Using WebRequest and WebResponse classes

Downloading and uploading data from the web has been a very common programming practice these days.

In this article, you'll see how to download and upload files through HTTP.  

Uploading and Downloading Files

The System.Net.WebClient class provides functionality to upload data to or download data from the Internet or intranet or a local file system. The WebClient class provides many ways to download and upload data. The following table describes WebClient class methods and properties briefly.

Member	Type	Description
BaseURI	Property	Current base URL address
Headers	Property	Headers in the form of name and value pair associated with the request.
QueryStrings	Property	Queries in the form of name and value pair associated with the request.
ResponseHeaders	Property	Headers in the form of name and value pair associated with the response.
DownloadData	Method	Download data from a URI and returns data as a byte array.
DownloadFile	Method	Download data from a URI and saves as a local file.
OpenRead	Method	Opens and reads a URI in stream form.
OpenWrite	Method	Opens a stream to write data to a URI.
UploadData	Method	Uploads data buffer to a URI.
UploadFile	Method	Uploads a local file to the given URI.
UploadValues	Method	Uploads name and value collection.

 
Using WebClient Class

Downloading Data

The WebClient provides three different methods to download data either from the Internet, intranet, or local file system.

WebClient constructor doesn't take any arguments. In the following code, URL is the file name you want to download such as http://www.c-sharpcorner.com/index.asp. You can download any type of files using these methods such as image files, html and so on.

string URL = textBox1.Text;
WebClient client = new WebClient();

The DownloadData method takes URI as a parameter, downloads data from a resource URI and returns a byte string.

byte [] bytedata = client.DownloadData(URL);

The DownloadFile method downloads data from a resource and saves it to the local file system. Hence it takes parameters, first is URI name and second is the file name stored as on the local system. The following code downloads a URL and saves it as temp.asp.

client.DownloadFile(URL, "C:\\temp.asp");

The OpenRead method downloads data from a resource and return data as a stream.

Stream data = client.OpenRead(URL);

Source Code:

// Address of URL
string URL = textBox1.Text;
try
{
// Get HTML data
WebClient client = new WebClient();
Stream data = client.OpenRead(URL);
StreamReader reader = new StreamReader(data);
string str = "";
str = reader.ReadLine();
while( str != null)
{
Console.WriteLine(str);
str = reader.ReadLine();
}
data.Close();
}
catch(WebException exp)
{
MessageBox.Show(exp.Message, "Exception");
}

Upload Data

The WebClient class provides four different ways to uploading data to a resource.

The OpenWrite method sends a data stream to the resource. It's reverse operation of OpenRead method. You pass URI as first parameter of OpenWrite.

OpenWrite(string);

The UploadData method sends a byte array to the resource and returns a byte array containing any response. It's a reverse operation of DownloadData method. It takes two arguments of string and array of bytes respectively.

UploadData(string, byte[]);

client.UploadData("http://www.mindcracker.com/testfile.bmp", data);

The UploadFile method sends a local file to the resource and returns a byte array containing any response. It's a reverse operation of DownloadFile. UploadFile also takes two parameters. First a URI name and second file to be uploaded.

UploadFile(string string);

client.UploadFile("http://www.mindcracker.com/tst.gif", @"c:\mcb.gif");

Or:

client.UploadFile("http://www.mindcracker.com/test.htm", @"c:\test.htm");   

The UploadValues sends a NameValueCollection to the resource and returns a byte array containing any response.

UploadValues(string, NameValueCollection);

Using WebRequest and WebResponse Classes


Although you can use WebClient class to upload and download data but there are more things involved in uploading and downloading data. What if you don't have right to upload to the server you are uploading to? Did you see us passing userid and passwords for the server somewhere? We didn't think so. So if you don't have permission to write to the server, you get this error.



So what we do now? That's where boundary of the WebClient class ends. And that's where the WebRequest and WebResponse classes come in the existence.

The WebRequest Class

The WebRequest is an abstract base class. So you actually don't use it directly. You use it through it derived classes - HttpWebRequest and FileWebRequest.

You use Create method of WebRequest to create an instance of WebRequest. GetResponseStream returns data stream. The following sample example downloads data stream from a web page.         

Sample Code

using System;
using System.Net;
using System.IO;
namespace WebRequestSamp
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Class1
{
static void Main(string[] args)
{
WebRequest request = WebRequest.Create(http://www.c-sharpcorner.com/index.asp);
WebResponse response = request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
string str = reader.ReadLine();
while(str != null)
{
Console.WriteLine(str);
str = reader.ReadLine();
}
}
}
} 

HttpWebRequest and HttpWebResponse classes works in same way too. Here is one sample example. 

Using HttpWebRequest and HttpWebResponse Classes

HttpWebRequest request = (HttpWebRequest)WebRequest.Create (http://www.microsoft.com );
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
String ver = response.ProtocolVersion.ToString();
StreamReader reader = new StreamReader(response.GetResponseStream() );
string str = reader.ReadLine();
while(str != null)
{
Console.WriteLine(str);
str = reader.ReadLine();
}

Well .. that's it for now. My next submission is Web Browser. It should be up on the site soon.