frontend: address router review feedback

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

Author: cpuguy83

frontend/client.go

@@ -20,6 +20,9 @@ const (
 	// for the builder.
 	KeyDefaultPlatform = "frontend.dalec.defaultPlatform"
 	KeyJSONSchema      = "frontend.dalec.schema"
+
+	resultJSONMetaKey = "result.json"
+	resultTextMetaKey = "result.txt"
 )
 
 const keyTarget = "target"
@@ -38,9 +41,7 @@ func (err *noSuchHandlerError) Error() string {
 	return fmt.Sprintf("no such handler for target %q: available targets: %s", err.Target, strings.Join(err.Available, ", "))
 }
 
-var (
-	_ gwclient.Client = (*clientWithCustomOpts)(nil)
-)
+var _ gwclient.Client = (*clientWithCustomOpts)(nil)
 
 type clientWithCustomOpts struct {
 	opts gwclient.BuildOpts
@@ -112,10 +113,10 @@ func handleResolveSpec(ctx context.Context, client gwclient.Client) (*gwclient.R
 	}
 
 	res := gwclient.NewResult()
-	res.AddMeta("result.json", dtJSON)
+	res.AddMeta(resultJSONMetaKey, dtJSON)
 	// result.txt here so that `docker buildx build --print` will output it directly.
 	// Otherwise it prints a go object.
-	res.AddMeta("result.txt", dtYaml)
+	res.AddMeta(resultTextMetaKey, dtYaml)
 
 	return res, nil
 }
@@ -130,17 +131,17 @@ func handleDefaultPlatform() (*gwclient.Result, error) {
 		return nil, err
 	}
 
-	res.AddMeta("result.json", dt)
-	res.AddMeta("result.txt", []byte(platforms.Format(p)))
+	res.AddMeta(resultJSONMetaKey, dt)
+	res.AddMeta(resultTextMetaKey, []byte(platforms.Format(p)))
 
 	return res, nil
 }
 
 func handleJSONSchema() (*gwclient.Result, error) {
 	res := gwclient.NewResult()
 	jsonSchema := dalec.GetJSONSchema()
-	res.AddMeta("result.json", jsonSchema)
-	res.AddMeta("result.txt", jsonSchema)
+	res.AddMeta(resultJSONMetaKey, jsonSchema)
+	res.AddMeta(resultTextMetaKey, jsonSchema)
 
 	return res, nil
 }

frontend/router.go

@@ -204,8 +204,8 @@ func (r *Router) describe() (*gwclient.Result, error) {
 
 	res := gwclient.NewResult()
 	res.Metadata = map[string][]byte{
-		"result.txt": buf.Bytes(),
-		"version":    []byte(subrequests.SubrequestsDescribeDefinition.Version),
+		resultTextMetaKey: buf.Bytes(),
+		"version":         []byte(subrequests.SubrequestsDescribeDefinition.Version),
 	}
 	return res, nil
 }
@@ -273,9 +273,9 @@ func queryForwardedTargets(ctx context.Context, client gwclient.Client, prefix s
 		return nil, err
 	}
 
-	dt, ok := res.Metadata["result.json"]
+	dt, ok := res.Metadata[resultJSONMetaKey]
 	if !ok {
-		return nil, errors.New("forwarded frontend did not return result.json")
+		return nil, errors.New("forwarded frontend did not return " + resultJSONMetaKey)
 	}
 
 	var remote bktargets.List
@@ -300,13 +300,13 @@ func dalecTargetListToResult(ls TargetList) (*gwclient.Result, error) {
 	if err != nil {
 		return nil, errors.Wrap(err, "error marshalling target list to json")
 	}
-	res.AddMeta("result.json", dtJSON)
+	res.AddMeta(resultJSONMetaKey, dtJSON)
 
 	buf := bytes.NewBuffer(nil)
 	if err := printTargets(ls, buf); err != nil {
 		return nil, err
 	}
-	res.AddMeta("result.txt", buf.Bytes())
+	res.AddMeta(resultTextMetaKey, buf.Bytes())
 
 	res.AddMeta("version", []byte(bktargets.SubrequestsTargetsDefinition.Version))
 	return res, nil
@@ -336,20 +336,17 @@ func printTargets(ls TargetList, w io.Writer) error {
 }
 
 // lookupTarget finds the route matching the given target string.
-// It tries exact match first, then longest prefix match.
 // An empty target is always an error — callers must specify a target key.
+// Otherwise it tries exact match first, then longest prefix match.
 func (r *Router) lookupTarget(ctx context.Context, target string) (matchedPath string, _ *Route, _ error) {
-	// 1. Exact match
-	if route, ok := r.routes[target]; ok {
-		return target, &route, nil
-	}
-
-	// 2. Empty target — no global default; prompt the user.
 	if target == "" {
 		return "", nil, handlerNotFound(target, maps.Keys(r.routes))
 	}
 
-	// 3. Longest prefix match
+	if route, ok := r.routes[target]; ok {
+		return target, &route, nil
+	}
+
 	var candidates []string
 	for k := range r.routes {
 		if strings.HasPrefix(target, k+"/") {

frontend/router_test.go

@@ -144,6 +144,15 @@ func TestRouterPrefixMatch(t *testing.T) {
 func TestRouterEmptyTargetReturnsError(t *testing.T) {
 	ctx := context.Background()
 	var r Router
+	var emptyRouteCalled bool
+
+	r.Add(ctx, Route{
+		FullPath: "",
+		Handler: func(context.Context, gwclient.Client) (*gwclient.Result, error) {
+			emptyRouteCalled = true
+			return nil, nil
+		},
+	})
 
 	r.Add(ctx, Route{
 		FullPath: "mydefault",
@@ -163,6 +172,9 @@ func TestRouterEmptyTargetReturnsError(t *testing.T) {
 	if !errors.As(err, &nsh) {
 		t.Fatalf("expected noSuchHandlerError, got %T: %v", err, err)
 	}
+	if emptyRouteCalled {
+		t.Fatal("expected empty target to error before matching empty route")
+	}
 }
 
 func TestRouterNotFound(t *testing.T) {