Make EventStream interface more flexible

Take a callback instead of an mpsc Sender. The
run method blocks and invokes the callback for
each batch of events. The caller controls the
threading. The callback can return false to terminate
the event stream.

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

fsevent/src/lib.rs

@@ -8,31 +8,33 @@ use std::{
     os::unix::ffi::OsStrExt,
     path::{Path, PathBuf},
     slice,
-    sync::mpsc::Sender,
     time::Duration,
 };
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Event {
     pub event_id: u64,
     pub flags: StreamFlags,
     pub path: PathBuf,
 }
 
-pub struct EventStream {
+pub struct EventStream<F> {
     stream: fs::FSEventStreamRef,
-    _sender: Box<Sender<Vec<Event>>>,
+    _callback: Box<F>,
 }
 
-unsafe impl Send for EventStream {}
+unsafe impl<F> Send for EventStream<F> {}
 
-impl EventStream {
-    pub fn new(paths: &[&Path], latency: Duration, event_sender: Sender<Vec<Event>>) -> Self {
+impl<F> EventStream<F>
+where
+    F: FnMut(&[Event]) -> bool,
+{
+    pub fn new(paths: &[&Path], latency: Duration, callback: F) -> Self {
         unsafe {
-            let sender = Box::new(event_sender);
+            let callback = Box::new(callback);
             let stream_context = fs::FSEventStreamContext {
                 version: 0,
-                info: sender.as_ref() as *const _ as *mut c_void,
+                info: callback.as_ref() as *const _ as *mut c_void,
                 retain: None,
                 release: None,
                 copy_description: None,
@@ -58,7 +60,7 @@ impl EventStream {
 
             let stream = fs::FSEventStreamCreate(
                 cf::kCFAllocatorDefault,
-                callback,
+                Self::trampoline,
                 &stream_context,
                 cf_paths,
                 fs::kFSEventStreamEventIdSinceNow,
@@ -71,7 +73,7 @@ impl EventStream {
 
             EventStream {
                 stream,
-                _sender: sender,
+                _callback: callback,
             }
         }
     }
@@ -92,9 +94,8 @@ impl EventStream {
             fs::FSEventStreamRelease(self.stream);
         }
     }
-}
 
-extern "C" fn callback(
+    extern "C" fn trampoline(
         stream_ref: fs::FSEventStreamRef,
         info: *mut ::std::os::raw::c_void,
         num: usize,                                 // size_t numEvents
@@ -106,7 +107,7 @@ extern "C" fn callback(
             let event_paths = event_paths as *const *const ::std::os::raw::c_char;
             let e_ptr = event_flags as *mut u32;
             let i_ptr = event_ids as *mut u64;
-        let sender = (info as *mut Sender<Vec<Event>>).as_mut().unwrap();
+            let callback = (info as *mut F).as_mut().unwrap();
 
             let paths = slice::from_raw_parts(event_paths, num);
             let flags = slice::from_raw_parts_mut(e_ptr, num);
@@ -127,12 +128,13 @@ extern "C" fn callback(
                 }
             }
 
-        if sender.send(events).is_err() {
+            if !callback(&events) {
                 fs::FSEventStreamStop(stream_ref);
                 cf::CFRunLoopStop(cf::CFRunLoopGetCurrent());
             }
         }
     }
+}
 
 // Synchronize with
 // /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/FSEvents.framework/Versions/A/Headers/FSEvents.h
@@ -242,7 +244,7 @@ impl std::fmt::Display for StreamFlags {
 }
 
 #[test]
-fn test_observe() {
+fn test_event_stream() {
     use std::{fs, sync::mpsc, time::Duration};
     use tempdir::TempDir;
 
@@ -251,7 +253,9 @@ fn test_observe() {
     fs::write(path.join("a"), "a contents").unwrap();
 
     let (tx, rx) = mpsc::channel();
-    let stream = EventStream::new(&[&path], Duration::from_millis(50), tx);
+    let stream = EventStream::new(&[&path], Duration::from_millis(50), move |events| {
+        tx.send(events.to_vec()).is_ok()
+    });
     std::thread::spawn(move || stream.run());
 
     fs::write(path.join("b"), "b contents").unwrap();
@@ -265,8 +269,4 @@ fn test_observe() {
     let event = events.last().unwrap();
     assert_eq!(event.path, path.join("a"));
     assert!(event.flags.contains(StreamFlags::ITEM_REMOVED));
-
-    let dir2 = TempDir::new("test_observe2").unwrap();
-    fs::rename(path, dir2.path().join("something")).unwrap();
-    let events = rx.recv_timeout(Duration::from_millis(500)).unwrap();
 }