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ipn/store: improve FileStore.WriteState atomicity

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If an error occurs with FileStore.WriteState, it should not record
the provided value as this results in an inconsistency between
what is cached in memory and what is stored on disk.

Also, update the documentation of StateStore.ReadState
to indicate that the returned value should be treated as immutable.
This property is assumed by the fact that FileStore.ReadState
returns the same slice of bytes for repeated calls to the same key.

Updates #cleanup

Signed-off-by: Joe Tsai <joetsai@digital-static.net>
This commit is contained in:
Joe Tsai 2023-11-06 11:45:10 -08:00
parent 60e768fd14
commit 2ad040db3b
2 changed files with 13 additions and 6 deletions
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5
ipn/store.go
View File

@ -68,8 +68,9 @@ func CurrentProfileKey(userID string) StateKey {
// StateStore persists state, and produces it back on request.
type StateStore interface {
// ReadState returns the bytes associated with ID. Returns (nil,
// ErrStateNotExist) if the ID doesn't have associated state.
// ReadState returns the bytes associated with ID.
// It returns (nil, ErrStateNotExist) if the ID doesn't have associated state.
// The returned value must not be mutated.
ReadState(id StateKey) ([]byte, error)
// WriteState saves bs as the state associated with ID.
//

14
ipn/store/stores.go
View File

@ -173,16 +173,22 @@ func (s *FileStore) ReadState(id ipn.StateKey) ([]byte, error) {
}
// WriteState implements the StateStore interface.
func (s *FileStore) WriteState(id ipn.StateKey, bs []byte) error {
func (s *FileStore) WriteState(id ipn.StateKey, bs []byte) (err error) {
s.mu.Lock()
defer s.mu.Unlock()
if bytes.Equal(s.cache[id], bs) {
bs0 := s.cache[id]
if bytes.Equal(bs0, bs) {
return nil
}
defer func() {
if err != nil {
s.cache[id] = bs0
}
}()
s.cache[id] = bytes.Clone(bs)
bs, err := json.MarshalIndent(s.cache, "", " ")
b, err := json.MarshalIndent(s.cache, "", " ")
if err != nil {
return err
}
return atomicfile.WriteFile(s.path, bs, 0600)
return atomicfile.WriteFile(s.path, b, 0600)
}