dscache: Use math/rand's Read for nonce.

filter/dscache/dscache.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package dscache
 
 import (
         "bytes"
         "crypto/sha1"
         "encoding/base64"
@@ skipping 65 matching lines @@
         ValueSizeLimit = (1000 * 1000) - InternalGAEPadding - MaxShardsLen
 
         // CacheEnableMeta is the gae metadata key name for whether or not dscache
         // is enabled for an entity type at all.
         CacheEnableMeta = "dscache.enable"
 
         // CacheExpirationMeta is the gae metadata key name for the default
         // expiration time (in seconds) for an entity type.
         CacheExpirationMeta = "dscache.expiration"
 
-        // NonceUint32s is the number of 32 bit uints to use in the 'lock' nonce.
-        NonceUint32s = 2
+        // NonceBytes is the number of bytes to use in the 'lock' nonce.
+        NonceBytes = 8
 
         // GlobalEnabledCheckInterval is how frequently IsGloballyEnabled should check
         // the globalEnabled datastore entry.
         GlobalEnabledCheckInterval = 5 * time.Minute
 )
 
 // internalValueSizeLimit is a var for testing purposes.
 var internalValueSizeLimit = ValueSizeLimit
 
 // CompressionType is the type of compression a single memcache entry has.
@@ skipping 36 matching lines @@
 
 // HashKey generates just the hashed portion of the MemcacheKey.
 func HashKey(k *datastore.Key) string {
         dgst := sha1.Sum(serialize.ToBytes(k))
         buf := bytes.Buffer{}
         enc := base64.NewEncoder(base64.StdEncoding, &buf)
         _, _ = enc.Write(dgst[:])
         enc.Close()
         return buf.String()[:buf.Len()-Sha1B64Padding]
 }