fix: auto-rewind source reader on seekable entry points

Callers previously had to manually `seek(SeekFrom::Start(0))` between
successive uses of the same reader (e.g. list_archive_files followed by
uncompress_archive_file), because libarchive only recognizes the archive
format from byte 0. Forgetting the rewind surfaced as an opaque
"unrecognized format" error.

Since the public entry points already require `Read + Seek`, rewind the
reader at the top of `run_with_archive` and `ArchiveIterator::new` so
reader reuse works out of the box.

Closes #117

Author: otavio

CHANGES.md

@@ -4,6 +4,11 @@
 
 ## [Unreleased] - ReleaseDate
 
+* Rewind the source reader at the start of every seekable entry point
+  (`list_archive_files`, `list_archive_entries`, `uncompress_archive`,
+  `uncompress_archive_file`, `ArchiveIterator`, and their `_with_encoding`
+  variants), so callers can reuse the same reader across successive calls
+  without a manual `seek(SeekFrom::Start(0))` between them [#117]
 * Fix RAR extraction failing with "Can't decompress an entry marked as a
   directory" whenever the archive contains directory entries. Data reads are
   now skipped for directory entries in `uncompress_archive`,

src/iterator.rs

@@ -180,6 +180,8 @@ impl<R: Read + Seek> ArchiveIterator<R> {
         R: Read + Seek,
     {
         let utf8_guard = ffi::UTF8LocaleGuard::new();
+        // libarchive only sniffs the format from offset 0.
+        source.seek(SeekFrom::Start(0))?;
         crate::zip_preflight::reject_unsupported_zip_methods(&mut source)?;
         let reader = source;
         let buffer = [0; READER_BUFFER_SIZE];

src/lib.rs

@@ -512,6 +512,8 @@ where
     R: Read + Seek,
 {
     let _utf8_guard = ffi::UTF8LocaleGuard::new();
+    // libarchive only sniffs the format from offset 0.
+    reader.seek(SeekFrom::Start(0))?;
     zip_preflight::reject_unsupported_zip_methods(&mut reader)?;
     unsafe {
         let archive_entry: *mut ffi::archive_entry = std::ptr::null_mut();

tests/integration_test.rs

@@ -153,6 +153,33 @@ fn successfully_list_archive_files() {
     );
 }
 
+#[test]
+fn reader_is_rewound_between_calls() {
+    let mut source = std::fs::File::open("tests/fixtures/tree.tar").unwrap();
+
+    let listed = list_archive_files(&mut source).unwrap();
+    assert!(listed.contains(&"tree/branch2/leaf".to_string()));
+
+    let mut target = Vec::new();
+    let written = uncompress_archive_file(&mut source, &mut target, "tree/branch2/leaf")
+        .expect("extract should succeed even though the reader was left past the archive");
+    assert_eq!(written, 14);
+    assert_eq!(String::from_utf8_lossy(&target), "Goodbye World\n");
+
+    let listed_again = list_archive_files(&mut source).unwrap();
+    assert_eq!(listed, listed_again);
+
+    let names: Vec<String> = ArchiveIteratorBuilder::new(&mut source)
+        .build()
+        .unwrap()
+        .filter_map(|c| match c {
+            ArchiveContents::StartOfEntry(name, _) => Some(name),
+            _ => None,
+        })
+        .collect();
+    assert_eq!(names, listed);
+}
+
 #[test]
 fn successfully_list_archive_entries() {
     let source = std::fs::File::open("tests/fixtures/tree.tar").unwrap();