On Sun, Apr 18, 2004 at 02:43:05PM -0500, Alan S. Jones wrote:
> My impression from reading the WinPcap list was that programs should not
> need to make any changes to work between WinPcap 3.0 and 3.1.
Applications using the raw packet-dll API *do* have to change:
http://winpcap.polito.it/misc/changelog.htm
"PacketGetAdapterNames() now returns the names of the adapter in ASCII
rather than in Unicode. Since the main purpose of
PacketGetAdapterNames() is feeding data to pcap_findalldevs() and since
pcap_findalldevs() needs ASCII names, the new PacketGetAdapterNames()
avoids a conversion in wpcap.dll and uniforms the data format with the
one of Windows 9x (this potentially simplifies the code of the
applications). As a consequence of this modification, old applications
won't work properly with the new PacketGetAdapteNames() on
NT/2k/XP/2k3."
That difference probably was directly exposed by "pcap_lookupdev()", so
that it returned names in ASCII as well.
> Is this a bug in WinPcap?
I'm not sure I'd call it one. It'd depend on how the WinPcap developers
said you *should* enumerate devices; if they recommended doing it, for
example, the way Ethereal does - it fetches the names with
"pcap_lookupdev()", and checks whether the first 2 bytes of the returned
string, treated as a 16-bit Unicode character, is < 256 or not, and:
if it is, the strings are assumed to be Unicode strings;
if it isn't, the strings are assumed to be ASCII strings
and did *not* recommend assuming that on Windows OT (95, 98, Me) they're
ASCII and on Windows NT (NT 4.0, W2K, WXP, W2K3) they're Unicode, then
it's probably not a bug, as Ethereal-style code should continue to work
with 3.1.
However, note that Ethereal also does something else:
if libpcap/WinPcap has "pcap_findalldevs()", it uses that rather
than SIOCGIFLIST on UN*X or "pcap_lookupdev()" on Windows;
and I'd recommend that other applications do so as well. (Yes, Ethereal
*does* make that determination at run time on Windows - it does a
"g_module_open()" on "wpcap" (which calls "LoadLibrary()" on
"wpcap.dll") and:
if that fails, doesn't support packet capture;
if that succeeds, looks up various symbols in WinPcap and calls
the relevant routines through the pointers it gets, if they're
present. That was originally done so we could build one version of
Ethereal rather than a with-WinPcap and a without-WinPcap version, so it
adapts to whatever you have installed, but it also means we can use APIs
present in some but not all versions of WinPcap, if present, and not use
them if not present. I think that's a fairly common technique in
Windowsland; I used it on Linux in Ethereal for a while, thanks to some
annoying SNMP library problems.)
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