponseHeaderModifier:
-		return validateFilterHeaderModifier(filter.Type, validator, filter.ResponseHeaderModifier, filterPath)
+		return validateFilterHeaderModifier(validator, filter.ResponseHeaderModifier, filterPath.Child(string(filter.Type)))
 	default:
 		valErr := field.NotSupported(
 			filterPath.Child("type"),
@@ -816,19 +816,15 @@ func validateFilterRewrite(
 }
 
 func validateFilterHeaderModifier(
-	filterType v1.HTTPRouteFilterType,
 	validator validation.HTTPFieldsValidator,
 	headerModifier *v1.HTTPHeaderFilter,
 	filterPath *field.Path,
 ) field.ErrorList {
-	filterTypeStr := string(filterType)
-	headerModifierPath := filterPath.Child(filterTypeStr)
-
 	if headerModifier == nil {
-		return field.ErrorList{field.Required(headerModifierPath, "requestHeaderModifier cannot be nil")}
+		return field.ErrorList{field.Required(filterPath, "cannot be nil")}
 	}
 
-	return validateFilterHeaderModifierFields(validator, headerModifier, headerModifierPath)
+	return validateFilterHeaderModifierFields(validator, headerModifier, filterPath)
 }
 
 func validateFilterHeaderModifierFields(

internal/mode/static/state/graph/httproute_test.go

@@ -2412,7 +2412,7 @@ func TestValidateFilterRequestHeaderModifier(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			g := NewWithT(t)
 			allErrs := validateFilterHeaderModifier(
-				gatewayv1.HTTPRouteFilterRequestHeaderModifier, test.validator, test.filter.RequestHeaderModifier, filterPath,
+				test.validator, test.filter.RequestHeaderModifier, filterPath,
 			)
 			g.Expect(allErrs).To(HaveLen(test.expectErrCount))
 		})