From 4e104b4db197ae9014065c4ee0b03021fc29f848 Mon Sep 17 00:00:00 2001
From: Lucas Soriano del Pino <lucas_soriano@fastmail.com>
Date: Wed, 1 Nov 2023 20:52:10 +1100
Subject: [PATCH] Remain backwards-compatible with SubChannels without
 channel_keys_id

---
 dlc-manager/src/sub_channel_manager.rs | 35 +++++++++++++++++++++-----
 dlc-manager/src/subchannel/mod.rs      |  5 +++-
 dlc-manager/src/subchannel/ser.rs      |  2 +-
 3 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/dlc-manager/src/sub_channel_manager.rs b/dlc-manager/src/sub_channel_manager.rs
index 5f0f386b..e1710c3e 100644
--- a/dlc-manager/src/sub_channel_manager.rs
+++ b/dlc-manager/src/sub_channel_manager.rs
@@ -316,6 +316,11 @@ where
                     SubChannelState::OffChainClosed => {
                         s.is_offer = true;
                         s.update_idx -= 1;
+
+                        // We do this to give older channels a chance to upgrade to the new version which
+                        // expects this field to be set to `Some`.
+                        s.channel_keys_id = Some(channel_details.channel_keys_id);
+
                         Some(s)
                     }
                     _ => return Err(Error::InvalidState(
@@ -411,7 +416,7 @@ where
                     counter_fund_pk: channel_details.counter_funding_pubkey.ok_or_else(|| {
                         Error::InvalidState("Counter funding PK is missing".to_string())
                     })?,
-                    channel_keys_id: channel_details.channel_keys_id,
+                    channel_keys_id: Some(channel_details.channel_keys_id),
                 }
             }
         };
@@ -1581,6 +1586,11 @@ where
         let sub_channel = match sub_channel {
             Some(mut s) => {
                 s.state = SubChannelState::Offered(offered_sub_channel);
+
+                // We do this to give older channels a chance to upgrade to the new version which
+                // expects this field to be set to `Some`.
+                s.channel_keys_id = Some(channel_details.channel_keys_id);
+
                 s
             }
             None => SubChannel {
@@ -1607,7 +1617,7 @@ where
                 counter_fund_pk: channel_details.counter_funding_pubkey.ok_or_else(|| {
                     Error::InvalidState("Counter funding PK is missing".to_string())
                 })?,
-                channel_keys_id: channel_details.channel_keys_id,
+                channel_keys_id: Some(channel_details.channel_keys_id),
             },
         };
 
@@ -3691,11 +3701,24 @@ where
         split_tx: &Transaction,
     ) -> Result<Signature, Error> {
         let mut signers = self.ln_channel_signers.lock().unwrap();
+
+        let channel_keys_id = match sub_channel.channel_keys_id {
+            Some(channel_keys_id) => channel_keys_id,
+            None => {
+                let channel_id = sub_channel.channel_id;
+                let channel_details = self
+                    .ln_channel_manager
+                    .get_channel_details(&channel_id)
+                    .ok_or_else(|| {
+                        Error::InvalidParameters(format!("Unknown LN channel {channel_id:02x?}"))
+                    })?;
+                channel_details.channel_keys_id
+            }
+        };
+
         let signer = signers.entry(sub_channel.channel_id).or_insert(
-            self.signer_provider.derive_ln_dlc_channel_signer(
-                sub_channel.fund_value_satoshis,
-                sub_channel.channel_keys_id,
-            ),
+            self.signer_provider
+                .derive_ln_dlc_channel_signer(sub_channel.fund_value_satoshis, channel_keys_id),
         );
         signer.get_holder_split_tx_signature(
             self.dlc_channel_manager.get_secp(),
diff --git a/dlc-manager/src/subchannel/mod.rs b/dlc-manager/src/subchannel/mod.rs
index f2ff072a..da557857 100644
--- a/dlc-manager/src/subchannel/mod.rs
+++ b/dlc-manager/src/subchannel/mod.rs
@@ -59,7 +59,10 @@ pub struct SubChannel {
     /// The revocation secrets from the remote party for already revoked split transactions.
     pub counter_party_secrets: CounterpartyCommitmentSecrets,
     /// The id used to derive the keys for the Lightning channel.
-    pub channel_keys_id: [u8; 32],
+    ///
+    /// This is an [`Option`] to maintain backwards compatibility with versions of this struct which
+    /// were persisted without this field.
+    pub channel_keys_id: Option<[u8; 32]>,
 }
 
 impl std::fmt::Debug for SubChannel {
diff --git a/dlc-manager/src/subchannel/ser.rs b/dlc-manager/src/subchannel/ser.rs
index 0dece5c0..58dd5940 100644
--- a/dlc-manager/src/subchannel/ser.rs
+++ b/dlc-manager/src/subchannel/ser.rs
@@ -25,7 +25,7 @@ impl_dlc_writeable!(SubChannel, {
     (own_fund_pk, writeable),
     (counter_fund_pk, writeable),
     (counter_party_secrets, writeable),
-    (channel_keys_id, writeable)
+    (channel_keys_id, option)
 });
 
 impl_dlc_writeable_enum!(SubChannelState,