Can a libtorrent programme know whether a torrent's webseed was used?

[cgdae]

Apologies if this is a naive question but i'm just starting to use libtorrent and haven't been able to figure it out from the documentation.

I'd like to know whether my torrent's bep-0019 webseed was used when getting the data, or whether libtorrent has used bittorrent peers. I've enabled all alerts (except for the very verbose dht_operation), but they don't seem to show the information i'm looking for.

The torrent is for a file called test.c, and the alerts i get are:

Alert: torrent_added: test.c added
Alert: add_torrent: added torrent: test.c
Alert: state_changed: test.c: state changed to: checking
Alert: external_ip: external IP received: ##.##.##.##
Alert: torrent_resumed: test.c resumed
Alert: file_completed: test.c: file 0 finished downloading
Alert: state_changed: test.c: state changed to: finished
Alert: torrent_finished: test.c torrent finished downloading
Alert: state_changed: test.c: state changed to: seeding

Is there information available saying which pieces (if any) have been obtained from a torrent's webseed?

Thanks in advance for any help.