Well, finally I started creating a web proxy.
I decided to explain my work here for two reasons:
1) For everyone who wants to start a similar project.
2) Most parts of these codes are copied from Stack pages, I've just collected them. ;)
I need experts to correct my mistakes and help me to continue.
Here is what I did:
ASP (Default.aspx):
I put a textbox named "txtURL" to enter the web address by user.
I put a button named "btnRun" to start processing.
For now, these components are enough!
C#:
Clicking on "btnRun", makes the page redirecting to: "www.domain.com/default.aspx?URL=(xxx)" - xxx will be replaced by web page address encrypted by a function.
This is the code for btnRun_Click:
protected void btnRun_Click(object sender, EventArgs e)
{
if (txtURL.Text.Length == 0) return;
if (!(txtURL.Text.ToLower().StartsWith("http://") || txtURL.Text.ToLower().StartsWith("https://")))
txtURL.Text = "http://" + txtURL.Text;
try
{
Response.Redirect("Default.aspx?URL=(" + Encrypt(txtURL.Text, mainKey) + ")", false);
}
catch (Exception ex)
{
ShowPopUpMsg(ex.Message);
}
I'll explain "Encrypt" and "ShowPopUpMsg" functions later.
By clicking on "btnRun", this page will be refreshed and the encrypted URL will be included in the address.
Now, in "Page_Load", we should read the encrypted URL (also a condition to detect postback):
protected void Page_Load(object sender, EventArgs e)
{
string url = Regex.Match(HttpContext.Current.Request.Url.AbsoluteUri, @"\(([^)]*)\)").Groups[1].Value;
if (url.Length == 0 || Page.IsPostBack) return;
From now, every code is added to "Page_Load", one after other.
Decrypt the URL and read the remote web page source-code:
try
{
txtURL.Text = Server.UrlDecode(Decrypt(url, mainKey));
string TheUrl = txtURL.Text;
string response = GetHtmlPage(TheUrl);
I'll explain "Decrypt" and "GetHtmlPage" later.
Now, we have the source-code in "response".
Next step is find the links in this source-code. Begining of the links is "href="xxx"" and xxx is the link. We must replace them with our links through the proxy:
response = response.Replace("href =", "href=");
response = response.Replace("href\n=", "href=");
response = response.Replace("href\t=", "href=");
HtmlWeb hw = new HtmlWeb();
HtmlDocument doc = hw.Load(txtURL.Text);
foreach (HtmlNode link in doc.DocumentNode.SelectNodes("//a[@href]"))
{
char[] c = { ' ', '\"' };
string s = link.OuterHtml;
int from = s.IndexOf("href=");
int to = SearchString(s, from, '\"');
s = s.Substring(from + 5, to - from - 5);
s.TrimStart(c);
if (s.StartsWith("\"")) s = s.Remove(0, 1);
"SearchString" is a function to return the closing quotation mark of "href". I'll explain this later.
There are two kind of links:
Links that refer to another domain-name. This links are begun with "http://" or "https://". We'll find them and replace the address:
string corrected = "href=\"" + "Default.aspx?URL=(" + Encrypt(s, mainKey) + ")" + "\"";
if ((s.ToLower().StartsWith("http://") || s.ToLower().StartsWith("https://")))
response = response.Replace("href=\"" + s + "\"", corrected);
Link that refer to current domain-name. This links are begun with "/". To replace them, we should first find the domain name then the whole address:
else
{
var uri = new Uri(txtURL.Text);
string domain = uri.GetComponents(UriComponents.Host, UriFormat.SafeUnescaped);
corrected = "href=\"" + "Default.aspx?URL=(";
if (txtURL.Text.ToLower().StartsWith("http://")) corrected += Encrypt("http://" + domain + s, mainKey);
if (txtURL.Text.ToLower().StartsWith("https://")) corrected += Encrypt("https://" + domain + s, mainKey);
corrected += ")" + "\"";
response = response.Replace("href=\"" + s + "\"", corrected);
}
Now, everything is done (refer to my current knowledge) and we should show the page with new links and finish "Page_Load":
}
Response.Write(response);
}
catch (Exception ex)
{
ShowPopUpMsg(ex.Message);
}
}
Function to search in a string:
private int SearchString(string mainString, int startLocation, char charToFind)
{
if (startLocation < 0) return -1;
bool next = false;
for (int i = startLocation; i < mainString.Length; i++)
if (mainString.Substring(i, 1) == charToFind.ToString() && next)
return i;
else
{
if (mainString.Substring(i, 1) == charToFind.ToString()) next = true;
continue;
}
return -1;
}
Function to read source-code:
private string GetHtmlPage(string URL)
{
String strResult;
WebResponse objResponse;
WebRequest objRequest = HttpWebRequest.Create(URL);
objResponse = objRequest.GetResponse();
using (StreamReader sr = new StreamReader(objResponse.GetResponseStream()))
{
strResult = sr.ReadToEnd();
sr.Close();
}
return strResult;
}
Function to show a popup message:
private void ShowPopUpMsg(string msg)
{
StringBuilder sb = new StringBuilder();
sb.Append("alert('");
sb.Append(msg.Replace("\n", "\\n").Replace("\r", "").Replace("'", "\\'"));
sb.Append("');");
ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "showalert", sb.ToString(), true);
}
Function to decrypt a string:
private string Decrypt(string s, string key)
{
try
{
byte[] keyArray; byte[] toEncryptArray = Convert.FromBase64String(s);
System.Configuration.AppSettingsReader settingsReader = new System.Configuration.AppSettingsReader();
MD5CryptoServiceProvider hashmd5 = new MD5CryptoServiceProvider();
keyArray = hashmd5.ComputeHash(UTF8Encoding.UTF8.GetBytes(key)); hashmd5.Clear();
TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();
tdes.Key = keyArray; tdes.Mode = CipherMode.ECB; tdes.Padding = PaddingMode.PKCS7;
ICryptoTransform cTransform = tdes.CreateDecryptor();
byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
tdes.Clear(); return UTF8Encoding.UTF8.GetString(resultArray);
}
catch { return null; }
}
Function to encrypt a string:
private string Encrypt(string s, string key)
{
try
{
byte[] keyArray; byte[] encryptArray = UTF8Encoding.UTF8.GetBytes(s);
System.Configuration.AppSettingsReader SettingReader = new System.Configuration.AppSettingsReader();
MD5CryptoServiceProvider Hashmd5 = new MD5CryptoServiceProvider();
keyArray = Hashmd5.ComputeHash(UTF8Encoding.UTF8.GetBytes(key)); Hashmd5.Clear();
TripleDESCryptoServiceProvider Tdes = new TripleDESCryptoServiceProvider();
Tdes.Key = keyArray; Tdes.Mode = CipherMode.ECB; Tdes.Padding = PaddingMode.PKCS7;
ICryptoTransform Ctransform = Tdes.CreateEncryptor();
byte[] resultarray = Ctransform.TransformFinalBlock(encryptArray, 0, encryptArray.Length);
Tdes.Clear(); return Convert.ToBase64String(resultarray, 0, resultarray.Length);
}
catch { return null; }
}
