如何调试Swift gRPC客户端与Node.js服务端的本地连接问题

我正在使用gRPC实现服务端与客户端的通信，服务端基于Node.js，客户端基于Swift。参照gRPC Swift官方教程构建Swift客户端，但无法与本地的Node.js服务端建立连接，希望获取调试方案。

我已通过Postman验证Node.js服务端可正常工作，以下是我的代码，烦请帮忙排查是否存在疏漏：

func prepareGrpc() {
    let group = PlatformSupport.makeEventLoopGroup(loopCount: 1)
    
    defer {
      try? group.syncShutdownGracefully()
    }

    do {
        let channel = try GRPCChannelPool.with(
            target: .host("localhost", port: 50051),
            transportSecurity: .plaintext,
            eventLoopGroup: group
        )
        
        client = BookStorePackage_BookAsyncClient(channel: channel)
    } catch {
        print("Can't prepare grpc")
    }
}

func createBook(id: Int32, bookName: String) async throws {
    do {
        let book: BookStorePackage_BookItem = .with {
            $0.id = id
            $0.book = bookName
        }
        
        let feature = try await client?.createBook(book)
        
        guard let created_book = feature else {
            print("Failed creating book")
            return
        }
        
        print("Created book with id: \(created_book.id), name: \(created_book.book)")
    } catch {
        print("Error in creating a book")
    }
}

更新 #

修改后的代码可运行，但出现如下错误，我不确定是否应该每次调用都打开和关闭连接，还是保持连接长期开启：

错误信息：

2023-07-02 13:09:00.936066-0700 bookStore[81602:30021510] [connection] nw_socket_handle_socket_event [C1.1.1:1] Socket SO_ERROR [61: Connection refused]

修改后的代码：

func createBook(id: Int32, bookName: String) async throws {
    let group = PlatformSupport.makeEventLoopGroup(loopCount: 1)

    // Make sure the group is shutdown when we're done with it.
    defer {
      try! group.syncShutdownGracefully()
    }

    // Configure the channel, we're not using TLS so the connection is `insecure`.
    let channel = try GRPCChannelPool.with(
      target: .host("localhost", port: 50051),
      transportSecurity: .plaintext,
      eventLoopGroup: group
    )

    defer {
      print("Closing the connection")
      try! channel.close().wait()
    }

    let bookClient = BookStorePackage_BookAsyncClient(channel: channel)

    let book: BookStorePackage_BookItem = .with {
        $0.id = id
        $0.book = bookName
    }

    do {
      let bookResponse = try await bookClient.createBook(book)
      print("Book response received: \(bookResponse.book) with \(bookResponse.id)")
    } catch {
      print("Book response failed: \(error)")
    }
}

内容的提问来源于stack exchange，提问作者Charles Simms