Megular Expressions

[MarcoPolo]

A very simple regular expression matcher for Multiaddr components. Supports capturing values. Matches in linear time (no back tracking).

The core logic is about 100 LOC. The sugar to make it nicer to use is about another 100 LOC.

Motivation

If we are going to treat Multiaddrs as encoding, then we need to make it more ergonomic to parse multiaddrs. Right now we have a lot of somewhat wrong manual parsers using ForEach. This should be able to replace those, make it cleaner, and most importantly make them obviously correct.

In draft while I try this out in go-libp2p.

Example

Parsing a WebTransport Multiaddr m.

var dnsName string
var ip4Addr string
var ip6Addr string
var udpPort string
var certHashesStr []string
matched, err := m.Match(
  meg.Or(
    meg.CaptureVal(ma.P_IP4, &ip4Addr),
    meg.CaptureVal(ma.P_IP6, &ip6Addr),
    meg.CaptureVal(ma.P_DNS4, &dnsName),
    meg.CaptureVal(ma.P_DNS6, &dnsName),
    meg.CaptureVal(ma.P_DNS, &dnsName),
  ),
  meg.CaptureVal(ma.P_UDP, &udpPort),
  meg.Val(ma.P_QUIC_V1),
  meg.Optional(
    meg.CaptureVal(ma.P_SNI, &wtAddr.sni),
  ),
  meg.Val(ma.P_WEBTRANSPORT),
  meg.CaptureZeroOrMore(ma.P_CERTHASH, &certHashesStr),
)
if err != nil {
  return webtransportAddr{}, err
}
if !matched {
  return webtransportAddr{}, errNotQUICAddr
}

[sukunrt]

This looks very useful to me modulo comments. See how nice the IsWebRTCDirectMultiaddr method is now vs compared to master.

I think we should make this package Experimental / Alpha and start using this in go-libp2p. After some experience we can remove the Experimental tag, till then we can keep iterating on a satisfactory api.

[sukunrt]

Just one unaddresses comment:
#263 (comment)

[sukunrt]

Do we need this?
I'd prefer a method in manet that returns (network string, ipPort netip.AddrPort)

[MarcoPolo]

This composes better. You can use this and capture other parts of the multiaddr in a single pass.

We don't need this, but I think it's helpful to demonstrate this pattern.

[sukunrt]

This looks good except for this comment: #263 (comment)

I'll approve once we resolve that.