feat: complete remaining Go backend modules

backend/internal/assets/remote_test.go

@@ -6,9 +6,24 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
+	"strings"
 	"testing"
+	"time"
 )
 
+type assetRoundTripFunc func(*http.Request) (*http.Response, error)
+
+func (function assetRoundTripFunc) RoundTrip(request *http.Request) (*http.Response, error) {
+	return function(request)
+}
+
+type remotePolicyFunc func(context.Context, *url.URL) error
+
+func (function remotePolicyFunc) Validate(ctx context.Context, target *url.URL) error {
+	return function(ctx, target)
+}
+
 func TestHTTPRemoteFetcherRestrictsProtocolAndSize(t *testing.T) {
 	fetcher := NewHTTPRemoteFetcher(http.DefaultClient, 4)
 	if _, err := fetcher.Fetch(context.Background(), "file:///etc/passwd"); !errors.Is(err, ErrRemoteProtocol) {
@@ -40,3 +55,37 @@ func TestHTTPRemoteFetcherReturnsBoundedBody(t *testing.T) {
 		t.Fatalf("blob = %#v body=%q", blob, body)
 	}
 }
+
+func TestPolicyHTTPRemoteFetcherValidatesInitialAndRedirectDestinations(t *testing.T) {
+	validated := make([]string, 0, 2)
+	policy := remotePolicyFunc(func(_ context.Context, target *url.URL) error {
+		validated = append(validated, target.Hostname())
+		if target.Hostname() == "private.test" {
+			return errors.New("private destination")
+		}
+		return nil
+	})
+	client := &http.Client{Timeout: time.Second, Transport: assetRoundTripFunc(func(request *http.Request) (*http.Response, error) {
+		if request.URL.Hostname() == "public.test" {
+			return &http.Response{StatusCode: http.StatusFound, Header: http.Header{"Location": []string{"http://private.test/asset"}}, Body: io.NopCloser(strings.NewReader("")), Request: request}, nil
+		}
+		t.Fatal("redirect target transport must not run")
+		return nil, nil
+	})}
+	fetcher, err := NewPolicyHTTPRemoteFetcher(client, 4, policy)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := fetcher.Fetch(context.Background(), "https://public.test/asset"); err == nil {
+		t.Fatal("policy-denied redirect was accepted")
+	}
+	if strings.Join(validated, ",") != "public.test,private.test" {
+		t.Fatalf("validated destinations = %v", validated)
+	}
+}
+
+func TestNewPublicHTTPRemoteFetcherRequiresPolicy(t *testing.T) {
+	if _, err := NewPublicHTTPRemoteFetcher(time.Second, 4, nil); err == nil {
+		t.Fatal("nil public destination policy accepted")
+	}
+}