System.InvalidOperationException：不允许 OnConnectedAsync Hub 方法内的客户端结果

Question

使用 SignalR .NET 7 中的新客户端结果功能时，我遇到一个错误：不允许在 OnConnectedAsync Hub 方法中使用客户端结果。

我的用例是我有多个客户端，我使用

OnConnectedAsync 方法缓存每个客户端的连接 ID，以便我可以向特定客户端发送消息并等待他们的响应。

这是我的集线器类，请注意，当我调用客户端方法时抛出异常：

return await Clients.Client(connectionMetadata.ConnectionId).InvokeAsync<bool>("CreateConnection", message, CancellationToken.None);

public class ConnectionCreationHub : Hub
{
    private readonly List<ConnectionMetadata> connectionIdsCache;
    private readonly ITokenValidator2 validator;

    public ConnectionCreationHub(
        ITokenValidator2 validator,
        List<ConnectionMetadata> connectionIdsCache)
    {
        this.validator = validator;
        this.connectionIdsCache = connectionIdsCache;
    }

    public async Task<bool> SendCreateConnectionMessage(
        Guid userId,
        string message)
    {
        var connectionMetadata =
            connectionIdsCache
                .FirstOrDefault(entry => entry.UserId.Equals(userId));

        if (connectionMetadata == null)
        {
            throw new Exception($"Client with userId {userId} not connected");
        }

        //The following line throws an error "System.InvalidOperationException: Client results inside OnConnectedAsync Hub methods are not allowed."
        return await Clients.Client(connectionMetadata.ConnectionId).InvokeAsync<bool>("CreateConnection", message, CancellationToken.None);
    }

    public override async Task OnConnectedAsync()
    {
        //Validate authorization token, and cache connection ID.
        var tokenClaims = await this.AuthorizeOrThrow(validator);

        var userId = tokenClaims.UserId;

        connectionIdsCache.Add(new(userId, Context.ConnectionId));

        await base.OnConnectedAsync();
    }

    public override async Task OnDisconnectedAsync(Exception? exception)
    {
        //Clean cache on client disconnected
        var connectionMetadata =
            connectionIdsCache
                .FirstOrDefault(entry => entry.ConnectionId == Context.ConnectionId);

        if (connectionMetadata != null)
        {
            connectionIdsCache.Remove(connectionMetadata);
        }

        await base.OnDisconnectedAsync(exception);
    }
}

我希望我的客户会收到该消息，但我收到了上述错误。请注意，只有使用

InvokeAsync 时才会发生这种情况。 *SendAsync 正在按预期工作。

以下是异常详细信息：

System.InvalidOperationException
  HResult=0x80131509
  Message=Client results inside OnConnectedAsync Hub methods are not allowed.
  Source=Microsoft.AspNetCore.SignalR.Core
  StackTrace:
   at Microsoft.AspNetCore.SignalR.Internal.HubCallerClients.NoInvokeSingleClientProxy.InvokeCoreAsync[T](String method, Object[] args, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.SignalR.ClientProxyExtensions.InvokeAsync[T](ISingleClientProxy clientProxy, String method, Object arg1, CancellationToken cancellationToken)
   at ConnectionCreationHub.<SendCreateConnectionMessage>d__3.MoveNext() in *\ConnectionCreationHub.cs:line 42

Answer 1

在 SignalR .NET 7 中，有一个限制，不允许在 OnConnectedAsync 方法的上下文中等待客户端结果，因为在 OnConnectedAsync 完成之前连接尚未完全建立。

已知问题：使用客户端结果时从 OnConnected 和 OnDisconnected 抛出

优化后的代码如下，大家可以参考一下。

public async Task<bool> SendCreateConnectionMessage(
    Guid userId,
    string message)
{
    var connectionMetadata =
        connectionIdsCache
            .FirstOrDefault(entry => entry.UserId.Equals(userId));

    if (connectionMetadata == null)
    {
        throw new Exception($"Client with userId {userId} not connected");
    }

    //We need to ensure that this invocation is not in the lifecycle context.
    bool result = false;
    try
    {
        result = await Clients.Client(connectionMetadata.ConnectionId)
            .InvokeAsync<bool>("CreateConnection", message, CancellationToken.None);
    }
    catch (Exception ex)
    {
        // Handle the exception.
        throw new Exception($"Error while trying to invoke client method: {ex.Message}", ex);
    }
    return result;
}