Implement Rust-owned adaptive Android password navigation (#96)

crates/storage/src/repository.rs

@@ -391,6 +391,60 @@ impl Repository {
         Ok(EncryptedEntry(bytes))
     }
 
+    /// A non-secret object revision; navigation never opens encrypted contents.
+    pub(crate) fn navigation_revision(
+        &self,
+        path: &Path,
+        entry: bool,
+    ) -> Result<String, RepositoryError> {
+        let relative = if entry {
+            EntryPath::parse(path)?.encrypted_relative_path()
+        } else {
+            DirectoryPath::parse(path)?.as_path().to_owned()
+        };
+        let metadata = if relative.as_os_str().is_empty() {
+            self.root
+                .dir_metadata()
+                .map_err(|error| io_error("inspect repository", path, error))?
+        } else {
+            let parent = self.open_directory(relative.parent().unwrap_or(Path::new("")))?;
+            child_metadata(
+                &parent,
+                relative.file_name().expect("relative object"),
+                &relative,
+            )?
+            .ok_or_else(|| RepositoryError::NotFound {
+                path: relative.clone(),
+            })?
+        };
+        if entry {
+            require_regular_file(metadata.clone(), &relative)?;
+        } else {
+            require_directory(metadata.clone(), &relative)?;
+        }
+        #[cfg(unix)]
+        {
+            use cap_std::fs::MetadataExt;
+            Ok(format!(
+                "{}:{}:{}:{}:{}:{}:{}",
+                metadata.dev(),
+                metadata.ino(),
+                metadata.len(),
+                metadata.mtime(),
+                metadata.mtime_nsec(),
+                if entry { metadata.ctime() } else { 0 },
+                if entry { metadata.ctime_nsec() } else { 0 }
+            ))
+        }
+        #[cfg(not(unix))]
+        Ok(format!(
+            "{}:{:?}:{:?}",
+            metadata.len(),
+            metadata.modified(),
+            metadata.created()
+        ))
+    }
+
     pub(crate) fn read_policy_file(
         &self,
         directory: &DirectoryPath,