Add cache for file to node relation in cluster proxy

cluster/proxy/cache_test.go

@@ -0,0 +1,72 @@
+package proxy
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+type testTimeSource struct {
+	now time.Time
+}
+
+func (t *testTimeSource) Now() time.Time {
+	return t.now
+}
+
+func TestCache(t *testing.T) {
+	ts := &testTimeSource{
+		now: time.Unix(0, 0),
+	}
+
+	c := NewCache[string](ts)
+
+	_, err := c.Get("foo")
+	require.Error(t, err)
+
+	c.Put("foo", "bar", 10*time.Second)
+
+	v, err := c.Get("foo")
+	require.NoError(t, err)
+	require.Equal(t, "bar", v)
+
+	ts.now = time.Unix(10, 0)
+
+	v, err = c.Get("foo")
+	require.NoError(t, err)
+	require.Equal(t, "bar", v)
+
+	ts.now = time.Unix(11, 0)
+
+	_, err = c.Get("foo")
+	require.Error(t, err)
+}
+
+func TestCachePurge(t *testing.T) {
+	ts := &testTimeSource{
+		now: time.Unix(0, 0),
+	}
+
+	c := NewCache[string](ts)
+
+	c.Put("foo", "bar", 10*time.Second)
+
+	v, err := c.Get("foo")
+	require.NoError(t, err)
+	require.Equal(t, "bar", v)
+
+	ts.now = time.Unix(59, 0)
+
+	c.Put("foz", "boz", 10*time.Second)
+
+	_, ok := c.entries["foo"]
+	require.True(t, ok)
+
+	ts.now = time.Unix(61, 0)
+
+	c.Put("foz", "boz", 10*time.Second)
+
+	_, ok = c.entries["foo"]
+	require.False(t, ok)
+}