restic/cmd/restic/exclude.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"github.com/restic/restic/internal/debug"
	"github.com/restic/restic/internal/fs"
)

// RejectFunc is a function that takes a filename and os.FileInfo of a
// file that would be included in the backup. The function returns true if it
// should be excluded (rejected) from the backup.
type RejectFunc func(filename string, fi os.FileInfo) bool

// rejectIfPresent returns a RejectFunc which itself returns whether a path
// should be excluded. The RejectFunc considers a file to be excluded when
// it resides in a directory with an exclusion file, that is specified by
// excludeFileSpec in the form "filename[:content]". The returned error is
// non-nil if the filename component of excludeFileSpec is empty.
func rejectIfPresent(excludeFileSpec string) (RejectFunc, error) {
	if excludeFileSpec == "" {
		return func(string, os.FileInfo) bool { return false }, nil
	}
	colon := strings.Index(excludeFileSpec, ":")
	if colon == 0 {
		return nil, fmt.Errorf("no name for exclusion tagfile provided")
	}
	tf, tc := "", ""
	if colon > 0 {
		tf = excludeFileSpec[:colon]
		tc = excludeFileSpec[colon+1:]
	} else {
		tf = excludeFileSpec
	}
	debug.Log("using %q as exclusion tagfile", tf)
	fn := func(filename string, _ os.FileInfo) bool {
		return isExcludedByFile(filename, tf, tc)
	}
	return fn, nil
}

// isExcludedByFile interprets filename as a path and returns true if that file
// is in a excluded directory. A directory is identified as excluded if it contains a
// tagfile which bears the name specified in tagFilename and starts with header.
func isExcludedByFile(filename, tagFilename, header string) bool {
	if tagFilename == "" {
		return false
	}
	dir, base := filepath.Split(filename)
	if base == tagFilename {
		return false // do not exclude the tagfile itself
	}
	tf := filepath.Join(dir, tagFilename)
	_, err := fs.Lstat(tf)
	if os.IsNotExist(err) {
		return false
	}
	if err != nil {
		Warnf("could not access exclusion tagfile: %v", err)
		return false
	}
	// when no signature is given, the mere presence of tf is enough reason
	// to exclude filename
	if len(header) == 0 {
		return true
	}
	// From this stage, errors mean tagFilename exists but it is malformed.
	// Warnings will be generated so that the user is informed that the
	// indented ignore-action is not performed.
	f, err := os.Open(tf)
	if err != nil {
		Warnf("could not open exclusion tagfile: %v", err)
		return false
	}
	defer f.Close()
	buf := make([]byte, len(header))
	_, err = io.ReadFull(f, buf)
	// EOF is handled with a dedicated message, otherwise the warning were too cryptic
	if err == io.EOF {
		Warnf("invalid (too short) signature in exclusion tagfile %q\n", tf)
		return false
	}
	if err != nil {
		Warnf("could not read signature from exclusion tagfile %q: %v\n", tf, err)
		return false
	}
	if bytes.Compare(buf, []byte(header)) != 0 {
		Warnf("invalid signature in exclusion tagfile %q\n", tf)
		return false
	}
	return true
}