lnrpc/devrpc: add new TriggerSweep dev rpc command

In this commit, we add a new TriggerSwep dev rpc command. This command
can be used in the itest to trigger a sweep on demand, which will be
useful to ensure that they still pass, now that some block beat handling
is more async.

Author: Roasbeef

lnrpc/devrpc/config_active.go

@@ -9,6 +9,13 @@ import (
 	"github.com/lightningnetwork/lnd/htlcswitch"
 )
 
+// UtxoSweeper defines the interface for the UTXO sweeper needed by the dev
+// RPC server.
+type UtxoSweeper interface {
+	// TriggerSweep triggers an immediate sweep attempt.
+	TriggerSweep() int
+}
+
 // Config is the primary configuration struct for the DEV RPC server. It
 // contains all the items required for the rpc server to carry out its
 // duties. Any fields with struct tags are meant to be parsed as normal
@@ -18,4 +25,5 @@ type Config struct {
 	ActiveNetParams *chaincfg.Params
 	GraphDB         *graphdb.ChannelGraph
 	Switch          *htlcswitch.Switch
+	Sweeper         UtxoSweeper
 }

lnrpc/devrpc/dev.pb.go

@@ -37,6 +37,14 @@ service Dev {
     once interop is confirmed.
     */
     rpc Quiesce (QuiescenceRequest) returns (QuiescenceResponse);
+
+    /* lncli: `triggersweeper`
+    TriggerSweeper triggers the sweeper to attempt to create and broadcast sweep
+    transactions for all pending inputs. This RPC is for testing purposes only,
+    allowing tests to deterministically control when sweeps are broadcast rather
+    than relying on the sweeper's automatic timing.
+    */
+    rpc TriggerSweeper (TriggerSweeperRequest) returns (TriggerSweeperResponse);
 }
 
 message ImportGraphResponse {
@@ -52,3 +60,11 @@ message QuiescenceResponse {
     // negotiation completes
     bool initiator = 1;
 }
+
+message TriggerSweeperRequest {
+}
+
+message TriggerSweeperResponse {
+    // The number of sweep transactions that were broadcast.
+    uint32 num_sweeps_broadcast = 1;
+}

lnrpc/devrpc/dev.pb.json.go

@@ -106,6 +106,16 @@
         }
       }
     },
+    "devrpcTriggerSweeperResponse": {
+      "type": "object",
+      "properties": {
+        "num_sweeps_broadcast": {
+          "type": "integer",
+          "format": "int64",
+          "description": "The number of sweep transactions that were broadcast."
+        }
+      }
+    },
     "lnrpcChannelAuthProof": {
       "type": "object",
       "properties": {