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527 lines
16 KiB
Go
527 lines
16 KiB
Go
// Copyright 2011 Google Inc. All rights reserved.
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// Use of this source code is governed by the Apache 2.0
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// license that can be found in the LICENSE file.
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// Package memcache provides a client for App Engine's distributed in-memory
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// key-value store for small chunks of arbitrary data.
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//
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// The fundamental operations get and set items, keyed by a string.
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//
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// item0, err := memcache.Get(c, "key")
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// if err != nil && err != memcache.ErrCacheMiss {
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// return err
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// }
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// if err == nil {
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// fmt.Fprintf(w, "memcache hit: Key=%q Val=[% x]\n", item0.Key, item0.Value)
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// } else {
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// fmt.Fprintf(w, "memcache miss\n")
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// }
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//
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// and
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//
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// item1 := &memcache.Item{
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// Key: "foo",
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// Value: []byte("bar"),
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// }
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// if err := memcache.Set(c, item1); err != nil {
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// return err
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// }
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package memcache // import "google.golang.org/appengine/memcache"
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import (
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"bytes"
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"encoding/gob"
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"encoding/json"
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"errors"
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"time"
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"github.com/golang/protobuf/proto"
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"golang.org/x/net/context"
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"google.golang.org/appengine"
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"google.golang.org/appengine/internal"
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pb "google.golang.org/appengine/internal/memcache"
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)
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var (
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// ErrCacheMiss means that an operation failed
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// because the item wasn't present.
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ErrCacheMiss = errors.New("memcache: cache miss")
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// ErrCASConflict means that a CompareAndSwap call failed due to the
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// cached value being modified between the Get and the CompareAndSwap.
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// If the cached value was simply evicted rather than replaced,
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// ErrNotStored will be returned instead.
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ErrCASConflict = errors.New("memcache: compare-and-swap conflict")
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// ErrNoStats means that no statistics were available.
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ErrNoStats = errors.New("memcache: no statistics available")
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// ErrNotStored means that a conditional write operation (i.e. Add or
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// CompareAndSwap) failed because the condition was not satisfied.
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ErrNotStored = errors.New("memcache: item not stored")
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// ErrServerError means that a server error occurred.
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ErrServerError = errors.New("memcache: server error")
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)
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// Item is the unit of memcache gets and sets.
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type Item struct {
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// Key is the Item's key (250 bytes maximum).
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Key string
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// Value is the Item's value.
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Value []byte
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// Object is the Item's value for use with a Codec.
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Object interface{}
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// Flags are server-opaque flags whose semantics are entirely up to the
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// App Engine app.
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Flags uint32
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// Expiration is the maximum duration that the item will stay
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// in the cache.
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// The zero value means the Item has no expiration time.
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// Subsecond precision is ignored.
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// This is not set when getting items.
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Expiration time.Duration
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// casID is a client-opaque value used for compare-and-swap operations.
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// Zero means that compare-and-swap is not used.
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casID uint64
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}
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const (
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secondsIn30Years = 60 * 60 * 24 * 365 * 30 // from memcache server code
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thirtyYears = time.Duration(secondsIn30Years) * time.Second
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)
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// protoToItem converts a protocol buffer item to a Go struct.
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func protoToItem(p *pb.MemcacheGetResponse_Item) *Item {
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return &Item{
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Key: string(p.Key),
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Value: p.Value,
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Flags: p.GetFlags(),
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casID: p.GetCasId(),
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}
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}
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// If err is an appengine.MultiError, return its first element. Otherwise, return err.
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func singleError(err error) error {
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if me, ok := err.(appengine.MultiError); ok {
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return me[0]
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}
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return err
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}
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// Get gets the item for the given key. ErrCacheMiss is returned for a memcache
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// cache miss. The key must be at most 250 bytes in length.
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func Get(c context.Context, key string) (*Item, error) {
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m, err := GetMulti(c, []string{key})
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if err != nil {
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return nil, err
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}
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if _, ok := m[key]; !ok {
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return nil, ErrCacheMiss
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}
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return m[key], nil
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}
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// GetMulti is a batch version of Get. The returned map from keys to items may
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// have fewer elements than the input slice, due to memcache cache misses.
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// Each key must be at most 250 bytes in length.
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func GetMulti(c context.Context, key []string) (map[string]*Item, error) {
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if len(key) == 0 {
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return nil, nil
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}
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keyAsBytes := make([][]byte, len(key))
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for i, k := range key {
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keyAsBytes[i] = []byte(k)
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}
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req := &pb.MemcacheGetRequest{
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Key: keyAsBytes,
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ForCas: proto.Bool(true),
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}
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res := &pb.MemcacheGetResponse{}
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if err := internal.Call(c, "memcache", "Get", req, res); err != nil {
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return nil, err
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}
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m := make(map[string]*Item, len(res.Item))
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for _, p := range res.Item {
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t := protoToItem(p)
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m[t.Key] = t
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}
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return m, nil
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}
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// Delete deletes the item for the given key.
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// ErrCacheMiss is returned if the specified item can not be found.
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// The key must be at most 250 bytes in length.
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func Delete(c context.Context, key string) error {
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return singleError(DeleteMulti(c, []string{key}))
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}
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// DeleteMulti is a batch version of Delete.
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// If any keys cannot be found, an appengine.MultiError is returned.
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// Each key must be at most 250 bytes in length.
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func DeleteMulti(c context.Context, key []string) error {
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if len(key) == 0 {
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return nil
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}
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req := &pb.MemcacheDeleteRequest{
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Item: make([]*pb.MemcacheDeleteRequest_Item, len(key)),
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}
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for i, k := range key {
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req.Item[i] = &pb.MemcacheDeleteRequest_Item{Key: []byte(k)}
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}
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res := &pb.MemcacheDeleteResponse{}
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if err := internal.Call(c, "memcache", "Delete", req, res); err != nil {
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return err
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}
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if len(res.DeleteStatus) != len(key) {
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return ErrServerError
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}
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me, any := make(appengine.MultiError, len(key)), false
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for i, s := range res.DeleteStatus {
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switch s {
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case pb.MemcacheDeleteResponse_DELETED:
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// OK
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case pb.MemcacheDeleteResponse_NOT_FOUND:
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me[i] = ErrCacheMiss
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any = true
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default:
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me[i] = ErrServerError
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any = true
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}
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}
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if any {
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return me
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}
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return nil
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}
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// Increment atomically increments the decimal value in the given key
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// by delta and returns the new value. The value must fit in a uint64.
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// Overflow wraps around, and underflow is capped to zero. The
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// provided delta may be negative. If the key doesn't exist in
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// memcache, the provided initial value is used to atomically
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// populate it before the delta is applied.
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// The key must be at most 250 bytes in length.
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func Increment(c context.Context, key string, delta int64, initialValue uint64) (newValue uint64, err error) {
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return incr(c, key, delta, &initialValue)
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}
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// IncrementExisting works like Increment but assumes that the key
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// already exists in memcache and doesn't take an initial value.
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// IncrementExisting can save work if calculating the initial value is
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// expensive.
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// An error is returned if the specified item can not be found.
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func IncrementExisting(c context.Context, key string, delta int64) (newValue uint64, err error) {
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return incr(c, key, delta, nil)
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}
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func incr(c context.Context, key string, delta int64, initialValue *uint64) (newValue uint64, err error) {
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req := &pb.MemcacheIncrementRequest{
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Key: []byte(key),
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InitialValue: initialValue,
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}
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if delta >= 0 {
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req.Delta = proto.Uint64(uint64(delta))
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} else {
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req.Delta = proto.Uint64(uint64(-delta))
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req.Direction = pb.MemcacheIncrementRequest_DECREMENT.Enum()
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}
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res := &pb.MemcacheIncrementResponse{}
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err = internal.Call(c, "memcache", "Increment", req, res)
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if err != nil {
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return
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}
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if res.NewValue == nil {
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return 0, ErrCacheMiss
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}
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return *res.NewValue, nil
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}
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// set sets the given items using the given conflict resolution policy.
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// appengine.MultiError may be returned.
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func set(c context.Context, item []*Item, value [][]byte, policy pb.MemcacheSetRequest_SetPolicy) error {
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if len(item) == 0 {
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return nil
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}
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req := &pb.MemcacheSetRequest{
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Item: make([]*pb.MemcacheSetRequest_Item, len(item)),
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}
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for i, t := range item {
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p := &pb.MemcacheSetRequest_Item{
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Key: []byte(t.Key),
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}
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if value == nil {
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p.Value = t.Value
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} else {
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p.Value = value[i]
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}
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if t.Flags != 0 {
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p.Flags = proto.Uint32(t.Flags)
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}
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if t.Expiration != 0 {
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// In the .proto file, MemcacheSetRequest_Item uses a fixed32 (i.e. unsigned)
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// for expiration time, while MemcacheGetRequest_Item uses int32 (i.e. signed).
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// Throughout this .go file, we use int32.
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// Also, in the proto, the expiration value is either a duration (in seconds)
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// or an absolute Unix timestamp (in seconds), depending on whether the
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// value is less than or greater than or equal to 30 years, respectively.
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if t.Expiration < time.Second {
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// Because an Expiration of 0 means no expiration, we take
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// care here to translate an item with an expiration
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// Duration between 0-1 seconds as immediately expiring
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// (saying it expired a few seconds ago), rather than
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// rounding it down to 0 and making it live forever.
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p.ExpirationTime = proto.Uint32(uint32(time.Now().Unix()) - 5)
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} else if t.Expiration >= thirtyYears {
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p.ExpirationTime = proto.Uint32(uint32(time.Now().Unix()) + uint32(t.Expiration/time.Second))
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} else {
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p.ExpirationTime = proto.Uint32(uint32(t.Expiration / time.Second))
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}
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}
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if t.casID != 0 {
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p.CasId = proto.Uint64(t.casID)
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p.ForCas = proto.Bool(true)
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}
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p.SetPolicy = policy.Enum()
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req.Item[i] = p
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}
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res := &pb.MemcacheSetResponse{}
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if err := internal.Call(c, "memcache", "Set", req, res); err != nil {
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return err
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}
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if len(res.SetStatus) != len(item) {
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return ErrServerError
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}
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me, any := make(appengine.MultiError, len(item)), false
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for i, st := range res.SetStatus {
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var err error
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switch st {
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case pb.MemcacheSetResponse_STORED:
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// OK
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case pb.MemcacheSetResponse_NOT_STORED:
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err = ErrNotStored
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case pb.MemcacheSetResponse_EXISTS:
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err = ErrCASConflict
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default:
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err = ErrServerError
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}
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if err != nil {
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me[i] = err
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any = true
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}
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}
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if any {
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return me
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}
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return nil
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}
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// Set writes the given item, unconditionally.
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func Set(c context.Context, item *Item) error {
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return singleError(set(c, []*Item{item}, nil, pb.MemcacheSetRequest_SET))
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}
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// SetMulti is a batch version of Set.
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// appengine.MultiError may be returned.
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func SetMulti(c context.Context, item []*Item) error {
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return set(c, item, nil, pb.MemcacheSetRequest_SET)
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}
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// Add writes the given item, if no value already exists for its key.
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// ErrNotStored is returned if that condition is not met.
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func Add(c context.Context, item *Item) error {
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return singleError(set(c, []*Item{item}, nil, pb.MemcacheSetRequest_ADD))
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}
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// AddMulti is a batch version of Add.
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// appengine.MultiError may be returned.
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func AddMulti(c context.Context, item []*Item) error {
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return set(c, item, nil, pb.MemcacheSetRequest_ADD)
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}
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// CompareAndSwap writes the given item that was previously returned by Get,
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// if the value was neither modified or evicted between the Get and the
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// CompareAndSwap calls. The item's Key should not change between calls but
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// all other item fields may differ.
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// ErrCASConflict is returned if the value was modified in between the calls.
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// ErrNotStored is returned if the value was evicted in between the calls.
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func CompareAndSwap(c context.Context, item *Item) error {
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return singleError(set(c, []*Item{item}, nil, pb.MemcacheSetRequest_CAS))
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}
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// CompareAndSwapMulti is a batch version of CompareAndSwap.
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// appengine.MultiError may be returned.
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func CompareAndSwapMulti(c context.Context, item []*Item) error {
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return set(c, item, nil, pb.MemcacheSetRequest_CAS)
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}
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// Codec represents a symmetric pair of functions that implement a codec.
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// Items stored into or retrieved from memcache using a Codec have their
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// values marshaled or unmarshaled.
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//
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// All the methods provided for Codec behave analogously to the package level
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// function with same name.
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type Codec struct {
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Marshal func(interface{}) ([]byte, error)
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Unmarshal func([]byte, interface{}) error
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}
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// Get gets the item for the given key and decodes the obtained value into v.
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// ErrCacheMiss is returned for a memcache cache miss.
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// The key must be at most 250 bytes in length.
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func (cd Codec) Get(c context.Context, key string, v interface{}) (*Item, error) {
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i, err := Get(c, key)
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if err != nil {
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return nil, err
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}
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if err := cd.Unmarshal(i.Value, v); err != nil {
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return nil, err
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}
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return i, nil
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}
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func (cd Codec) set(c context.Context, items []*Item, policy pb.MemcacheSetRequest_SetPolicy) error {
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var vs [][]byte
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var me appengine.MultiError
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for i, item := range items {
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v, err := cd.Marshal(item.Object)
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if err != nil {
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if me == nil {
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me = make(appengine.MultiError, len(items))
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}
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me[i] = err
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continue
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}
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if me == nil {
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vs = append(vs, v)
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}
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}
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if me != nil {
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return me
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}
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return set(c, items, vs, policy)
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}
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// Set writes the given item, unconditionally.
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func (cd Codec) Set(c context.Context, item *Item) error {
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return singleError(cd.set(c, []*Item{item}, pb.MemcacheSetRequest_SET))
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}
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// SetMulti is a batch version of Set.
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// appengine.MultiError may be returned.
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func (cd Codec) SetMulti(c context.Context, items []*Item) error {
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return cd.set(c, items, pb.MemcacheSetRequest_SET)
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}
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// Add writes the given item, if no value already exists for its key.
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// ErrNotStored is returned if that condition is not met.
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func (cd Codec) Add(c context.Context, item *Item) error {
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return singleError(cd.set(c, []*Item{item}, pb.MemcacheSetRequest_ADD))
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}
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// AddMulti is a batch version of Add.
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// appengine.MultiError may be returned.
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func (cd Codec) AddMulti(c context.Context, items []*Item) error {
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return cd.set(c, items, pb.MemcacheSetRequest_ADD)
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}
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// CompareAndSwap writes the given item that was previously returned by Get,
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// if the value was neither modified or evicted between the Get and the
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// CompareAndSwap calls. The item's Key should not change between calls but
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// all other item fields may differ.
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// ErrCASConflict is returned if the value was modified in between the calls.
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// ErrNotStored is returned if the value was evicted in between the calls.
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func (cd Codec) CompareAndSwap(c context.Context, item *Item) error {
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return singleError(cd.set(c, []*Item{item}, pb.MemcacheSetRequest_CAS))
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}
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// CompareAndSwapMulti is a batch version of CompareAndSwap.
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// appengine.MultiError may be returned.
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func (cd Codec) CompareAndSwapMulti(c context.Context, items []*Item) error {
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return cd.set(c, items, pb.MemcacheSetRequest_CAS)
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}
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var (
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// Gob is a Codec that uses the gob package.
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Gob = Codec{gobMarshal, gobUnmarshal}
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// JSON is a Codec that uses the json package.
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JSON = Codec{json.Marshal, json.Unmarshal}
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)
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func gobMarshal(v interface{}) ([]byte, error) {
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var buf bytes.Buffer
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if err := gob.NewEncoder(&buf).Encode(v); err != nil {
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return nil, err
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}
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return buf.Bytes(), nil
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}
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func gobUnmarshal(data []byte, v interface{}) error {
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return gob.NewDecoder(bytes.NewBuffer(data)).Decode(v)
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}
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// Statistics represents a set of statistics about the memcache cache.
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// This may include items that have expired but have not yet been removed from the cache.
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type Statistics struct {
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Hits uint64 // Counter of cache hits
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Misses uint64 // Counter of cache misses
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ByteHits uint64 // Counter of bytes transferred for gets
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Items uint64 // Items currently in the cache
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Bytes uint64 // Size of all items currently in the cache
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Oldest int64 // Age of access of the oldest item, in seconds
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}
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// Stats retrieves the current memcache statistics.
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func Stats(c context.Context) (*Statistics, error) {
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req := &pb.MemcacheStatsRequest{}
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res := &pb.MemcacheStatsResponse{}
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if err := internal.Call(c, "memcache", "Stats", req, res); err != nil {
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return nil, err
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}
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if res.Stats == nil {
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return nil, ErrNoStats
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}
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return &Statistics{
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Hits: *res.Stats.Hits,
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Misses: *res.Stats.Misses,
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ByteHits: *res.Stats.ByteHits,
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Items: *res.Stats.Items,
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Bytes: *res.Stats.Bytes,
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Oldest: int64(*res.Stats.OldestItemAge),
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}, nil
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}
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|
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// Flush flushes all items from memcache.
|
|
func Flush(c context.Context) error {
|
|
req := &pb.MemcacheFlushRequest{}
|
|
res := &pb.MemcacheFlushResponse{}
|
|
return internal.Call(c, "memcache", "FlushAll", req, res)
|
|
}
|
|
|
|
func namespaceMod(m proto.Message, namespace string) {
|
|
switch m := m.(type) {
|
|
case *pb.MemcacheDeleteRequest:
|
|
if m.NameSpace == nil {
|
|
m.NameSpace = &namespace
|
|
}
|
|
case *pb.MemcacheGetRequest:
|
|
if m.NameSpace == nil {
|
|
m.NameSpace = &namespace
|
|
}
|
|
case *pb.MemcacheIncrementRequest:
|
|
if m.NameSpace == nil {
|
|
m.NameSpace = &namespace
|
|
}
|
|
case *pb.MemcacheSetRequest:
|
|
if m.NameSpace == nil {
|
|
m.NameSpace = &namespace
|
|
}
|
|
// MemcacheFlushRequest, MemcacheStatsRequest do not apply namespace.
|
|
}
|
|
}
|
|
|
|
func init() {
|
|
internal.RegisterErrorCodeMap("memcache", pb.MemcacheServiceError_ErrorCode_name)
|
|
internal.NamespaceMods["memcache"] = namespaceMod
|
|
}
|