no_proxy=::1 is not honored by curl in Bionic and earlier versions

[Balint Reczey]

Bionic:

env no_proxy=::1 http_proxy=http://foo:8080 curl -v http://[::1]:80/bar.html
* Could not resolve proxy: foo
* Closing connection 0
curl: (5) Could not resolve proxy: foo

Focal:

$ env no_proxy=::1 http_proxy=http://foo:8080 curl -v http://[::1]:80/bar.html
* Uses proxy env variable no_proxy == '::1'
* Trying ::1:80...
* TCP_NODELAY set
* Immediate connect fail for ::1: Network is unreachable
* Closing connection 0
curl: (7) Couldn't connect to server

[Balint Reczey (rbalint)]

Upstream bug:
https://github.com/curl/curl/issues/2353

[Balint Reczey (rbalint)]

Recently the autopkgtest infrastructure configuration has been changed to add ::1 to no_proxy. This works on Focal and up, but breaks unknown number of tests in Bionic and earlier releases.

commit f3679e7609b2f03d59aca28fe7329e4228350200
Author: Steve Langasek <email address hidden>
Date: Fri Dec 4 12:00:02 2020 -0800

    Include ipv6 localhost in the list of addresses not to use the proxy for.

    This fixes schleuder autopkgtest failure on armhf, which tries to connect
    to [::1]:4443 and fails because it's routed to the proxy.

    This failure does not affect the VM-based autopkgtest runners because
    containers also have some strangeness regarding binding to ::1 being treated
    as bindv6only=1, and schleuder's test only requires that ipv4 *or* ipv6
    succeeds; but the change is appropriate across all architectures.

 lxc-slave-admin/setup-adt-lxc.commands | 2 +-
 tools/armhf-lxd-slave.userdata | 2 +-
 worker-config-production/worker-bos01-arm64.conf | 2 +-
 worker-config-production/worker-bos01-ppc64el.conf | 2 +-
 worker-config-production/worker-bos01-s390x.conf | 2 +-
 worker-config-production/worker-bos01.conf | 2 +-
 worker-config-production/worker-bos02-arm64.conf | 2 +-
 worker-config-production/worker-bos02-ppc64el.conf | 2 +-
 worker-config-production/worker-bos02-s390x.conf | 2 +-
 worker-config-production/worker-canonistack.conf | 2 +-
 worker-config-production/worker-lxd.conf | 2 +-
 worker-config-production/worker.conf | 2 +-
 12 files changed, 12 insertions(+), 12 deletions(-)

[Steve Langasek (vorlon)]

While there is a curl bug here that older versions do not honor ipv6 addresses in no_proxy, there's no information here that explains why you think this caused a *regression* in autopkgtests. Tests attempting to use the http proxy to connect to ::1 will fail with or without adding ::1 to no_proxy. So how does having it listed in no_proxy cause a regression?

[Balint Reczey (rbalint)]

Maybe it was just a coincidence, but those regressions disappeared immediately when reverting the ::1 addition:

LP: #1907959
https://autopkgtest.ubuntu.com/packages/s/samtools/bionic/amd64

LP: #1907955
https://autopkgtest.ubuntu.com/packages/r/ruby2.5/bionic/amd64

Since you are around would you be so kind and address @laney's more than wone yeare old comments in the following MR so the cowboy deployed can be dropped and does not make extra work for @laney to land fixes?
https://code.launchpad.net/~ubuntu-release/autopkgtest-cloud/+git/autopkgtest-cloud/+merge/376587