dce8c4c381 rpc: getblockfrompeer (Sjors Provoost)
b884ababc2 rpc: move Ensure* helpers to server_util.h (Sjors Provoost)
Pull request description:
This adds an RPC method to fetch a block directly from a peer. This can used to fetch stale blocks with lower proof of work that are normally ignored by the node (`headers-only` in `getchaintips`).
Usage:
```
bitcoin-cli getblockfrompeer HASH peer_n
```
Closes #20155
Limitations:
* you have to specify which peer to fetch the block from
* the node must already have the header
ACKs for top commit:
jnewbery:
ACK dce8c4c381
fjahr:
re-ACK dce8c4c381
Tree-SHA512: 843ba2b7a308f640770d624d0aa3265fdc5c6ea48e8db32269b96a082b7420f7953d1d8d1ef2e6529392c7172dded9d15639fbc9c24e7bfa5cfb79e13a5498c8
Blindly chose a cap of 10000 iterations for every loop, except for
the two in script_ops.cpp and scriptnum_ops.cpp which appeared to
(sometimes) be deserializing individual bytes; capped those to one
million to ensure that sometimes we try working with massive scripts.
There was also one fuzzer-controlled loop in timedata.cpp which was
already capped, so I left that alone.
git grep 'while (fuzz' should now run clean except for timedata.cpp
