Add 'offline' mode

[nachog00]

It might be worthwhile to add an offline mode. That is, to allow devs to shut off the fetcher logic completely.

If they are bringing in their own binaries, we should't be slowing them down with async fetching and potentially slow verifying of hashes on every build.

[ala-mode]

I agree. Verifying shouldn't take too long, but fetching can be resource intensive. Not sure about an exact design but maybe if (all?) binaries are specified, the user would get a message (maybe we should add a message for when we are fetching binaries too?) and bypass fetching completely. Also it makes sense to not fetch for any reason if the user passes an argument to accomplish this.

I think we would want a command line flag or similar. How can we hook our build script into such a technique?

[ala-mode]

simply pasting in comments from #24 (duplicate issue) ....

nachog00 :
If connection completely off, binaries cannot be downloaded.
We need to warn the user and prompt them to either fix their connection or turn on fetcher's offline mode

ala-mode :
IIRC the message a user gets while offline is a DNS error or something similar. I agree we should have a more informative (error?) message.

[nachog00]

With fetcher-core (#31 ), an 'offline mode' doesn't make sense anymore, I think. Closing this for now.