dotcloud/docker

package daemon // import "github.com/docker/docker/daemon"

import (
    "os"
    "path/filepath"

    "github.com/docker/docker/pkg/ioutils"
    "github.com/google/uuid"
    "github.com/pkg/errors"
)

const idFilename = "engine-id"

// LoadOrCreateID loads the engine's ID from the given root, or generates a new ID
// if it doesn't exist. It returns the ID, and any error that occurred when
// saving the file.
//
// Note that this function expects the daemon's root directory to already have
// been created with the right permissions and ownership (usually this would
// be done by daemon.CreateDaemonRoot().
func LoadOrCreateID(root string) (string, error) {
    var id string
    idPath := filepath.Join(root, idFilename)
    idb, err := os.ReadFile(idPath)
    if os.IsNotExist(err) {
        id = uuid.New().String()
        if err := ioutils.AtomicWriteFile(idPath, []byte(id), os.FileMode(0o600)); err != nil {
            return "", errors.Wrap(err, "error saving ID file")
        }
    } else if err != nil {
        return "", errors.Wrapf(err, "error loading ID file %s", idPath)
    } else {
        id = string(idb)
    }
    return id, nil
}