Preserving binary data in streams

Using C#, I was surprised how complicated it seemed to preserve binary info from a stream. I'm trying to download a PNG datafile using the WebRequest class, but just transfering the resulting Stream to a file, without corrupting it was more verbose than I thought. First, just using StreamReader and StreamWriter was no good as the ReadToEnd() function returns a string, which effectivly doubles the size of the PNG file (probably due to the UTF conversion)

So my question is, do I really have to write all this code, or is there a cleaner way of doing it?

            Stream srBytes = webResponse.GetResponseStream();
            // Write to file
            Stream swBytes = new FileStream("map(" + i.ToString() + ").png",FileMode.Create,FileAccess.Write);
            int count = 0;
            byte[] buffer = new byte[4096];
            do
            {
                count = srBytes.Read(buffer, 0, buffer.Length);
                swBytes.Write(buffer, 0, count);
            }
            while (coun开发者_StackOverflow中文版t != 0);
            swBytes.Close();

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Using StreamReader/StreamWriter is definitely a mistake, yes - because that's trying to load the file as text, which it's not.

Options:

• Use WebClient.DownloadFile as SLaks suggested
• In .NET 4, use Stream.CopyTo(Stream) to copy the data in much the same way as you've got here

• Otherwise, write your own utility method to do the copying, then you only need to do it once; you could even write this as an extension method, which means when you upgrade to .NET 4 you can just get rid of the utility method and use the built-in one with no change to the calling code:

  public static class StreamExtensions
  {
      public static void CopyTo(this Stream source, Stream destination)
      {
          if (source == null)
          {
              throw new ArgumentNullException("source");
          }
          if (destination == null)
          {
              throw new ArgumentNullException("destination");
          }
          byte[] buffer = new byte[8192];
          int bytesRead;
          while ((bytesRead = source.Read(buffer, 0, buffer.Length)) > 0)
          {
              destination.Write(buffer, 0, bytesRead);
          }
      }
  }
  

Note that you should be using using statements for the web response, response stream and output stream in order to make sure they're always closed appropriately, like this:

using (WebResponse response = request.GetResponse())
using (Stream responseStream = response.GetResponseStream())
using (Stream outputStream = File.OpenWrite("map(" + i + ").png"))
{
    responseStream.CopyTo(outputStream);
}

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You can call WebClient.DownloadFile(url, localPath).

In .Net 4.0, you can simplify your current code by calling Stream.CopyTo.