refactor(bitswap) use new net package

[btc]

No description provided.

[whyrusleeping]

Question: How do i go about receiving a message from the net? (how does bitswap do this now?)

[btc]

BitSwap and DHT register Handlers. BitSwap's handler implementation is here:

https://github.com/jbenet/go-ipfs/blob/net-dht-stash/bitswap/transmission/service_wrapper.go#L29

@jbenet just made some interface improvements so the way this gets wired up will be better.

The procedure is as follows:

1. in core, on startup a Network is created. (https://github.com/jbenet/go-ipfs/blob/0b20da3126a86cf1ac72d753d0301a778046407b/core/core.go#L96)
2. Then the bitswap service is created and registered on the network. (https://github.com/jbenet/go-ipfs/blob/0b20da3126a86cf1ac72d753d0301a778046407b/core/core.go#L97)
3. Then bitswap's message handler registers itself on the service. (eg shows dht https://github.com/jbenet/go-ipfs/blob/0b20da3126a86cf1ac72d753d0301a778046407b/core/core.go#L105)

Note that the handler can be DHT or Bitswap sessions or some helper object. In the snippets above, the DHT session is used.

In bitswap, presently a helper is used. I'm going to change Bitswap to behave the way the DHT does!

[jbenet]

Adding to the above, the dht still gets network because it may have to connect to (network.Dial) new peers

[btc]

bitswap now uses the new net layer. increasing granularity. specific remaining tasks are tracked in

#97
#96
#95

[jbenet]

@perfmode thanks for linking things here! super helpful to reading :) 👍