keywords: BSD compat for a few keywords

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

keywords_bsd.go

@@ -3,8 +3,12 @@
 package mtree
 
 import (
+	"archive/tar"
+	"fmt"
 	"io"
 	"os"
+	"os/user"
+	"syscall"
 )
 
 var (
@@ -12,4 +16,42 @@ var (
 		// ideally this will pull in from here https://www.freebsd.org/cgi/man.cgi?query=chflags&sektion=2
 		return "", nil
 	}
+
+	unameKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return 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 "", err
+		}
+		return fmt.Sprintf("uname=%s", u.Username), nil
+	}
+	uidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("uid=%d", hdr.Uid), nil
+		}
+		stat := info.Sys().(*syscall.Stat_t)
+		return fmt.Sprintf("uid=%d", stat.Uid), nil
+	}
+	gidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("gid=%d", hdr.Gid), nil
+		}
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
+			return fmt.Sprintf("gid=%d", stat.Gid), nil
+		}
+		return "", nil
+	}
+	nlinkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
+			return fmt.Sprintf("nlink=%d", stat.Nlink), nil
+		}
+		return "", nil
+	}
+	xattrKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		return "", nil
+	}
 )

keywords_linux.go

@@ -1,3 +1,5 @@
+// +build linux
+
 package mtree
 
 import (

keywords_unsupported.go

@@ -1,4 +1,4 @@
-// +build !linux
+// +build !linux,!darwin,!freebsd,!netbsd,!openbsd
 
 package mtree