LSP-Plugin: Add MPP support

doc/lightningd-config.5.md

@@ -896,6 +896,12 @@ of the prior channel balance and the new one.
 subprotocol describing the creation of just-in-time-channel (JIT-channels)
 between a LSP and this client.
 
+* **experimental-lsps-client-zero-reserve** [plugin `cln-lsps-client`]
+
+  Specifying this stops requiring the LSP to maintain a channel reserve on the
+JIT-channels it opens to this client. This is left unset by default, as some
+LSPs can not handle a zero reserve.
+
 * **experimental-lsps2-service** [plugin `cln-lsps-service`]
 
   Specifying this enables a LSP JIT-Channel service according to the lsps
@@ -908,6 +914,12 @@ a *experimental-lsps2-promise-secret* to be set.
  string that acts as the secret for promises according to ([blip][blip] #52).
  Is required if *experimental-lsps2-service* is set.
 
+* **experimental-lsps2-zero-reserve** [plugin `cln-lsps-service`]
+
+  Specifying this requires no channel reserve from the client on the
+JIT-channels this service opens. This is left unset by default, as some
+implementations can not handle an explicit zero reserve.
+
 BUGS
 ----
 

plugins/lsps-plugin/Cargo.toml

@@ -7,22 +7,31 @@ rust-version.workspace = true
 [[bin]]
 name = "cln-lsps-client"
 path = "src/client.rs"
+required-features = ["cln"]
 
 [[bin]]
 name = "cln-lsps-service"
 path = "src/service.rs"
+required-features = ["cln"]
+
+[features]
+default = ["cln"]
+cln = ["cln-plugin", "cln-rpc"]
 
 [dependencies]
 anyhow = "1.0"
 async-trait = "0.1"
-bitcoin = "0.32.2"
+bitcoin = { version = "0.32", features = ["serde"] }
 chrono = { version = "0.4.42", features = ["serde"] }
-cln-plugin = { workspace = true }
-cln-rpc = { workspace = true }
+cln-plugin = { workspace = true, optional = true }
+cln-rpc = { workspace = true, optional = true }
 hex = "0.4"
 log = "0.4"
 rand = "0.10"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0", features = ["raw_value"] }
 thiserror = "2.0"
 tokio = { version = "1.44", features = ["full"] }
+
+[dev-dependencies]
+tokio = { version = "1.44", features = ["full", "test-util"] }

plugins/lsps-plugin/src/client.rs

@@ -46,8 +46,28 @@ const OPTION_ENABLED: options::FlagConfigOption = options::ConfigOption::new_fla
     "Enables an LSPS client on the node.",
 );
 
+/// Opt-in: do not require the LSP to maintain a channel reserve on JIT
+/// channels. Left unset by default as some LSPs (e.g. Megalithic) cannot
+/// handle a zero reserve.
+const OPTION_ZERO_RESERVE: options::FlagConfigOption = options::ConfigOption::new_flag(
+    "experimental-lsps-client-zero-reserve",
+    "Do not require the LSP to maintain a channel reserve on JIT channels.",
+);
+
 const DEFAULT_REQUEST_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(60);
 
+/// Hook response accepting a zero-conf JIT channel from the LSP.
+fn openchannel_jit_response(zero_reserve: bool) -> serde_json::Value {
+    let mut resp = serde_json::json!({
+        "result": "continue",
+        "mindepth": 0,
+    });
+    if zero_reserve {
+        resp["reserve"] = 0.into();
+    }
+    resp
+}
+
 #[derive(Clone)]
 pub struct State {
     sender: ClnSender,
@@ -87,6 +107,7 @@ async fn main() -> Result<(), anyhow::Error> {
                 .filters(vec![HookFilter::Int(i64::from(LSPS0_MESSAGE_TYPE))]),
         )
         .option(OPTION_ENABLED)
+        .option(OPTION_ZERO_RESERVE)
         .rpcmethod(
             "lsps-listprotocols",
             "list protocols supported by lsp",
@@ -269,7 +290,7 @@ async fn on_lsps_lsps2_approve(
 ) -> Result<serde_json::Value, anyhow::Error> {
     let req: ClnRpcLsps2Approve = serde_json::from_value(v)?;
     let ds_rec = DatastoreRecord {
-        jit_channel_scid: req.jit_channel_scid.clone(),
+        jit_channel_scid: req.jit_channel_scid,
         client_trusts_lsp: req.client_trusts_lsp.unwrap_or_default(),
     };
     let ds_rec_json = serde_json::to_string(&ds_rec)?;
@@ -485,7 +506,7 @@ async fn on_lsps_lsps2_invoice(
     // 5. Approve jit_channel_scid for a jit channel opening.
     let appr_req = ClnRpcLsps2Approve {
         lsp_id: req.lsp_id,
-        jit_channel_scid: buy_res.jit_channel_scid,
+        jit_channel_scid: buy_res.jit_channel_scid.into(),
         payment_hash: public_inv.payment_hash.to_string(),
         client_trusts_lsp: Some(buy_res.client_trusts_lsp),
     };
@@ -711,10 +732,7 @@ async fn on_openchannel(
         }
         // Fixme: Check that we actually use client-trusts-LSP mode - can be
         // found in the ds record.
-        return Ok(serde_json::json!({
-            "result": "continue",
-            "mindepth": 0,
-        }));
+        Ok(openchannel_jit_response(p.option(&OPTION_ZERO_RESERVE)?))
     } else {
         // Not a requested JIT-channel opening, continue.
         Ok(serde_json::json!({"result": "continue"}))
@@ -857,11 +875,6 @@ macro_rules! ok_or_continue {
     };
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-struct LspsBuyJitChannelResponse {
-    bolt11: String,
-}
-
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct InvoiceRequest {
     pub amount_msat: cln_rpc::primitives::AmountOrAny,
@@ -921,3 +934,19 @@ struct DatastoreRecord {
     jit_channel_scid: ShortChannelId,
     client_trusts_lsp: bool,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn openchannel_jit_response_reserve_is_opt_in() {
+        let resp = openchannel_jit_response(false);
+        assert_eq!(resp["result"], "continue");
+        assert_eq!(resp["mindepth"], 0);
+        assert!(resp.get("reserve").is_none());
+
+        let resp = openchannel_jit_response(true);
+        assert_eq!(resp["reserve"], 0);
+    }
+}

plugins/lsps-plugin/src/cln_adapters/hooks.rs

@@ -23,9 +23,9 @@ where
         plugin.state().pending().complete(&id, hook.payload).await;
     }
 
-    return Ok(serde_json::json!({
+    Ok(serde_json::json!({
       "result": "continue"
-    }));
+    }))
 }
 
 pub async fn service_custommsg_hook<S>(plugin: Plugin<S>, v: Value) -> Result<Value>

plugins/lsps-plugin/src/cln_adapters/mod.rs

@@ -3,3 +3,8 @@ pub mod rpc;
 pub mod sender;
 pub mod state;
 pub mod types;
+
+pub use rpc::{
+    ClnActionExecutor, ClnDatastore, ClnPolicyProvider, ClnRecoveryProvider,
+    ClnRpcClient,
+};