Consider Typing Errors for Requests with Nil Responses

[jamesross3]

There are some error cases for requests where the response is nil; these cases fall outside the scope of the existing error decoder middleware implementation. Examples of errors like this are:

• dial timeout
• timeout exceeded while awaiting headers
• DNS lookup no such host
• certificate signed by unknown authority

Ideally, CGR provides some methods that enable us to identify these errors (similar to typing conjure errors / attaching status codes to errors)

[jamesross3]

@nmiyake / @tabboud / @bmoylan / @whickman for opinions here

[bmoylan]

Yeah I would be very supportive of this. The errors coming out of the standard library are almost all well-typed, so this conversion should be relatively straightforward (and can grow over time if we don't hit 100% coverage in the first version).

[tabboud]

Definitely agree that this would be a valuable addition!

Similarly, @bmoylan just added a way to identify Timeout errors and tag them in the metrics middleware.

I would be fully supportive of adding a way to wire these errors back through so clients could use something like errors.Is with well defined types.

[jamesross3]

also interested in whether these error types should affect our existing retry behavior here