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

Updated on 11/18/2009 at 5:34PM EST

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.

/// Example of how to use the method.
public void test()
{
	Int64 bytesRead = WriteBinaryFile("http://yourdomain.com/file.pdf", "/files/downloaded.pdf");
}

/// 

/// Read a binary file from a URL and write it to disk.
/// 
/// URL to the web resource.
/// Web-style path for the destination file on disk, including new file name.
/// Number of bytes read, or zero if no file was returned.
public static Int64 WriteBinaryFile(String URL, String FilePath)
{
	Int64 bytesWritten = 0;

	try
	{
		WebResponse objResponse;
		objResponse = WebRequest.Create(URL).GetResponse();
		Byte[] ByteBucket = new Byte[objResponse.ContentLength];
		BinaryReader readStream = new BinaryReader(objResponse.GetResponseStream());
		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, Convert.ToInt32(objResponse.ContentLength));
			fileToWrite.Write(ByteBucket, 0, currentBytesRead);
			totalBytesRead += currentBytesRead;

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

		#endregion

		fileToWrite.Close();
		bytesWritten = objResponse.ContentLength;
	}

	catch
	{
		bytesWritten = 0;
	}

	return bytesWritten;
}

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