// UpdateEntryWithEtag updates an entry in persistent storage in a way that
// detects concurrent modification. It also prevents users from modifying
// entries they do not own by returning ErrNoSuchId. t, the transaction,
// must be non nil.
func UpdateEntryWithEtag(
store SafeUpdateEntryRunner,
t db.Transaction,
id int64,
tag uint64,
key *vsafe.Key,
update functional.Filterer) error {
if t == nil {
panic("Transaction must be non-nil")
}
var origEntry vsafe.EntryWithEtag
err := EntryByIdWithEtag(store, t, id, key, &origEntry)
if err != nil {
return err
}
err = update.Filter(&origEntry.Entry)
if err == functional.Skipped {
return nil
}
if err != nil {
return err
}
if tag != origEntry.Etag {
return ErrConcurrentModification
}
origEntry.Id = id
return UpdateEntry(store, t, key, &origEntry.Entry)
}
func (f FakeStore) EntryByIdWithEtag(
t db.Transaction, id int64, e *vsafe.EntryWithEtag) error {
// Only computes etag on the string fields
if int(id) > len(f) {
return vsafedb.ErrNoSuchId
}
e.Entry = *f[id-1]
e.Etag = 57
return nil
}