From 760bb7f25f2ed76545ad40e5b014c9fb2c37cd42 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sosth=C3=A8ne=20Gu=C3=A9don?= <sosthene@nitrokey.com>
Date: Mon, 13 Mar 2023 14:36:35 +0100
Subject: [PATCH] Expose directory `tell`, `seek` and `rewind` functionnality

---
 src/fs.rs    | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/tests.rs | 26 +++++++++++++++++++--
 2 files changed, 90 insertions(+), 2 deletions(-)

diff --git a/src/fs.rs b/src/fs.rs
index 421c39edb..6d2f127ec 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -1033,6 +1033,11 @@ impl ReadDirAllocation {
     }
 }
 
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct DirIterationTell {
+    tell_result: u32,
+}
+
 pub struct ReadDir<'a, 'b, S: driver::Storage> {
     alloc: RefCell<&'b mut ReadDirAllocation>,
     fs: &'b Filesystem<'a, S>,
@@ -1040,6 +1045,67 @@ pub struct ReadDir<'a, 'b, S: driver::Storage> {
     path: PathBuf,
 }
 
+impl<'a, 'b, S: driver::Storage> ReadDir<'a, 'b, S> {
+    /// Return the position of the directory
+    ///
+    /// The returned offset is only meant to be consumed by seek and may not make
+    /// sense, but does indicate the current position in the directory iteration.
+    ///
+    /// Returns the position of the directory, which can be returned to using [`seek`](Self::seek).
+    pub fn tell(&self) -> Result<DirIterationTell> {
+        let value = unsafe {
+            ll::lfs_dir_tell(
+                &mut self.fs.alloc.borrow_mut().state,
+                &mut self.alloc.borrow_mut().state,
+            )
+        };
+        if value < 0 {
+            Err(io::result_from((), value).unwrap_err())
+        } else {
+            Ok(DirIterationTell {
+                tell_result: value as u32,
+            })
+        }
+    }
+
+    /// Change the position of the directory
+    ///
+    /// The new off must be a value previous returned from [`tell`](Self::tell) and specifies
+    /// an absolute offset in the directory seek.
+    pub fn seek(&mut self, state: DirIterationTell) -> Result<DirIterationTell> {
+        let value = unsafe {
+            ll::lfs_dir_seek(
+                &mut self.fs.alloc.borrow_mut().state,
+                &mut self.alloc.borrow_mut().state,
+                state.tell_result,
+            )
+        };
+        if value < 0 {
+            Err(io::result_from((), value).unwrap_err())
+        } else {
+            Ok(DirIterationTell {
+                tell_result: value as u32,
+            })
+        }
+    }
+
+    /// Change the position of the directory to the beginning of the directory
+    pub fn rewind(&mut self) -> Result<()> {
+        let res = unsafe {
+            ll::lfs_dir_rewind(
+                &mut self.fs.alloc.borrow_mut().state,
+                &mut self.alloc.borrow_mut().state,
+            )
+        };
+
+        if res < 0 {
+            Err(io::result_from((), res).unwrap_err())
+        } else {
+            Ok(())
+        }
+    }
+}
+
 impl<'a, 'b, S: driver::Storage> Iterator for ReadDir<'a, 'b, S> {
     type Item = Result<DirEntry>;
 
diff --git a/src/tests.rs b/src/tests.rs
index 2e9bf0a9f..a5bb1e285 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -449,12 +449,16 @@ fn test_iter_dirs() {
             file.set_len(37)?;
             fs.create_file_and_then(b"/tmp/file.b\0".try_into()?, |file| file.set_len(42))
         })?;
+        let mut tells = Vec::new();
 
-        fs.read_dir_and_then(b"/tmp\0".try_into()?, |dir| {
+        fs.read_dir_and_then(b"/tmp\0".try_into()?, |mut dir| {
             let mut found_files: usize = 0;
             let mut sizes = [0usize; 4];
+            let mut i = 0;
 
-            for (i, entry) in dir.enumerate() {
+            tells.push(dir.tell()?);
+            while let Some(entry) = dir.next() {
+                tells.push(dir.tell()?);
                 let entry = entry?;
 
                 // assert_eq!(entry.file_name(), match i {
@@ -467,13 +471,31 @@ fn test_iter_dirs() {
 
                 sizes[i] = entry.metadata().len();
                 found_files += 1;
+                i += 1;
             }
 
             assert_eq!(sizes, [0, 0, 37, 42]);
             assert_eq!(found_files, 4);
 
+            for (i, tell) in tells.iter().enumerate() {
+                dir.rewind().unwrap();
+                let mut found_files: usize = 0;
+                let mut sizes = Vec::new();
+                dir.seek(*tell)?;
+
+                for entry in &mut dir {
+                    let entry = entry?;
+                    sizes.push(entry.metadata().len());
+                    found_files += 1;
+                }
+
+                assert_eq!(sizes, [0, 0, 37, 42][i..]);
+                assert_eq!(found_files, 4 - i);
+            }
             Ok(())
         })
+        .unwrap();
+        Ok(())
     })
     .unwrap();
 }