[英]NetworkStream Async Read -> Cancel
目前我尝试从网络流读取和写入异步。 我的软件是客户端部分,服务器可以自行发送信息或响应我发送给他的命令。
所以我需要一个插座
所以我认为创建一个信号量和一个后台任务来处理服务器发送的消息是一个很好的方法,如果我想发送一个命令,我会阻止信号量并拥有对套接字的读/写操作的完全访问权限。
这是我目前所做的。
private TcpClient _tcpClient = new TcpClient();
protected SemaphoreSlim ClientSemaphore { get; } = new SemaphoreSlim(1, 1);
public async Task ConnectAsync()
{
if (_tcpClient.Connected)
{
await DisconnectAsync();
}
await _tcpClient.ConnectAsync(Hostname, RemotePort);
//here the background Task is started
_ = AutoReceiveMessages();
}
private async Task AutoReceiveMessages()
{
while (_tcpClient.Connected)
{
//enter and lock semaphore
await ClientSemaphore.WaitAsync();
try
{
//read from socket until timeout (ms)
var msg = await ReadFromSocket(2000);
foreach (var cmd in SplitMessageInTelegrams(msg))
{
Console.WriteLine("MESSAGE --> " + cmd);
}
}
catch (Exception ex)
{
}
finally
{
//release semaphore
ClientSemaphore.Release();
}
}
}
private async Task<string> ReadFromSocket(double timeout = 0)
{
var buf = new byte[4096];
var stream = _tcpClient.GetStream();
//read from stream or timeout
var amountReadTask = stream.ReadAsync(buf, 0, buf.Length);
var timeoutTask = Task.Delay(TimeSpan.FromMilliseconds(timeout));
await Task.WhenAny(timeoutTask, amountReadTask)
.ConfigureAwait(false);
//timeout
if (!amountReadTask.IsCompleted)
{
throw new TimeoutException("Timeout");
}
//no timeout
return Encoding.ASCII.GetString(buf, 0, amountReadTask.Result);
}
但这不像我预期的那样工作......我使用这种方法向服务器发送消息,在 WireShark 中我看到服务器响应相同的消息
protected async Task SendTelegramAsync(ITelegram telegram)
{
await ClientSemaphore.WaitAsync();
try
{
_ = telegram ?? throw new ArgumentException($"{nameof(telegram)}");
if (!_tcpClient.Connected) throw new InvalidOperationException("Socket not connected!");
var buf = new byte[4096];
var stream = _tcpClient.GetStream();
var msg = Encoding.ASCII.GetBytes("\x02" + telegram.GetCommandMessage() + "\x03");
Console.WriteLine("WRITE --> " + msg);
await stream.WriteAsync(msg, 0, msg.Length);
//comment AutoReceiveMessage and remove comment from this
//and I get responses from the server
//var test = await ReadFromSocket(2000);
}
finally
{
ClientSemaphore.Release();
}
}
我知道在这种情况下我不需要信号量,但后来我想创建序列,因此一个命令由多次写入和读取组成,只要执行该命令,我就不想使用 AutoReceiveMessages 方法。
现在的问题是
所以我认为问题与后台任务和 ReadAsync 有关,但我无法弄清楚......
知道了!
stream.DataAvailable 是您的朋友(或我的朋友 :))。
如果我在 ReadAsync 之前检查是否 DataIsAvailable 那么我就没有问题了。
if (_tcpClient.GetStream().DataAvailable)
var msg = await ReadFromSocket(DEFAULT_TIMEOUT);
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