Use the configured network rather than extracing from the net graph

When we were only generating snapshots that contained parts of the
network graph, extracting the chain hash from the network graph
announcements themselves was fine. However, now that we also
serialize empty snapshots as a "no changes since your last sync"
file, we need to initialize the chain_hash to the real network.

Luckily, `config::network()` already exists to make this easy, so
we simply switch to that.

Fixes #92

Author: TheBlueMatt

src/serialization.rs

@@ -2,7 +2,6 @@ use std::cmp::max;
 use std::collections::HashMap;
 use std::time::{SystemTime, UNIX_EPOCH};
 
-use bitcoin::Network;
 use bitcoin::blockdata::constants::ChainHash;
 use lightning::ln::msgs::{UnsignedChannelAnnouncement, UnsignedChannelUpdate};
 use lightning::types::features::NodeFeatures;
@@ -130,12 +129,10 @@ pub(super) fn serialize_delta_set(channel_delta_set: DeltaSet, node_delta_set: N
 		full_update_defaults: Default::default(),
 		node_announcement_feature_defaults: vec![],
 		node_mutations: Default::default(),
-		chain_hash: ChainHash::using_genesis_block(Network::Bitcoin),
+		chain_hash: ChainHash::using_genesis_block(config::network()),
 		latest_seen: 0,
 	};
 
-	let mut chain_hash_set = false;
-
 	let mut full_update_histograms = FullUpdateValueHistograms {
 		cltv_expiry_delta: Default::default(),
 		htlc_minimum_msat: Default::default(),
@@ -156,13 +153,8 @@ pub(super) fn serialize_delta_set(channel_delta_set: DeltaSet, node_delta_set: N
 	let non_incremental_previous_update_threshold_timestamp = SystemTime::now().checked_sub(config::CHANNEL_REMINDER_AGE).unwrap().duration_since(UNIX_EPOCH).unwrap().as_secs() as u32;
 
 	for (scid, channel_delta) in channel_delta_set.into_iter() {
-
 		// any announcement chain hash is gonna be the same value. Just set it from the first one.
 		let channel_announcement_delta = channel_delta.announcement.as_ref().unwrap();
-		if !chain_hash_set {
-			chain_hash_set = true;
-			serialization_set.chain_hash = channel_announcement_delta.announcement.chain_hash;
-		}
 
 		let current_announcement_seen = channel_announcement_delta.seen;
 		let is_new_announcement = current_announcement_seen >= last_sync_timestamp;