gateway: CDN-Loop

[lidel]

Problem

• ipfs.io backed by saturn looping to itself
• saturn looping to itself to the same L1 and always failing due to gaulty L1 and the internal ring hashing
• any two gateway operators multiplexing on top of each other

Solution

Find and document a way for gateway operators and CDNs to avoid loops.

Prior Art

CDN-Loop seems to be the best candidate?

Ref.

• https://datatracker.ietf.org/doc/html/rfc8586
• https://blog.cloudflare.com/preventing-request-loops-using-cdn-loop/
• https://developer.fastly.com/reference/http/http-headers/CDN-Loop/

Example

Request that was sent to ipfs.io, then hit saturn backend, and then hit one of Saturn L1s would have:

CDN-Loop: saturn-l1-id, saturn.tech; ipfs.io;  

This allows:

1. ipfs.io to detect and drop requests that loop to itself
2. saturn to either detect drop requests that loop to itself or route request to a DIFFERENT L1