tusd/etcd3locker/locker.go

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// Package etcd3locker provides a locking mechanism using an etcd3 cluster
//
// To initialize a locker, a pre-existing connected etcd3 client must be present
//
// client, err := clientv3.New(clientv3.Config{
// Endpoints: []string{harness.Endpoint},
// DialTimeout: 5 * time.Second,
// })
//
// For the most basic locker (e.g. non-shared etcd3 cluster / use default TTLs),
// a locker can be instantiated like the following:
//
// locker, err := etcd3locker.New(client)
// if err != nil {
// return nil, fmt.Errorf("Failed to create etcd locker: %v", err.Error())
// }
//
// The locker will need to be included in composer that is used by tusd:
//
// composer := tusd.NewStoreComposer()
// locker.UseIn(composer)
//
// For a shared etcd3 cluster, you may want to modify the prefix that etcd3locker uses:
//
// locker, err := etcd3locker.NewWithPrefix(client, "my-prefix")
// if err != nil {
// return nil, fmt.Errorf("Failed to create etcd locker: %v", err.Error())
// }
//
//
// For full control over all options, an etcd3.LockerOptions may be passed into
// etcd3.NewWithLockerOptions like the following example:
//
// ttl := 15 // seconds
// options := etcd3locker.NewLockerOptions(ttl, "my-prefix")
// locker, err := etcd3locker.NewWithLockerOptions(client, options)
// if err != nil {
// return nil, fmt.Errorf("Failed to create etcd locker: %v", err.Error())
// }
//
// Tested on etcd 3.1/3.2/3.3
//
package etcd3locker
import (
"errors"
"sync"
"time"
"github.com/tus/tusd"
etcd3 "go.etcd.io/etcd/clientv3"
"go.etcd.io/etcd/clientv3/concurrency"
)
var (
ErrLockNotHeld = errors.New("Lock not held")
GrantTimeout = 1500 * time.Millisecond
)
type Etcd3Locker struct {
// etcd3 client session
Client *etcd3.Client
// locks is used for storing Etcd3Locks before they are
// unlocked. If you want to release a lock, you need the same locker
// instance and therefore we need to save them temporarily.
locks map[string]*etcd3Lock
mutex sync.Mutex
prefix string
sessionTimeout int
}
// New constructs a new locker using the provided client.
func New(client *etcd3.Client) (*Etcd3Locker, error) {
return NewWithLockerOptions(client, DefaultLockerOptions())
}
// This method may be used if a different prefix is required for multi-tenant etcd clusters
func NewWithPrefix(client *etcd3.Client, prefix string) (*Etcd3Locker, error) {
lockerOptions := DefaultLockerOptions()
lockerOptions.SetPrefix(prefix)
return NewWithLockerOptions(client, lockerOptions)
}
// This method may be used if we want control over both prefix/session TTLs. This is used for testing in particular.
func NewWithLockerOptions(client *etcd3.Client, opts LockerOptions) (*Etcd3Locker, error) {
locksMap := map[string]*etcd3Lock{}
return &Etcd3Locker{Client: client, prefix: opts.Prefix(), sessionTimeout: opts.Timeout(), locks: locksMap, mutex: sync.Mutex{}}, nil
}
// UseIn adds this locker to the passed composer.
func (locker *Etcd3Locker) UseIn(composer *tusd.StoreComposer) {
composer.UseLocker(locker)
}
// LockUpload tries to obtain the exclusive lock.
func (locker *Etcd3Locker) LockUpload(id string) error {
session, err := locker.createSession()
if err != nil {
return err
}
lock := newEtcd3Lock(session, locker.getId(id))
err = lock.Acquire()
if err != nil {
return err
}
locker.mutex.Lock()
defer locker.mutex.Unlock()
// Only add the lock to our list if the acquire was successful and no error appeared.
locker.locks[locker.getId(id)] = lock
return nil
}
// UnlockUpload releases a lock. If no such lock exists, no error will be returned.
func (locker *Etcd3Locker) UnlockUpload(id string) error {
locker.mutex.Lock()
defer locker.mutex.Unlock()
// Complain if no lock has been found. This can only happen if LockUpload
// has not been invoked before or UnlockUpload multiple times.
lock, ok := locker.locks[locker.getId(id)]
if !ok {
return ErrLockNotHeld
}
err := lock.Release()
if err != nil {
return err
}
defer delete(locker.locks, locker.getId(id))
return lock.CloseSession()
}
func (locker *Etcd3Locker) createSession() (*concurrency.Session, error) {
return concurrency.NewSession(locker.Client, concurrency.WithTTL(locker.sessionTimeout))
}
func (locker *Etcd3Locker) getId(id string) string {
return locker.prefix + id
}