go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/logdog/common/storage/cache.go (about)

     1  // Copyright 2016 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package storage
    16  
    17  import (
    18  	"bufio"
    19  	"context"
    20  	"crypto/sha256"
    21  	"encoding/hex"
    22  	"time"
    23  )
    24  
    25  // CacheKey is a single cache item's key.
    26  type CacheKey struct {
    27  	// Schema is the item's schema value. If empty, the item is schemaless.
    28  	Schema string
    29  
    30  	// Type is the item's type identifier. If empty, the item has no type.
    31  	Type string
    32  
    33  	// Key is the item's individual key. It uniquely identifies the Item within
    34  	// the scope of the Schema and Type.
    35  	Key string
    36  }
    37  
    38  // Cache is a simple cache interface. It is capable of storage and retrieval.
    39  type Cache interface {
    40  	// Put caches an Items into the cache. If an item already exists in the cache,
    41  	// it will be overridden.
    42  	//
    43  	// The data in val may be directly retained by the cache, and the caller
    44  	// promises not to mutate it after being passed to Put.
    45  	//
    46  	// If exp, the supplied expiration Duration, is >0, the cache should only
    47  	// store the data if it can expire it after this period of time.
    48  	//
    49  	// This method does not return whether or not the caching storage was
    50  	// successful.
    51  	Put(c context.Context, key CacheKey, val []byte, exp time.Duration)
    52  
    53  	// Get retrieves a cached entry. If the entry was present, the returned
    54  	// boolean will be true.
    55  	//
    56  	// The returned byte slice may not be modified by the caller.
    57  	//
    58  	// This method does not distinguish between an error and missing data. Either
    59  	// valid data is returned, or it is not.
    60  	Get(c context.Context, key CacheKey) ([]byte, bool)
    61  }
    62  
    63  // HashKey composes a hex-encoded SHA256 string from the supplied parts. The
    64  // local schema version and KeyType are included in the hash.
    65  func HashKey(parts ...string) string {
    66  	hash := sha256.New()
    67  	bio := bufio.NewWriter(hash)
    68  
    69  	// Add a full NULL-delimited key sequence segment to our hash.
    70  	for i, part := range parts {
    71  		// Write the separator, except for the first key.
    72  		if i > 0 {
    73  			if _, err := bio.WriteRune('\x00'); err != nil {
    74  				panic(err)
    75  			}
    76  		}
    77  
    78  		if _, err := bio.WriteString(part); err != nil {
    79  			panic(err)
    80  		}
    81  	}
    82  	if err := bio.Flush(); err != nil {
    83  		panic(err)
    84  	}
    85  
    86  	// Return the hex-encoded hash sum.
    87  	return hex.EncodeToString(hash.Sum(nil))
    88  }