Add 'ProvidePeerBackupStorage' to 'InitContext' and 'NodeContext'

Introduce the 'ProvidePeerBackupStorage' feature to enable nodes to distribute
and store peer storage backups for channel partners. This functionality enhances
resilience by ensuring critical peer data is backed up and can be retrieved if needed.

- Added 'ProvidePeerBackupStorage' to the 'InitContext' & 'NodeContext'.
- Set feature bit for this feature inside 'provide_init_features()'

Author: Aditya Sharma

lightning-types/src/features.rs

@@ -70,6 +70,8 @@
 //!     (see the [`Trampoline` feature proposal](https://github.com/lightning/bolts/pull/836) for more information).
 //! - `DnsResolver` - supports resolving DNS names to TXT DNSSEC proofs for BIP 353 payments
 //!     (see [bLIP 32](https://github.com/lightning/blips/blob/master/blip-0032.md) for more information).
+//! - `ProvidePeerBackupStorage` - Indicates that we offer the capability to store data of our peers
+//! 	(see https://github.com/lightning/bolts/pull/1110 for more info).
 //!
 //! LDK knows about the following features, but does not support them:
 //! - `AnchorsNonzeroFeeHtlcTx` - the initial version of anchor outputs, which was later found to be
@@ -150,7 +152,7 @@ mod sealed {
 			// Byte 4
 			OnionMessages,
 			// Byte 5
-			ChannelType | SCIDPrivacy,
+			ProvidePeerBackupStorage | ChannelType | SCIDPrivacy,
 			// Byte 6
 			ZeroConf,
 			// Byte 7
@@ -171,7 +173,7 @@ mod sealed {
 			// Byte 4
 			OnionMessages,
 			// Byte 5
-			ChannelType | SCIDPrivacy,
+			ProvidePeerBackupStorage | ChannelType | SCIDPrivacy,
 			// Byte 6
 			ZeroConf | Keysend,
 			// Byte 7
@@ -522,6 +524,16 @@ mod sealed {
 		supports_onion_messages,
 		requires_onion_messages
 	);
+	define_feature!(
+		43,
+		ProvidePeerBackupStorage,
+		[InitContext, NodeContext],
+		"Feature flags for `provide_peer_backup_storage`.",
+		set_provide_peer_backup_storage_optional,
+		set_provide_peer_backup_storage_required,
+		supports_provide_peer_storage,
+		requires_provide_peer_storage
+	);
 	define_feature!(
 		45,
 		ChannelType,
@@ -1104,6 +1116,14 @@ mod tests {
 		assert!(!features1.requires_unknown_bits_from(&features2));
 		assert!(!features2.requires_unknown_bits_from(&features1));
 
+		features1.set_provide_peer_backup_storage_required();
+		assert!(features1.requires_unknown_bits_from(&features2));
+		assert!(!features2.requires_unknown_bits_from(&features1));
+
+		features2.set_provide_peer_backup_storage_optional();
+		assert!(!features1.requires_unknown_bits_from(&features2));
+		assert!(!features2.requires_unknown_bits_from(&features1));
+
 		features1.set_data_loss_protect_required();
 		assert!(features1.requires_unknown_bits_from(&features2));
 		assert!(!features2.requires_unknown_bits_from(&features1));

lightning/src/ln/channelmanager.rs

@@ -11415,6 +11415,7 @@ pub fn provided_init_features(config: &UserConfig) -> InitFeatures {
 	features.set_scid_privacy_optional();
 	features.set_zero_conf_optional();
 	features.set_route_blinding_optional();
+	features.set_provide_peer_backup_storage_optional();
 	if config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx {
 		features.set_anchors_zero_fee_htlc_tx_optional();
 	}