[Winpcap-users] While testing Gianlucas winpcap3.1 [prerelease]...

Gianluca Varenni gianluca.varenni at gmail.com
Mon Aug 1 21:11:15 GMT 2005

----- Original Message ----- 
From: "Marc Wetzel" <mwse at gmx.de>
To: <winpcap-users at winpcap.org>
Sent: Monday, August 01, 2005 12:43 PM
Subject: Re: [Winpcap-users] While testing Gianlucas winpcap3.1 

>>> But you might remember, that I had trouble using winpcap3.1.b4/WAN 
>>> devices with Delphi,
>>> because of some kind of COM initialization problems.
>>> It only worked if I do a CoInitializeEx(NIL, COINIT_MULTITHREADED) at 
>>> the very start of the code.
>> I know. This is one of the biggest headaches I had with WinPcap and 
>> NdisWan.
> It really really only works if I set it to COINIT_MULTITHREADED (not the 
> other way around).

Uhm, are you using Windows XP? If you are using the test dlls on my web 
pages (i.e. the latest build of the dlls, in practice) every attempt to 
open/list the wan adapters fails if COM has been initialized as 
COINIT_MULTITHREADED *on the same thread*.

> I use winpcap the following way... maybe there is a problem with my code?
> in the main process I fetch the devices (pcap_findalldevs) to look if 
> there is a WAN device.
> I such device is found I create a new thread and tell it to open the 
> specific device (I found out in the main process)
> inside the thread I use pcap_open to open this device...

That's ok.

> And I really have to initialize to COINIT_MULTITHREADED, get it going (in 
> beta4)
> In beta4 this had nothing to do with pcap_findalldevs(). This just ever 
> worked, regardless which
> ComThreadModel I choosed.
> The failure just happened on pcap_open()

In beta4, there were a series of bugs related to COM initialization (coupled 
to a series of bugs in the MS NetMon
COM component for which I've put some patches only after 3.1beta4, i.e. in 
the test DLLs on my web). These bugs caused a whole series of random 
effects: application crashes, Wan adapters not listed....

> I just tested it again (this time I tried to use multiple threads opening 
> NdisWanBh)
> And I found out, that my second call to pcap_open blocks until I close the 
> first winpcap handle.

Wait, wait. NdisWanBh should NOT be listed by WinPcap. If it's listed, it 
probably means that your WinPcap installation has something really weird. 
Are you sure it's NdisWanBh??

>>> #2:
>>> With the prerelease I have now other problems...
>>> If I use CoInitializeEx(NIL, COINIT_MULTITHREADED) I only see my 
>>> Ethernet-Device (using pcap_findalldevs).
>> This is correct. Basically, the NetMon COM component used by WinPcap to 
>> capture from PPP does NOT work in the MULTITHREADED threading model on 
>> Windows XP. As a consequence, that device is not listed *if* COM has 
>> already been initialized with that threading model.
> Is there any official documentation to this? I didnt found anything on 
> MSDN on this subject.

Nope. The MSDN documentation says almost *nothing* about the NetMon 
component (and all its issues/bugs).

>>> And if I comment the CoInitializeEx call out, I see all devices as 
>>> expected, but then it fails
>>> in the call to  pcap_open() with the error message "The system cannot 
>>> find the device" (just as before).
>> Uhm, are you sure? I've thoroughly tested it without any problem on my 
>> machine. Have you tried building a small C app (or one in the devpack) 
>> and see if it works?
>> If you don't initialize COM, winpcap initializes it with 
>> CoInitialize(NULL) before opening the GenericDialupAdapter.
> Delphi normally does not initialize COM. Only if needed (by using certain 
> libraries, I dont use).
>>> Just an addendum:
>>> #3:
>>> Using CoInitializeEx(NIL, COINIT_MULTITHREADED) in a Com-Application is 
>>> not possible,
>>> e.g. embedding the IE-ActiveX object will always fail. This means that 
>>> having an application which uses
>>> both the IE-ActiveX and winpcap (sniffing on WAN devices) is not 
>>> possible.
>>> Sniffing ethernet devices is not touched by this problem.
>>> Maybe I am completely wrong?
>>> Does anybody have a clue, or is this a bug?
>> I think that's what I explained before. On Windows XP the MS NetMon COM 
>> component does NOT support the MULTITHREADED threading model. At the 
>> moment I haven't found an easy solution to this issue.
> Gianluca,
> Is there maybe a newer release I can test against?

No. No further patches have been added to the dialup/NdisWan code. The test 
dlls on my web area are the latest ones from that point of view.

Have a nice day

> /Marc
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