wrap connection and timeout exceptions

[binarycode]

This PR implements exception wrapping: any underlying exceptions caused by broken connection, timeouts, etc. are wrapped in Faraday exception classes.

The list of exceptions is based on the one used in NetHttp adapter (https://github.com/lostisland/faraday/blob/master/lib/faraday/adapter/net_http.rb). I'm not sure all of the exceptions are relevant and if other ones (like for example Protocol::HTTP*::*Error or Async::HTTP::Protocol::RequestFailed or smth like that) should be included. The most common unwrapped exceptions that I've stumbled upon while using this adapter were Errno::ETIMEDOUT, Errno::ECONNREFUSED and Errno::EHOSTUNREACH.

[ioquatix]

I don’t think it should be possible for Timeout::Error to occur. What errors are you seeing?

[binarycode]

Yeah, you're right, looks like this exception is specific to NetHttp adapter, and should be removed.

[ioquatix]

@technoweenie what do you think of this?

What is the intent of the separate Faraday exception classes?

How do users consume the timeout exception vs the connection exception vs the ssl exception? What is the use case?

Do you know Ruby has Exception#cause?

@binarycode do you think we should just catch all errors and wrap them? OpenSSL should always be defined with async-http as there is no alternative.

[binarycode]

As far as I understand (from reading lostisland/faraday#718) the Faraday::TimeoutError is intended to cover both cases of open timeout and read response timeout. While this might not be completely correct, as the open timeout should probably be covered by Faraday::ConnectionFailure, it is preseved for backward compatibility.

One way the Faraday::TimeoutError exception is different from Faraday::ConnectionFailure is that the timeout one is automatically retried by default by retry middleware (https://github.com/lostisland/faraday/blob/master/lib/faraday/request/retry.rb).

I think that we should wrap the exceptions as consistent with other adapters as possible, and looks like Errno::ETIMEDOUT is wrapped into Faraday::TimeoutError by most of them.

[ioquatix]

Can you rebase on master so I can merge.

[binarycode]

done

[ioquatix]

Thanks!