Using the Internet Transfer Control: Part 1

Tuesday Nov 19th 2002 by Sam Huggill
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Using the Internet Transfer Control: Part 1

There are many reasons why you might want to include the web in your application, and most of them will include retrieving data - this means that you will need to good control to perform these operations. This is where the Inet control steps in. It comes with Visual Basic Pro and Enterprise editions, and can be very useful.

To load the control, open VB, click Project, Components. Scroll down and select Microsoft Internet Transfer Control.

The Internet Transfer Control exposes some useful properties. First of all, the AccessType property. This can have three different values. There are as follows:

  1. icUseDefault
  2. icDirect
  3. icNamedProxy

icUseDefault is the one you will use most of the time, but icDirect and icNamedProxy allow you to really make your application very flexible. The Inet control exposes a Proxy property which allows you to specify the name/IP address of a computer to go through to get data.

When it comes to protocols, the Inet control has them all! Just take a look:

  1. icUnknown
  2. icDefault
  3. icFTP
  4. icGopher
  5. icHTTP
  6. icHTTPS

Most of the time you will be using icHTTP and icFTP, although you may stray across the others at some time. Most of the names are self explanatory, so I won't bother saying what each one does. The control also gives the following properties:

  • URL - The complete URL of what you want to communicate with. e.g. http://www.vbsquare.com/
  • RemoteHost - The name/IP address of the remote host you are connecting with.
  • RemotePort - The port to connect on. For HTTP connections, you want port 80. For FTP, port 21.
  • Document - The name of an individual document
  • UserName - Username to login with
  • Password - Password that goes with the username

Pretty cool huh? Take a look at the following list of ports to get you on your way:

  • HTTP: - 80
  • FTP: - 21
  • NNTP: 119
  • Telnet: - 23
  • SMTP: - 25
  • Gopher: - 70
  • POP 3: - 110
  • IRC: - 6667

Obviously these are only default ports, and you should check with the host computer when attempting to connect.

So, now that you have all this wonderful information, how do you use the control? Well, for demonstration purposes I will show you how to download a web page.

When downloading data, you will use the Inet controls OpenURL method. It takes two parameters, URL and DataType. Both are optional, so you can set them using the properties and omit them when you make the call. Unfortunately the Inet control does not provide a string data type, so we use the one closest to it, named icByteArray. But this means we have to work a bit with the returned data. We can use the UBound function to work with the bytearray data, and write it to a string value. Take a look:

Dim b() As Byte
Dim intCount As Integer
Dim strData As String

Inet1.Cancel ' Stops any current operations

b() = Inet1.OpenURL("http://www.vbsquare.com/ _
      index.html", icByteArray)

For intCount = 0 To UBound(b) - 1

  strData = strData & Chr(b(intCount))

Next intCount

And if you wanted to save the data to a file instead of a string variable, just use:

Open "myfile.txt" For Binary Access Write As #1

Put #1, , b()

Close #1

There we go. A nice simple web page downloader.

If you think you can do any better (which I am sure you can) then email me the files and I will post them. Please, give me some feedback on this HowTo. I am trying to get the balance right, am I doing it? Are you interested in more internet comms? Or do you want more database / client/server information? Did you think this HowTo was too basic or too advanced? Too long or too short? Tell me what you thought at sam@vbsquare.com Tell me what you are working on at the moment, and what you want to see in this newsletter: sam@vbsquare.com or use the online feedback form at http://www.vbsquare.com/feedback.htm

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