fix(fuse): a file read just as its create lands has its bytes (B179)

crates/pdfs-fuse/src/lib.rs

@@ -3225,8 +3225,19 @@ impl Core {
     /// `None` while it is still queued. Read from the row, which has it before
     /// the tree does.
     pub(crate) fn landed_row_uid(&self, ino: u64) -> Option<NodeUid> {
-        state::ino_lid(ino)
-            .and_then(|lid| self.db.uid_of_lid(lid).ok().flatten())
+        state::ino_lid(ino).and_then(|lid| self.landed_lid_uid(lid))
+    }
+
+    /// [`Core::landed_row_uid`] for a node known by its stand-in `uid`.
+    pub(crate) fn landed_stand_in_uid(&self, uid: &NodeUid) -> Option<NodeUid> {
+        pdfs_core::db::local_lid(&uid.to_string()).and_then(|lid| self.landed_lid_uid(lid))
+    }
+
+    fn landed_lid_uid(&self, lid: i64) -> Option<NodeUid> {
+        self.db
+            .uid_of_lid(lid)
+            .ok()
+            .flatten()
             .and_then(|uid| parse_node_uid(&uid))
             .filter(|uid| !is_local_uid(uid))
     }

crates/pdfs-fuse/src/reads.rs

@@ -499,9 +499,14 @@ impl Core {
         }
         // A node created offline and never written has no blob and no remote: it
         // is an empty file, and asking the API about a `local~` uid would only
-        // earn a 404 (offline.md Phase 3b).
+        // earn a 404 (offline.md Phase 3b). Unless its create landed since the
+        // read looked: the landing moved the queued write to the uid Drive
+        // gave it, and the row says which (`docs/BUGS.md` B179).
         if is_local_uid(uid) {
-            return Ok(Vec::new());
+            return match self.landed_stand_in_uid(uid) {
+                Some(real) => self.read_range(&real, mtime, fsize, offset, len, cache_blocks),
+                None => Ok(Vec::new()),
+            };
         }
         self.read_range_remote(uid, mtime, fsize, offset, len, cache_blocks)
     }

crates/pdfs-fuse/src/sim/daemon.rs

@@ -609,6 +609,41 @@ mod tests {
         let _ = std::fs::remove_dir_all(&dir);
     }
 
+    #[test]
+    #[ignore = "mounts FUSE: run with `cargo test -p pdfs-fuse sim:: -- --ignored`"]
+    fn a_file_read_as_its_create_lands_has_its_bytes() {
+        // The landing moved the queued write to the uid Drive gave the file.
+        // A read that still knew the file by its stand-in found no write
+        // queued under it, took the file for one never written and read it
+        // empty (B179).
+        let drive = FakeDrive::new();
+        let dir = scratch("read-as-create-lands");
+        let daemon = Daemon::start(&dir, drive.client(1, Faults::lan())).unwrap();
+        let mnt = daemon.mountpoint.clone();
+        let create = daemon.client.hold_reply_to_next_create();
+        std::fs::write(mnt.join("a.txt"), b"old").unwrap();
+        assert!(wait_until(Duration::from_secs(30), || create.reached()));
+        std::fs::write(mnt.join("a.txt"), b"newer").unwrap();
+        let uid = drive.lookup("a.txt").unwrap();
+        let landing = daemon.client.hold_next_landing(&uid);
+        drop(create);
+        assert!(wait_until(Duration::from_secs(30), || landing.reached()));
+        assert_eq!(std::fs::read(mnt.join("a.txt")).unwrap(), b"newer");
+        drop(landing);
+        assert!(
+            wait_until(Duration::from_secs(30), || {
+                daemon.pending().is_ok_and(|items| items.is_empty())
+                    && drive.tree().get("a.txt") == Some(&Entry::File(Arc::new(b"newer".to_vec())))
+            }),
+            "{:?} {:?}",
+            daemon.pending(),
+            drive.tree()
+        );
+
+        assert!(matches!(daemon.stop(), Ok(MountOutcome::Shutdown)));
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[test]
     #[ignore = "mounts FUSE: run with `cargo test -p pdfs-fuse sim:: -- --ignored`"]
     fn a_file_moved_while_its_create_was_on_the_wire_keeps_its_new_name() {