feature: Add light_client_root_hash(network) to Block

* use the right variant in LightClientRootHash::from_bytes()
* make block.header.light_client_root_hash pub(super)
* add tests for LightClientRootHash and block.light_client_root_hash

zebra-chain/src/block.rs

@@ -18,9 +18,11 @@ use proptest_derive::Arbitrary;
 
 use crate::transaction::Transaction;
 use crate::types::BlockHeight;
+use crate::Network;
 
 pub use hash::BlockHeaderHash;
 pub use header::BlockHeader;
+pub use light_client::LightClientRootHash;
 
 /// A block in your blockchain.
 ///
@@ -91,6 +93,23 @@ impl Block {
     pub fn hash(&self) -> BlockHeaderHash {
         BlockHeaderHash::from(self)
     }
+
+    /// Get the parsed light client root hash for this block.
+    ///
+    /// The interpretation of the light client root hash depends on the
+    /// configured `network`, and this block's height.
+    ///
+    /// Returns None if this block does not have a block height.
+    pub fn light_client_root_hash(&self, network: Network) -> Option<LightClientRootHash> {
+        match self.coinbase_height() {
+            Some(height) => Some(LightClientRootHash::from_bytes(
+                self.header.light_client_root_hash,
+                network,
+                height,
+            )),
+            None => None,
+        }
+    }
 }
 
 impl<'a> From<&'a Block> for BlockHeaderHash {

zebra-chain/src/block/header.rs

@@ -37,8 +37,9 @@ pub struct BlockHeader {
     /// The light client root hash.
     ///
     /// This field is interpreted differently, based on the current
-    /// block height. See LightClientRootHash for details.
-    pub light_client_root_hash: [u8; 32],
+    /// block height. Use `block.light_client_root_hash(network)` to get the
+    /// parsed `LightClientRootHash` for this block.
+    pub(super) light_client_root_hash: [u8; 32],
 
     /// The block timestamp is a Unix epoch time (UTC) when the miner
     /// started hashing the header (according to the miner).

zebra-chain/src/block/light_client.rs

@@ -2,7 +2,7 @@
 
 use crate::note_commitment_tree::SaplingNoteTreeRootHash;
 use crate::types::BlockHeight;
-use crate::Network;
+use crate::{Network, NetworkUpgrade, NetworkUpgrade::*};
 
 /// Light client root hashes.
 ///
@@ -50,12 +50,20 @@ impl LightClientRootHash {
         network: Network,
         height: BlockHeight,
     ) -> LightClientRootHash {
-        // TODO(teor): use the correct network upgrade here, after moving the
-        //             network upgrades from zebra-consensus to zebra-chain.
-        LightClientRootHash::PreSaplingReserved(bytes)
+        use LightClientRootHash::*;
+
+        match NetworkUpgrade::current(network, height) {
+            Genesis | BeforeOverwinter | Overwinter => PreSaplingReserved(bytes),
+            Sapling | Blossom => FinalSaplingRoot(SaplingNoteTreeRootHash(bytes)),
+            Heartwood if Some(height) == Heartwood.activation_height(network) => {
+                ChainHistoryActivationReserved(bytes)
+            }
+            Heartwood | Canopy => ChainHistoryRoot(ChainHistoryMmrRootHash(bytes)),
+        }
     }
 
     /// Returns the serialized bytes for this LightClientRootHash.
+    #[allow(dead_code)]
     pub fn to_bytes(self) -> [u8; 32] {
         use LightClientRootHash::*;
 

zebra-chain/src/block/tests.rs

@@ -228,6 +228,14 @@ proptest! {
 
         prop_assert_eq![header, other_header];
     }
+
+    #[test]
+    fn light_client_roundtrip(bytes in any::<[u8; 32]>(), network in any::<Network>(), block_height in any::<BlockHeight>()) {
+        let light_hash = LightClientRootHash::from_bytes(bytes, network, block_height);
+        let other_bytes = light_hash.to_bytes();
+
+        prop_assert_eq![bytes, other_bytes];
+    }
 }
 
 proptest! {
@@ -239,12 +247,22 @@ proptest! {
                                           .unwrap_or(16)))]
 
     #[test]
-    fn block_roundtrip(block in any::<Block>()) {
+    fn block_roundtrip(block in any::<Block>(), network in any::<Network>()) {
         let bytes = block.zcash_serialize_to_vec()?;
         let bytes = &mut bytes.as_slice();
 
+        // Check the light client root hash
+        let light_hash = block.light_client_root_hash(network);
+        if let Some(light_hash) = light_hash {
+            let light_hash_bytes = light_hash.to_bytes();
+            prop_assert_eq![block.header.light_client_root_hash, light_hash_bytes];
+        } else {
+            prop_assert_eq![block.coinbase_height(), None];
+        }
+
         // Check the block size limit
         if bytes.len() <= MAX_BLOCK_BYTES as _ {
+            // Check deserialization
             let other_block = bytes.zcash_deserialize_into()?;
 
             prop_assert_eq![block, other_block];