localhost does not resolve

[alex-shapiro]

I tried to open an async connection to a server running locally at ws://localhost:4000 and received the following error:

IoError(Error { repr: Os { code: 61, message: "Connection refused" } })

However, the following work:

• opening an async websocket connection to ws://127.0.0.1:4000. So my code connects once DNS is resolved.
• opening an async websocket connection to ws://echo.websocket.org. So websocket DNS resolution does work in some cases.
• opening a synchronous websocket connection to ws://localhost:4000. So local DNS resolution works but only for synchronous connections.
• opening an async HTTP connection to http://localhost:4000 with Hyper 0.11. Does Hyper 0.11 use a different Tokio primitive to resolve DNS?

I'm not exactly sure what's going on. It's not a big deal - I'm manually resolving localhost to 127.0.0.1 - but I'm kind of curious.

[illegalprime]

Good catch! It's probably this code:
https://github.com/cyderize/rust-websocket/blob/master/src/client/builder.rs#L800

Instead of calling next() you should create a TcpStream with that iterator and then turn it into an async one with the async TcpStream's API.

[alex-shapiro]

That means the DNS lookup would be done synchronously, right?

[illegalprime]

hmm... that's a good point. I wonder how hyper 0.11 is doing it

[alex-shapiro]

Looks like Hyper wraps a synchronous DNS call inside a future: https://github.com/hyperium/hyper/blob/master/src/client/dns.rs#L52.

[illegalprime]

We can try looping over the ToSocketAddr in the future (make one async DNS call, if that fails try again). This would get a really complicated type though.