Brave: LAN discovery & announcement (mDNS, DNS-SD)

[lidel]

Part of work on Embedded JS-IPFS in Brave #716 🦁 and epic about local discovery in browsers (ipfs/in-web-browsers#45)

Context

#754 introduced TCP transport and mDNS-based discovery of nodes in LAN via js-libp2p-mdns.

libp2p-mdns is pretty useful, as it aims to support both existing mDNS discovery service provided by every go-ipfs node (mdns:compat) and the new DNS Service Discovery (DNS-SD) described in libp2p/specs/discovery/mdns.md that aims to eventually replace it.

TL;DR
In other words, embedded js-ipfs running in Brave (#716) is able to discover go-ipfs on the same network and connect to it over regular TCP transport:

Known Issues

• mdns discovery is passive at the moment
  • mdns:compat runs two services: one that queries, and one that responds to queries. Responder tries to listen on port 5353 and fails to start if something is already using the port.
  • chrome.sockets.udp does not support opening sockets with SO_REUSEADDR or SO_REUSEPORT (bugs.chromium.org#238819
  • this means it is very likely responding to mdns queries won't be enabled for most users, and DNS discovery is mostly passive (js-ipfs can discover other nodes and connect to them, but if we have two Brave nodes on the network those need to discover each other by other means)

Areas to explore

• fix/tweak existing mdns spec or create a new discovery module specific to brave/browsers
• https://developer.chrome.com/apps/sockets_udp provides APIs related to multicast groups
  • manifest may require multicastMembership: "" – Multicast sample has invalid permissions. GoogleChrome/chrome-extensions-samples#119 (comment)
• https://developer.chrome.com/apps/mdns seems to be read-only, but worth revisiting

References

• SO_REUSEADDR and SO_REUSEPORT in http://man7.org/linux/man-pages/man7/socket.7.html
• Chromium bugs / threads about address reuse in chrome.sockets.udp
  • Issue 246867: socket API should support address reuse
  • Issue 238819: Add support for address reuse in UDP sockets in platform apps
  • groups.google.com/chromium.org: UDP socket API address reuse?

[lidel]

#967 (comment)