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debbisect: handle non-absolute Location headers

Mike Gerow requested to merge gerow-guest/devscripts:debbisect-headers into main

snapshot.d.o sometimes returns location headers that aren't absolute:

$ cat ~/example.txt
$ curl --head http://snapshot.debian.org/archive/debian/20240525T055828Z/
HTTP/1.1 302 FOUND
Date: Tue, 27 Aug 2024 22:41:41 GMT
Server: Apache
X-Content-Type-Options: nosniff
X-Frame-Options: sameorigin
Referrer-Policy: no-referrer
X-Xss-Protection: 1
Permissions-Policy: interest-cohort=()
Content-Length: 253
Location: /archive/debian/20240525T031625Z/
Cache-Control: max-age=600, public
Expires: Tue, 27 Aug 2024 22:51:41 GMT
X-Clacks-Overhead: GNU Terry Pratchett
Content-Type: text/html; charset=utf-8
X-Varnish: 18921807 18775977
Age: 453
Via: 1.1 varnish (Varnish/7.1)
connection: close

$ curl --head http://snapshot.debian.org/archive/debian/20240525T055828Z/
HTTP/1.1 302 FOUND
Date: Tue, 27 Aug 2024 22:48:52 GMT
Server: Apache
X-Content-Type-Options: nosniff
X-Frame-Options: sameorigin
Referrer-Policy: no-referrer
X-Xss-Protection: 1
Permissions-Policy: interest-cohort=()
Content-Length: 273
Location: http://snapshot.debian.org/archive/debian/20240525T031625Z/
Cache-Control: max-age=600, public
Expires: Tue, 27 Aug 2024 22:58:52 GMT
X-Clacks-Overhead: GNU Terry Pratchett
Content-Type: text/html; charset=utf-8
X-Varnish: 82071043 88047937
Age: 12
Via: 1.1 varnish (Varnish/6.5)
connection: close

This can result in debbisect failing early with a somewhat unclear assertion failure:

Traceback (most recent call last):
  File "/usr/bin/debbisect", line 1229, in <module>
    main()
  File "/usr/bin/debbisect", line 1216, in main
    res = bisect(good, bad, staticargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/bin/debbisect", line 549, in bisect
    newts = sanitize_timestamp(good + diff / 2)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/bin/debbisect", line 124, in sanitize_timestamp
    assert location.startswith(prefix)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError

This fixes the issue by handling both kinds of Location headers.

Signed-off-by: Mike Gerow gerow@mgerow.com

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