signrpc: fix p2tr support in ComputeInputScript

lnrpc/signrpc/signer.proto

@@ -22,8 +22,8 @@ service Signer {
     /*
     ComputeInputScript generates a complete InputIndex for the passed
     transaction with the signature as defined within the passed SignDescriptor.
-    This method should be capable of generating the proper input script for
-    both regular p2wkh output and p2wkh outputs nested within a regular p2sh
+    This method should be capable of generating the proper input script for both
+    regular p2wkh/p2tr outputs and p2wkh outputs nested within a regular p2sh
     output.
 
     Note that when using this method to sign inputs belonging to the wallet,

lnrpc/signrpc/signer.swagger.json

@@ -18,7 +18,7 @@
   "paths": {
     "/v2/signer/inputscript": {
       "post": {
-        "summary": "ComputeInputScript generates a complete InputIndex for the passed\ntransaction with the signature as defined within the passed SignDescriptor.\nThis method should be capable of generating the proper input script for\nboth regular p2wkh output and p2wkh outputs nested within a regular p2sh\noutput.",
+        "summary": "ComputeInputScript generates a complete InputIndex for the passed\ntransaction with the signature as defined within the passed SignDescriptor.\nThis method should be capable of generating the proper input script for both\nregular p2wkh/p2tr outputs and p2wkh outputs nested within a regular p2sh\noutput.",
         "description": "Note that when using this method to sign inputs belonging to the wallet,\nthe only items of the SignDescriptor that need to be populated are pkScript\nin the TxOut field, the value in that same field, and finally the input\nindex.",
         "operationId": "Signer_ComputeInputScript",
         "responses": {

lnrpc/signrpc/signer_grpc.pb.go

@@ -31,8 +31,8 @@ type SignerClient interface {
 	//
 	//ComputeInputScript generates a complete InputIndex for the passed
 	//transaction with the signature as defined within the passed SignDescriptor.
-	//This method should be capable of generating the proper input script for
-	//both regular p2wkh output and p2wkh outputs nested within a regular p2sh
+	//This method should be capable of generating the proper input script for both
+	//regular p2wkh/p2tr outputs and p2wkh outputs nested within a regular p2sh
 	//output.
 	//
 	//Note that when using this method to sign inputs belonging to the wallet,
@@ -255,8 +255,8 @@ type SignerServer interface {
 	//
 	//ComputeInputScript generates a complete InputIndex for the passed
 	//transaction with the signature as defined within the passed SignDescriptor.
-	//This method should be capable of generating the proper input script for
-	//both regular p2wkh output and p2wkh outputs nested within a regular p2sh
+	//This method should be capable of generating the proper input script for both
+	//regular p2wkh/p2tr outputs and p2wkh outputs nested within a regular p2sh
 	//output.
 	//
 	//Note that when using this method to sign inputs belonging to the wallet,

lnrpc/signrpc/signer_server.go

@@ -489,7 +489,8 @@ func (s *Server) SignOutputRaw(_ context.Context, in *SignReq) (*SignResp,
 // ComputeInputScript generates a complete InputIndex for the passed
 // transaction with the signature as defined within the passed SignDescriptor.
 // This method should be capable of generating the proper input script for both
-// regular p2wkh output and p2wkh outputs nested within a regular p2sh output.
+// regular p2wkh/p2tr outputs and p2wkh outputs nested within a regular p2sh
+// output.
 //
 // Note that when using this method to sign inputs belonging to the wallet, the
 // only items of the SignDescriptor that need to be populated are pkScript in
@@ -519,7 +520,33 @@ func (s *Server) ComputeInputScript(ctx context.Context,
 		return nil, fmt.Errorf("unable to decode tx: %v", err)
 	}
 
-	sigHashCache := input.NewTxSigHashesV0Only(&txToSign)
+	var (
+		sigHashCache      = input.NewTxSigHashesV0Only(&txToSign)
+		prevOutputFetcher = txscript.NewMultiPrevOutFetcher(nil)
+	)
+
+	// If we're spending one or more SegWit v1 (Taproot) inputs, then we
+	// need the full UTXO information available.
+	if len(in.PrevOutputs) > 0 {
+		if len(in.PrevOutputs) != len(txToSign.TxIn) {
+			return nil, fmt.Errorf("provided previous outputs " +
+				"doesn't match number of transaction inputs")
+		}
+
+		// Add all previous inputs to our sighash prev out fetcher so we
+		// can calculate the sighash correctly.
+		for idx, txIn := range txToSign.TxIn {
+			prevOutputFetcher.AddPrevOut(
+				txIn.PreviousOutPoint, &wire.TxOut{
+					Value:    in.PrevOutputs[idx].Value,
+					PkScript: in.PrevOutputs[idx].PkScript,
+				},
+			)
+		}
+		sigHashCache = txscript.NewTxSigHashes(
+			&txToSign, prevOutputFetcher,
+		)
+	}
 
 	signDescs := make([]*input.SignDescriptor, 0, len(in.SignDescs))
 	for _, signDesc := range in.SignDescs {
@@ -532,9 +559,10 @@ func (s *Server) ComputeInputScript(ctx context.Context,
 				Value:    signDesc.Output.Value,
 				PkScript: signDesc.Output.PkScript,
 			},
-			HashType:   txscript.SigHashType(signDesc.Sighash),
-			SigHashes:  sigHashCache,
-			InputIndex: int(signDesc.InputIndex),
+			HashType:          txscript.SigHashType(signDesc.Sighash),
+			SigHashes:         sigHashCache,
+			PrevOutputFetcher: prevOutputFetcher,
+			InputIndex:        int(signDesc.InputIndex),
 		})
 	}