add(rpc): Adds getblockheader RPC method (#8967)

* Adds getblockheader RPC method

* Updates snapshots, adds hash/height/next_block_hash fields to verbose response

* updates getblock snapshot

* updates getblockheader response type to hex-encode fields, adds ToHex impl for sapling::tree::Root, adds snapshot and vector tests for new RPC method, adds snapshots.

* rustfmt

* fixes snapshots, matches zcashd more closely

* fixes vectors test

* updates lwd failure messages (probably doesn't matter, but seems better to handle it now than risk debugging it later)

* fixes getblock_rpc test, fixes/reverses finalsaplingroot field byte-order.

* fixes vector test, addresses remaining differences with zcashd (except the `chainwork` field), updates snapshots, and avoids a possible panic when there's a chain reorg between state queries.

* Adds a comment noting that the `relative_to_network()` method was copied from zcashd

* Apply suggestions from code review

Co-authored-by: Alfredo Garcia <[email protected]>

---------

Co-authored-by: Alfredo Garcia <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

zebra-chain/src/sapling/tree.rs

@@ -147,6 +147,26 @@ impl TryFrom<[u8; 32]> for Root {
     }
 }
 
+impl ToHex for &Root {
+    fn encode_hex<T: FromIterator<char>>(&self) -> T {
+        <[u8; 32]>::from(*self).encode_hex()
+    }
+
+    fn encode_hex_upper<T: FromIterator<char>>(&self) -> T {
+        <[u8; 32]>::from(*self).encode_hex_upper()
+    }
+}
+
+impl ToHex for Root {
+    fn encode_hex<T: FromIterator<char>>(&self) -> T {
+        (&self).encode_hex()
+    }
+
+    fn encode_hex_upper<T: FromIterator<char>>(&self) -> T {
+        (&self).encode_hex_upper()
+    }
+}
+
 impl ZcashSerialize for Root {
     fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
         writer.write_all(&<[u8; 32]>::from(*self)[..])?;

zebra-chain/src/work/difficulty.rs

@@ -290,6 +290,30 @@ impl CompactDifficulty {
 
         Ok(difficulty)
     }
+
+    /// Returns a floating-point number representing a difficulty as a multiple
+    /// of the minimum difficulty for the provided network.
+    // Copied from <https://github.com/zcash/zcash/blob/99ad6fdc3a549ab510422820eea5e5ce9f60a5fd/src/rpc/blockchain.cpp#L34-L74>
+    // TODO: Explain here what this ported code is doing and why, request help to do so with the ECC team.
+    pub fn relative_to_network(&self, network: &Network) -> f64 {
+        let network_difficulty = network.target_difficulty_limit().to_compact();
+
+        let [mut n_shift, ..] = self.0.to_be_bytes();
+        let [n_shift_amount, ..] = network_difficulty.0.to_be_bytes();
+        let mut d_diff = f64::from(network_difficulty.0 << 8) / f64::from(self.0 << 8);
+
+        while n_shift < n_shift_amount {
+            d_diff *= 256.0;
+            n_shift += 1;
+        }
+
+        while n_shift > n_shift_amount {
+            d_diff /= 256.0;
+            n_shift -= 1;
+        }
+
+        d_diff
+    }
 }
 
 impl fmt::Debug for CompactDifficulty {

zebra-chain/src/work/equihash.rs

@@ -2,6 +2,7 @@
 
 use std::{fmt, io};
 
+use hex::ToHex;
 use serde_big_array::BigArray;
 
 use crate::{
@@ -112,7 +113,6 @@ impl Solution {
     }
 
     /// Returns a [`Solution`] of `[0; SOLUTION_SIZE]` to be used in block proposals.
-    #[cfg(feature = "getblocktemplate-rpcs")]
     pub fn for_proposal() -> Self {
         // TODO: Accept network as an argument, and if it's Regtest, return the shorter null solution.
         Self::Common([0; SOLUTION_SIZE])
@@ -195,3 +195,23 @@ impl ZcashDeserialize for Solution {
         Self::from_bytes(&solution)
     }
 }
+
+impl ToHex for &Solution {
+    fn encode_hex<T: FromIterator<char>>(&self) -> T {
+        self.value().encode_hex()
+    }
+
+    fn encode_hex_upper<T: FromIterator<char>>(&self) -> T {
+        self.value().encode_hex_upper()
+    }
+}
+
+impl ToHex for Solution {
+    fn encode_hex<T: FromIterator<char>>(&self) -> T {
+        (&self).encode_hex()
+    }
+
+    fn encode_hex_upper<T: FromIterator<char>>(&self) -> T {
+        (&self).encode_hex_upper()
+    }
+}