Enable wumbo channels to be created

We remove MAX_FUNDING_SATOSHIS const since we no longer do this check, and instead
check that the funding amount is less than the total bitcoin supply. This adds
a const that is used for the new wumbo feature as well as in closing_signed

lightning/src/ln/channel.rs

@@ -734,9 +734,8 @@ pub const COMMITMENT_TX_WEIGHT_PER_HTLC: u64 = 172;
 
 pub const ANCHOR_OUTPUT_VALUE_SATOSHI: u64 = 330;
 
-/// Maximum `funding_satoshis` value, according to the BOLT #2 specification
-/// it's 2^24.
-pub const MAX_FUNDING_SATOSHIS: u64 = 1 << 24;
+/// Total bitcoin supply in satoshis.
+pub const TOTAL_BITCOIN_SUPPLY_SATOSHIS: u64 = 21_000_000 * 1_0000_0000;
 
 /// The maximum network dust limit for standard script formats. This currently represents the
 /// minimum output value for a P2SH output before Bitcoin Core 22 considers the entire
@@ -850,8 +849,8 @@ impl<Signer: Sign> Channel<Signer> {
 		let holder_signer = keys_provider.get_channel_signer(false, channel_value_satoshis);
 		let pubkeys = holder_signer.pubkeys().clone();
 
-		if channel_value_satoshis >= MAX_FUNDING_SATOSHIS {
-			return Err(APIError::APIMisuseError{err: format!("funding_value must be smaller than {}, it was {}", MAX_FUNDING_SATOSHIS, channel_value_satoshis)});
+		if channel_value_satoshis >= TOTAL_BITCOIN_SUPPLY_SATOSHIS {
+			return Err(APIError::APIMisuseError { err: format!("funding_value must be smaller than the total bitcoin supply, it was {}", channel_value_satoshis) });
 		}
 		let channel_value_msat = channel_value_satoshis * 1000;
 		if push_msat > channel_value_msat {
@@ -1076,8 +1075,11 @@ impl<Signer: Sign> Channel<Signer> {
 		}
 
 		// Check sanity of message fields:
-		if msg.funding_satoshis >= MAX_FUNDING_SATOSHIS {
-			return Err(ChannelError::Close(format!("Funding must be smaller than {}. It was {}", MAX_FUNDING_SATOSHIS, msg.funding_satoshis)));
+		if msg.funding_satoshis > config.peer_channel_config_limits.max_funding_satoshis {
+			return Err(ChannelError::Close(format!("Per our config, funding must be at most {}. It was {}", config.peer_channel_config_limits.max_funding_satoshis, msg.funding_satoshis)));
+		}
+		if msg.funding_satoshis >= TOTAL_BITCOIN_SUPPLY_SATOSHIS {
+			return Err(ChannelError::Close(format!("Funding must be smaller than the total bitcoin supply. It was {}", msg.funding_satoshis)));
 		}
 		if msg.channel_reserve_satoshis > msg.funding_satoshis {
 			return Err(ChannelError::Close(format!("Bogus channel_reserve_satoshis ({}). Must be not greater than funding_satoshis: {}", msg.channel_reserve_satoshis, msg.funding_satoshis)));
@@ -4110,7 +4112,7 @@ impl<Signer: Sign> Channel<Signer> {
 		if !self.pending_inbound_htlcs.is_empty() || !self.pending_outbound_htlcs.is_empty() {
 			return Err(ChannelError::Close("Remote end sent us a closing_signed while there were still pending HTLCs".to_owned()));
 		}
-		if msg.fee_satoshis > 21_000_000 * 1_0000_0000 { //this is required to stop potential overflow in build_closing_transaction
+		if msg.fee_satoshis > TOTAL_BITCOIN_SUPPLY_SATOSHIS { // this is required to stop potential overflow in build_closing_transaction
 			return Err(ChannelError::Close("Remote tried to send us a closing tx with > 21 million BTC fee".to_owned()));
 		}
 
@@ -6298,7 +6300,7 @@ mod tests {
 	use ln::PaymentHash;
 	use ln::channelmanager::{HTLCSource, PaymentId};
 	use ln::channel::{Channel, InboundHTLCOutput, OutboundHTLCOutput, InboundHTLCState, OutboundHTLCState, HTLCCandidate, HTLCInitiator};
-	use ln::channel::MAX_FUNDING_SATOSHIS;
+	use ln::channel::TOTAL_BITCOIN_SUPPLY_SATOSHIS;
 	use ln::features::InitFeatures;
 	use ln::msgs::{ChannelUpdate, DataLossProtect, DecodeError, OptionalField, UnsignedChannelUpdate};
 	use ln::script::ShutdownScript;
@@ -6333,12 +6335,6 @@ mod tests {
 		}
 	}
 
-	#[test]
-	fn test_max_funding_satoshis() {
-		assert!(MAX_FUNDING_SATOSHIS <= 21_000_000 * 100_000_000,
-		        "MAX_FUNDING_SATOSHIS is greater than all satoshis in existence");
-	}
-
 	#[test]
 	fn test_no_fee_check_overflow() {
 		// Previously, calling `check_remote_fee` with a fee of 0xffffffff would overflow in

lightning/src/ln/functional_tests.rs

@@ -58,9 +58,12 @@ use ln::chan_utils::CommitmentTransaction;
 #[test]
 fn test_insane_channel_opens() {
 	// Stand up a network of 2 nodes
+	use ln::channel::TOTAL_BITCOIN_SUPPLY_SATOSHIS;
+	let mut cfg = UserConfig::default();
+	cfg.peer_channel_config_limits.max_funding_satoshis = TOTAL_BITCOIN_SUPPLY_SATOSHIS + 1;
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
-	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, Some(cfg)]);
 	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
 	// Instantiate channel parameters where we push the maximum msats given our
@@ -92,11 +95,12 @@ fn test_insane_channel_opens() {
 		} else { assert!(false); }
 	};
 
-	use ln::channel::MAX_FUNDING_SATOSHIS;
 	use ln::channelmanager::MAX_LOCAL_BREAKDOWN_TIMEOUT;
 
 	// Test all mutations that would make the channel open message insane
-	insane_open_helper(format!("Funding must be smaller than {}. It was {}", MAX_FUNDING_SATOSHIS, MAX_FUNDING_SATOSHIS).as_str(), |mut msg| { msg.funding_satoshis = MAX_FUNDING_SATOSHIS; msg });
+	insane_open_helper(format!("Per our config, funding must be at most {}. It was {}", TOTAL_BITCOIN_SUPPLY_SATOSHIS + 1, TOTAL_BITCOIN_SUPPLY_SATOSHIS + 2).as_str(), |mut msg| { msg.funding_satoshis = TOTAL_BITCOIN_SUPPLY_SATOSHIS + 2; msg });
+
+	insane_open_helper(format!("Funding must be smaller than the total bitcoin supply. It was {}", TOTAL_BITCOIN_SUPPLY_SATOSHIS).as_str(), |mut msg| { msg.funding_satoshis = TOTAL_BITCOIN_SUPPLY_SATOSHIS; msg });
 
 	insane_open_helper("Bogus channel_reserve_satoshis", |mut msg| { msg.channel_reserve_satoshis = msg.funding_satoshis + 1; msg });