2 files changed, 136 insertions, 0 deletions
diff --git a/internal/serving/disk/projectroot/root.go b/internal/serving/disk/projectroot/root.go
new file mode 100644
index 00000000..64f830c0
--- /dev/null
+++ b/internal/serving/disk/projectroot/root.go
@@ -0,0 +1,47 @@
+package projectroot
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+
+	"gitlab.com/gitlab-org/gitlab-pages/internal/feature"
+	"gitlab.com/gitlab-org/gitlab-pages/internal/vfs"
+)
+
+// projectRoot implements the more low-level vfs.Root interface and can be used in its
+// stead. The difference is, it always resolves the files inside the project's
+// rootDirectory by prepending that dir to any open request.
+type projectRoot struct {
+	rootDirectory string
+	vfsRoot       vfs.Root
+}
+
+func New(rootDirectory string, vfsRoot vfs.Root) vfs.Root {
+	if !feature.ConfigurableRoot.Enabled() || rootDirectory == "" {
+		// In case the GitLab API is not up-to-date this string may be empty.
+		// In that case default to the legacy behavior
+		rootDirectory = "public"
+	}
+
+	return &projectRoot{
+		rootDirectory: rootDirectory,
+		vfsRoot:       vfsRoot,
+	}
+}
+
+func (r *projectRoot) Open(ctx context.Context, name string) (vfs.File, error) {
+	return r.vfsRoot.Open(ctx, r.getPath(name))
+}
+
+func (r *projectRoot) Lstat(ctx context.Context, name string) (os.FileInfo, error) {
+	return r.vfsRoot.Lstat(ctx, r.getPath(name))
+}
+
+func (r *projectRoot) Readlink(ctx context.Context, name string) (string, error) {
+	return r.vfsRoot.Readlink(ctx, r.getPath(name))
+}
+
+func (r *projectRoot) getPath(name string) string {
+	return filepath.Join(r.rootDirectory, name)
+}
diff --git a/internal/serving/disk/projectroot/root_test.go b/internal/serving/disk/projectroot/root_test.go
new file mode 100644
index 00000000..b8549d10
--- /dev/null
+++ b/internal/serving/disk/projectroot/root_test.go
@@ -0,0 +1,89 @@
+package projectroot
+
+import (
+	"context"
+	"os"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"gitlab.com/gitlab-org/gitlab-pages/internal/feature"
+	"gitlab.com/gitlab-org/gitlab-pages/internal/vfs"
+)
+
+// In case this moch struct ever grows in complexity,
+// consider using mockgen instead:
+// e.g. internal/domain/mock/resolver_mock.go
+type mockRoot struct {
+	lstatCalledWith    string
+	readlinkCalledWith string
+	openCalledWith     string
+}
+
+func (m *mockRoot) Lstat(ctx context.Context, name string) (os.FileInfo, error) {
+	m.lstatCalledWith = name
+	return nil, nil
+}
+
+func (m *mockRoot) Readlink(ctx context.Context, name string) (string, error) {
+	m.readlinkCalledWith = name
+	return "", nil
+}
+
+func (m *mockRoot) Open(ctx context.Context, name string) (vfs.File, error) {
+	m.openCalledWith = name
+	return nil, nil
+}
+
+func TestProjectRoot(t *testing.T) {
+	tests := map[string]struct {
+		path           string
+		rootDir        string
+		expectedPath   string
+		featureEnabled bool
+	}{
+		"when the root dir is provided": {
+			path:           "some/path",
+			rootDir:        "my_root_dir",
+			expectedPath:   "my_root_dir/some/path",
+			featureEnabled: true,
+		},
+		"when the root dir is not provided": {
+			path:           "some/path",
+			rootDir:        "",
+			expectedPath:   "public/some/path",
+			featureEnabled: true,
+		},
+		"when the feature is disabled": {
+			path:           "some/path",
+			rootDir:        "my_root_dir",
+			expectedPath:   "public/some/path",
+			featureEnabled: false,
+		},
+		"when the feature is disabled and no root path is provided": {
+			path:           "some/path",
+			rootDir:        "",
+			expectedPath:   "public/some/path",
+			featureEnabled: false,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Setenv(feature.ConfigurableRoot.EnvVariable,
+				strconv.FormatBool(test.featureEnabled))
+			originalRoot := &mockRoot{}
+			wrappedRoot := New(test.rootDir, originalRoot)
+
+			wrappedRoot.Lstat(context.Background(), test.path)
+			require.Equal(t, test.expectedPath, originalRoot.lstatCalledWith)
+
+			wrappedRoot.Readlink(context.Background(), test.path)
+			require.Equal(t, test.expectedPath, originalRoot.readlinkCalledWith)
+
+			wrappedRoot.Open(context.Background(), test.path)
+			require.Equal(t, test.expectedPath, originalRoot.openCalledWith)
+		})
+	}
+}