Cache headers in REST #33809

it would be nice to serve appropriate cache headers in the REST interface so that you can just slap nginx/cloudflare in front of it and have a nice caching proxy. Eg getXbyheight requests would get cached for 5 seconds and getYbyhash requests could get cached for a month/year.

@achow101 said she'd work on this

Cache-Control headers can be easily handled at the nginx layer. Rather than adding this logic directly in Bitcoin REST code, it might make sense to include a sample nginx config under contrib/ with reasonable defaults for REST endpoints.

# Example include: rest-cache.conf
location /rest/block/ {
    # Cache block lookups by hash for a long time (immutable)
    if ($uri ~ "^/rest/block/[0-9a-f]+\.json$") {
        add_header Cache-Control "public, max-age=31536000, immutable";
    }

    # Cache height-based lookups briefly (chain tip changes)
    if ($uri ~ "^/rest/block/[0-9]+\.json$") {
        add_header Cache-Control "public, max-age=5";
    }
}

This could be included in nginx server or location blocks to provide sensible defaults without changing the rest implementation itself.

End users could then fine tune it as needed, for example adding rate limiting, conditional caching or more advanced cache key logic depending on their deployment setup.

@achow101 said she'd work on this

I don't remember saying this, and I have no intention of working on this in the foreseeable future.

Proposed solution: https://github.com/bitcoin/bitcoin/pull/34794