Auto merge of #176 - antrik:fix-inprocess-error_handling, r=jdm

Fix error handling in `inprocess` back-end

Two fixes (along with test cases) for handling of sender/receiver closed conditions.

Author: bors-servo

src/platform/inprocess/mod.rs

@@ -100,7 +100,8 @@ impl OsIpcReceiver {
             Ok(MpscChannelMessage(d,c,s)) => Ok((d,
                                                  c.into_iter().map(OsOpaqueIpcChannel::new).collect(),
                                                  s)),
-            Err(_) => Err(MpscError::ChannelClosedError),
+            Err(mpsc::TryRecvError::Disconnected) => Err(MpscError::ChannelClosedError),
+            Err(_) => Err(MpscError::UnknownError),
         }
     }
 }
@@ -141,7 +142,7 @@ impl OsIpcSender {
                 -> Result<(),MpscError>
     {
         match self.sender.borrow().send(MpscChannelMessage(data.to_vec(), ports, shared_memory_regions)) {
-            Err(_) => Err(MpscError::ChannelClosedError),
+            Err(_) => Err(MpscError::BrokenPipeError),
             Ok(_) => Ok(()),
         }
     }
@@ -376,6 +377,7 @@ impl OsIpcSharedMemory {
 #[derive(Debug, PartialEq)]
 pub enum MpscError {
     ChannelClosedError,
+    BrokenPipeError,
     UnknownError,
 }
 
@@ -396,7 +398,10 @@ impl From<MpscError> for Error {
     fn from(mpsc_error: MpscError) -> Error {
         match mpsc_error {
             MpscError::ChannelClosedError => {
-                Error::new(ErrorKind::BrokenPipe, "MPSC channel closed")
+                Error::new(ErrorKind::ConnectionReset, "MPSC channel sender closed")
+            }
+            MpscError::BrokenPipeError => {
+                Error::new(ErrorKind::BrokenPipe, "MPSC channel receiver closed")
             }
             MpscError::UnknownError => Error::new(ErrorKind::Other, "Other MPSC channel error"),
         }

src/platform/test.rs

@@ -699,6 +699,20 @@ fn no_senders_notification() {
     assert!(result.unwrap_err().channel_is_closed());
 }
 
+/// Checks that a broken pipe notification is returned by `send()`
+/// after the receive end was closed.
+#[test]
+fn no_receiver_notification() {
+    let (sender, receiver) = platform::channel().unwrap();
+    drop(receiver);
+    let data: &[u8] = b"1234567";
+    let result = sender.send(data, vec![], vec![]);
+    assert!(result.is_err());
+    // We don't have an actual method for distinguishing a "broken pipe" error --
+    // but at least it's not supposed to signal the same condition as closing the sender.
+    assert!(!result.unwrap_err().channel_is_closed());
+}
+
 #[test]
 fn shared_memory() {
     let (tx, rx) = platform::channel().unwrap();
@@ -730,6 +744,23 @@ fn try_recv() {
     assert!(rx.try_recv().is_err());
 }
 
+/// Checks that a channel closed notification is returned by `try_recv()`.
+///
+/// Also checks that the "no data" notification returned by `try_recv()`
+/// when no data is pending but before the channel is closed,
+/// is distinguishable from the actual "channel closed" notification.
+#[test]
+fn no_senders_notification_try_recv() {
+    let (sender, receiver) = platform::channel().unwrap();
+    let result = receiver.try_recv();
+    assert!(result.is_err());
+    assert!(!result.unwrap_err().channel_is_closed());
+    drop(sender);
+    let result = receiver.try_recv();
+    assert!(result.is_err());
+    assert!(result.unwrap_err().channel_is_closed());
+}
+
 #[test]
 fn try_recv_large() {
     let (tx, rx) = platform::channel().unwrap();