Allow configurable prioritization of requests

[synzhu]

Can we allow the user customize the behavior for how we prioritize WANTHAVE or WANTBLOCK requests?

For example:

• we may not want to respond to requests for a certain block even though we have that block
• we may want to implement some sort of prioritization for requests, e.g always finish responding to all requests for block 42 before responding to any requests for block 41

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[Stebalien]

• The entry point to this code is https://github.com/ipfs/go-bitswap/tree/master/internal/decision.
• You'll probably need to modify the PeerCompare function to take some form of priority into account when deciding between peers.
• If you want to avoid sending blocks, you'll likely want to filter them out of incoming want requests in Engine.MessageReceived. Just make sure to send "don't haves" if requested.
• You can also filter blocks by wrapping the blockstore passed into bitswap.New, but this will prevent bitswap from ever seeing the blocks, regardless of who's asking.

[aschmahmann]

@smnzhu how much of this issue is remaining given the already merged PRs?

[susarlanikhilesh]

• The entry point to this code is https://github.com/ipfs/go-bitswap/tree/master/internal/decision.
• You'll probably need to modify the PeerCompare function to take some form of priority into account when deciding between peers.
• If you want to avoid sending blocks, you'll likely want to filter them out of incoming want requests in Engine.MessageReceived. Just make sure to send "don't haves" if requested.
• You can also filter blocks by wrapping the blockstore passed into bitswap.New, but this will prevent bitswap from ever seeing the blocks, regardless of who's asking.

I need something similar. Like I don't want to request a node even if it has data. I know it's peer ID, I want to avoid pulling blocks from that peer. Where exactly you think I should looks for. I need to stay swarm connected to that peer. So, want_have sends to all the peers connected. But I want to avoid it for that one single peer Thank you