poll oneoff tests: what if we read a non-empty file?

crates/test-programs/wasi-tests/src/bin/poll_oneoff_files.rs

@@ -150,16 +150,37 @@ unsafe fn test_fd_readwrite(readable_fd: wasi::Fd, writable_fd: wasi::Fd, error_
 
 unsafe fn test_fd_readwrite_valid_fd(dir_fd: wasi::Fd) {
     // Create a file in the scratch directory.
-    let readable_fd = wasi::path_open(
+    let nonempty_file = wasi::path_open(
         dir_fd,
         0,
         "readable_file",
         wasi::OFLAGS_CREAT,
+        wasi::RIGHTS_FD_WRITE,
+        0,
+        0,
+    )
+    .expect("create writable file");
+    // Write to file
+    let contents = &[1u8];
+    let ciovec = wasi::Ciovec {
+        buf: contents.as_ptr() as *const _,
+        buf_len: contents.len(),
+    };
+    wasi::fd_write(nonempty_file, &[ciovec]).expect("write");
+    wasi::fd_close(nonempty_file).expect("close");
+
+    // Now open the file for reading
+    let readable_fd = wasi::path_open(
+        dir_fd,
+        0,
+        "readable_file",
+        0,
         wasi::RIGHTS_FD_READ | wasi::RIGHTS_POLL_FD_READWRITE,
         0,
         0,
     )
     .expect("opening a readable file");
+
     assert_gt!(
         readable_fd,
         libc::STDERR_FILENO as wasi::Fd,

crates/wasi-common/src/sched/subscription.rs

@@ -62,6 +62,7 @@ pub enum Subscription<'a> {
     MonotonicClock(MonotonicClockSubscription<'a>),
 }
 
+#[derive(Debug)]
 pub enum SubscriptionResult {
     Read(Result<(u64, RwEventFlags), Error>),
     Write(Result<(u64, RwEventFlags), Error>),

crates/wasi-common/tokio/tests/poll_oneoff.rs

@@ -2,7 +2,7 @@ use anyhow::{Context, Error};
 use wasi_common::{
     file::{FdFlags, OFlags},
     sched::{Poll, RwEventFlags, SubscriptionResult, Userdata},
-    WasiDir,
+    WasiDir, WasiFile,
 };
 use wasi_tokio::{sched::poll_oneoff, Dir};
 
@@ -13,24 +13,34 @@ async fn empty_file_readable() -> Result<(), Error> {
     let d = workspace.open_dir("d").context("open dir")?;
     let d = Dir::from_cap_std(d);
 
-    let mut readable_f = d
-        .open_file(false, "f", OFlags::CREATE, true, false, FdFlags::empty())
+    let mut f = d
+        .open_file(false, "f", OFlags::CREATE, false, true, FdFlags::empty())
         .await
-        .context("create readable file")?;
+        .context("create writable file f")?;
+    let to_write: Vec<u8> = vec![0];
+    f.write_vectored(&vec![std::io::IoSlice::new(&to_write)])
+        .await
+        .context("write to f")?;
+    drop(f);
+
+    let mut f = d
+        .open_file(false, "f", OFlags::empty(), true, false, FdFlags::empty())
+        .await
+        .context("open f as readable")?;
 
     let mut poll = Poll::new();
-    poll.subscribe_read(&mut *readable_f, Userdata::from(123));
+    poll.subscribe_read(&mut *f, Userdata::from(123));
     poll_oneoff(&mut poll).await?;
 
     let events = poll.results();
 
-    assert_eq!(events.len(), 1);
+    assert_eq!(events.len(), 1, "expected 1 event, got: {:?}", events);
     match events[0] {
-        (SubscriptionResult::Read(Ok((0, flags))), ud) => {
+        (SubscriptionResult::Read(Ok((1, flags))), ud) => {
             assert_eq!(flags, RwEventFlags::empty());
             assert_eq!(ud, Userdata::from(123));
         }
-        _ => panic!(""),
+        _ => panic!("expected (Read(Ok(1, empty), 123), got: {:?}", events[0]),
     }
 
     Ok(())