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// +build appengine
// Package memcache provides an implementation of httpcache.Cache that uses App
// Engine's memcache package to store cached responses.
//
// When not built for Google App Engine, this package will provide an
// implementation that connects to a specified memcached server. See the
// memcache.go file in this package for details.
package memcache
import (
"appengine"
"appengine/memcache"
)
// Cache is an implementation of httpcache.Cache that caches responses in App
// Engine's memcache.
type Cache struct {
appengine.Context
}
// cacheKey modifies an httpcache key for use in memcache. Specifically, it
// prefixes keys to avoid collision with other data stored in memcache.
func cacheKey(key string) string {
return "httpcache:" + key
}
// Get returns the response corresponding to key if present.
func (c *Cache) Get(key string) (resp []byte, ok bool) {
item, err := memcache.Get(c.Context, cacheKey(key))
if err != nil {
if err != memcache.ErrCacheMiss {
c.Context.Errorf("error getting cached response: %v", err)
}
return nil, false
}
return item.Value, true
}
// Set saves a response to the cache as key.
func (c *Cache) Set(key string, resp []byte) {
item := &memcache.Item{
Key: cacheKey(key),
Value: resp,
}
if err := memcache.Set(c.Context, item); err != nil {
c.Context.Errorf("error caching response: %v", err)
}
}
// Delete removes the response with key from the cache.
func (c *Cache) Delete(key string) {
if err := memcache.Delete(c.Context, cacheKey(key)); err != nil {
c.Context.Errorf("error deleting cached response: %v", err)
}
}
// New returns a new Cache for the given context.
func New(ctx appengine.Context) *Cache {
return &Cache{ctx}
}
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