dce8c4c38111556ca480aa0e63c46b71f66b508f rpc: getblockfrompeer (Sjors Provoost)
b884ababc29ce963826d8a4327ed6a5e629ff175 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 dce8c4c38111556ca480aa0e63c46b71f66b508f
fjahr:
re-ACK dce8c4c38111556ca480aa0e63c46b71f66b508f
Tree-SHA512: 843ba2b7a308f640770d624d0aa3265fdc5c6ea48e8db32269b96a082b7420f7953d1d8d1ef2e6529392c7172dded9d15639fbc9c24e7bfa5cfb79e13a5498c8