Free VB eBook - The most elementary single-thread Proxy in Visual Basic. In creating this manual we set ourselves the task to develop a minimum program code playing the role of Proxy-server (transmitting information from one port to another). It is easy to add filtration functions to the program (it will be shown in the supplement), log records, information substitution records (link addresses, advertisement in HTML - for web site promotion).
      Create standard Visual Basic project. Deploy element Label “this computer’s IP” on the form
      
      
      
      Connect a new Winsock component to the project for work with the network according to TCP/IP protocol
      
            
      
       - Winsock component
      
      Deploy two Winsock copies on the form. Winsock1 – for the server part and Oflameron for the client part. The server part (Winsock1) receives queries from the Web-browser (for example, Internet Explorer) through the port, for example, 125 and transmits it to the client part. The client part Oflameron (Winsock2) through standard port 80 transmits queries to the real Web-server.

      
      
      
      Write the Proxy server part
      
      Private Sub Form_Load()
      Form1.Visible = True
      ''Switch the server part to port listening ( Listen )
      If Winsock1.State <> sckConnected And Winsock1.State <> sckListening Then  ''If there is no connection yet and the port cannot be heard
      Beep
        Winsock1.Close  ''Close the connection
        Winsock1.LocalPort = 125  ''Port number for listening
        Winsock1.Listen  ''Begin listening port 125
      End If
      DoEvents
      Loop ''Repeat
      End Sub
      
      Connections processing
      
      Private Sub Winsock1_ConnectionRequest(ByVal requestID As Long)  ''If there is query for connection
      Winsock1.Close  ''Stop listening the port
      Winsock1.Accept requestID  ''Connect the client (browser) according to the number of the query
      End Sub
      
      Winsock1_ConnectionRequest – query for connection
      
      
      
      Announce the variable
      Dim ToServer As String  ''To send the query from the client part of Proxy to Web-server
      
      Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)  ''Processing of incoming data (queries from Web-browser)
      Dim ServerData As String  ''Announce the variable for the received data ServerData
      Winsock1.GetData ServerData  ''Accept data into the variable
      ToServer = ServerData  ''Copy the query into the variable for sending to the Web-server
      Oflameron_SendToWebserver  ''Send the query to the Web-server
      End Sub
      
      Line “ToServer = ServerData” - is not mandatory, it is worthwhile, if it is necessary to process data writing in the log, filter, search for data in queries, substitute information (for example, change URL in downloaded web-pages for one’s own) etc.
      
      The entire VB project of this development stage is in the file vbpt1.zip
      
      Write the Client part of Proxy
      
      For work with real Web-server. Connection to Web-server, sending of queries and data receipt.
      
      Announce the variables
      
      Dim Webport  ''Port number
      Dim Data As String  ''To receive data from Web-server
      
      Private Sub Oflameron_SendToWebserver()  ''Connect to Web-server
      Oflameron.Close  ''Close the connection
      Oflameron.RemoteHost = "10.62.182.54"  ''Web-server address or its IP address
      Oflameron.RemotePort = 80  ''Port number. Standard for HTTP
      Oflameron.Connect  ''Connect to Web-server
        Webport = Oflameron.RemotePort  ''Remember the port number (optional line)
      End Sub
      
      Procedure Oflameron_Connect performs actions as soon as the Web-server is connected
      
      Private Sub Oflameron_Connect()  ''Sent query to Web-server
      If Oflameron.State <> sckConnected Then Exit Sub  ''Check. If there is no connection, abandon the procedure
      Oflameron.SendData ToServer  ''Send the query line to the Web-server
      End Sub
      
      The procedure of data receipt from the Web-server
      
      Private Sub Oflameron_DataArrival(ByVal bytesTotal As Long)  ''The call will be initiated as soon as some data is received from the Web-server
        Text1.Text = Oflameron.State
      If Oflameron.State <> sckClosing Then
        Oflameron.GetData Data  ''It will contain data obtained from the Web-server
        Winsock1.SendData Data  ''Send the obtained data from Web server to Web-browser
      End If
      End Sub

      
       - put port number 125 for the server part of Proxy
      
      Change Proxy and port settings in Internet Explorer, if you use IE
      
      
      
      So that queries were sent to our Proxy
      
      
      
      LAN adjustment
      
      
      
      Where - the address of our Proxy (IP-address of your computer) and port 125, which will listen to the server part of your Proxy
      
      Upload the page from the Web-server to Internet Explorer website
      
      Proxy-server operates –sends queries and received data.
      
      This is a working example of a most elementary Proxy-server in the minimal code configuration. It allows to understand important specifics of network programming, create a working copy of the program.
      
      The entire VB project of this development stage is in the file vbpt2.zip