如何在 C# 中两次读取 Http 响应流？

Question

I am trying to read an Http response stream twice via the following:

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
stream = response.GetResponseStream();
RssReader reader = new RssReader(stream);
do
{
  element = reader.Read();
  if (element is RssChannel)
  {
    feed.Channels.Add((RssChannel)element);
  }
} while (element != null);

StreamReader sr = new StreamReader(stream);
feed._FeedRawData = sr.ReadToEnd();

However when the StreamReader code executes there is no data returned because the stream has now reached the end. I tried to reset the stream via stream.Position = 0 but this throws an exception (I think because the stream can't have its position changed manually).

Basically, I would like to parse the stream for XML and have access to the raw data (in string format).

Any ideas?

Answer 1

Copy it into a new MemoryStream first. Then you can re-read the MemoryStream as many times as you like:

Stream responseStream = CopyAndClose(resp.GetResponseStream());
// Do something with the stream
responseStream.Position = 0;
// Do something with the stream again


private static Stream CopyAndClose(Stream inputStream)
{
    const int readSize = 256;
    byte[] buffer = new byte[readSize];
    MemoryStream ms = new MemoryStream();

    int count = inputStream.Read(buffer, 0, readSize);
    while (count > 0)
    {
        ms.Write(buffer, 0, count);
        count = inputStream.Read(buffer, 0, readSize);
    }
    ms.Position = 0;
    inputStream.Close();
    return ms;
}

Answer 2

Copying the stream to a MemoryStream as suggested by Iain is the right approach. But since .NET Framework 4 (released 2010) we have Stream.CopyTo . Example from the docs:

// Create the streams.
MemoryStream destination = new MemoryStream();

using (FileStream source = File.Open(@"c:\temp\data.dat",
    FileMode.Open))
{

    Console.WriteLine("Source length: {0}", source.Length.ToString());

    // Copy source to destination.
    source.CopyTo(destination);
}

Console.WriteLine("Destination length: {0}", destination.Length.ToString());

Afterwards you can read destination as many times as you like:

// re-set to beginning and convert stream to string
destination.Position = 0;
StreamReader streamReader = new StreamReader(destination);
string text = streamReader.ReadToEnd();
// re-set to beginning and read again
destination.Position = 0;
RssReader cssReader = new RssReader(destination);

(I have seen Endy's comment but since it is an appropriate, current answer, it should have its own answer entry.)

Answer 3

have you tried resetting the stream position? if this does not work you can copy the stream to a MemoryStream and there you can reset the position (ie to 0) as often as you want.