Cache support for DnsOverHttps.Builder().post(true)

[calbot]

The Cache class key uses the request url and therefore cannot cache DNS over HTTPS requests when the DNS query address is sent in a Post request with DnsOverHttps.Builder().post(true). When the get form of the DNS request is used it is base64 encoded so it isn't really private which domain is being requested so it would be good to be able to have both privacy of DoH and caching.

[yschimke]

@swankjesse I can't see a good way to handle this. We can do a complicated interceptor dance to fool caching. But I think I'm preferring some internal Tag for CacheKey?

[swankjesse]

@yschimke that’s a good idea. Or this?

class RequestBody {
  ...
  /** 
   * Returns a non-null key if this request can be cached. If non-null,
   * this key is used in combination to the request URL to create the
   * ultimate cache key.
   */
  open fun cacheKey(): ByteString? {
    return null;
  }
}

[yschimke]

Yeah that works. And is more constrained. The tag approach would allow mucking with any cache key

[yschimke]

A similar requirement...

#8211

But wouldn't work with a RequestBody.