Client::poll_ready() returns an Error if next stream ID would overflow (#103)

Closes #102

src/proto/connection.rs

@@ -250,7 +250,7 @@ where
     B: IntoBuf,
 {
     /// Returns `Ready` when new the connection is able to support a new request stream.
-    pub fn poll_send_request_ready(&mut self) -> Async<()> {
+    pub fn poll_send_request_ready(&mut self) -> Poll<(), ::Error> {
         self.streams.poll_send_request_ready()
     }
 

src/proto/streams/send.rs

@@ -299,6 +299,10 @@ where
         Ok(())
     }
 
+    pub fn ensure_next_stream_id(&self) -> Result<StreamId, UserError> {
+        self.next_stream_id.map_err(|_| OverflowedStreamId)
+    }
+
     /// Returns a new StreamId if the local actor can initiate a new stream.
     fn try_open(&self) -> Result<StreamId, UserError> {
         if P::is_server() {
@@ -306,6 +310,6 @@ where
             return Err(UnexpectedFrameType);
         }
 
-        self.next_stream_id.map_err(|_| OverflowedStreamId)
+        self.ensure_next_stream_id()
     }
 }

src/proto/streams/streams.rs

@@ -403,11 +403,13 @@ impl<B> Streams<B, client::Peer>
 where
     B: Buf,
 {
-    pub fn poll_send_request_ready(&mut self) -> Async<()> {
+    pub fn poll_send_request_ready(&mut self) -> Poll<(), ::Error> {
         let mut me = self.inner.lock().unwrap();
         let me = &mut *me;
 
-        me.counts.poll_open_ready()
+        me.actions.send.ensure_next_stream_id()?;
+
+        Ok(me.counts.poll_open_ready())
     }
 }