Retrieving HTTPS Data

BrentDT
Originally in Liberty BASIC Newsletter #37

This demo reads a remote file into memory. Hopefully Yahoo doesn't mind my choice of URLs. Please note the strange hanging behavior at the "Close #inet" statement.

After doing a little testing, I found my hanging was the result of some ad-blocking software I have installed. When I disabled it the hanging ceased. It may be rare but you may want to keep this possibility in mind when using my code in your own programs. I can only suggest not closing #inet until after all your windows are closed at exit to avoid any possibility of a user's thinking your app is faulty.

Demo

 'CODE BEGINS 
 'Retrieving HTTPS Data Demo 
 'By Brent D. Thorn, 9/2005 
 
 remoteFile$ = "https://login.yahoo.com/" 
 
 CHUNK.SIZE = 512 ' enough bytes to hold a single line of HTML 
 
 Open "wininet" For DLL As #inet 
 
 'It would be a good idea to test for an Internet 
 'connection before proceding. This demo assumes 
 'you have one already. 
 
 ' Register a new user agent. Use proxy settings 
 ' set up in Internet Options Control Panel. 
 CallDLL #inet, "InternetOpenA", _ 
 "My User Agent" As Ptr, _ 
 0 As Long, _ 'INTERNET_OPEN_TYPE_PRECONFIG 
 _NULL As Long, _ 
 _NULL As Long, _ 
 0 As ULong, _ 
 hInet As ULong 
 If hInet = 0 Then [ErrExit] 
 
 ' Open a request to a remote file 
 CallDLL #inet, "InternetOpenUrlA", _ 
 hInet As ULong, _ 
 remoteFile$ As Ptr, _ 
 _NULL As Long, _ 
 0 As Long, _ 
 2147483648 As ULong, _ 'INTERNET_FLAG_RELOAD 
 _NULL As Long, _ 
 hFile As ULong 
 If hFile = 0 Then [ErrExit] 
 
 ' Start reading in the file by chunks. 
 Buffer$ = "" 
 chunk$ = Space$(CHUNK.SIZE)+Chr$(0) 
 Struct pdw, NumberOfBytesRead As ULong 
 Do 
 CallDLL #inet, "InternetReadFile", _ 
 hFile As ULong, _ 
 chunk$ As Ptr, _ 
 CHUNK.SIZE As ULong, _ 
 pdw As Struct, _ 
 ret As Long 
 
 If pdw.NumberOfBytesRead.struct = 0 Then Exit Do 
 
 Buffer$ = Buffer$ + Left$(chunk$, pdw.NumberOfBytesRead.struct) 
 Loop Until 0 
 
 Print Buffer$ 
 
 [ErrExit] 
 ' If you get an error, find GetLastError on MSDN. There 
 ' you will find a link to a list of error codes. 
 CallDLL #kernel32, "GetLastError", ret As ULong 
 If ret Then Print "Error ";ret 
 
 ' Free the handles we created and exit. 
 
 If hFile Then _ 
 CallDLL #inet, "InternetCloseHandle", _ 
 hFile As ULong, ret As Long 
 
 If hInet Then _ 
 CallDLL #inet, "InternetCloseHandle", _ 
 hInet As ULong, ret As Long 
 
 ' Strangely, the next line causes LB to hang for around 45 
 ' seconds on my computer, a 2.2 GHz running XP on dial-up. 
 Close #inet 
 
 End 
 'CODE ENDS

HTTPSData

Retrieving HTTPS Data

Demo