Add a method to write a link name without canonicalization

src/header.rs

@@ -435,6 +435,18 @@ impl Header {
         })
     }
 
+    /// Sets the link name for this header without any transformation.
+    ///
+    /// This function is like [`Self::set_link_name`] but accepts an arbitrary byte array.
+    /// Hence it will not perform any canonicalization, such as replacing duplicate `//` with `/`.
+    pub fn set_link_name_literal<P: AsRef<[u8]>>(&mut self, p: P) -> io::Result<()> {
+        self._set_link_name_literal(p.as_ref())
+    }
+
+    fn _set_link_name_literal(&mut self, bytes: &[u8]) -> io::Result<()> {
+        copy_into(&mut self.as_old_mut().linkname, bytes)
+    }
+
     /// Returns the mode bits for this file
     ///
     /// May return an error if the field is corrupted.

tests/all.rs

@@ -935,6 +935,28 @@ fn long_linkname_gnu() {
     }
 }
 
+#[test]
+fn linkname_literal() {
+    for t in [tar::EntryType::Symlink, tar::EntryType::Link] {
+        let mut b = Builder::new(Vec::<u8>::new());
+        let mut h = Header::new_gnu();
+        h.set_entry_type(t);
+        h.set_size(0);
+        let path = "usr/lib/systemd/systemd-sysv-install";
+        let target = "../../..//sbin/chkconfig";
+        h.set_link_name_literal(target).unwrap();
+        t!(b.append_data(&mut h, path, std::io::empty()));
+
+        let contents = t!(b.into_inner());
+        let mut a = Archive::new(&contents[..]);
+
+        let e = &t!(t!(a.entries()).next().unwrap());
+        assert_eq!(e.header().entry_type(), t);
+        assert_eq!(e.path().unwrap().to_str().unwrap(), path);
+        assert_eq!(e.link_name().unwrap().unwrap().to_str().unwrap(), target);
+    }
+}
+
 #[test]
 fn encoded_long_name_has_trailing_nul() {
     let td = t!(TempBuilder::new().prefix("tar-rs").tempdir());