How to Read a Binary File Over HTTP and Write to Disk Using ASP.NET and C#


Have you ever had the need to grab a binary file from a remote server over HTTP, and save it to your server, using ASP.NET? It may not sound like a common request, or even a difficult one. But there are a few tricks to accomplishing your goal. One challenge I encountered was that using a BinaryReader required some buffering code. A blind call to read the stream would often only return a portion of the file.

The following C# method works quite well, no matter how fast or reliable your internet connection is. Can you feel the love I put into this gem? Oh, wait. That's just gas.

The Method...

/// Read a binary file from a URL and write it to disk.
/// URL: URL to the web resource.
/// FilePath: Web-style path for the destination file on disk, including
/// new file name.
/// RETURNS: Number of bytes read, or zero if no file was returned.

public static Int64 WriteBinaryFile(String URL, String FilePath)
    Int64 bytesWritten = 0;

        WebResponse objResponse;
         objResponse = WebRequest.Create(URL).GetResponse();
         Byte[] ByteBucket = new Byte[objResponse.ContentLength];
         BinaryReader readStream = new BinaryReader(
         FileStream fileToWrite =
                  new FileStream(HttpContext.Current.Server.MapPath(
                  FilePath), FileMode.Create, FileAccess.Write);

         Int32 currentBytesRead = 0;
         Int32 totalBytesRead = 0;
         Boolean done = false;

         #region Use a buffer to prevent truncated files

         while (!done)
                  currentBytesRead = readStream.Read(ByteBucket, 0,
                  fileToWrite.Write(ByteBucket, 0, currentBytesRead);

                  totalBytesRead += currentBytesRead;

                  if (totalBytesRead == objResponse.ContentLength)
                           done = true;



         bytesWritten = objResponse.ContentLength;

         bytesWritten = 0;

    return bytesWritten;

Calling the Method...

public void test()
    Int64 bytesRead =

Michael directs all design initiatives, heads marketing, and builds cool software for Fynydd. He's also a husband, father, avid reader, advocate for reason and science, and autodidact.

Fynydd is a software design and development company that creates awesome user experiences for all kinds of devices. Our expertise has helped people to do things like:

  • Create a new product or service.
  • Automate processes and workflows.
  • Bring a mobile strategy to life.
  • Better interact with their customers.

How can we help you? Contact us and let us know.