Review by kuba

[Stebalien]

No description provided.

[Kubuxu]

I would rename this variable: https://github.com/libp2p/go-reuseport-transport/blob/master/reuseport.go#L59 it was a bit confusing at first.

Shouldn't we use global in this case? https://github.com/libp2p/go-reuseport-transport/blob/master/multidialer.go#L43-L47

[Kubuxu]

We might want to catch: EHOSTUNREACH and redial using a different address.

[Stebalien]

We might want to catch: EHOSTUNREACH and redial using a different address.

Different source or target? We always use the unspecified IP address for the source (this library just picks the source port). It's up to the transport to try multiple target addresses.

[Kubuxu]

In case of a local network, we use a random address for Dial afaik.

[Stebalien]

We pick a random source port from the set of reasonable source ports but we never manually specify the source address.

Note: The swarm no longer specifies source addresses when dialing. I moved that logic into the transport because the swarm doesn't really know enough to do so intelligently.

Really, the correct way to implement this library would be to:

1. Ask the kernel, if I dial IP X, which source address will I use.
2. Try a random port out of all the ports we have open on that source address.

Unfortunately, the "ask the kernel" part involves using netlink. We could do this (e.g., with the netlink package) but that adds some complexity (and I'd like to do it later, if ever).

[Stebalien]

Shouldn't we use global in this case? https://github.com/libp2p/go-reuseport-transport/blob/master/multidialer.go#L43-L47

No, but that needs a comment. Basically, we always prefer using the unspecified address over the global address because we don't actually know if the global address can dial the target. The logic is:

1. If we're dialing loopback, choose a source-port in order of preference:
   1. A port in-use by an explicit loopback listener.
   2. A port in-use by a listener on an unspecified address (must also be listening on localhost).
   3. A port in-use by a listener on a global address. We don't have any other better options (other than picking a random port).
2. If we're dialing a global address, choose a source-port in order of preference:
   1. A port in-use by a listener on an unspecified address (the most general case).
   2. A port in-use by a listener on the global address.
3. Fail on link-local dials (go-ipfs currently forbids this and I figured we could try lifting this restriction later).

[Stebalien]

Changes: 73d48b5...f431c22

[Stebalien]

@Kubuxu when you get a chance, final review?

[Kubuxu]

SGWM