错误“此流不支持搜索操作"在 C# 中

问题描述

我正在尝试使用 byte 流从 url 获取图像.但我收到此错误消息:

I'm trying to get an image from an url using a byte stream. But i get this error message:

此流不支持搜索操作.

这是我的代码:

byte[] b;
HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(url);
WebResponse myResp = myReq.GetResponse();

Stream stream = myResp.GetResponseStream();
int i;
using (BinaryReader br = new BinaryReader(stream))
{
    i = (int)(stream.Length);
    b = br.ReadBytes(i); // (500000);
}
myResp.Close();
return b;

伙计们，我做错了什么?

What am i doing wrong guys?

推荐答案

您可能想要这样的东西.要么检查长度失败，要么 BinaryReader 在幕后进行搜索.

You probably want something like this. Either checking the length fails, or the BinaryReader is doing seeks behind the scenes.

HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(url);
WebResponse myResp = myReq.GetResponse();

byte[] b = null;
using( Stream stream = myResp.GetResponseStream() )
using( MemoryStream ms = new MemoryStream() )
{
  int count = 0;
  do
  {
    byte[] buf = new byte[1024];
    count = stream.Read(buf, 0, 1024);
    ms.Write(buf, 0, count);
  } while(stream.CanRead && count > 0);
  b = ms.ToArray();
}

我使用反射器检查过，是对 stream.Length 的调用失败了.GetResponseStream 返回一个 ConnectStream，并且该类的 Length 属性会引发您看到的异常.正如其他发布者所提到的，您无法可靠地获得 HTTP 响应的长度，因此这是有道理的.

I checked using reflector, and it is the call to stream.Length that fails. GetResponseStream returns a ConnectStream, and the Length property on that class throws the exception that you saw. As other posters mentioned, you cannot reliably get the length of a HTTP response, so that makes sense.