Bug #115487 - automatic proxy discovery problems

Travers Carter tcarter at noggin.com.au
Mon May 31 11:46:12 BST 2010


I have been looking at bug 11547 regarding automatic proxy discovery (WPAD) 
not working [https://bugs.kde.org/show_bug.cgi?id=115487] 

I believe I've figured why it doesn't work in almost all cases, but one of the 
problems is that kpac_dhcp_helper needs to find the host's IP address in order 
to construct a DHCPINFORM query, presently it uses 
gethostname()+gethostbyname() to try and do this, but it would appear that 
this isn't really all that reliable in practise.

Dan Williams (the NetworkManager maintainer) suggested that kpac_dhcp_client 
should either look up the IP address of the default route's interface, or 
possibly query NetworkManager via D-Bus if it is running.

See https://bugzilla.gnome.org/show_bug.cgi?id=619931#c2

As far as I have been able to find there is no portable to look up the routing 
table across OSes.  Under linux it is possible to ask the kernel for the 
relevant entry for a given destination including a preferred source address 
via the netlink(7) interface.  Would a patch implementing optional support for 
this in kpac_dhcp_helper (preferably via libnl -
http://www.infradead.org/~tgr/libnl/) be considered an acceptable option and 
dependency? is there a better option? obviously it would only help on Linux 
and other OSes would still fall back on gethostname()+gethostbyname()

Travers Carter

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