Add chain hash type using consts

src/blockdata/constants.rs

@@ -176,15 +176,40 @@ pub fn genesis_block(network: Network) -> Block {
     }
 }
 
+// Mainnet value can be verified at https://github.com/lightning/bolts/blob/master/00-introduction.md
+const GENESIS_BLOCK_HASH_BITCOIN: [u8; 32] = [111, 226, 140, 10, 182, 241, 179, 114, 193, 166, 162, 70, 174, 99, 247, 79, 147, 30, 131, 101, 225, 90, 8, 156, 104, 214, 25, 0, 0, 0, 0, 0];
+const GENESIS_BLOCK_HASH_TESTNET: [u8; 32] = [67, 73, 127, 215, 248, 38, 149, 113, 8, 244, 163, 15, 217, 206, 195, 174, 186, 121, 151, 32, 132, 233, 14, 173, 1, 234, 51, 9, 0, 0, 0, 0];
+const GENESIS_BLOCK_HASH_SIGNET: [u8; 32] = [246, 30, 238, 59, 99, 163, 128, 164, 119, 160, 99, 175, 50, 178, 187, 201, 124, 159, 249, 240, 31, 44, 66, 37, 233, 115, 152, 129, 8, 0, 0, 0];
+const GENESIS_BLOCK_HASH_REGTEST: [u8; 32] = [6, 34, 110, 70, 17, 26, 11, 89, 202, 175, 18, 96, 67, 235, 91, 191, 40, 195, 79, 58, 94, 51, 42, 31, 199, 178, 183, 60, 241, 136, 145, 15];
+
+/// The uniquely identifying hash of the target blockchain.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ChainHash([u8; 32]);
+impl_array_newtype!(ChainHash, u8, 32);
+impl_bytes_newtype!(ChainHash, 32);
+
+impl ChainHash {
+    /// Returns the hash of the `network` genesis block for use as a chain hash.
+    ///
+    /// See [BOLT 0](https://github.com/lightning/bolts/blob/ffeece3dab1c52efdb9b53ae476539320fa44938/00-introduction.md#chain_hash)
+    /// for specification.
+    pub fn using_genesis_block(network: Network) -> Self {
+        match network {
+            Network::Bitcoin => ChainHash(GENESIS_BLOCK_HASH_BITCOIN),
+            Network::Testnet => ChainHash(GENESIS_BLOCK_HASH_TESTNET),
+            Network::Signet => ChainHash(GENESIS_BLOCK_HASH_SIGNET),
+            Network::Regtest => ChainHash(GENESIS_BLOCK_HASH_REGTEST),
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use core::default::Default;
+    use super::*;
     use crate::hashes::hex::FromHex;
-
     use crate::network::constants::Network;
     use crate::consensus::encode::serialize;
-    use crate::blockdata::constants::{genesis_block, bitcoin_genesis_tx};
-    use crate::blockdata::constants::{MAX_SEQUENCE, COIN_VALUE};
 
     #[test]
     fn bitcoin_genesis_first_transaction() {
@@ -250,5 +275,49 @@ mod test {
         assert_eq!(format!("{:x}", gen.header.block_hash()),
                    "00000008819873e925422c1ff0f99f7cc9bbb232af63a077a480a3633bee1ef6".to_string());
     }
+
+    // The *_chain_hash tests are sanity/regression tests, they verify that the const byte array
+    // representing the genesis block is the same as that created by hashing the genesis block.
+    fn chain_hash_and_genesis_block(network: Network) {
+        use hashes::{sha256, Hash};
+
+        // The genesis block hash is a double-sha256 and it is displayed backwards.
+        let genesis_hash = genesis_block(network).block_hash();
+        // We abuse the sha256 hash here so we get a LowerHex impl that does not print the hex backwards.
+        let hash = sha256::Hash::from_slice(&genesis_hash.into_inner()).unwrap();
+        let want = format!("{:02x}", hash);
+
+        let chain_hash = ChainHash::using_genesis_block(network);
+        let got = format!("{:02x}", chain_hash);
+
+        // Compare strings because the spec specifically states how the chain hash must encode to hex.
+        assert_eq!(got, want);
+    }
+
+    macro_rules! chain_hash_genesis_block {
+        ($($test_name:ident, $network:expr);* $(;)*) => {
+            $(
+                #[test]
+                fn $test_name() {
+                    chain_hash_and_genesis_block($network);
+                }
+            )*
+        }
+    }
+
+    chain_hash_genesis_block! {
+        mainnet_chain_hash_genesis_block, Network::Bitcoin;
+        testnet_chain_hash_genesis_block, Network::Testnet;
+        signet_chain_hash_genesis_block, Network::Signet;
+        regtest_chain_hash_genesis_block, Network::Regtest;
+    }
+
+    // Test vector taken from: https://github.com/lightning/bolts/blob/master/00-introduction.md
+    #[test]
+    fn mainnet_chain_hash_test_vector() {
+        let got = format!("{:x}", ChainHash::using_genesis_block(Network::Bitcoin));
+        let want = "6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000";
+        assert_eq!(got, want);
+    }
 }
 

src/internal_macros.rs

@@ -84,7 +84,7 @@ macro_rules! impl_array_newtype {
             pub fn into_bytes(self) -> [$ty; $len] { self.0 }
         }
 
-        impl<'a> ::core::convert::From<&'a [$ty]> for $thing {
+        impl<'a> core::convert::From<&'a [$ty]> for $thing {
             fn from(data: &'a [$ty]) -> $thing {
                 assert_eq!(data.len(), $len);
                 let mut ret = [0; $len];
@@ -109,7 +109,7 @@ macro_rules! impl_array_newtype {
 
 macro_rules! display_from_debug {
     ($thing:ident) => {
-        impl ::core::fmt::Display for $thing {
+        impl core::fmt::Display for $thing {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> Result<(), ::core::fmt::Error> {
                 ::core::fmt::Debug::fmt(self, f)
             }
@@ -365,13 +365,13 @@ macro_rules! impl_bytes_newtype {
 
         impl ::core::fmt::Display for $t {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                fmt::LowerHex::fmt(self, f)
+                ::core::fmt::LowerHex::fmt(self, f)
             }
         }
 
         impl ::core::fmt::Debug for $t {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                fmt::LowerHex::fmt(self, f)
+                ::core::fmt::LowerHex::fmt(self, f)
             }
         }