Fill out the Block Message type

Should we serialize out `Block` or leave explicit like so? ¯\_(ツ)_/¯

zebra-chain/src/block.rs

@@ -12,9 +12,9 @@ use crate::transaction::Transaction;
 ///
 /// This is useful when one block header is pointing to its parent
 /// block header in the block chain. ⛓️
-pub struct BlockHash([u8; 32]);
+pub struct BlockHeaderHash([u8; 32]);
 
-impl From<BlockHeader> for BlockHash {
+impl From<BlockHeader> for BlockHeaderHash {
     fn from(block_header: BlockHeader) -> Self {
         let mut hash_writer = Sha256dWriter::default();
         block_header
@@ -54,8 +54,15 @@ impl From<MerkleTree<Transaction>> for MerkleRootHash {
 pub struct BlockHeader {
     /// A SHA-256d hash in internal byte order of the previous block’s
     /// header. This ensures no previous block can be changed without
-    /// also changing this block’s header .
-    previous_block_hash: BlockHash,
+    /// also changing this block’s header.
+    // This is usually called a 'block hash', as it is frequently used
+    // to identify the entire block, since the hash preimage includes
+    // the merkle root of the transactions in this block. But
+    // _technically_, this is just a hash of the block _header_, not
+    // the direct bytes of the transactions as well as the header. So
+    // for now I want to call it a `BlockHeaderHash` because that's
+    // more explicit.
+    previous_block_hash: BlockHeaderHash,
 
     /// A SHA-256d hash in internal byte order. The merkle root is
     /// derived from the SHA256d hashes of all transactions included
@@ -67,8 +74,8 @@ pub struct BlockHeader {
     /// [Sapling onward] The root LEBS2OSP256(rt) of the Sapling note
     /// commitment tree corresponding to the nal Sapling treestate of
     /// this block.
-    // TODO: replace type with custom SaplingRoot or similar type
-    // hash_final_sapling_root: SaplingRootHash,
+    // TODO: replace type with custom SaplingRootHash or similar type
+    hash_final_sapling_root: [u8; 32],
 
     /// The block timestamp is a Unix epoch time (UTC) when the miner
     /// started hashing the header (according to the miner).
@@ -121,6 +128,6 @@ pub struct Block {
     /// "block" messages.
     pub header: BlockHeader,
 
-    /// Block transactions.
+    /// The block transactions.
     pub transactions: Vec<Transaction>,
 }

zebra-network/src/protocol/message.rs

@@ -4,6 +4,7 @@ use std::net;
 
 use chrono::{DateTime, Utc};
 
+use zebra_chain::block::{BlockHeaderHash, MerkleRootHash};
 use zebra_chain::{transaction::Transaction, types::BlockHeight};
 
 use crate::meta_addr::MetaAddr;
@@ -134,7 +135,40 @@ pub enum Message {
     /// A `block` message.
     ///
     /// [Bitcoin reference](https://en.bitcoin.it/wiki/Protocol_documentation#block)
-    Block {/* XXX add fields */},
+    Block {
+        /// Block version information (note, this is signed).
+        version: Version,
+
+        /// The hash value of the previous block (header) this
+        /// particular block references.
+        prev_block: BlockHeaderHash,
+
+        /// The reference to a Merkle tree collection which is a hash
+        /// of all transactions related to this block.
+        merkle_root: MerkleRootHash,
+
+        /// The root of the Sapling note commitment tree corresponding
+        /// to the final Sapling treestate of this block.
+        // TODO: more than just an array of bytes.
+        final_sapling_root: [u8; 32],
+
+        /// A Unix timestamp recording when this block was created.
+        time: DateTime<Utc>,
+
+        /// The calculated difficulty target being used for this
+        /// block.
+        bits: u32,
+
+        /// The nonce used to generate this block, to allow variations
+        /// of the header and compute different hashes.
+        nonce: [u8; 32],
+
+        /// The Equihash solution.
+        solution: [u8; 1344],
+
+        /// Transactions.
+        txns: Vec<Transaction>,
+    },
 
     /// A `getblocks` message.
     ///