feat: reprovider

[vasco-santos]

In the context of js-ipfs reannouncing blocks to the network ipfs/js-ipfs#2160, this PR aims to add a Provider layer controlled by js-ipfs. This provider will be used by bitswap.

Needs:

• Different strategies
• ipfs/js-ipfs-bitswap#199
• documentation - should be a part of ipfs/js-ipfs#2204

[vasco-santos]

@alanshaw @dirkmc could I get your feedback on this PR?

It is important to also look at the bitswapPR in this context.

FYI, for getting this to the finish line I only need to add the proper logic for the reprovide strategies. However, there is some code in Dirk's PR for the garbage collection ipfs/js-ipfs#2022 that would be great to use for this. So, it would be great to have that merged first.

[dirkmc]

Looks like it's on the right track @vasco-santos 👍
I left a few comments for minor things in the code.

I wonder if it would make sense to persist the time at which the last provide occurred, so that if a node restarts it doesn't wait the full 12 hours to reprovide?

[vasco-santos]

Thanks @dirkmc ! I think that I addressed all your comments!

Regarding persisting the time of the last provide, the first reprovide will happen once the node starts, after a short delay. So, I think it should not be necessary

[alanshaw]

@vasco-santos what's the status of this PR - still draft?

[vasco-santos]

I was waiting on #2022 getting merged, which had a lot of useful code to integrate here without duplicating.

[daviddias]

Hi! js-ipfs master just got a whole new set of automated tests with #2528, #2440 and also running some of the test suites from our early testers (hi5 to @achingbrain for setting it all up!). Would you mind rebasing the master branch on this PR to ensure it runs all the latest tests? Thank you!

[achingbrain]

I'm going to close this because I think since the .provide method lives on libp2p's ContentRouter interface, re-provides should be handled by the various implementations of content routers since they all may have different rules about provider record validity, etc.

Some may call out to a remote service that does the re-provide for us, for example, or some may have shorter lived records than others, who knows!