Visual Basic 6.0 Tutorial - The most elementary single-thread Proxy-server 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).
(img/1.jpg)
Connect a new Winsock component to the project for work 717c216h with the network according to IP protocol
(img/2.jpg - img/4.jpg)
- 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.
(img/6.jpg)
Write the Proxy server part
Private Sub Form_Load()
Form1.Visible = True
Do ''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
(img/7.jpg)
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
(img/8.jpg)
- put port number 125 for the server
part of Proxy
Change Proxy and port settings in Internet Explorer, if you use Internet Explorer
(img/io.jpg)
So that queries were sent to our Proxy
(img/lan.jpg)
LAN adjustment
(img/address.jpg)
Where 
(img/port.jpg) - 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
(img/demo.jpg)
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 and Winsock, create a working copy of the program.
The entire VB project of this development stage is in
the file vbpt2.zip
© by Valery V Shmeleff (Oflameron)
|
