WebRequest Class

We can use WebRequest perform a post.

Just need code in this way:

C#

string urlPost = "http://adventureworks.com/api/post.xml";
string postData = "status=something strange";
UTF8Encoding encoding = new UTF8Encoding();

byte[] byteData = encoding.GetBytes(postData);

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlPost);

request.Method = "POST";

request.ContentType = "application/x-www-form-urlencoded";

request.ContentLength = byteData.Length;

request.Credentials = new NetworkCredential("xx", "xx");

Stream requestStream = request.GetRequestStream();

requestStream.Write(byteData, 0, byteData.Length);

requestStream.Close();

Maybe you think the request is working.

No, until you chek the response, the request is not performed.

C#

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

string responseStatus = response.StatusDescription;

If File.Exists(destPath) Then
	Try
        	imgRequest = WebRequest.Create(imgPath.TrimStart)
                imgResp = imgRequest.GetResponse
                lastMod = DateTime.Parse(imgResp.Headers("Last-Modified"))

                imgInfo = New FileInfo(destPath)
                If DateTime.Compare(imgInfo.CreationTime, lastMod) > 0 Then
                	Console.WriteLine("SKIP - " & destPath)
                        Continue For
                End If
        Catch ex As Exception
        	Console.WriteLine("ERROR - " & imgPath)
        Finally
        	If imgResp IsNot Nothing Then
                	imgResp.Close()
        	End If
	End Try
End If

Note this code does not include variables declaration or the For cycle that scan all the files. Also it refer to images, but of course it can be used with any kind of file.

The following sample shows how to use the WebRequest class to screen scrape the contents of a Web page and use a regular expression to list the urls of the images on the page.

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Net;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        //read images from a url and display them in the console window
        List<string> imageUrls = GetAllImagesFromUrl("http://www.msn.com");
                
        foreach (string img in imageUrls)
        {
            Console.WriteLine(img);
        }
        Console.Read();
    }
    /// <summary>
    /// Given a web page url, it will retrieve the Html from that page and parse the image tags in that page
    /// </summary>
    /// <param name="url">The Web page url in this format "http;//www.msn.com"</param>
    /// <returns>Returns a list of image urls as strings based on the url of a Web page</returns>
    public static List<string> GetAllImagesFromUrl(string url)
    {
        List<string> urlList = new List<string>();
        string rawHtml = String.Empty;

        //read the contents of the web page into a string
        using (StreamReader sr = new StreamReader(new WebClient().OpenRead(url)))
        {
            rawHtml = sr.ReadToEnd();
        }

        //regular expression to part out <img> tags from the html
        string regExPattern = @"< \s* img [^\>]* src \s* = \s* [\""\']? ( [^\""\'\s>]* )";

        Regex r = new Regex(regExPattern, RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);
        MatchCollection matches = r.Matches(rawHtml);
        
        foreach (Match m in matches)
        {
            urlList.Add(m.Groups[1].Value);
        }

        return urlList;
    }

  
}

This sample is adopted from a Google images sample I wrote that shows how to asynchronously do WebRequests to screen scrape images from images.google.com. More information and full source code at: http://blogs.msdn.com/danielfe/archive/2004/07/26/197811.aspx