Visual Basic Programming Code Examples

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Read an internet web page with API calls



Read an internet web page with API calls

The following routine uses API calls to read/download an internet file. A routine demonstrating how to use this code can be found at the bottom of this post.

Option Explicit
Private Declare Function InternetOpen Lib "wininet" Alias "InternetOpenA" (ByVal sAgent As String, ByVal lAccessType As Long, ByVal sProxyName As String, ByVal sProxyBypass As String, ByVal lFlags As Long) As Long
Private Declare Function InternetCloseHandle Lib "wininet" (ByVal hInet As Long) As Integer
Private Declare Function InternetReadFile Lib "wininet" (ByVal hFile As Long, ByVal sBuffer As String, ByVal lNumBytesToRead As Long, lNumberOfBytesRead As Long) As Integer
Private Declare Function InternetOpenUrl Lib "wininet" Alias "InternetOpenUrlA" (ByVal hInternetSession As Long, ByVal lpszUrl As String, ByVal lpszHeaders As String, ByVal dwHeadersLength As Long, ByVal dwFlags As Long, ByVal dwContext As Long) As Long


'Purpose     :  Retreview text from a web site
'Inputs      :  sURL                The URL and file name to extract the text from
'               [lBufferSize]       The number of characters to extract.
'                                   If value is -1 the reads the whole page.
'Outputs     :  The text found on the web site
'Notes       :  NOT SUITABLE FOR ACCESSING THE INTERNET THROUGH A PROXY SERVER


Function InternetGetText(sURL As String, Optional lBufferSize As Long = -1) As String
    Dim lhOpen As Long, lhFile As Long, sBuffer As String, lRet As Long
    Const clBufferIncrement As Long = 2000
    Const scUserAgent = "VBUsers"
    Const INTERNET_OPEN_TYPE_PRECONFIG = 0, INTERNET_FLAG_EXISTING_CONNECT = &H20000000
    Const INTERNET_OPEN_TYPE_DIRECT = 1, INTERNET_OPEN_TYPE_PROXY = 3
    Const INTERNET_FLAG_RELOAD = &H80000000
    
    If lBufferSize = -1 Then
        'Create an arbitary buffer to read the whole file in parts
        sBuffer = String$(clBufferIncrement, Chr$(0))
    Else
        'Create a specified buffer size
        sBuffer = String$(lBufferSize, Chr$(0))
    End If
    'Create an internet connection
    lhOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_DIRECT, vbNullString, vbNullString, 0)
    'Open the url
    lhFile = InternetOpenUrl(lhOpen, sURL, vbNullString, ByVal 0&, INTERNET_FLAG_RELOAD, ByVal 0&)
    If lhFile = 0 Then
        'Try using proxy
        InternetCloseHandle lhFile
        InternetCloseHandle lhOpen
        'Create an internet connection
        lhOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_PRECONFIG, vbNullString, vbNullString, 0)
        'Open the url
        lhFile = InternetOpenUrl(lhOpen, sURL, vbNullString, ByVal 0&, INTERNET_FLAG_EXISTING_CONNECT, ByVal 0&)
    End If
    If lBufferSize = -1 And lhFile <> 0 Then
        'Read the whole page
        Do
            InternetReadFile lhFile, sBuffer, clBufferIncrement, lRet
            InternetGetText = InternetGetText & Left$(sBuffer, lRet)
        Loop While lRet = clBufferIncrement
    Else
        'Read the specified number of bytes from the file
        InternetReadFile lhFile, sBuffer, lBufferSize, lRet
        InternetGetText = InternetGetText & Left$(sBuffer, lRet)
    End If
    'clean up
    InternetCloseHandle lhFile
    InternetCloseHandle lhOpen
End Function

'Demonstration routine
'(Note the Debug window will only show the last 255 lines)
Sub Test()
    Dim sInterPage As String
    sInterPage = InternetGetText("http://example")
    Debug.Print sInterPage
End Sub