// New takes a state snapshot of the given Raft instance into a temporary file
// and returns an object that gives access to the file as an io.Reader. You must
// arrange to call Close() on the returned object or else you will leak a
// temporary file.
func New(logger *log.Logger, r *raft.Raft) (*Snapshot, error) {
// Take the snapshot.
future := r.Snapshot()
if err := future.Error(); err != nil {
return nil, fmt.Errorf("Raft error when taking snapshot: %v", err)
}
// Open up the snapshot.
metadata, snap, err := future.Open()
if err != nil {
return nil, fmt.Errorf("failed to open snapshot: %v:", err)
}
defer func() {
if err := snap.Close(); err != nil {
logger.Printf("[ERR] snapshot: Failed to close Raft snapshot: %v", err)
}
}()
// Make a scratch file to receive the contents so that we don't buffer
// everything in memory. This gets deleted in Close() since we keep it
// around for re-reading.
archive, err := ioutil.TempFile("", "snapshot")
if err != nil {
return nil, fmt.Errorf("failed to create snapshot file: %v", err)
}
// If anything goes wrong after this point, we will attempt to clean up
// the temp file. The happy path will disarm this.
var keep bool
defer func() {
if keep {
return
}
if err := os.Remove(archive.Name()); err != nil {
logger.Printf("[ERR] snapshot: Failed to clean up temp snapshot: %v", err)
}
}()
// Wrap the file writer in a gzip compressor.
compressor := gzip.NewWriter(archive)
// Write the archive.
if err := write(compressor, metadata, snap); err != nil {
return nil, fmt.Errorf("failed to write snapshot file: %v", err)
}
// Finish the compressed stream.
if err := compressor.Close(); err != nil {
return nil, fmt.Errorf("failed to compress snapshot file: %v", err)
}
// Sync the compressed file and rewind it so it's ready to be streamed
// out by the caller.
if err := archive.Sync(); err != nil {
return nil, fmt.Errorf("failed to sync snapshot: %v", err)
}
if _, err := archive.Seek(0, 0); err != nil {
return nil, fmt.Errorf("failed to rewind snapshot: %v", err)
}
keep = true
return &Snapshot{archive, metadata.Index}, nil
}
