channel: Panic in .recv_timeout(Duration::MAX)

[MightyPork]

https://github.com/crossbeam-rs/crossbeam/blob/master/crossbeam-channel/src/channel.rs#L863

Calling recv_timeout() with Duration::MAX causes panic due to Instant overflow.

This happens quite naturally when the duration comes from some calculation, meaning "wait forever".

I don't think it should crash, insted wait the longest possible time.

[taiki-e]

It would be ideal if there were a method like Instant::saturating_add, but unfortunately it does not exist, so for now it seems we have to wait a few decades or wait forever.

[MightyPork]

There's checked add, so I'm thinking something like

self.recv_deadline(match Instant::now().checked_add(timeout) {
    Some(deadline) => deadline,
    None => Instant::now() + Duration::from_secs(86400 * 365 * 30) // hack from tokio-rs
})

[taiki-e]

Sounds good to me.

[taiki-e]

Fixed in crossbeam-channel 0.5.3.

[MightyPork]

I was planning to make a PR xD

thanks for fixing it, this was quite the footgun 👍

[ibraheemdev]

I fixed this in the PR to std with:

    pub fn recv_timeout(&self, timeout: Duration) -> Result<T, RecvTimeoutError> {
-        self.recv_deadline(Instant::now() + timeout)
+        match Instant::now().checked_add(timeout) {
+            Some(deadline) => self.recv_deadline(deadline),
+            // So far in the future that it's practically the same as waiting indefinitely.
+            None => self.recv().map_err(RecvTimeoutError::from),
+        }
    }

[taiki-e]

@ibraheemdev I agree that is also reasonable approach.