Caching policies added.

We used httpcache library to implement this. As it was not possible to support different policies, I mostly copied and modified it.

cache/leveldbcache/leveldbcache.go

@@ -0,0 +1,51 @@
+// Package leveldbcache provides an implementation of cache.Cache that
+// uses github.com/syndtr/goleveldb/leveldb
+package leveldbcache
+
+import (
+	"github.com/syndtr/goleveldb/leveldb"
+)
+
+// Cache is an implementation of cache.Cache with leveldb storage
+type Cache struct {
+	Db *leveldb.DB
+}
+
+// Get returns the response corresponding to key if present
+func (c *Cache) Get(key string) (resp []byte, ok bool) {
+	var err error
+	resp, err = c.Db.Get([]byte(key), nil)
+	if err != nil {
+		return []byte{}, false
+	}
+	return resp, true
+}
+
+// Set saves a response to the cache as key
+func (c *Cache) Set(key string, resp []byte) {
+	_ = c.Db.Put([]byte(key), resp, nil)
+}
+
+// Delete removes the response with key from the cache
+func (c *Cache) Delete(key string) {
+	_ = c.Db.Delete([]byte(key), nil)
+}
+
+// New returns a new Cache that will store leveldb in path
+func New(path string) (*Cache, error) {
+	cache := &Cache{}
+
+	var err error
+	cache.Db, err = leveldb.OpenFile(path, nil)
+
+	if err != nil {
+		return nil, err
+	}
+	return cache, nil
+}
+
+// NewWithDB returns a new Cache using the provided leveldb as underlying
+// storage.
+func NewWithDB(db *leveldb.DB) *Cache {
+	return &Cache{db}
+}