Update ChannelConfig serialization to be TLV-based

This was missed prior to 0.0.98, so requires a
backwards-compatibility wrapper inside the `Channel` serialization
logic, but it's not very complicated to do so.

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -4439,7 +4439,7 @@ fn is_unsupported_shutdown_script(their_features: &InitFeatures, script: &Script
 	return !script.is_p2pkh() && !script.is_p2sh() && !script.is_v0_p2wpkh() && !script.is_v0_p2wsh()
 }
 
-const SERIALIZATION_VERSION: u8 = 1;
+const SERIALIZATION_VERSION: u8 = 2;
 const MIN_SERIALIZATION_VERSION: u8 = 1;
 
 impl_writeable_tlv_based_enum!(InboundHTLCRemovalReason,;
@@ -4481,7 +4481,13 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
 		write_ver_prefix!(writer, SERIALIZATION_VERSION, MIN_SERIALIZATION_VERSION);
 
 		self.user_id.write(writer)?;
-		self.config.write(writer)?;
+
+		// Write out the old serialization for the config object. This is read by version-1
+		// deserializers, but we will read the version in the TLV at the end instead.
+		self.config.fee_proportional_millionths.write(writer)?;
+		self.config.cltv_expiry_delta.write(writer)?;
+		self.config.announced_channel.write(writer)?;
+		self.config.commit_upfront_shutdown_pubkey.write(writer)?;
 
 		self.channel_id.write(writer)?;
 		(self.channel_state | ChannelState::PeerDisconnected as u32).write(writer)?;
@@ -4669,7 +4675,10 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
 
 		self.channel_update_status.write(writer)?;
 
-		write_tlv_fields!(writer, {(0, self.announcement_sigs, option)});
+		write_tlv_fields!(writer, {
+			(0, self.announcement_sigs, option),
+			(1, self.config, required),
+		});
 
 		Ok(())
 	}
@@ -4679,10 +4688,21 @@ const MAX_ALLOC_SIZE: usize = 64*1024;
 impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 		where K::Target: KeysInterface<Signer = Signer> {
 	fn read<R : ::std::io::Read>(reader: &mut R, keys_source: &'a K) -> Result<Self, DecodeError> {
-		let _ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);
+		let ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);
 
 		let user_id = Readable::read(reader)?;
-		let config: ChannelConfig = Readable::read(reader)?;
+
+		let mut config = Some(ChannelConfig::default());
+		if ver == 1 {
+			// Read the old serialization of the ChannelConfig from version 0.0.98.
+			config.as_mut().unwrap().fee_proportional_millionths = Readable::read(reader)?;
+			config.as_mut().unwrap().cltv_expiry_delta = Readable::read(reader)?;
+			config.as_mut().unwrap().announced_channel = Readable::read(reader)?;
+			config.as_mut().unwrap().commit_upfront_shutdown_pubkey = Readable::read(reader)?;
+		} else {
+			// Read the 8 bytes of backwards-compatibility ChannelConfig data.
+			let mut _val: u64 = Readable::read(reader)?;
+		}
 
 		let channel_id = Readable::read(reader)?;
 		let channel_state = Readable::read(reader)?;
@@ -4842,15 +4862,18 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 		let channel_update_status = Readable::read(reader)?;
 
 		let mut announcement_sigs = None;
-		read_tlv_fields!(reader, {(0, announcement_sigs, option)});
+		read_tlv_fields!(reader, {
+			(0, announcement_sigs, option),
+			(1, config, option), // Note that if none is provided we will *not* overwrite the existing one.
+		});
 
 		let mut secp_ctx = Secp256k1::new();
 		secp_ctx.seeded_randomize(&keys_source.get_secure_random_bytes());
 
 		Ok(Channel {
 			user_id,
 
-			config,
+			config: config.unwrap(),
 			channel_id,
 			channel_state,
 			secp_ctx,

lightning/src/util/config.rs

@@ -205,11 +205,11 @@ impl Default for ChannelConfig {
 }
 
 //Add write and readable traits to channelconfig
-impl_writeable!(ChannelConfig, 4+2+1+1, {
-	fee_proportional_millionths,
-	cltv_expiry_delta,
-	announced_channel,
-	commit_upfront_shutdown_pubkey
+impl_writeable_tlv_based!(ChannelConfig, {
+	(0, fee_proportional_millionths, required),
+	(2, cltv_expiry_delta, required),
+	(4, announced_channel, required),
+	(6, commit_upfront_shutdown_pubkey, required),
 });
 
 /// Top-level config which holds ChannelHandshakeLimits and ChannelConfig.

lightning/src/util/ser_macros.rs

@@ -173,7 +173,7 @@ macro_rules! decode_tlv_stream {
 			last_seen_type = Some(typ.0);
 
 			// Finally, read the length and value itself:
-			let length: ser::BigSize = Readable::read($stream)?;
+			let length: ser::BigSize = ser::Readable::read($stream)?;
 			let mut s = ser::FixedLengthReader::new($stream, length.0);
 			match typ.0 {
 				$($type => {
@@ -503,7 +503,7 @@ mod tests {
 	use prelude::*;
 	use std::io::Cursor;
 	use ln::msgs::DecodeError;
-	use util::ser::{Readable, Writeable, HighZeroBytesDroppedVarInt, VecWriter};
+	use util::ser::{Writeable, HighZeroBytesDroppedVarInt, VecWriter};
 	use bitcoin::secp256k1::PublicKey;
 
 	// The BOLT TLV test cases don't include any tests which use our "required-value" logic since