Make UnboundedCache a newtype and implement ser. logic

After we implemented serialization logic for all the sub-types in the
last commit, here we switch the `UnboundedCache` type to be a newtype
wrapper around a `HashMap` (rather than a straight typedef) and
implement TLV-based serialization logic on it.

lightning-block-sync/src/init.rs

@@ -321,8 +321,8 @@ mod tests {
 			(fork_chain_3.tip().block_hash, &listener_3 as &dyn chain::Listen),
 		];
 		let mut cache = fork_chain_1.header_cache(2..=4);
-		cache.extend(fork_chain_2.header_cache(3..=4));
-		cache.extend(fork_chain_3.header_cache(4..=4));
+		cache.inner.extend(fork_chain_2.header_cache(3..=4).inner);
+		cache.inner.extend(fork_chain_3.header_cache(4..=4).inner);
 		match synchronize_listeners(&main_chain, Network::Bitcoin, &mut cache, listeners).await {
 			Ok(header) => assert_eq!(header, main_chain.tip()),
 			Err(e) => panic!("Unexpected error: {:?}", e),
@@ -364,8 +364,8 @@ mod tests {
 			(fork_chain_3.tip().block_hash, &listener_3 as &dyn chain::Listen),
 		];
 		let mut cache = fork_chain_1.header_cache(2..=4);
-		cache.extend(fork_chain_2.header_cache(3..=4));
-		cache.extend(fork_chain_3.header_cache(4..=4));
+		cache.inner.extend(fork_chain_2.header_cache(3..=4).inner);
+		cache.inner.extend(fork_chain_3.header_cache(4..=4).inner);
 		match synchronize_listeners(&main_chain, Network::Bitcoin, &mut cache, listeners).await {
 			Ok(header) => assert_eq!(header, main_chain.tip()),
 			Err(e) => panic!("Unexpected error: {:?}", e),
@@ -387,8 +387,8 @@ mod tests {
 		let mut cache = fork_chain.header_cache(2..=2);
 		match synchronize_listeners(&main_chain, Network::Bitcoin, &mut cache, listeners).await {
 			Ok(_) => {
-				assert!(cache.contains_key(&new_tip.block_hash));
-				assert!(cache.contains_key(&old_tip.block_hash));
+				assert!(cache.inner.contains_key(&new_tip.block_hash));
+				assert!(cache.inner.contains_key(&old_tip.block_hash));
 			},
 			Err(e) => panic!("Unexpected error: {:?}", e),
 		}

lightning-block-sync/src/lib.rs

@@ -49,6 +49,7 @@ use bitcoin::hash_types::BlockHash;
 use bitcoin::pow::Work;
 
 use lightning::chain::Listen;
+use lightning::util::hash_tables::{new_hash_map, HashMap};
 use lightning::{chain, impl_writeable_tlv_based};
 
 use std::future::Future;
@@ -218,22 +219,36 @@ pub trait Cache {
 }
 
 /// Unbounded cache of block headers keyed by block hash.
-pub type UnboundedCache = std::collections::HashMap<BlockHash, ValidatedBlockHeader>;
+pub struct UnboundedCache {
+	pub(crate) inner: HashMap<BlockHash, ValidatedBlockHeader>,
+}
+
+impl UnboundedCache {
+	/// Returns a new `UnboundedCache`
+	pub fn new() -> Self {
+		let inner = new_hash_map();
+		Self { inner }
+	}
+}
 
 impl Cache for UnboundedCache {
 	fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader> {
-		self.get(block_hash)
+		self.inner.get(block_hash)
 	}
 
 	fn block_connected(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader) {
-		self.insert(block_hash, block_header);
+		self.inner.insert(block_hash, block_header);
 	}
 
 	fn block_disconnected(&mut self, block_hash: &BlockHash) -> Option<ValidatedBlockHeader> {
-		self.remove(block_hash)
+		self.inner.remove(block_hash)
 	}
 }
 
+impl_writeable_tlv_based!(UnboundedCache, {
+	(0, inner, required),
+});
+
 impl<'a, P: Poll, C: Cache, L: Deref> SpvClient<'a, P, C, L>
 where
 	L::Target: chain::Listen,

lightning-block-sync/src/test_utils.rs

@@ -131,7 +131,7 @@ impl Blockchain {
 		for i in heights {
 			let value = self.at_height(i);
 			let key = value.header.block_hash();
-			assert!(cache.insert(key, value).is_none());
+			assert!(cache.inner.insert(key, value).is_none());
 		}
 		cache
 	}