12ff4be9c7 test: ensure -rpcallowip is compatible with RFC4193 (Matthew Zipkin)
c02bd3c187 config: Explain RFC4193 and CJDNS interaction in help and init error (Matthew Zipkin)
f728b6b111 init: Configure reachable networks before we start the RPC server (Matthew Zipkin)
Pull request description:
Closes https://github.com/bitcoin/bitcoin/issues/32433
`MaybeFlipIPv6toCJDNS()` relies on `g_reachable_nets` to distinguish between CJDNS addresses and other IPv6 addresses. In particular, [RFC4193](https://www.rfc-editor.org/rfc/rfc4193#section-3.1) address or "Unique Local Address" with the L-bit unset also begins with the `fc` prefix. #32433 highlights a use case for these addresses that have nothing to do with CJDNS.
On master we don't parse init flags like `-cjdnsreachable` until *after* the HTTP server has started, causing conflicts with `-rpcallowip` because CJDNS doesn't support subnets.
This PR ensures that `NET_CJDNS` is only present in the reachable networks list if set by `-cjdnsreachable` *before* `-rpcallowip` is checked. If it is set all `fc` addresses are assumed to be CJDNS, can not have subnets, and can't be set for `-rpcallowip`.
I also noted this specific parameter interaction in the init help as well as the error message if configured incorrectly.
This can be tested locally:
`bitcoind -regtest -rpcallowip=fc00:dead:beef::/64 -rpcuser=u -rpcpassword=p`
On master this will just throw an error that doesn't even mention IPv6 at all.
On the branch, this will succeed and can be tested by adding the ULA to a local interface.
On linux: `sudo ip -6 addr add fc00:dead:beef::1/64 dev lo`
On macos: `sudo ifconfig lo0 inet6 fc00:dead:beef::1/128 add`
then: `curl -v -g -6 --interface fc00:dead:beef::1 u:p@[::1]:18443 --data '{"method":"getblockcount"}'`
If the `rpcallowip` option is removed, the RPC request will fail to authorize.
Finally, adding `-cjdnsreachable` to the start up command will throw an error and specify the incompatibility:
> RFC4193 is allowed only if -cjdnsreachable=0.
ACKs for top commit:
achow101:
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tapcrafter:
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ryanofsky:
Code review ACK 12ff4be9c7
willcl-ark:
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