mirror of
https://github.com/golang/go
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83 lines
2.0 KiB
Go
83 lines
2.0 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package cache
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import (
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"fmt"
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"net/http"
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"time"
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"appengine"
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"appengine/memcache"
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)
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const (
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nocache = "nocache"
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timeKey = "cachetime"
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expiry = 600 // 10 minutes
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)
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func newTime() uint64 { return uint64(time.Now().Unix()) << 32 }
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// Now returns the current logical datastore time to use for cache lookups.
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func Now(c appengine.Context) uint64 {
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t, err := memcache.Increment(c, timeKey, 0, newTime())
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if err != nil {
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c.Errorf("cache.Now: %v", err)
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return 0
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}
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return t
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}
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// Tick sets the current logical datastore time to a never-before-used time
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// and returns that time. It should be called to invalidate the cache.
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func Tick(c appengine.Context) uint64 {
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t, err := memcache.Increment(c, timeKey, 1, newTime())
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if err != nil {
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c.Errorf("cache.Tick: %v", err)
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return 0
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}
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return t
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}
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// Get fetches data for name at time now from memcache and unmarshals it into
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// value. It reports whether it found the cache record and logs any errors to
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// the admin console.
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func Get(r *http.Request, now uint64, name string, value interface{}) bool {
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if now == 0 || r.FormValue(nocache) != "" {
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return false
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}
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c := appengine.NewContext(r)
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key := fmt.Sprintf("%s.%d", name, now)
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_, err := memcache.JSON.Get(c, key, value)
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if err == nil {
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c.Debugf("cache hit %q", key)
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return true
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}
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c.Debugf("cache miss %q", key)
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if err != memcache.ErrCacheMiss {
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c.Errorf("get cache %q: %v", key, err)
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}
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return false
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}
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// Set puts value into memcache under name at time now.
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// It logs any errors to the admin console.
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func Set(r *http.Request, now uint64, name string, value interface{}) {
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if now == 0 || r.FormValue(nocache) != "" {
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return
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}
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c := appengine.NewContext(r)
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key := fmt.Sprintf("%s.%d", name, now)
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err := memcache.JSON.Set(c, &memcache.Item{
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Key: key,
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Object: value,
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Expiration: expiry,
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})
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if err != nil {
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c.Errorf("set cache %q: %v", key, err)
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}
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}
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