Very basic Pax header writer

[gwitrand-ovh]

Basic implem of PaxBuilder that can add the header with the data provided, implem on tar::builder

Today the lib is able to read the pax headers, even if they have arbitrary values but can't write some headers back. This update lets you do that very simply.

Usage:

let mut pax_builder: PaxBuilder = PaxBuilder::new();

let value: String = "a_value".to_string();
let key: String = "a_key".to_string();

pax_builder.add(&key, &value);

let res_write_pax: Result<(), io::Error> = my_open_tar_archive.append_pax_extensions(&pax_builder);

[cgwalters]

Thanks for your contribution! Procedural notes:

• If you wouldn't mind please squash your commits, I don't think any of the 4 stand alone
• Can you rework your commit message to be "Linux kernel style" which I try to use, see e.g. https://cbea.ms/git-commit/

I'd propose something like this:

Add support for writing PAX headers

While this crate has always supported reading these attributes,
writing them was up to the user. Add an API to do this.

[cgwalters]

Marking requested changes per above

[gwitrand-ovh]

Thanks for your contribution! Procedural notes:

* If you wouldn't mind please squash your commits, I don't think any of the 4 stand alone

* Can you rework your commit message to be "Linux kernel style" which I try to use, see e.g. https://cbea.ms/git-commit/

I'd propose something like this:

Add support for writing PAX headers
While this crate has always supported reading these attributes,
writing them was up to the user. Add an API to do this.

Marking requested changes per above

All comments fixed.
Also updated the tests and code doc to comply.

[cgwalters]

Can you add these changes? First we don't need to require passing owned data, and according to the spec the value can be arbitrary binary data.

diff --git a/src/pax.rs b/src/pax.rs
index 5a06967..d149428 100644
--- a/src/pax.rs
+++ b/src/pax.rs
@@ -154,9 +154,9 @@ impl<T: Write> crate::Builder<T> {
     /// Takes in an iterator over the list of headers to add to convert it into a header set formatted.
     ///
     /// Returns io::Error if an error occurs, else it returns ()
-    pub fn append_pax_extensions<'a>(
+    pub fn append_pax_extensions<'key, 'value>(
         &mut self,
-        headers: impl IntoIterator<Item = (String, String)>,
+        headers: impl IntoIterator<Item = (&'key str, &'value [u8])>,
     ) -> Result<(), io::Error> {
         // Store the headers formatted before write
         let mut data: Vec<u8> = Vec::new();
@@ -172,7 +172,9 @@ impl<T: Write> crate::Builder<T> {
                 max_len *= 10;
             }
             let len = rest_len + len_len;
-            write!(&mut data, "{} {}={}\n", len, key, value)?;
+            write!(&mut data, "{} {}=", len, key)?;
+            data.extend_from_slice(value);
+            data.push(b'\n');
         }
 
         // Ignore the header append if it's empty.
diff --git a/tests/all.rs b/tests/all.rs
index 9f93de4..3caff4b 100644
--- a/tests/all.rs
+++ b/tests/all.rs
@@ -932,12 +932,12 @@ fn pax_simple_write() {
     let file: File = t!(File::create(&pax_path));
     let mut ar: Builder<BufWriter<File>> = Builder::new(BufWriter::new(file));
 
-    let mut pax_builder: Vec<(String, String)> = Vec::new();
-    let key: String = "arbitrary_pax_key".to_string();
-    let value: String = "arbitrary_pax_value".to_string();
-    pax_builder.push((key, value));
+    let pax_extensions = [
+        ("arbitrary_pax_key", b"arbitrary_pax_value".as_slice()),
+        ("SCHILY.xattr.security.selinux", b"foo_t"),
+    ];
 
-    t!(ar.append_pax_extensions(pax_builder.into_iter()));
+    t!(ar.append_pax_extensions(pax_extensions));
     t!(ar.append_file("test2", &mut t!(File::open(&pax_path))));
     t!(ar.finish());
     drop(ar);
@@ -950,9 +950,11 @@ fn pax_simple_write() {
     assert!(pax_headers.is_some(), "pax_headers is None");
     let mut pax_headers = pax_headers.unwrap();
     let pax_arbitrary = t!(pax_headers.next().unwrap());
-
     assert_eq!(pax_arbitrary.key(), Ok("arbitrary_pax_key"));
     assert_eq!(pax_arbitrary.value(), Ok("arbitrary_pax_value"));
+    let xattr = t!(pax_headers.next().unwrap());
+    assert_eq!(xattr.key().unwrap(), pax_extensions[1].0);
+    assert_eq!(xattr.value_bytes(), pax_extensions[1].1);
 
     assert!(entries.next().is_none());
 }

[cgwalters]

Just two minor nits but they're not important so merging, we can do followup fixes if we want.

Thanks for your contribution!

[cgwalters]

I don't care too much but this change seem spurious i.e. unnecessary

[cgwalters]

This isn't an extension trait anymore

[cgwalters]

When I was playing with this I noticed that my suggestion of using key: &str clashes with the existing PaxExtensions reader, which gives back &[u8].

I dunno how much of a real world problem this is. It does sure look to me like in e.g. the python tar parser it's actually expected to be UTF-8.

[cgwalters]

For general interest I used this to fix a bug in my software - thank you for submitting this patch! cc ostreedev/ostree-rs-ext#679