feat(kuma-cp) add GatewayRoute route generation (kumahq#2782)

Add machinery to generate Envoy routes from GatewayRoute resources. This
is split into a generator that translates GatewayRoute resources into a
generic route table structure, and a generator that translates the generic
structure into Envoy resources. The generic route table structure provides
an API-independent way to configure Envoy.

This change only generates routes (not cluster or endpoints), but the full
semantics of GatewayRoute are supported, including path prefix matches,
multiple match criteria and correct route match ordering.

Signed-off-by: James Peach <james.peach@konghq.com>

api/mesh/v1alpha1/gateway_route.proto

@@ -272,12 +272,16 @@ message GatewayRoute {
 
       // Filters are request processing steps that are applied to
       // matched requests.
+      //
+      // If the redirect filter is specified, it must be the only
+      // filter given.
       repeated Filter filters = 2;
 
       // Backends is the set of services to which the gateway will
-      // forward requests.
-      repeated Backend backends = 3
-          [ (doc.required) = true, (validate.rules).repeated .min_items = 1 ];
+      // forward requests. If a redirect filter is specified, no
+      // backends are allowed. Otherwise, at least one backend
+      // must be given.
+      repeated Backend backends = 3 [ (doc.required) = false ];
     };
 
     // Hostnames lists the server names for which this route is valid. The

pkg/core/resources/apis/mesh/gateway_route_validator.go

@@ -104,24 +104,46 @@ func validateGatewayRouteHTTPRule(
 	path validators.PathBuilder,
 	conf *mesh_proto.GatewayRoute_HttpRoute_Rule,
 ) validators.ValidationError {
+	var hasRedirect bool
+
 	if len(conf.GetMatches()) < 1 {
 		return validators.MakeRequiredFieldErr(path.Field("matches"))
 	}
 
-	if len(conf.GetBackends()) < 1 {
-		return validators.MakeRequiredFieldErr(path.Field("backends"))
-	}
-
 	var err validators.ValidationError
 
 	for i, m := range conf.GetMatches() {
 		err.Add(validateGatewayRouteHTTPMatch(path.Field("matches").Index(i), m))
 	}
 
 	for i, f := range conf.GetFilters() {
+		if f.GetRedirect() != nil {
+			hasRedirect = true
+		}
+
 		err.Add(validateGatewayRouteHTTPFilter(path.Field("filters").Index(i), f))
 	}
 
+	// It doesn't make sense to redirect and also mirror or rewrite request headers.
+	if hasRedirect && len(conf.GetFilters()) != 1 {
+		err.AddViolationAt(path.Field("filters"), "redirects cannot be used with other filters")
+
+		// Return since the redirect filter error makes the backend length check ambiguous.
+		return err
+	}
+
+	switch len(conf.GetBackends()) {
+	case 0:
+		// Redirection doesn't forward, so there must not be any backend.
+		if !hasRedirect {
+			err.AddViolationAt(path.Field("backends"), "cannot be empty")
+		}
+	default:
+		if hasRedirect {
+			err.AddViolationAt(path.Field("backends"), "must be empty when using redirect filters")
+		}
+	}
+
 	for i, b := range conf.GetBackends() {
 		err.Add(validateGatewayRouteBackend(path.Field("backends").Index(i), b))
 	}

pkg/core/resources/apis/mesh/gateway_route_validator_test.go

@@ -23,6 +23,7 @@ func (g GatewayRouteGenerator) New() model.Resource {
 
 var _ = Describe("GatewayRoute", func() {
 	DescribeValidCases(GatewayRouteGenerator(NewGatewayRouteResource),
+
 		Entry("HTTP route", `
 type: GatewayRoute
 name: route
@@ -53,19 +54,18 @@ conf:
           value: kong
       filters:
       - request_header:
-        set:
-        - name: x-foo
-          value: foo
-        add:
-        - name: x-added
-          value: added
-        remove:
-        - x-deleted
-      - redirect:
-         scheme: http
-         hostname: foo.example.com
-         port: 80
-         status_code: 307
+          set:
+          - name: x-foo
+            value: foo
+          - name: x-foo
+            value: foo
+          add:
+          - name: x-added
+            value: added
+          - name: x-added
+            value: added
+          remove:
+          - x-deleted
       - mirror:
          percentage: 1.12
          backend:
@@ -78,6 +78,41 @@ conf:
       - weight: 5
         destination:
           kuma.io/service: target-2
+`),
+		Entry("HTTP redirect", `
+type: GatewayRoute
+name: route
+mesh: default
+selectors:
+- match:
+    kuma.io/service: gateway
+conf:
+  http:
+    hostnames:
+    - foo.example.com
+    rules:
+    - matches:
+      - method: GET
+        path:
+          match: EXACT
+          value: /
+        headers:
+        - match: EXACT
+          name: x-foo
+          value: "my great foo"
+        - match: REGEX
+          name: x-count
+          value: "[0-9]+"
+        query_parameters:
+        - match: EXACT
+          name: customer
+          value: kong
+      filters:
+      - redirect:
+         scheme: http
+         hostname: foo.example.com
+         port: 80
+         status_code: 307
 `),
 	)
 
@@ -496,10 +531,6 @@ conf:
       - redirect:
           hostname: example.com
           status_code: 301
-      backends:
-      - weight: 5
-        destination:
-          kuma.io/service: target-2
 `),
 		ErrorCase("redirect filter with empty hostname", validators.Violation{
 			Field:   "conf.http.rules[0].filters[0].redirect.hostname",
@@ -521,10 +552,6 @@ conf:
       - redirect:
           scheme: https
           status_code: 301
-      backends:
-      - weight: 5
-        destination:
-          kuma.io/service: target-2
 `),
 		ErrorCase("redirect filter with invalid port", validators.Violation{
 			Field:   "conf.http.rules[0].filters[0].redirect.port",
@@ -548,10 +575,6 @@ conf:
           hostname: example.com
           port: 128555
           status_code: 301
-      backends:
-      - weight: 5
-        destination:
-          kuma.io/service: target-2
 `),
 		ErrorCase("redirect filter with invalid status", validators.Violation{
 			Field:   "conf.http.rules[0].filters[0].redirect.status_code",
@@ -574,10 +597,59 @@ conf:
           scheme: https
           hostname: example.com
           status_code: 500
+`),
+		ErrorCase("redirect filter with backend routes", validators.Violation{
+			Field:   "conf.http.rules[0].backends",
+			Message: "must be empty when using redirect filters",
+		}, `
+type: GatewayRoute
+name: route
+mesh: default
+selectors:
+- match:
+    kuma.io/service: gateway
+conf:
+  http:
+    rules:
+    - matches:
+      - path:
+          value: /
+      filters:
+      - redirect:
+          scheme: https
+          hostname: example.com
+          status_code: 300
       backends:
       - weight: 5
         destination:
           kuma.io/service: target-2
+`),
+		ErrorCase("redirect prevents other filters", validators.Violation{
+			Field:   "conf.http.rules[0].filters",
+			Message: "redirects cannot be used with other filters",
+		}, `
+type: GatewayRoute
+name: route
+mesh: default
+selectors:
+- match:
+    kuma.io/service: gateway
+conf:
+  http:
+    rules:
+    - matches:
+      - path:
+          value: /
+      filters:
+      - redirect:
+          scheme: https
+          hostname: example.com
+          status_code: 300
+      - mirror:
+        backends:
+        - weight: 5
+          destination:
+            kuma.io/service: target-2
 `),
 	)
 })