chain: create a new work module for proof-of-work

This extracts the `difficulty` module from `block` and the
`equihash_solution` module from the crate root.  The PoW calculations
are significantly more complicated than the other block code and pretty
dissimilar from it, so it makes more sense to create a common proof of
work module.

The `EquihashSolution` and `EQUIHASH_SOLUTION_SIZE` are renamed to
`equihash::Solution` and `equihash::SOLUTION_SIZE` and imported that
way, except in `block/header.rs`, to avoid a conflict with the
`equihash` crate.  In the future it would be better to encapsulate the
equihash solution check into the `equihash::Solution` type so that
callers only need to import our `work::equihash`.

The test organization leaves a little to be desired but I think that
this can be improved as we fill out the proof of work implementation.

zebra-chain/src/block.rs

@@ -1,7 +1,6 @@
 //! Definitions of block datastructures.
 #![allow(clippy::unit_arg)]
 
-mod difficulty;
 mod hash;
 mod header;
 mod height;

zebra-chain/src/block/header.rs

@@ -1,10 +1,10 @@
 use chrono::{DateTime, Duration, Utc};
 
-use crate::equihash_solution::EquihashSolution;
 use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::ZcashSerialize;
+use crate::work::{difficulty::CompactDifficulty, equihash::Solution};
 
-use super::{difficulty::CompactDifficulty, BlockHeaderHash, Error};
+use super::{BlockHeaderHash, Error};
 
 /// Block header.
 ///
@@ -65,7 +65,7 @@ pub struct BlockHeader {
     pub nonce: [u8; 32],
 
     /// The Equihash solution.
-    pub solution: EquihashSolution,
+    pub solution: Solution,
 }
 
 impl BlockHeader {
@@ -80,7 +80,7 @@ impl BlockHeader {
         self.zcash_serialize(&mut input)
             .expect("serialization into a vec can't fail");
 
-        let input = &input[0..EquihashSolution::INPUT_LENGTH];
+        let input = &input[0..Solution::INPUT_LENGTH];
 
         equihash::is_valid_solution(n, k, input, nonce, solution)?;
 

zebra-chain/src/block/serialize.rs

@@ -2,11 +2,10 @@ use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use chrono::{TimeZone, Utc};
 use std::io;
 
-use crate::block::difficulty::CompactDifficulty;
-use crate::equihash_solution::EquihashSolution;
 use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::ZcashDeserializeInto;
 use crate::serialization::{ReadZcashExt, SerializationError, ZcashDeserialize, ZcashSerialize};
+use crate::work::{difficulty::CompactDifficulty, equihash};
 
 use super::Block;
 use super::BlockHeader;
@@ -71,7 +70,7 @@ impl ZcashDeserialize for BlockHeader {
             time: Utc.timestamp(reader.read_u32::<LittleEndian>()? as i64, 0),
             difficulty_threshold: CompactDifficulty(reader.read_u32::<LittleEndian>()?),
             nonce: reader.read_32_bytes()?,
-            solution: EquihashSolution::zcash_deserialize(reader)?,
+            solution: equihash::Solution::zcash_deserialize(reader)?,
         })
     }
 }

zebra-chain/src/block/tests.rs

@@ -1,12 +1,12 @@
 use super::*;
 
-use crate::block::{difficulty::CompactDifficulty, light_client::LightClientRootHash};
-use crate::equihash_solution::EquihashSolution;
+use crate::block::light_client::LightClientRootHash;
 use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::{
     sha256d, SerializationError, ZcashDeserialize, ZcashDeserializeInto, ZcashSerialize,
 };
 use crate::transaction::LockTime;
+use crate::work::{difficulty::CompactDifficulty, equihash};
 use crate::Network;
 
 use crate::test::generate;
@@ -48,7 +48,7 @@ impl Arbitrary for BlockHeader {
             (0i64..(u32::MAX as i64)),
             any::<CompactDifficulty>(),
             any::<[u8; 32]>(),
-            any::<EquihashSolution>(),
+            any::<equihash::Solution>(),
         )
             .prop_map(
                 |(

zebra-chain/src/lib.rs

@@ -17,7 +17,6 @@ pub mod addresses;
 pub mod amount;
 pub mod block;
 pub mod commitments;
-pub mod equihash_solution;
 pub mod keys;
 pub mod notes;
 pub mod parameters;
@@ -26,6 +25,7 @@ pub mod serialization;
 pub mod transaction;
 pub mod treestate;
 pub mod types;
+pub mod work;
 
 pub use ed25519_zebra;
 pub use redjubjub;

zebra-chain/src/work.rs

@@ -0,0 +1,7 @@
+//! Proof-of-work implementation.
+
+pub mod difficulty;
+pub mod equihash;
+
+#[cfg(test)]
+mod tests;

zebra-chain/src/block/difficulty/tests.rs → zebra-chain/src/work/difficulty/tests.rs

@@ -1,5 +1,3 @@
-//! Tests for difficulty and work
-
 use super::*;
 
 use crate::block::Block;