Downloading Files with the WebRequest and WebResponse Classes

A few years ago I was being tasked with writing a console application that would download and save from the Web a file name that was passed to it via the command line. The application took me about 4 hours to write and involved a lot of Sockets programming and data conversion. With .NET, the WebRequest and WebResponse classes now reduce this task to about 5 minutes!

Here’s a simple function that you can easily plug into your C# application that will download a specified server file and save it to a local file. Instead of describing the function and then presenting it, the function contains comments that document exactly what is going on.

// Remember to add the following using statements to your code
// using System.Net;
// using System.IO;

public static int DownloadFile(String remoteFilename,
                               String localFilename)
{
  // Function will return the number of bytes processed
  // to the caller. Initialize to 0 here.
  int bytesProcessed = 0;

  // Assign values to these objects here so that they can
  // be referenced in the finally block
  Stream remoteStream  = null;
  Stream localStream   = null;
  WebResponse response = null;

  // Use a try/catch/finally block as both the WebRequest and Stream
  // classes throw exceptions upon error
  try
  {
    // Create a request for the specified remote file name
    WebRequest request = WebRequest.Create(remoteFilename);
    if (request != null)
    {
      // Send the request to the server and retrieve the
      // WebResponse object 
      response = request.GetResponse();
      if (response != null)
      {
        // Once the WebResponse object has been retrieved,
        // get the stream object associated with the response's data
        remoteStream = response.GetResponseStream();

        // Create the local file
        localStream = File.Create(localFilename);

        // Allocate a 1k buffer
        byte[] buffer = new byte[1024];
        int bytesRead;

        // Simple do/while loop to read from stream until
        // no bytes are returned
        do
        {
          // Read data (up to 1k) from the stream
          bytesRead = remoteStream.Read (buffer, 0, buffer.Length);

          // Write the data to the local file
          localStream.Write (buffer, 0, bytesRead);

          // Increment total bytes processed
          bytesProcessed += bytesRead;
        } while (bytesRead > 0);
      }
    }
  }
  catch(Exception e)
  {
    Console.WriteLine(e.Message);
  }
  finally
  {
    // Close the response and streams objects here 
    // to make sure they're closed even if an exception
    // is thrown at some point
    if (response     != null) response.Close();
    if (remoteStream != null) remoteStream.Close();
    if (localStream  != null) localStream.Close();
  }

  // Return total bytes processed to caller.
  return bytesProcessed;
}

Finally, here’s an example of using the DownloadFile function.

int read = DownloadFile("http://www.mysite.com/problem1.jpg",
                        "d:test.jpg");
Console.WriteLine("{0} bytes written", read);