Add memcache implementation of cache (#1848)

cache/memcache/memcache.go

@@ -0,0 +1,80 @@
+// Package memcache is a memcache implementation of the Cache
+package memcache
+
+import (
+	"encoding/json"
+
+	"github.com/bradfitz/gomemcache/memcache"
+	"github.com/micro/go-micro/v2/cache"
+)
+
+type memcacheCache struct {
+	options cache.Options
+	client  *memcache.Client
+}
+
+type memcacheItem struct {
+	Key   string
+	Value interface{}
+}
+
+func (m *memcacheCache) Init(opts ...cache.Option) error {
+	for _, o := range opts {
+		o(&m.options)
+	}
+	return nil
+}
+
+func (m *memcacheCache) Get(key string) (interface{}, error) {
+	item, err := m.client.Get(key)
+	if err != nil {
+		return nil, err
+	}
+
+	var mc *memcacheItem
+
+	if err := json.Unmarshal(item.Value, &mc); err != nil {
+		return nil, err
+	}
+
+	return mc.Value, nil
+}
+
+func (m *memcacheCache) Set(key string, val interface{}) error {
+	b, err := json.Marshal(val)
+	if err != nil {
+		return err
+	}
+
+	return m.client.Set(&memcache.Item{
+		Key:   key,
+		Value: b,
+	})
+}
+
+func (m *memcacheCache) Delete(key string) error {
+	return m.client.Delete(key)
+}
+
+func (m *memcacheCache) String() string {
+	return "memcache"
+}
+
+// NewCache returns a new memcache Cache
+func NewCache(opts ...cache.Option) cache.Cache {
+	var options cache.Options
+	for _, o := range opts {
+		o(&options)
+	}
+
+	// get and set the nodes
+	nodes := options.Nodes
+	if len(nodes) == 0 {
+		nodes = []string{"localhost:11211"}
+	}
+
+	return &memcacheCache{
+		options: options,
+		client:  memcache.New(nodes...),
+	}
+}