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// Copyright 2016 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package storage
import (
// CacheKey is a single cache item's key.
type CacheKey struct {
// Schema is the item's schema value. If empty, the item is schemaless.
Schema string
// Type is the item's type identifier. If empty, the item has no type.
Type string
// Key is the item's individual key. It uniquely identifies the Item within
// the scope of the Schema and Type.
Key string
// Cache is a simple cache interface. It is capable of storage and retrieval.
type Cache interface {
// Put caches an Items into the cache. If an item already exists in the cache,
// it will be overridden.
// The data in val may be directly retained by the cache, and the caller
// promises not to mutate it after being passed to Put.
// If exp, the supplied expiration Duration, is >0, the cache should only
// store the data if it can expire it after this period of time.
// This method does not return whether or not the caching storage was
// successful.
Put(c context.Context, key CacheKey, val []byte, exp time.Duration)
// Get retrieves a cached entry. If the entry was present, the returned
// boolean will be true.
// The returned byte slice may not be modified by the caller.
// This method does not distinguish between an error and missing data. Either
// valid data is returned, or it is not.
Get(c context.Context, key CacheKey) ([]byte, bool)
// HashKey composes a hex-encoded SHA256 string from the supplied parts. The
// local schema version and KeyType are included in the hash.
func HashKey(parts ...string) string {
hash := sha256.New()
bio := bufio.NewWriter(hash)
// Add a full NULL-delimited key sequence segment to our hash.
for i, part := range parts {
// Write the separator, except for the first key.
if i > 0 {
if _, err := bio.WriteRune('\x00'); err != nil {
if _, err := bio.WriteString(part); err != nil {
if err := bio.Flush(); err != nil {
// Return the hex-encoded hash sum.
return hex.EncodeToString(hash.Sum(nil))