chore: add files cache for reading template tar archives from db (#17141)

coderd/util/lazy/valuewitherror.go

@@ -0,0 +1,25 @@
+package lazy
+
+type ValueWithError[T any] struct {
+	inner Value[result[T]]
+}
+
+type result[T any] struct {
+	value T
+	err   error
+}
+
+// NewWithError allows you to provide a lazy initializer that can fail.
+func NewWithError[T any](fn func() (T, error)) *ValueWithError[T] {
+	return &ValueWithError[T]{
+		inner: Value[result[T]]{fn: func() result[T] {
+			value, err := fn()
+			return result[T]{value: value, err: err}
+		}},
+	}
+}
+
+func (v *ValueWithError[T]) Load() (T, error) {
+	result := v.inner.Load()
+	return result.value, result.err
+}

coderd/util/lazy/valuewitherror_test.go

@@ -0,0 +1,52 @@
+package lazy_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/coderd/util/lazy"
+)
+
+func TestLazyWithErrorOK(t *testing.T) {
+	t.Parallel()
+
+	l := lazy.NewWithError(func() (int, error) {
+		return 1, nil
+	})
+
+	i, err := l.Load()
+	require.NoError(t, err)
+	require.Equal(t, 1, i)
+}
+
+func TestLazyWithErrorErr(t *testing.T) {
+	t.Parallel()
+
+	l := lazy.NewWithError(func() (int, error) {
+		return 0, xerrors.New("oh no! everything that could went horribly wrong!")
+	})
+
+	i, err := l.Load()
+	require.Error(t, err)
+	require.Equal(t, 0, i)
+}
+
+func TestLazyWithErrorPointers(t *testing.T) {
+	t.Parallel()
+
+	a := 1
+	l := lazy.NewWithError(func() (*int, error) {
+		return &a, nil
+	})
+
+	b, err := l.Load()
+	require.NoError(t, err)
+	c, err := l.Load()
+	require.NoError(t, err)
+
+	*b++
+	*c++
+	require.Equal(t, 3, a)
+}