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compressor.go
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compressor.go
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package compressor
import (
"context"
"fmt"
"io"
"io/fs"
"os"
"path"
"path/filepath"
"strings"
"time"
)
// File abstraction for interacting with archives.
type File struct {
fs.FileInfo
// The file header as used/provided by the archive format.
Header interface{}
// The path of the file as it appears in the archive.
FileName string
// For symbolic and hard links.
// Not all archive formats are supported.
LinkTarget string
// A callback function that opens a file to read its contents.
// The file must be closed when the reading is finished.
// Not used for files that have no content (directories and links).
Open func() (io.ReadCloser, error)
}
// FromDiskOptions specifies options for gathering files from the disk.
type FromDiskOptions struct {
// If true, symbolic links will be dereferenced,
// that is, the link will not be added as a link,
// but what the link points to will be added as a file.
FollowSymboliclinks bool
// If true, some attributes of the file will not be saved.
// The name, size, type and permissions will be saved.
ClearAttributes bool
}
// noAttrFileInfo is used to zero some file attributes.
type noAttrFileInfo struct {
fs.FileInfo
}
// skipList keeps a list of non-intersecting paths as long as its add method is used.
// Identical items are rejected, more specific paths are replaced with broader ones,
// and more specific paths won't be added when a broader one already exists in the list.
// Slashes are ignored.
type skipList []string
// FileHandler is a callback function that is used to handle files when reading them from an archive.
// It is similar to fs.WalkDirFunc. Handler functions that open files must not overlap or execute at the same time,
// since files can be read from the same sequential thread. Always close the file before returning it.
// If a special error value of fs.SkipDir is returned, the file directory (or the file itself,
// if it is a directory) will not be passed. Note that since the contents of an archive are not necessarily ordered,
// skipping directories requires memory, and skipping a large number of directories can lead to memory overruns.
// Any other error returned will abort the pass.
type FileHandler func(ctx context.Context, f File) error
func (f File) Stat() (fs.FileInfo, error) {
return f.FileInfo, nil
}
// Mode preserves only the type and permission bits.
func (no noAttrFileInfo) Mode() fs.FileMode {
return no.FileInfo.Mode() & (fs.ModeType | fs.ModePerm)
}
func (noAttrFileInfo) ModTime() time.Time {
return time.Time{}
}
func (noAttrFileInfo) Sys() interface{} {
return nil
}
func (s *skipList) add(dir string) {
var dontAdd bool
trimmedDir := strings.TrimSuffix(dir, "/")
for i := 0; i < len(*s); i++ {
trimmedElem := strings.TrimSuffix((*s)[i], "/")
if trimmedDir == trimmedElem {
return
}
// don't add dir if a broader path already exists in the list
if strings.HasPrefix(trimmedDir, trimmedElem+"/") {
dontAdd = true
continue
}
// if dir is broader than a path in the list, remove more specific path in list
if strings.HasPrefix(trimmedElem, trimmedDir+"/") {
*s = append((*s)[:i], (*s)[i+1:]...)
i--
}
}
if !dontAdd {
*s = append(*s, dir)
}
}
// FilesFromDisk returns a list of files by traversing the directories in a given filename map.
// The keys are the names on disk, and the values are the associated names in the archive.
// Map keys pointing to directories on disk will be looked up and added to the archive recursively,
// with the root in the named directory. They must use a platform path separator
// (backslash in Windows; slash in all others). For convenience, map keys ending with a delimiter ('/', or '\' in Windows)
// will only list the contents of the folder without adding the folder itself to the archive.
// Map values should normally use a slash ('/') as a separator regardless of platform,
// since most archive formats standardize this rune as a directory separator for filenames in the archive.
// For convenience, map values that are an empty string are interpreted as the base filename (no path) in the root of the archive;
// and map values ending with a slash will use the base filename in the given archive folder.
// The files will be assembled according to the settings specified in the options.
// This function is mainly used when preparing a list of files to add to the archive.
func FilesFromDisk(options *FromDiskOptions, filenames map[string]string) (files []File, err error) {
for rootOnDisk, rootInArchive := range filenames {
walkErr := filepath.WalkDir(rootOnDisk, func(filename string, d fs.DirEntry, err error) error {
var linkTarget string
if err != nil {
return err
}
info, err := d.Info()
if err != nil {
return err
}
nameInArchive := nameOnDiskToNameInArchive(filename, rootOnDisk, rootInArchive)
// is the root folder, add its contents to the rootInArchive target folder
if info.IsDir() && nameInArchive == "" {
return nil
}
// handle symbolic links
if isSymlink(info) {
if options != nil && options.FollowSymboliclinks {
// dereference symlinks
filename, err = os.Readlink(filename)
if err != nil {
return fmt.Errorf("%s: readlink: %w", filename, err)
}
info, err = os.Stat(filename)
if err != nil {
return fmt.Errorf("%s: statting dereferenced symlink: %w", filename, err)
}
} else {
// preserve symlinks
linkTarget, err = os.Readlink(filename)
if err != nil {
return fmt.Errorf("%s: readlink: %w", filename, err)
}
}
}
// handle file attributes
if options != nil && options.ClearAttributes {
info = noAttrFileInfo{info}
}
file := File{
FileInfo: info,
FileName: nameInArchive,
LinkTarget: linkTarget,
Open: func() (io.ReadCloser, error) {
return os.Open(filename)
},
}
files = append(files, file)
return nil
})
if walkErr != nil {
return nil, walkErr
}
}
return files, nil
}
// trimTopDir removes the top or first directory from the path.
// It expects a path with a forward slash.
// For example, "a/b/c" => "b/c".
func trimTopDir(dir string) string {
if len(dir) > 0 && dir[0] == '/' {
dir = dir[1:]
}
if pos := strings.Index(dir, "/"); pos >= 0 {
return dir[pos+1:]
}
return dir
}
// topDir returns the top or first directory in the path.
// It expects a forward-slashed path.
// For example, "a/b/c" => "a".
func topDir(dir string) string {
if len(dir) > 0 && dir[0] == '/' {
dir = dir[1:]
}
if pos := strings.Index(dir, "/"); pos >= 0 {
return dir[:pos]
}
return dir
}
// nameOnDiskToNameInArchive converts the file name from disk to the name in the archive,
// following the rules defined by FilesFromDisk. nameOnDisk is the full name of the file on disk,
// which is expected to be prefixed by rootOnDisk and will be placed in the rootInArchive folder in the archive.
func nameOnDiskToNameInArchive(nameOnDisk, rootOnDisk, rootInArchive string) string {
if strings.HasSuffix(rootOnDisk, string(filepath.Separator)) {
rootInArchive = trimTopDir(rootInArchive)
} else if rootInArchive == "" {
rootInArchive = filepath.Base(rootOnDisk)
}
if strings.HasSuffix(rootInArchive, "/") {
rootInArchive += filepath.Base(rootOnDisk)
}
truncPath := strings.TrimPrefix(nameOnDisk, rootOnDisk)
return path.Join(rootInArchive, filepath.ToSlash(truncPath))
}
// openAndCopyFile opens file for reading, copies its contents to w, then closes file.
func openAndCopyFile(file File, w io.Writer) error {
fileReader, err := file.Open()
if err != nil {
return err
}
defer fileReader.Close()
_, err = io.Copy(w, fileReader)
return err
}
// fileIsIncluded returns true if the filename is included in the filenameList,
// i.e. it is in the list, its parent folder/path is in the list, or the list is nil.
func fileIsIncluded(filenameList []string, filename string) bool {
// include all files if there is no specific list
if filenameList == nil {
return true
}
for _, fn := range filenameList {
// exact matches are of course included
if filename == fn {
return true
}
// also consider the file included if its parent folder/path is in the list
if strings.HasPrefix(filename, strings.TrimSuffix(fn, "/")+"/") {
return true
}
}
return false
}
func isSymlink(info fs.FileInfo) bool {
return info.Mode()&os.ModeSymlink != 0
}