在iOS上使用c# net7.0解析MJPEG流

Question

我想在iOS上用net7.0解析MJPEG流。我目前的解决方案是在windows和android上工作，但在iOS上我无法接收原始流。

何为MJPEG?MJPEG是一个恒定的jpeg流。内容以标题信息开始，之后是图像，然后在内容中再次出现标题。响应示例:

Content-Type: image/jpeg
Content-Length: 50706

{Image}
Content-Type: image/jpeg
Content-Length: 50750

{Image2}

在标题之后，总是有两个换行符。因此，我解析响应以找到2个换行符，解析Content-Lenght并知道，下面的50706字节是图像。我从流解析中提取图像，以获取接下来的2个换行符，等等。

我的代码是这样的:

HttpResponseMessage headerResponse = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
Stream stream = headerResponse.Content.ReadAsStreamAsync();
{Parsing stuff} ...

我现在的问题是，iOS没有交出原始内容。内容流中没有标头信息。是这样的:

{Image}
{Image2}

所以我没有办法将流分割成单个图像。headerResponse.Content.GetContentLegth()不是正确的值，在解析流时也没有改变。我已经尝试了不同的httpclient (NSUrlSessionHandler, CFNetworkHandler)

所以有一种方法，以防止iOS从内容流中删除标题信息?

Answer 1

它现在运行，感谢我在互联网上找到的2个帖子:Swift Mjpeg流只显示单帧和下载文件的Xamarin iOS在后台

我的解决方案是两者的混合

public class MyImageReceiver
{
public async Task Get(string requestUri, Action<IEnumerable<byte>> imageReceived, int timeout, CancellationToken cancellationToken)
{
bool isTimeout = false;
DateTime lastImageReceivedAt = DateTime.Now;
var config = NSUrlSessionConfiguration.DefaultSessionConfiguration;
using (NSUrl nsUrl = NSUrl.FromString(requestUri))
using (NSMutableUrlRequest request = new NSMutableUrlRequest(nsUrl,
cachePolicy: NSUrlRequestCachePolicy.ReloadIgnoringLocalCacheData,
timeoutInterval: 2000))
using (CameraPictureClientSessionDelegate cameraPictureClientSessionDelegate = new CameraPictureClientSessionDelegate())
using (NSUrlSession session = NSUrlSession.FromConfiguration(config, cameraPictureClientSessionDelegate, null))
using (NSUrlSessionDataTask streamingTask = session.CreateDataTask(request: request))
{
request.HttpMethod = "GET";

cameraPictureClientSessionDelegate.ImageReceived += (s, e) =>
{
lastImageReceivedAt = DateTime.Now;
_waitHandle.Release();
imageReceived(e);
};

streamingTask.Resume();
do
{
await _waitHandle.WaitAsync(timeout, cancellationToken);
if ((DateTime.Now - lastImageReceivedAt).TotalMilliseconds > timeout)
{
isTimeout = true;
}
}
while ((streamingTask.State == NSUrlSessionTaskState.Running
|| streamingTask.State == NSUrlSessionTaskState.Suspended)
&& !cancellationToken.IsCancellationRequested
&& !isTimeout);
if (streamingTask.State == NSUrlSessionTaskState.Running
|| streamingTask.State == NSUrlSessionTaskState.Suspended)
{
streamingTask.Cancel();
}
if (isTimeout)
{
throw new TimeoutException();
}
}
}
}

和委托

public class CameraPictureClientSessionDelegate :
NSUrlSessionDataDelegate,
INSUrlSessionTaskDelegate
{
private SemaphoreSlim _semaphore = new SemaphoreSlim(1);
public event EventHandler<IEnumerable<byte>> ImageReceived;
List<byte> _data = new List<byte>();
public override void DidReceiveData(NSUrlSession session, NSUrlSessionDataTask dataTask, NSData data)
{
try
{
_semaphore.Wait();
_data.AddRange(data.ToArray());
}
finally
{
_semaphore.Release();
}
}
public override void DidReceiveResponse(NSUrlSession session, NSUrlSessionDataTask dataTask, NSUrlResponse response, Action<NSUrlSessionResponseDisposition> completionHandler)
{
try
{
_semaphore.Wait();
if (_data.Count > 0)
{
ImageReceived?.Invoke(this, _data);
_data = new List<byte>();
}
}
finally
{
_semaphore.Release();
}
completionHandler(NSUrlSessionResponseDisposition.Allow);
}
}