read_dir_first: stop at the first file that is alphabetically "after"…

… `not_before`

In fido-authenticator, if we change the paths of RK  to be:
"rp_id.rk_id" instead of the current "rp_id/rk_id", we still want to be able
to iterate over the keys even though we only  know the "rp_id" and not the
"rk_id". Therefore we need to be able to stop at "rp_id.***" when giving "rp_id" in `not_before`

This is technically a breaking change because now, given the files:

- "aaa"
- "aaabbb"

 "read_dir_first"  with "aaa" as `not_before` would only yield "aaa"
due to littlefs-project/littlefs#923.
Now this will yield both files, and yield "aaabbb" first.

I beleive this behaviour is technically more correct as it is likely what
would be expected to be yield expecting alphabetical order
(though the order of the entries is still incorrect).

Cargo.toml

@@ -133,4 +133,4 @@ features = ["serde-extensions", "virt"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [patch.crates-io]
-littlefs2 = { git = "https://github.com/trussed-dev/littlefs2.git", rev = "ebd27e49ca321089d01d8c9b169c4aeb58ceeeca" }
+littlefs2 = { git = "https://github.com/sosthene-nitrokey/littlefs2.git", rev = "77a45fa38f8bd0dd0197cce7735f43e9340fa3c6" }

src/store/filestore.rs

@@ -1,3 +1,5 @@
+use core::cmp::Ordering;
+
 use crate::{
     error::{Error, Result},
     // service::ReadDirState,
@@ -164,7 +166,10 @@ impl<S: Store> ClientFilestore<S> {
                     // if there is a "not_before" entry, skip all entries before it.
                     .find(|(_, entry)| {
                         if let Some(not_before) = not_before {
-                            entry.file_name() == not_before.as_ref()
+                            match entry.file_name().cmp_str(not_before) {
+                                Ordering::Less => false,
+                                Ordering::Equal | Ordering::Greater => true,
+                            }
                         } else {
                             true
                         }

tests/filesystem.rs

@@ -1,5 +1,7 @@
 #![cfg(feature = "virt")]
 
+use std::assert_eq;
+
 use trussed::{
     client::{CryptoClient, FilesystemClient},
     error::Error,
@@ -85,15 +87,95 @@ fn iterating(location: Location) {
     });
 }
 
+fn iterating_first(location: Location) {
+    use littlefs2::path;
+    client::get(|client| {
+        let files = [
+            path!("foo"),
+            path!("bar"),
+            path!("baz"),
+            path!("foobar"),
+            path!("foobaz"),
+        ];
+
+        let files_sorted_lfs = {
+            let mut files = files.clone();
+            files.sort_by(|a, b| a.cmp_lfs(b));
+            files
+        };
+
+        assert_eq!(
+            files_sorted_lfs,
+            [
+                path!("bar"),
+                path!("baz"),
+                path!("foobar"),
+                path!("foobaz"),
+                path!("foo"),
+            ]
+        );
+
+        let files_sorted_str = {
+            let mut files = files.clone();
+            files.sort_by(|a, b| a.cmp_str(b));
+            files
+        };
+        assert_eq!(
+            files_sorted_str,
+            [
+                path!("bar"),
+                path!("baz"),
+                path!("foo"),
+                path!("foobar"),
+                path!("foobaz"),
+            ]
+        );
+
+        for f in files {
+            syscall!(client.write_file(
+                location,
+                PathBuf::from(f),
+                Bytes::from_slice(f.as_ref().as_bytes()).unwrap(),
+                None
+            ));
+        }
+
+        let first_entry = syscall!(client.read_dir_first(location, PathBuf::from(""), None))
+            .entry
+            .unwrap();
+        assert_eq!(first_entry.path(), files_sorted_lfs[0]);
+        for f in &files_sorted_lfs[1..] {
+            let entry = syscall!(client.read_dir_next()).entry.unwrap();
+            assert_eq!(&entry.path(), f);
+        }
+        assert!(syscall!(client.read_dir_next()).entry.is_none());
+
+        let first_entry =
+            syscall!(client.read_dir_first(location, PathBuf::from(""), Some(PathBuf::from("fo"))))
+                .entry
+                .unwrap();
+        assert_eq!(first_entry.path(), path!("foobar"));
+
+        for f in &(files_sorted_lfs[3..]) {
+            let entry = syscall!(client.read_dir_next()).entry.unwrap();
+            assert_eq!(&entry.path(), f);
+        }
+        assert!(syscall!(client.read_dir_next()).entry.is_none());
+    });
+}
+
 #[test]
 fn iterating_internal() {
     iterating(Location::Internal);
+    iterating_first(Location::Internal);
 }
 #[test]
 fn iterating_external() {
     iterating(Location::External);
+    iterating_first(Location::Internal);
 }
 #[test]
 fn iterating_volatile() {
     iterating(Location::Volatile);
+    iterating_first(Location::Internal);
 }