Bug#722497: apt-cacher-ng, apt: "Waiting for headers" without progress

[Eduard Bloch <edi@gmx.de>]

Hallo,
* Gabriele Stilli [Thu, Dec 12 2013, 10:24:37PM]:
> Package: apt-cacher-ng, apt
> Followup-For: Bug #722497
> 
> Hello,
> 
> I was experiencing this bug too. The client stopped at almost every file,
> waiting for 1 minute before starting the download. This didn't happen
> 100% of the times, though. This was up to version 0.7.19-1 of
> apt-cacher-ng. However, I just updated to 0.7.20-2 and the insane
> behaviour seems stopped and the updates work smoothly.

I don't think it's an apt-cacher-ng issue. I am watching this right now
on a laptop in my LAN. AFAICS (with wireshark) the network buffer
contains a well formated response and correct data in the queue (see
below). In the meantime, apt just hangs. No CPU activity at all for 30
seconds. Then it suddenly start working like nothing happened. It seems
to be reproducable for large files with resumed transfer (i.e. a 206
response) but that's just guessing.

For the program versions, see headers below.

Regards,
Eduard.

GET http://debian.netcologne.de/debian/pool/main/t/texlive-extra/texlive-fonts-extra_2013.20131219-1_all.deb HTTP/1.1
Host: debian.netcologne.de
Range: bytes=125659297-
If-Range: Fri, 20 Dec 2013 03:54:06 GMT
User-Agent: Debian APT-HTTP/1.3 (0.9.14.1)


HTTP/1.1 206 Partial Response
Content-Length: 35229121
Content-Range: bytes 125659297-160888417/160888418
Last-Modified: Fri, 20 Dec 2013 03:54:06 GMT
Content-Type: application/x-debian-package
Date: Sat Dec 21 15:14:56 2013
Server: Debian Apt-Cacher NG/0.7.24
X-Original-Source: http://ftp.ch.debian.org/debian/pool/main/t/texlive-extra/texlive-fonts-extra_2013.20131219-1_all.deb
Connection: Keep-Alive


.wYZTI.P...h.P...d..,vZ7.t(. .6.M..w.EE.n.%.y.(&.I.].......=.<..c......T.klC],P7.t..)5....;.N.V.c........O..1...|3Ni..FI[......%....!..O..k.4O.XS.fHg.:.;.f...K.N.3..>F.u...tg.........................FOf...+..y.u......
.{\..
`."..^....^`L].r..*afp.I.%f.BV.R..S><3u..8...}....NR6U1.<..
.....\a=..h6.3~.^...;|.q..#:..m........e.S|a=]L._.ZF...)/.h...0.R..Dk..e:C.
3... ..Tx1....w....._s+..5?|...UJ...?...'.l\A..G..,,_........W..=..H.a.....6.7D.]
^._..u..x..Z...Fa.u=..........}>.........ByMn.V...w. .............dKj..~i0BR.........A.$..n..
......].#...A....g...$57..]..._?....9 D+.Pe.k..._cZ(&fl..A...J.T...8...o..|.....m4U.[...Y....:.......h...|.5.