feat: endpoint for gRPC submit.WatchMempool (#180)

Signed-off-by: Chris Gianelloni <[email protected]>

internal/utxorpc/submit.go

@@ -166,3 +166,91 @@ func (s *submitServiceServer) ReadMempool(
 }
 
 // WatchMempool
+func (s *submitServiceServer) WatchMempool(
+	ctx context.Context,
+	req *connect.Request[submit.WatchMempoolRequest],
+	stream *connect.ServerStream[submit.WatchMempoolResponse],
+) error {
+
+	predicate := req.Msg.GetPredicate() // Predicate
+	fieldMask := req.Msg.GetFieldMask()
+	log.Printf(
+		"Got a WatchMempool request with predicate %v and fieldMask %v",
+		predicate,
+		fieldMask,
+	)
+
+	// Connect to node
+	oConn, err := node.GetConnection(nil)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		// Close Ouroboros connection
+		oConn.Close()
+	}()
+
+	// Start clients
+	oConn.LocalTxMonitor().Client.Start()
+
+	// Collect TX hashes from the mempool
+	needsAcquire := false
+	for {
+		if needsAcquire {
+			err = oConn.LocalTxMonitor().Client.Acquire()
+			if err != nil {
+				log.Printf("ERROR: %s", err)
+				return err
+			}
+		}
+		txRawBytes, err := oConn.LocalTxMonitor().Client.NextTx()
+		if err != nil {
+			log.Printf("ERROR: %s", err)
+			return err
+		}
+		// No transactions in mempool, release and continue
+		if txRawBytes == nil {
+			err := oConn.LocalTxMonitor().Client.Release()
+			if err != nil {
+				log.Printf("ERROR: %s", err)
+				return err
+			}
+			needsAcquire = true
+			continue
+		}
+
+		txType, err := ledger.DetermineTransactionType(txRawBytes)
+		if err != nil {
+			return err
+		}
+		tx, err := ledger.NewTransactionFromCbor(txType, txRawBytes)
+		if err != nil {
+			return err
+		}
+		cTx := tx.Utxorpc() // *cardano.Tx
+		resp := &submit.WatchMempoolResponse{}
+		var act submit.AnyChainTx
+		var actr submit.AnyChainTx_Raw
+		actr.Raw = txRawBytes
+		act.Type = &actr
+		record := &submit.TxInMempool{
+			Tx:    &act,
+			Stage: submit.Stage_STAGE_MEMPOOL,
+		}
+		resp.Tx = record
+		if record.Tx.String() == cTx.String() {
+			if predicate == nil {
+				err := stream.Send(resp)
+				if err != nil {
+					return err
+				}
+			} else {
+				// TODO: filter from all Predicate types
+				err := stream.Send(resp)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+}