github.com/hugh712/snapd@v0.0.0-20200910133618-1a99902bd583/overlord/snapshotstate/backend/restorestate.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2018 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package backend
    21  
    22  import (
    23  	"fmt"
    24  	"os"
    25  	"regexp"
    26  
    27  	"github.com/snapcore/snapd/logger"
    28  	"github.com/snapcore/snapd/randutil"
    29  )
    30  
    31  // RestoreState stores information that can be used to cleanly revert (or finish
    32  // cleaning up) a snapshot Restore.
    33  //
    34  // This is useful when a Restore is part of a chain of operations, and a later
    35  // one failing necessitates undoing the Restore.
    36  type RestoreState struct {
    37  	Done    bool     `json:"done,omitempty"`
    38  	Created []string `json:"created,omitempty"`
    39  	Moved   []string `json:"moved,omitempty"`
    40  	// Config is here for convenience; this package doesn't touch it
    41  	Config map[string]interface{} `json:"config,omitempty"`
    42  }
    43  
    44  // Cleanup the backed up data from disk.
    45  func (rs *RestoreState) Cleanup() {
    46  	if rs.Done {
    47  		logger.Noticef("Internal error: attempting to clean up a snapshot.RestoreState twice.")
    48  		return
    49  	}
    50  	rs.Done = true
    51  	for _, dir := range rs.Moved {
    52  		if err := os.RemoveAll(dir); err != nil {
    53  			logger.Noticef("Cannot remove directory tree rooted at %q: %v.", dir, err)
    54  		}
    55  	}
    56  }
    57  
    58  func restoreStateFilename(fn string) string {
    59  	return fmt.Sprintf("%s.~%s~", fn, randutil.RandomString(9))
    60  }
    61  
    62  var restoreStateRx = regexp.MustCompile(`\.~[a-zA-Z0-9]{9}~$`)
    63  
    64  func restoreState2orig(fn string) string {
    65  	if idx := restoreStateRx.FindStringIndex(fn); len(idx) > 0 {
    66  		return fn[:idx[0]]
    67  	}
    68  	return ""
    69  }
    70  
    71  // Revert the backed up data: remove what was added, move back what was moved aside.
    72  func (rs *RestoreState) Revert() {
    73  	if rs.Done {
    74  		logger.Noticef("Internal error: attempting to revert a snapshot.RestoreState twice.")
    75  		return
    76  	}
    77  	rs.Done = true
    78  	for _, dir := range rs.Created {
    79  		logger.Debugf("Removing %q.", dir)
    80  		if err := os.RemoveAll(dir); err != nil {
    81  			logger.Noticef("While undoing changes because of a previous error: cannot remove %q: %v.", dir, err)
    82  		}
    83  	}
    84  	for _, dir := range rs.Moved {
    85  		orig := restoreState2orig(dir)
    86  		if orig == "" {
    87  			// dir is not restore state?!?
    88  			logger.Debugf("Skipping restore of %q: unrecognised filename.", dir)
    89  			continue
    90  		}
    91  		logger.Debugf("Restoring %q to %q.", dir, orig)
    92  		if err := os.Rename(dir, orig); err != nil {
    93  			logger.Noticef("While undoing changes because of a previous error: cannot restore %q to %q: %v.", dir, orig, err)
    94  		}
    95  	}
    96  }