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// Copyright 2021 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 session defines API for the session storage.
package session
import (
// ID identifies a session.
type ID []byte
// String is used to format the ID for logging.
func (id ID) String() string {
return base64.RawStdEncoding.EncodeToString(id)
// GenerateID generates a new random session ID or panics if there's not enough
// entropy.
func GenerateID() ID {
id := make([]byte, 20)
if _, err := rand.Read(id); err != nil {
panic(fmt.Sprintf("failed to generate session ID: %s", err))
return id
// Store is a persistent transactional-capable storage of user sessions.
// Session IDs are assumed to be generated by GenerateID, i.e. be high-entropy
// random blobs.
type Store interface {
// FetchSession fetches an existing session with the given ID.
// Returns (nil, nil) if there's no such session. All errors are transient.
FetchSession(ctx context.Context, id ID) (*sessionpb.Session, error)
// UpdateSession transactionally updates or creates a session.
// If fetches the session, calls the callback to mutate it, and stores the
// result. If it is a new session, the callback receives an empty proto.
// The callback may be called multiple times in case the transaction is
// retried. Errors from callbacks are returned as is. All other errors are
// transient.
UpdateSession(ctx context.Context, id ID, cb func(*sessionpb.Session) error) error