mwolfe02 mwolfe02 - 3 months ago 18
HTTP Question

InternetOpenUrl hangs and fails on third and subsequent calls

This is some bizarre, but reproducible, behavior. I can call InternetOpenUrl exactly two times per URL and everything works as I would expect. If I call it again after that, it times out at exactly 60 seconds and does not return a handle to the web resource.

I created the following minimum code example to demonstrate the problem (this is an adaptation of the AllAPI Mentalis sample):

Private Const scUserAgent = "API-Guide test program"
Private Const INTERNET_OPEN_TYPE_DIRECT = 1
Private Const INTERNET_FLAG_RELOAD = &H80000000

Private Declare Function GetTickCount Lib "kernel32" () As Long
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" _
(ByRef hInet As Long) As Long
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

Sub TestInternetOpenUrl(sURL As String)
Dim hOpen As Long, hFile As Long, i As Integer, Start As Long
For i = 1 To 4
Start = GetTickCount
'Create an internet connection
hOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_DIRECT, _
vbNullString, vbNullString, 0)
'Open the url
hFile = InternetOpenUrl(hOpen, sURL, vbNullString, ByVal 0&, _
INTERNET_FLAG_RELOAD, ByVal 0&)
'clean up
InternetCloseHandle hFile
InternetCloseHandle hOpen
Debug.Print i; GetTickCount - Start; " ms elapsed ("; hFile; ")"
DoEvents
Next i
End Sub


Here are the results of two test runs:

TestInternetOpenUrl "http://www.yahoo.com"
1 390 ms elapsed ( 13369203 )
2 187 ms elapsed ( 13369217 )
3 60000 ms elapsed ( 0 )
4 60000 ms elapsed ( 0 )

TestInternetOpenUrl "http://www.duckduckgo.com"
1 203 ms elapsed ( 13369448 )
2 93 ms elapsed ( 13369460 )
3 60047 ms elapsed ( 0 )
4 60047 ms elapsed ( 0 )

Answer

I got this working on my end by changing how you are closing the handle. I was able to execute 30 iterations, and it worked well.

Here's the revised working code. In addition there appeared to be an issue with the API call to InternetCloseHandle (using ByRef instead of ByVal) which is corrected below:

Private Const scUserAgent = "API-Guide test program"
Private Const INTERNET_OPEN_TYPE_DIRECT = 1
Private Const INTERNET_FLAG_RELOAD = &H80000000

Private Declare Function GetTickCount Lib "kernel32" () As Long
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.dll" (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

Private Sub CloseHandle(ByRef hHandle As Long)
   If (hHandle <> 0) Then
        Call InternetCloseHandle(hHandle)
        hHandle = 0
    End If
End Sub

Sub TestInternetOpenUrl(sURL As String)
    Dim hOpen As Long, hFile As Long, i As Integer, Start As Long
    Dim ret As Boolean: ret = False

    For i = 1 To 4
        Start = GetTickCount
        'Create an internet connection
        hOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_DIRECT, _
                             vbNullString, vbNullString, 0)
        'Open the url
        hFile = InternetOpenUrl(hOpen, sURL, vbNullString, ByVal 0&, _
                                INTERNET_FLAG_RELOAD, ByVal 0&)

        CloseHandle (hFile)
        CloseHandle (hOpen)

        Debug.Print i; GetTickCount - Start; " ms elapsed ("; hFile; ")"
        DoEvents
    Next i
End Sub

I profiled the code quickly by running this 30 times by using yahoo. Below are the relevant descriptive stats. It's taking about half a second for each call.

Click here for Stats

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