*: add an update/restore functionality

This allows for restoring some attributes of files from the state in an
mtree Manifest

Reported-by: Matthew Garrett <Matthewgarrett@google.com>
Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

keywordfuncs_linux.go

@@ -0,0 +1,96 @@
+// +build linux
+
+package mtree
+
+import (
+	"archive/tar"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"os"
+	"os/user"
+	"strings"
+	"syscall"
+
+	"github.com/vbatts/go-mtree/pkg/govis"
+	"github.com/vbatts/go-mtree/xattr"
+)
+
+var (
+	// this is bsd specific https://www.freebsd.org/cgi/man.cgi?query=chflags&sektion=2
+	flagsKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		return emptyKV, nil
+	}
+
+	unameKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return KeyVal(fmt.Sprintf("uname=%s", hdr.Uname)), nil
+		}
+
+		stat := info.Sys().(*syscall.Stat_t)
+		u, err := user.LookupId(fmt.Sprintf("%d", stat.Uid))
+		if err != nil {
+			return emptyKV, err
+		}
+		return KeyVal(fmt.Sprintf("uname=%s", u.Username)), nil
+	}
+	uidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return KeyVal(fmt.Sprintf("uid=%d", hdr.Uid)), nil
+		}
+		stat := info.Sys().(*syscall.Stat_t)
+		return KeyVal(fmt.Sprintf("uid=%d", stat.Uid)), nil
+	}
+	gidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return KeyVal(fmt.Sprintf("gid=%d", hdr.Gid)), nil
+		}
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
+			return KeyVal(fmt.Sprintf("gid=%d", stat.Gid)), nil
+		}
+		return emptyKV, nil
+	}
+	nlinkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
+			return KeyVal(fmt.Sprintf("nlink=%d", stat.Nlink)), nil
+		}
+		return emptyKV, nil
+	}
+	xattrKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (KeyVal, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			if len(hdr.Xattrs) == 0 {
+				return emptyKV, nil
+			}
+			klist := []KeyVal{}
+			for k, v := range hdr.Xattrs {
+				encKey, err := govis.Vis(k, DefaultVisFlags)
+				if err != nil {
+					return emptyKV, err
+				}
+				klist = append(klist, KeyVal(fmt.Sprintf("xattr.%s=%s", encKey, base64.StdEncoding.EncodeToString([]byte(v)))))
+			}
+			return KeyVal(strings.Join(KeyValToString(klist), " ")), nil
+		}
+		if !info.Mode().IsRegular() && !info.Mode().IsDir() {
+			return emptyKV, nil
+		}
+
+		xlist, err := xattr.List(path)
+		if err != nil {
+			return emptyKV, err
+		}
+		klist := make([]KeyVal, len(xlist))
+		for i := range xlist {
+			data, err := xattr.Get(path, xlist[i])
+			if err != nil {
+				return emptyKV, err
+			}
+			encKey, err := govis.Vis(xlist[i], DefaultVisFlags)
+			if err != nil {
+				return emptyKV, err
+			}
+			klist[i] = KeyVal(fmt.Sprintf("xattr.%s=%s", encKey, base64.StdEncoding.EncodeToString(data)))
+		}
+		return KeyVal(strings.Join(KeyValToString(klist), " ")), nil
+	}
+)