锈与错误链和WebSocket板条箱冲突

Question

I'm trying to use error-chain with the websocket crate, but running into an issue that I'm not sure how to resolve. WsUpgrade::accept has the following signature:

fn accept(self) -> Result<Client<S>, (S, IoError)>

Note that the Err variant is a tuple. I want to configure error-chain to handle calls to this method, so I tried to do so as follows in the relevant consuming module:

mod errors {
    error_chain! {
        foreign_links {
            WebSock((::std::net::TcpStream, ::std::io::Error));
        }
    }
}

This results in the following error, seemingly related to the presence of the tuple.

error: expected identifier, found `(`
  --> src/lib/websock.rs:23:21
   |
23 |             WebSock((::std::net::TcpStream, ::std::io::Error));
   |                     ^

How can I resolve this? Hopefully I've missed something simple.

Answer 1

A simple solution would be to introduce a type alias:

mod errors {
    type WebSocketError = (::std::net::TcpStream, ::std::io::Error);
    error_chain! {
        foreign_links {
            WebSock(WebSocketError);
        }
    }
}

However, this type does not implement traits required by error-chain (such as Error and Display ), so it can't be used there.

I think the simplest solution is to convert the error manually using Result::map_err before passing the value to error-chain. For example, the following construction will produce Result<Client<S>, IoError> :

x.accept().map_err(|e| e.1)