Win32::API help

Zukoff has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Win32::API help by pKai (Priest) on Nov 06, 2006 at 17:29 UTC
Your code is O. K., no additional tutorial needed! The code runs fine for me on `This is perl, v5.8.6 built for MSWin32-x86-multi-thread (with 3 registered patches, see perl -V for more detail) Copyright 1987-2004, Larry Wall Binary build 811 provided by ActiveState Corp. http://www.ActiveState. +com` [download] but fails with an error popup on `This is perl, v5.8.8 built for MSWin32-x86-multi-thread (with 21 registered patches, see perl -V for more detail) Copyright 1987-2006, Larry Wall Binary build 816 [255195] provided by ActiveState http://www.ActiveSta +te.com` [download] On both installations Win32::API identifies as $VERSION==0.41	[reply] [d/l] [select]
Re: Win32::API help by ikegami (Patriarch) on Nov 06, 2006 at 17:44 UTC
<c>my $dwReserved = pack('d',8); I'm a bit rusty, but isn't the packing handled for you?	[reply]
Re^2: Win32::API help by pKai (Priest) on Nov 06, 2006 at 18:04 UTC
Trial and error says the `pack` is needed. In my "working" installation a plain digit 8 results in no download at all, while coded as in the OP the file loads fine.	[reply] [d/l]
Re^3: Win32::API help by BrowserUk (Patriarch) on Nov 06, 2006 at 18:38 UTC
Using `pack 'd', ...` to pack a value defined as a `DWORD` is very suspect. Does using `pack 'V', ...` work equally well? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re: Win32::API help by ikegami (Patriarch) on Nov 06, 2006 at 23:35 UTC
That pack is definitely wrong. `$dwReserved` should be simply `8`. The signature is completely wrong `HRESULT -> N or I, not sure URLDownloadToFile( LPUNKNOWN pCaller, -> P LPCTSTR szURL, -> P LPCTSTR szFileName, -> P DWORD dwReserved, -> N LPBINDSTATUSCALLBACK lpfnCB -> P );` [download] `Win32::API->Import( 'urlmon', 'URLDownloadToFile', 'PPPNP', 'N', ); my $pCaller = 0; my $szURL = 'http://somedomain.com/pic.jpg'; my $szFileName = 'c:\1img.jpg'; my $dwReserved = 8; # Download from offline cache my $lpfnCB = 0; my $res = URLDownloadToFile( $pCaller, $szURL, $szFileName, $dwReserved, $lpfnCB, ) or die Win32::FormatMessage(Win32::GetLastError);` [download] If that doesn't work, also make sure the DLL function was compiled using the `__stdcall` (aka `WINAPI`) calling convention. Win32::API can't call it properly if it wasn't. `HRESULT WINAPI URLDownloadToFile( LPUNKNOWN pCaller, LPCTSTR szURL, LPCTSTR szFileName, DWORD dwReserved, LPBINDSTATUSCALLBACK lpfnCB );` [download] Update: Replaced `undef` with `$pCaller` and `$lpfnCB`.	[reply] [d/l] [select]
Re^2: Win32::API help by BrowserUk (Patriarch) on Nov 07, 2006 at 02:06 UTC
That won't work. The result is a trap (protection violation), because Win32::API doesn't know how to translate undef into a C-type `null`. This is 5.8.8, but you get the same result from 5.8.6: C:\test>\AS817\perl\bin\perl5.8.8.exe -Mlib=\perl\site\lib -MWin32::A +PI -mstrict -w Win32::API->Import( 'urlmon', 'URLDownloadToFile', 'PPPNP', 'N', ); my $pCaller = 0; my $szURL = 'http://somedomain.com/pic.jpg'; my $szFileName = 'c:\1img.jpg'; my $dwReserved = 8; # Download from offline cache my $lpfnCB = 0; my $res = URLDownloadToFile( undef, $szURL, $szFileName, $dwReserved, undef, ) or die Win32::FormatMessage(Win32::GetLastError); ^Z Use of uninitialized value in subroutine entry at (eval 2) line 2, <DA +TA> line 164. Use of uninitialized value in subroutine entry at (eval 2) line 2, <DA +TA> line 164. [download] This way doesn't result in a trap, though I've failed to make it download any file. Possibly because 0x8 means fetch it from the cache, but as I don't use IE, it won't find it there. `C:\test>perl -Mlib=\perl\site\lib -MWin32::API -mstrict -w Win32::API->Import( 'urlmon', 'URLDownloadToFile', 'PPPNP', 'N', ); printf "%08x\n", URLDownloadToFile( 0, 'http://images.google.com/intl/en/images/images_res.gif', 'google.gif', 8, 0, ) or die $^E; ^Z 800c0005` [download] The return code `0x800c005` apparently means file or server not found. `The following codes are other common error codes: - 80100003. During install, one or more files are missing from downlo +ad folder. - 800bxxxx. Anything starting with 800b is a trust failure (for examp +le, 800b010b - trust check failed). - 800Cxxxx. Anything starting with 800C is a Urlmon failure (for exam +ple, 800C0005 - file or server not found, 800C000B - connection timeout). - 80040004. User canceled.` [download] Which doesn't make a great deal of sense as my browser can fetch the gif above, but at least the call has successfully been made without trapping. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^3: Win32::API help by ikegami (Patriarch) on Nov 07, 2006 at 02:08 UTC
oops, I meant to put zero (well, `$pCaller` and `$lpfnCB`, which I set to zero). Thanks.	[reply] [d/l] [select]
Re^2: Win32::API help by pKai (Priest) on Nov 07, 2006 at 11:53 UTC
The signature is completely wrong Well, not completely I would say. Changing the D -> N for the `dwReserved` (nice catch), does the trick for me on the formerly crashing (as in system/OS popup) 5.8.8. As for the 2 pointers (1st and 5th argument). Using P is O. K. of course, but since these have to be given as Null anyway, going whith longs (N) is fine too, with the additional convenience to choose between either `0` or `undef` as a valid initialization value. It's a bit confusing that all 5.8.6 installations I tried were far more forgiving and ran the OP code successfully for me.	[reply] [d/l] [select]
Re: Win32::API help by pKai (Priest) on Nov 07, 2006 at 12:01 UTC
One final thing to notice (since the immediate problem (crash) seems to be resolved with the above suggestions): Your error checking logic has to be inverted. Otherwise you end up dying with "Command completed successfully" after a successful download. ;-)	[reply]