// 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 (h *Handler) doPost(w http.ResponseWriter, r *http.Request, id int64) {
var err error
session := common.GetUserSession(r)
if !common.VerifyXsrfToken(r, kSingle) {
err = common.ErrXsrf
} else if http_util.HasParam(r.Form, "delete") {
if isIdValid(id) {
err = h.Store.RemoveEntry(nil, id, session.User.GetOwner())
}
} else if http_util.HasParam(r.Form, "cancel") {
// Do nothing
} else {
var mutation functional.Filterer
mutation, err = toEntry(r.Form)
if err == nil {
if isIdValid(id) {
tag, _ := strconv.ParseUint(r.Form.Get("etag"), 10, 64)
err = h.Doer.Do(func(t db.Transaction) error {
return vsafedb.UpdateEntryWithEtag(
h.Store, t, id, tag, session.Key(), mutation)
})
} else {
var newId int64
var entry vsafe.Entry
mutation.Filter(&entry)
newId, err = vsafedb.AddEntry(h.Store, nil, session.Key(), &entry)
if err == nil {
id = newId
}
}
}
}
if err == vsafedb.ErrConcurrentModification {
err = errors.New("Someone else updated this entry after you started. Click cancel and try again.")
}
if err != nil {
http_util.WriteTemplate(
w,
kTemplate,
newView(
r.Form,
isIdValid(id),
session.Key().Id,
common.NewXsrfToken(r, kSingle),
err))
} else {
goBack(w, r, id)
}
}