I reported this originally in bug #1051481
"apt-cacher-ng: Illegal SRV name (underscore not valid except first character of label)"
in September 2023 and it was fixed in f9330e88 2024-07-17.

At that time it seems I forgot to also report it for auto-apt-proxy!

Got bitten by it again now whilst writing an extension that uses
systemd-resolved/resolvectl instead of avahi-browse to do the lookup.

Specifically, systemd-resolved correctly refuses to advertise the
illegal SRV name so look-ups were failing 'mysteriously'.

systemd-resolved[1424470]: /etc/systemd/dnssd/squid-deb-proxy.dnssd:3: Service type is invalid. Ignoring.

$ cat /etc/systemd/dnssd/squid-deb-proxy.dnssd
[Service]
Name=Squid deb proxy on %H systemd
Type=_apt_proxy._tcp
Port=8000

The definition is in RFC6335 section 5.1 "Service Name Syntax":

Valid service names are hereby normatively defined as follows:

   o  MUST be at least 1 character and no more than 15 characters long

   o  MUST contain only US-ASCII [ANSI.X3.4-1986] letters 'A' - 'Z' and
      'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or
      decimal 45)

   o  MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')

   o  MUST NOT begin or end with a hyphen

   o  hyphens MUST NOT be adjacent to other hyphens

We believe that the bug you reported is fixed in the latest version of
auto-apt-proxy, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1128058@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Antonio Terceiro <terceiro@debian.org> (supplier of updated auto-apt-proxy package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Tue, 18 Aug 2026 11:05:20 -0300
Source: auto-apt-proxy
Architecture: source
Version: 18
Distribution: unstable
Urgency: medium
Maintainer: Antonio Terceiro <terceiro@debian.org>
Changed-By: Antonio Terceiro <terceiro@debian.org>
Closes: 1120071 1124369 1128058 1142542
Changes:
 auto-apt-proxy (18) unstable; urgency=medium
 .
   [ Paride Legovini ]
   * Revert "autopkgtest: drop test for squid-deb-proxy"
 .
   [ Antonio Terceiro ]
   * Log a message when default gateway can't be looked up
   * hit(): prevent apt-helper call from recursing into auto-apt-proxy
     (Closes: #1142542)
   * detect_squid_deb_proxy: fix log message
   * Give higher precedence to squid-deb-proxy
   * auto-apt-proxy.conf: drop unused auto-apt-proxy::Debug "setting"
   * wait for network to be online
   * Add ability to lookup default gateway with networkctl
   * Use a unique output directory per run
   * avahi: iterate over all address broadcast as potential proxies
   * avahi: handle unrouteable addresss (Closes: #1124369)
 .
   [ Tj ]
   * use legal SRV name (Closes: #1128058)
   * Rename AUTO_APT_PROXY_AVAHI_NAME to AUTO_APT_PROXY_MDNS_NAME
   * Add systemd-resolved mDNS support
 .
   [ Kirt Runolfson ]
   * Restore DNS hostname resolution for apt-proxy (Closes: #1120071)
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