in-memory lru cache of limited capacity

fix memLimit flag usage

use megabytes as a unit for memory store capacity

fix incorrect item rearrangement in lru cache

use latest 1.x Go on trais

pkg/store/mem_test.go

@@ -0,0 +1,74 @@
+package store
+
+import (
+	"context"
+	"math/rand"
+	"testing"
+)
+
+func TestMemoryStore(t *testing.T) {
+	ctx := context.Background()
+	m := Memory(t.Log, -1)
+	m.Put(ctx, Snapshot{Module: "foo", Version: "v1.0.0", Data: []byte("hello")})
+	m.Put(ctx, Snapshot{Module: "bar", Version: "v1.0.0", Data: []byte{}})
+	m.Put(ctx, Snapshot{Module: "baz", Version: "v1.0.0", Data: []byte("world")})
+	if res, err := m.Get(ctx, "foo", "v1.0.0"); err != nil {
+		t.Fatal(err)
+	} else if res.Module != "foo" || res.Version != "v1.0.0" || string(res.Data) != "hello" {
+		t.Fatal(res)
+	}
+}
+
+func TestMemoryStoreOverflow(t *testing.T) {
+	ctx := context.Background()
+	m := Memory(t.Log, 10)
+	m.Put(ctx, Snapshot{Module: "foo", Version: "v1.0.0", Data: make([]byte, 4)})
+	m.Put(ctx, Snapshot{Module: "bar", Version: "v1.0.0", Data: make([]byte, 7)})
+
+	// "foo" should be removed, because adding "bar" exceeds the capacity
+	if res, err := m.Get(ctx, "foo", "v1.0.0"); err == nil {
+		t.Fatal(res)
+	} else if _, err := m.Get(ctx, "bar", "v1.0.0"); err != nil {
+		t.Fatal(err)
+	}
+
+	m.Put(ctx, Snapshot{Module: "baz", Version: "v1.0.0", Data: make([]byte, 3)})
+
+	// both "bar" and "baz" should be in store
+	if _, err := m.Get(ctx, "bar", "v1.0.0"); err != nil {
+		t.Fatal(err)
+	} else if _, err := m.Get(ctx, "baz", "v1.0.0"); err != nil {
+		t.Fatal(err)
+	}
+
+	m.Get(ctx, "bar", "v1.0.0")
+	m.Put(ctx, Snapshot{Module: "qux", Version: "v1.0.0", Data: make([]byte, 3)})
+
+	// "bar" should remain in store, since it was accessed recently, "baz" should be removed
+	if _, err := m.Get(ctx, "bar", "v1.0.0"); err != nil {
+		t.Fatal(err)
+	} else if res, err := m.Get(ctx, "baz", "v1.0.0"); err == nil {
+		t.Fatal(res)
+	}
+}
+
+func TestMemoryStoreRandom(t *testing.T) {
+	snaphots := []Snapshot{
+		Snapshot{Module: "a", Version: "v1.0.0", Data: make([]byte, 1)},
+		Snapshot{Module: "b", Version: "v1.0.0", Data: make([]byte, 3)},
+		Snapshot{Module: "c", Version: "v1.0.0", Data: make([]byte, 5)},
+		Snapshot{Module: "d", Version: "v1.0.0", Data: make([]byte, 7)},
+		Snapshot{Module: "e", Version: "v1.0.0", Data: make([]byte, 11)},
+		Snapshot{Module: "f", Version: "v1.0.0", Data: make([]byte, 13)},
+	}
+
+	m := Memory(t.Log, 12)
+	for i := 0; i < 100; i++ {
+		ctx := context.Background()
+		if rand.Int()%5 > 2 {
+			m.Put(ctx, snaphots[rand.Intn(len(snaphots))])
+		} else {
+			m.Get(ctx, snaphots[rand.Intn(len(snaphots))].Module, "v1.0.0")
+		}
+	}
+}