Implement store read cache (#1366)

* Implement store read cache

* Added cache tests and fixed a bug in memory store

store/cache/cache_test.go

@@ -0,0 +1,97 @@
+package cache
+
+import (
+	"sort"
+	"testing"
+
+	"github.com/micro/go-micro/v2/store"
+	"github.com/micro/go-micro/v2/store/memory"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCache(t *testing.T) {
+	l0, l1, l2 := memory.NewStore(store.Namespace("l0")), memory.NewStore(store.Prefix("l1")), memory.NewStore(store.Suffix("l2"))
+	_, _, _ = l0.Init(), l1.Init(), l2.Init()
+
+	assert := assert.New(t)
+
+	nonCache := NewCache(l0)
+	assert.NotNil(nonCache.Init(), "Expected a cache initialised with just 1 store to fail")
+
+	// Basic functionality
+	cachedStore := NewCache(l0, l1, l2)
+	assert.Nil(cachedStore.Init(), "Init should not error")
+	assert.Equal(cachedStore.Options(), store.Options{}, "Options on store/cache are nonsensical")
+	expectedString := "cache [memory memory memory]"
+	assert.Equal(cachedStore.String(), expectedString, "Cache couldn't describe itself as expected")
+
+	// Read/Write tests
+	_, err := cachedStore.Read("test")
+	assert.Equal(store.ErrNotFound, err, "Read non existant key")
+	r1 := &store.Record{
+		Key:   "aaa",
+		Value: []byte("bbb"),
+	}
+	r2 := &store.Record{
+		Key:   "aaaa",
+		Value: []byte("bbbb"),
+	}
+	r3 := &store.Record{
+		Key:   "aaaaa",
+		Value: []byte("bbbbb"),
+	}
+	// Write 3 records directly to l2
+	l2.Write(r1)
+	l2.Write(r2)
+	l2.Write(r3)
+	// Ensure it's not in l0
+	assert.Equal(store.ErrNotFound, func() error { _, err := l0.Read(r1.Key); return err }())
+	// Read from cache, ensure it's in all 3 stores
+	results, err := cachedStore.Read(r1.Key)
+	assert.Nil(err, "cachedStore.Read() returned error")
+	assert.Len(results, 1, "cachedStore.Read() should only return 1 result")
+	assert.Equal(r1, results[0], "Cached read didn't return the record that was put in")
+	results, err = l0.Read(r1.Key)
+	assert.Nil(err)
+	assert.Equal(r1, results[0], "l0 not coherent")
+	results, err = l1.Read(r1.Key)
+	assert.Nil(err)
+	assert.Equal(r1, results[0], "l1 not coherent")
+	results, err = l2.Read(r1.Key)
+	assert.Nil(err)
+	assert.Equal(r1, results[0], "l2 not coherent")
+	// Multiple read
+	results, err = cachedStore.Read("aa", store.ReadPrefix())
+	assert.Nil(err, "Cachedstore multiple read errored")
+	assert.Len(results, 3, "ReadPrefix should have read all records")
+	// l1 should now have all 3 records
+	l1results, err := l1.Read("aa", store.ReadPrefix())
+	assert.Nil(err, "l1.Read failed")
+	assert.Len(l1results, 3, "l1 didn't contain a full cache")
+	sort.Slice(results, func(i, j int) bool { return results[i].Key < results[j].Key })
+	sort.Slice(l1results, func(i, j int) bool { return l1results[i].Key < l1results[j].Key })
+	assert.Equal(results[0], l1results[0], "l1 cache not coherent")
+	assert.Equal(results[1], l1results[1], "l1 cache not coherent")
+	assert.Equal(results[2], l1results[2], "l1 cache not coherent")
+
+	// Test List and Delete
+	keys, err := cachedStore.List(store.ListPrefix("a"))
+	assert.Nil(err, "List should not error")
+	assert.Len(keys, 3, "List should return 3 keys")
+	for _, k := range keys {
+		err := cachedStore.Delete(k)
+		assert.Nil(err, "Delete should not error")
+		_, err = cachedStore.Read(k)
+		// N.B. - this may not pass on stores that are eventually consistent
+		assert.Equal(store.ErrNotFound, err, "record should be gone")
+	}
+
+	// Test Write
+	err = cachedStore.Write(r1)
+	assert.Nil(err, "Write shouldn't fail")
+	l2result, err := l2.Read(r1.Key)
+	assert.Nil(err)
+	assert.Len(l2result, 1)
+	assert.Equal(r1, l2result[0], "Write didn't make it all the way through to l2")
+
+}