feat: add an API to inspect request's IP address

[bajtos]

The new endpoint tells the caller what IP addresses we see, as coming from
the IP stack, Fly.io and CloudFare. This is useful to verify our understanding
of how all reverse proxies interact together.

Links:

• feat: record "inet_group" in measurements #104
• Limit rewards per IPv4 /24 subnet spark#29
• https://developers.cloudflare.com/fundamentals/reference/http-request-headers/
• https://developers.cloudflare.com/support/troubleshooting/restoring-visitor-ips/restoring-original-visitor-ips/

[bajtos]

Works like a charm:

{
  "remoteAddress": "172.16.133.194",
  "flyClientAddr": "141.101.96.93",  
  "cloudfareAddr": "77.X.Y.Z",
  "forwardedFor": "77.X.Z.Z, 137.66.43.45",
  "headers": // ...
}

• 172.16.133.194 is a private address (presumably in Fly.io's datacenter)
• 137.66.43.45 is Fly.io
• 141.101.96.93 is CloudFare

[juliangruber]

btw, I see only my ipv6 here:

{
"remoteAddress": "172.16.147.122",
"flyClientAddr": "172.68.110.118",
"cloudfareAddr": "2a01:...:5afc",
"forwardedFor": "2a01:...:5afc, 137.66.43.45",
...
}

Not sure if that affects your work

[juliangruber]

typo: cloudflareAddr

[bajtos]

Oh, wow. CloudFlare's dashboard does not allow you to disable IPv6 support via web UI and the docs say this feature is available to customers on the Enterprise plan only. Yet the REST API allows me to disable IPv6, as explained here: https://www.mediarealm.com.au/articles/cloudflare-disable-ipv6/

@juliangruber when you have a moment, could you please send another request to this new endpoint to see if you get back an IPv4 address (not IPv6)?

Related docs:

• Understanding and configuring Cloudflare’s IPv6 support

If this approach does not work, then I'll try the next quick workaround that should be good enough for short term:

• Enable Pseudo IPv4
• https://developers.cloudflare.com/fundamentals/reference/http-request-headers/

[juliangruber]

@juliangruber when you have a moment, could you please send another request to this new endpoint to see if you get back an IPv4 address (not IPv6)?

Success!