1 files changed, 95 insertions, 0 deletions
diff --git a/lib/linux/stat.go b/lib/linux/stat.go
new file mode 100644
index 0000000..c4d4ad9
--- /dev/null
+++ b/lib/linux/stat.go
@@ -0,0 +1,95 @@
+// Based on https://github.com/datawire/ocibuild/blob/master/pkg/python/stat.go
+
+package linux
+
+type StatMode uint32
+
+//nolint:deadcode,varcheck // not all of these modes will be used
+const (
+	// 16 bits = 5⅓ octal characters
+
+	ModeFmt StatMode = 0o17_0000 // mask for the type bits
+
+	_ModeFmtUnused000  StatMode = 0o00_0000
+	ModeFmtNamedPipe   StatMode = 0o01_0000 // type: named pipe (FIFO)
+	ModeFmtCharDevice  StatMode = 0o02_0000 // type: character device
+	_ModeFmtUnused003  StatMode = 0o03_0000
+	ModeFmtDir         StatMode = 0o04_0000 // type: directory
+	_ModeFmtUnused005  StatMode = 0o05_0000
+	ModeFmtBlockDevice StatMode = 0o06_0000 // type: block device
+	_ModeFmtUnused007  StatMode = 0o07_0000
+	ModeFmtRegular     StatMode = 0o10_0000 // type: regular file
+	_ModeFmtUnused011  StatMode = 0o11_0000
+	ModeFmtSymlink     StatMode = 0o12_0000 // type: symbolic link
+	_ModeFmtUnused013  StatMode = 0o13_0000
+	ModeFmtSocket      StatMode = 0o14_0000 // type: socket file
+	_ModeFmtUnused015  StatMode = 0o15_0000
+	_ModeFmtUnused016  StatMode = 0o16_0000
+	_ModeFmtUnused017  StatMode = 0o17_0000
+
+	ModePerm StatMode = 0o00_7777 // mask for permission bits
+
+	ModePermSetUID StatMode = 0o00_4000 // permission: set user id
+	ModePermSetGID StatMode = 0o00_2000 // permission: set group ID
+	ModePermSticky StatMode = 0o00_1000 // permission: sticky bit
+
+	ModePermUsrR StatMode = 0o00_0400 // permission: user: read
+	ModePermUsrW StatMode = 0o00_0200 // permission: user: write
+	ModePermUsrX StatMode = 0o00_0100 // permission: user: execute
+
+	ModePermGrpR StatMode = 0o00_0040 // permission: group: read
+	ModePermGrpW StatMode = 0o00_0020 // permission: group: write
+	ModePermGrpX StatMode = 0o00_0010 // permission: group: execute
+
+	ModePermOthR StatMode = 0o00_0004 // permission: other: read
+	ModePermOthW StatMode = 0o00_0002 // permission: other: write
+	ModePermOthX StatMode = 0o00_0001 // permission: other: execute
+)
+
+// IsDir reports whether mode describes a directory.
+//
+// That is, it tests that the ModeFmt bits are set to ModeFmtDir.
+func (mode StatMode) IsDir() bool {
+	return mode&ModeFmt == ModeFmtDir
+}
+
+// IsRegular reports whether m describes a regular file.
+//
+// That is, it tests that the ModeFmt bits are set to ModeFmtRegular.
+func (mode StatMode) IsRegular() bool {
+	return mode&ModeFmt == ModeFmtRegular
+}
+
+// String returns a textual representation of the mode.
+//
+// This is the format that POSIX specifies for showing the mode in the
+// output of the `ls -l` command.  POSIX does not specify the
+// character to use to indicate a ModeFmtSocket file; this method uses
+// 's' (GNU `ls` behavior; though POSIX notes that many
+// implementations use '=' for sockets).
+func (mode StatMode) String() string {
+	buf := [10]byte{
+		// type: This string is easy; it directly pairs with
+		// the above ModeFmtXXX list above; the character in
+		// the string left-to-right corresponds with the
+		// constant in the list top-to-bottom.
+		"?pc?d?b?-?l?s???"[mode>>12],
+
+		// owner
+		"-r"[(mode>>8)&0o1],
+		"-w"[(mode>>7)&0o1],
+		"-xSs"[((mode>>6)&0o1)|((mode>>10)&0o2)],
+
+		// group
+		"-r"[(mode>>5)&0o1],
+		"-w"[(mode>>4)&0o1],
+		"-xSs"[((mode>>3)&0o1)|((mode>>9)&0o2)],
+
+		// group
+		"-r"[(mode>>2)&0o1],
+		"-w"[(mode>>1)&0o1],
+		"-xTt"[((mode>>0)&0o1)|((mode>>8)&0o2)],
+	}
+
+	return string(buf[:])
+}