Fix hanging clients on RequestDispatch error #423
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It is possible for the sending of a request to race with the dropping of RequestDispatch: a client could send a request, then the dispatch could be dropped before processing the request. If that happens, the client will never receive a shutdown notice. To fix this, the request dispatch must first close the pending requests channel, then drain all remaining requests from the channel, and for each request, complete it with an error. A few (hopefully minor) breaking changes were made: - All ChannelError source errors are now wrapped in Arcs, so that the errors can be cloned and sent to all pending requests. - RpcError::Receive was renamed to RpcError::Transport to accommodate the range of errors that can now be received by the client. Its source error is now a ChannelError. - RpcError::Send's source error is now the transport error rather than ChannelError::Write(Transport::Error), because ChannelError::Write wasn't adding any additional information.
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Previously, when hitting an error, RequestDispatch would stop immediately without doing any cleanup. The pending requests channel would be close on drop, but any requests that were already in the channel would hang indefinitely.
With this PR, RequestDispatch will do a better cleanup job: it will close and drain the the pending requests, completing each request with the same error that caused the RequestDispatch to halt.
Fixes #415