[Bug-wget] Unexpected wget -N behaviour for 1.17 onwards?

[Lawrence Wade]

Hi Everyone,

This might be a corroboration of this
http://lists.gnu.org/archive/html/bug-wget/2018-10/msg00049.html
and this
https://bugs.launchpad.net/ubuntu/+source/wget/+bug/1715481

I use wget to backup my cellphone running Palapa Web Server, and it
has worked well for me for years. Since upgrading to OpenSUSE Leap 15,
I have been having corrupted files.

My method is
$ wget -r -N 192.168.2.100:8080
and if the connection is interrupted for any reason, the next time I
call wget it would complete any incomplete files. And since Leap 15, I
have been getting gradually corrupted backups. I was tearing my hair
out looking at wgetrc and other things.

With one long file that I knew was incomplete, I got a Not Modified -
omitting download, even though I knew the file sizes were different
between the server and wget's copy - though the wget man page
explicitly states that if the file sizes do not match, -N will trigger
a download.

I tried on OpenSUSE 42.3 (wget 1.14) and the incomplete file triggered
a download, even though wgetrc was identical.

Again, on Leap 15, I compiled 1.20.1 (latest), 1.17.1, and then
finally with 1.16.3 the behaviour went back to what I expected (and I
got my corrupted phone backups fixed).

Was a bug possibly introduced in 1.17 with the support for --if-modified-since?

Version shipping with OpenSUSE Leap 15:
GNU Wget 1.19.5 built on linux-gnu.
+cares +digest +gpgme +https +ipv6 +iri +large-file +metalink +nls
+ntlm +opie +psl +ssl/openssl

Last version I tried where "wget -r -N" works as expected:
GNU Wget 1.16.3 built on linux-gnu.
+digest +https +ipv6 -iri +large-file +nls +ntlm +opie +psl +ssl/gnutls

I'm open to the possibility that there may be something else causing
this bug, I have not found many mentions of it, but then again it is
subtle. You get pretty confident when you just let wget do its thing,
so there may be a lot of incomplete files out there... :)

Thanks so much for your help. I can provide any other info that would
be helpful.

Lawrence Wade
Ottawa, Canada