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

crates/storage/src/mobile_authentication.rs

@@ -737,6 +737,50 @@ impl MobileAuthentication {
             .map_err(MobileAuthenticationError::authentication)
     }
 
+    /// Open only the entry selected from a still-current navigation page.
+    pub fn navigation_entry(
+        &self,
+        directory: &str,
+        row_id: &str,
+        revision: &str,
+        passphrase: Option<SecretBytes>,
+        unix_seconds: u64,
+    ) -> Result<MobileEntryPresentation, MobileAuthenticationError> {
+        let validate = || {
+            let page = crate::mobile_passwords::navigation::navigate_repository(
+                &self.repository,
+                directory,
+                Some(row_id),
+                Some(revision),
+                false,
+            )
+            .map_err(|_| {
+                entry_detail(
+                    "Selection Is Unavailable",
+                    "Refresh the folder and select the entry again.",
+                )
+            })?;
+            page.selected
+                .filter(|row| {
+                    row.row.kind() == crate::mobile_passwords::MobilePasswordRowKind::Entry
+                })
+                .ok_or_else(|| {
+                    entry_detail(
+                        "Selection Changed",
+                        "Refresh the folder and select the entry again.",
+                    )
+                })
+        };
+        let selected = validate()?;
+        self.unlock_entry(selected.row.path(), passphrase)?;
+        let presentation = self.entry_page(selected.row.path(), unix_seconds)?;
+        if let Err(error) = validate() {
+            self.manual_lock()?;
+            return Err(error);
+        }
+        Ok(presentation)
+    }
+
     pub fn entry_page(
         &self,
         path: &str,

crates/storage/src/mobile_passwords.rs

@@ -2,6 +2,8 @@
 
 use crate::mobile::MobileIcon;
 
+pub mod navigation;
+
 use std::{error::Error, fmt};
 
 use crate::{
@@ -91,7 +93,7 @@ impl MobilePasswordPage {
         &self.rows
     }
 
-    fn from_repository(
+    pub(crate) fn from_repository(
         repository: &Repository,
         path: Option<&str>,
     ) -> Result<Self, MobilePasswordError> {
@@ -255,7 +257,7 @@ impl MobilePasswordError {
         }
     }
 
-    fn repository(error: RepositoryError) -> Self {
+    pub(crate) fn repository(error: RepositoryError) -> Self {
         let kind = match error {
             RepositoryError::InvalidPath { .. } => MobilePasswordErrorKind::InvalidPath,
             RepositoryError::NotFound { .. } => MobilePasswordErrorKind::DirectoryMissing,

crates/storage/src/mobile_passwords/navigation.rs

@@ -0,0 +1,233 @@
+//! Revision-checked, authentication-free Android directory navigation.
+use super::{
+    MobilePasswordError, MobilePasswordErrorKind, MobilePasswordPage, MobilePasswordRow,
+    MobilePasswordRowKind,
+};
+use crate::{
+    mobile_private_storage::{PrivateStorage, exclusive_lock},
+    repository::{DirectoryPath, Repository},
+};
+use cap_std::{ambient_authority, fs::Dir};
+use data_encoding::HEXLOWER;
+use sha2::{Digest, Sha256};
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct NavigationRow {
+    pub row: MobilePasswordRow,
+    pub revision: String,
+}
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct PasswordNavigation {
+    pub path: String,
+    pub title: String,
+    pub parent: Option<String>,
+    pub revision: String,
+    pub rows: Vec<NavigationRow>,
+    pub selected: Option<NavigationRow>,
+    pub stale: bool,
+}
+
+/// Only identifiers and revisions cross this boundary; there is no secret provider.
+pub fn navigate(
+    storage: &PrivateStorage,
+    path: &str,
+    selected: Option<&str>,
+    revision: Option<&str>,
+    activate: bool,
+) -> Result<PasswordNavigation, MobilePasswordError> {
+    let root =
+        Dir::open_ambient_dir(storage.root(), ambient_authority()).map_err(|_| unavailable())?;
+    let _lock = exclusive_lock(&root, "runtime.lock").map_err(|_| unavailable())?;
+    let config = storage
+        .configuration()
+        .map_err(|_| unavailable())?
+        .ok_or_else(unavailable)?;
+    let repository = Repository::open(config.vault()).map_err(MobilePasswordError::repository)?;
+    navigate_repository(&repository, path, selected, revision, activate)
+}
+
+fn unavailable() -> MobilePasswordError {
+    MobilePasswordError {
+        kind: MobilePasswordErrorKind::Configuration,
+        title: "Passwords Are Unavailable".into(),
+        detail: "Unlock the device or recover its private store, then refresh.".into(),
+    }
+}
+
+pub(crate) fn navigate_repository(
+    repository: &Repository,
+    requested: &str,
+    selected: Option<&str>,
+    expected: Option<&str>,
+    activate: bool,
+) -> Result<PasswordNavigation, MobilePasswordError> {
+    let mut path = DirectoryPath::parse(requested)
+        .map_err(MobilePasswordError::repository)?
+        .as_path()
+        .to_owned();
+    let page = loop {
+        match MobilePasswordPage::from_repository(repository, path.to_str()) {
+            Ok(page) => break page,
+            Err(error)
+                if error.kind() == MobilePasswordErrorKind::DirectoryMissing
+                    && !path.as_os_str().is_empty() =>
+            {
+                path.pop();
+            }
+            Err(error) => return Err(error),
+        }
+    };
+    let mut hash = Sha256::new();
+    hash.update(
+        repository
+            .navigation_revision(&path, false)
+            .map_err(MobilePasswordError::repository)?,
+    );
+    let rows = page
+        .rows()
+        .iter()
+        .map(|row| {
+            let revision = repository
+                .navigation_revision(
+                    std::path::Path::new(row.path()),
+                    row.kind() == MobilePasswordRowKind::Entry,
+                )
+                .map_err(MobilePasswordError::repository)?;
+            let revision = HEXLOWER.encode(&Sha256::digest(revision.as_bytes()));
+            hash.update(row.id().as_bytes());
+            hash.update([0]);
+            hash.update(revision.as_bytes());
+            Ok(NavigationRow {
+                row: row.clone(),
+                revision,
+            })
+        })
+        .collect::<Result<Vec<_>, MobilePasswordError>>()?;
+    let revision = HEXLOWER.encode(&hash.finalize());
+    let stale = page.path() != requested || expected.is_some_and(|value| value != revision);
+    let selection = if stale || expected.is_none() {
+        None
+    } else {
+        selected
+            .and_then(|id| rows.iter().find(|row| row.row.id() == id))
+            .cloned()
+    };
+    if activate
+        && let Some(row) = &selection
+        && row.row.kind() == MobilePasswordRowKind::Directory
+    {
+        return navigate_repository(repository, row.row.path(), None, None, false);
+    }
+    Ok(PasswordNavigation {
+        parent: path
+            .parent()
+            .map(|parent| parent.to_string_lossy().into_owned()),
+        path: page.path().into(),
+        title: page.title().into(),
+        rows,
+        revision,
+        stale: stale || selected.is_some() && selection.is_none(),
+        selected: selection,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+    use tempfile::tempdir;
+
+    #[test]
+    fn traverses_without_reading_or_decrypting_entries_and_restores_verified_selection() {
+        let temporary = tempdir().unwrap();
+        fs::create_dir_all(temporary.path().join("仕事/銀行/Empty")).unwrap();
+        fs::write(
+            temporary.path().join("仕事/銀行/a long Unicode 密碼.gpg"),
+            b"not even valid ciphertext",
+        )
+        .unwrap();
+        let repository = Repository::open(temporary.path()).unwrap();
+        let root = navigate_repository(&repository, "", None, None, false).unwrap();
+        let folder = navigate_repository(
+            &repository,
+            "",
+            Some(&root.rows[0].row.id),
+            Some(&root.revision),
+            true,
+        )
+        .unwrap();
+        assert_eq!(folder.path, "仕事");
+        let bank = navigate_repository(&repository, "仕事/銀行", None, None, false).unwrap();
+        let entry = bank
+            .rows
+            .iter()
+            .find(|row| row.row.kind() == MobilePasswordRowKind::Entry)
+            .unwrap();
+        let selected = navigate_repository(
+            &repository,
+            &bank.path,
+            Some(entry.row.id()),
+            Some(&bank.revision),
+            true,
+        )
+        .unwrap();
+        assert_eq!(
+            selected.selected.as_ref().unwrap().row.path(),
+            "仕事/銀行/a long Unicode 密碼"
+        );
+        assert_eq!(
+            selected,
+            navigate_repository(
+                &repository,
+                &selected.path,
+                Some(entry.row.id()),
+                Some(&selected.revision),
+                false
+            )
+            .unwrap()
+        );
+        let empty = navigate_repository(&repository, "仕事/銀行/Empty", None, None, false).unwrap();
+        assert!(empty.rows.is_empty());
+        assert_eq!(empty.parent.as_deref(), Some("仕事/銀行"));
+        let deep = (0..32)
+            .map(|index| format!("level-{index}"))
+            .collect::<Vec<_>>()
+            .join("/");
+        fs::create_dir_all(temporary.path().join(&deep)).unwrap();
+        let page = navigate_repository(&repository, &deep, None, None, false).unwrap();
+        assert_eq!(page.path, deep);
+        assert!(page.rows.is_empty());
+    }
+
+    #[test]
+    fn replacement_rows_and_disappearing_ancestors_cannot_reuse_stale_actions() {
+        let temporary = tempdir().unwrap();
+        fs::create_dir_all(temporary.path().join("a/b/c")).unwrap();
+        fs::write(temporary.path().join("a/b/login.gpg"), b"original").unwrap();
+        let repository = Repository::open(temporary.path()).unwrap();
+        let page = navigate_repository(&repository, "a/b", None, None, false).unwrap();
+        fs::write(temporary.path().join("replacement"), b"original").unwrap();
+        fs::rename(
+            temporary.path().join("replacement"),
+            temporary.path().join("a/b/login.gpg"),
+        )
+        .unwrap();
+        let stale = navigate_repository(
+            &repository,
+            "a/b",
+            Some("entry:a/b/login"),
+            Some(&page.revision),
+            true,
+        )
+        .unwrap();
+        assert!(stale.stale);
+        assert!(stale.selected.is_none());
+        assert_ne!(page.revision, stale.revision);
+        fs::remove_dir_all(temporary.path().join("a/b")).unwrap();
+        let restored =
+            navigate_repository(&repository, "a/b/c", None, Some(&page.revision), false).unwrap();
+        assert_eq!(restored.path, "a");
+        assert!(restored.stale);
+        assert!(navigate_repository(&repository, "../escape", None, None, false).is_err());
+    }
+}

crates/storage/src/mobile_private_storage.rs

@@ -687,7 +687,10 @@ pub(crate) fn private_permissions(
         } else {
             0o600 | (file.metadata()?.permissions().mode() & 0o100)
         };
-        file.set_permissions(Permissions::from_mode(mode))?;
+        // Avoid changing object revisions when an already-private store is reopened.
+        if file.metadata()?.permissions().mode() & 0o7777 != mode {
+            file.set_permissions(Permissions::from_mode(mode))?;
+        }
     }
     #[cfg(not(unix))]
     let _ = (file, directory);
@@ -700,6 +703,23 @@ mod tests {
     use crate::{mobile::MobileShellState, repository::SecretBytes};
     use std::os::unix::{fs::PermissionsExt, fs::symlink};
 
+    #[test]
+    fn enforcing_private_permissions_preserves_an_already_private_object_revision() {
+        use cap_std::fs::{MetadataExt, PermissionsExt as _};
+        let temporary = tempfile::tempdir().unwrap();
+        let directory = Dir::open_ambient_dir(temporary.path(), ambient_authority()).unwrap();
+        let file = directory.create("entry").unwrap();
+        private_permissions(&file, false).unwrap();
+        let before = file.metadata().unwrap();
+        private_permissions(&file, false).unwrap();
+        let after = file.metadata().unwrap();
+        assert_eq!(
+            (before.ctime(), before.ctime_nsec()),
+            (after.ctime(), after.ctime_nsec())
+        );
+        assert_eq!(after.permissions().mode() & 0o7777, 0o600);
+    }
+
     fn roots(root: &Path) -> PrivateDirectories {
         for name in ["files", "no-backup", "cache"] {
             fs::create_dir_all(root.join(name)).unwrap();

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,