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syncdir.go
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syncdir.go
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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2016 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package osutil
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"os"
"path/filepath"
"sort"
)
// FileState is an interface for conveying the desired state of a some file.
type FileState interface {
State() (reader io.ReadCloser, size int64, mode os.FileMode, err error)
}
// FileReference describes the desired content by referencing an existing file.
type FileReference struct {
Path string
}
// State returns a reader of the referenced file, along with other meta-data.
func (fref FileReference) State() (io.ReadCloser, int64, os.FileMode, error) {
file, err := os.Open(fref.Path)
if err != nil {
return nil, 0, os.FileMode(0), err
}
fi, err := file.Stat()
if err != nil {
return nil, 0, os.FileMode(0), err
}
return file, fi.Size(), fi.Mode(), nil
}
// FileReferencePlusMode describes the desired content by referencing an existing file and providing custom mode.
type FileReferencePlusMode struct {
FileReference
Mode os.FileMode
}
// State returns a reader of the referenced file, substituting the mode.
func (fcref FileReferencePlusMode) State() (io.ReadCloser, int64, os.FileMode, error) {
reader, size, _, err := fcref.FileReference.State()
if err != nil {
return nil, 0, os.FileMode(0), err
}
return reader, size, fcref.Mode, nil
}
// MemoryFileState describes the desired content by providing an in-memory copy.
type MemoryFileState struct {
Content []byte
Mode os.FileMode
}
// State returns a reader of the in-memory contents of a file, along with other meta-data.
func (blob *MemoryFileState) State() (io.ReadCloser, int64, os.FileMode, error) {
return ioutil.NopCloser(bytes.NewReader(blob.Content)), int64(len(blob.Content)), blob.Mode, nil
}
// ErrSameState is returned when the state of a file has not changed.
var ErrSameState = fmt.Errorf("file state has not changed")
// EnsureDirStateGlobs ensures that directory content matches expectations.
//
// EnsureDirStateGlobs enumerates all the files in the specified directory that
// match the provided set of pattern (globs). Each enumerated file is checked
// to ensure that the contents, permissions are what is desired. Unexpected
// files are removed. Missing files are created and differing files are
// corrected. Files not matching any pattern are ignored.
//
// Note that EnsureDirStateGlobs only checks for permissions and content. Other
// security mechanisms, including file ownership and extended attributes are
// *not* supported.
//
// The content map describes each of the files that are intended to exist in
// the directory. Map keys must be file names relative to the directory.
// Sub-directories in the name are not allowed.
//
// If writing any of the files fails, EnsureDirStateGlobs switches to erase mode
// where *all* of the files managed by the glob pattern are removed (including
// those that may have been already written). The return value is an empty list
// of changed files, the real list of removed files and the first error.
//
// If an error happens while removing files then such a file is not removed but
// the removal continues until the set of managed files matching the glob is
// exhausted.
//
// In all cases, the function returns the first error it has encountered.
func EnsureDirStateGlobs(dir string, globs []string, content map[string]FileState) (changed, removed []string, err error) {
// Check syntax before doing anything.
if _, index, err := matchAny(globs, "foo"); err != nil {
return nil, nil, fmt.Errorf("internal error: EnsureDirState got invalid pattern %q: %s", globs[index], err)
}
for baseName := range content {
if filepath.Base(baseName) != baseName {
return nil, nil, fmt.Errorf("internal error: EnsureDirState got filename %q which has a path component", baseName)
}
if ok, _, _ := matchAny(globs, baseName); !ok {
if len(globs) == 1 {
return nil, nil, fmt.Errorf("internal error: EnsureDirState got filename %q which doesn't match the glob pattern %q", baseName, globs[0])
}
return nil, nil, fmt.Errorf("internal error: EnsureDirState got filename %q which doesn't match any glob patterns %q", baseName, globs)
}
}
// Change phase (create/change files described by content)
var firstErr error
for baseName, fileState := range content {
filePath := filepath.Join(dir, baseName)
err := EnsureFileState(filePath, fileState)
if err == ErrSameState {
continue
}
if err != nil {
// On write failure, switch to erase mode. Desired content is set
// to nothing (no content) changed files are forgotten and the
// writing loop stops. The subsequent erase loop will remove all
// the managed content.
firstErr = err
content = nil
changed = nil
break
}
changed = append(changed, baseName)
}
// Delete phase (remove files matching the glob that are not in content)
matches := make(map[string]bool)
for _, glob := range globs {
m, err := filepath.Glob(filepath.Join(dir, glob))
if err != nil {
sort.Strings(changed)
return changed, nil, err
}
for _, path := range m {
matches[path] = true
}
}
for path := range matches {
baseName := filepath.Base(path)
if content[baseName] != nil {
continue
}
err := os.Remove(path)
if err != nil {
if firstErr == nil {
firstErr = err
}
continue
}
removed = append(removed, baseName)
}
sort.Strings(changed)
sort.Strings(removed)
return changed, removed, firstErr
}
func matchAny(globs []string, path string) (ok bool, index int, err error) {
for index, glob := range globs {
if ok, err := filepath.Match(glob, path); ok || err != nil {
return ok, index, err
}
}
return false, 0, nil
}
// EnsureDirState ensures that directory content matches expectations.
//
// This is like EnsureDirStateGlobs but it only supports one glob at a time.
func EnsureDirState(dir string, glob string, content map[string]FileState) (changed, removed []string, err error) {
return EnsureDirStateGlobs(dir, []string{glob}, content)
}
// fileStateEqualTo returns whether the file exists in the expected state.
func fileStateEqualTo(filePath string, state FileState) (bool, error) {
other := &FileReference{Path: filePath}
// Open views to both files so that we can compare them.
readerA, sizeA, modeA, err := state.State()
if err != nil {
return false, err
}
defer readerA.Close()
readerB, sizeB, modeB, err := other.State()
if err != nil {
if os.IsNotExist(err) {
// Not existing is not an error
return false, nil
}
return false, err
}
defer readerB.Close()
// If the files have different size or different mode they are not
// identical and need to be re-created. Mode change could be optimized to
// avoid re-writing the whole file.
if modeA.Perm() != modeB.Perm() || sizeA != sizeB {
return false, nil
}
// The files have the same size so they might be identical.
// Do a block-wise comparison to determine that.
return streamsEqualChunked(readerA, readerB, 0), nil
}
// EnsureFileState ensures that the file is in the expected state. It will not
// attempt to remove the file if no content is provided.
func EnsureFileState(filePath string, state FileState) error {
equal, err := fileStateEqualTo(filePath, state)
if err != nil {
return err
}
if equal {
// Return a special error if the file doesn't need to be changed
return ErrSameState
}
reader, _, mode, err := state.State()
if err != nil {
return err
}
return AtomicWrite(filePath, reader, mode, 0)
}