Disable DNS in chutney by default, and add an option to enable it

Due to #21900 (moved), we need to explicitly specify ServerDNSResolvConfFile /dev/null for chutney to work on macOS when the network is unavailable.

We should also set ServerDNSDetectHijacking 0.

This should be the default, because:

• users who run chutney might not want it using DNS in a detectable pattern, and
• it makes chutney more reliable, because it no longer depends on a working DNS.

Some users will want chutney to be able to use hostnames, so we should add a tools/test-network.sh option and environmental variable to re-enable the default ServerDNSResolvConfFile setting (or, even better, use a custom ServerDNSResolvConfFile).

There seems to be no reason to turn on ServerDNSDetectHijacking: some users might be using chutney with internal DNS names.

added component::core tor/chutney owner::teor parent::19573 points::0.5 priority::medium resolution::fixed severity::normal status::closed type::defect labels

#19573 (moved) will use this option.

Trac:
Parent: N/A to #19573 (moved)

This is fixed in da1781e in my branch no-zombies: https://github.com/teor2345/chutney/commits/no-zombies

Trac:
Status: new to needs_review

That commit seems plausible, though I do wonder why we're making DNS broken-by-default. Would it be better instead to have DNS work by default for chutney started from a command line, and have it disabled specifically when running tests that won't use it? (I'll believe either answer)

Replying to nickm:

That commit seems plausible, though I do wonder why we're making DNS broken-by-default. Would it be better instead to have DNS work by default for chutney started from a command line, and have it disabled specifically when running tests that won't use it? (I'll believe either answer)

Due to Tor bug #21900 (moved), we have two choices:

• make chutney work offline by default (but break DNS), or
• allow DNS in chutney by default (but break offline use).

I don't mind which default we choose, as long as there is a way to flip it. So I emailed tor-dev to see what other chutney users want.

Trac:
Status: needs_review to needs_information

This is now in no-dns-rebased

I want DNS to work by default in chutney, and I want offline use to work even on macOS (and other OSs that have no resolv.conf).

I think a good way to fix this is to do the thing that will work once #21900 (moved) is fixed in tor.

So we should make working DNS the default, and have an --offline option. (Or, even better, we could check if the ServerDNSResolvConfFile exists, and if it doesn't, we should apply a workaround, which can be switched off.)

Trac:
Status: needs_information to needs_revision

Here's a design for this:

• If the default ServerDNSResolvConfFile is missing, or is a symlink with a missing target (thanks, Apple!), chutney applies a workaround ServerDNSResolvConfFile /dev/null
• An environmental variable can be used to set ServerDNSResolvConfFile
  • This can be used to implement --offline: CHUTNEY_DNS_CONF=/dev/null
  • This can be used to implement --dns-conf=X: CHUTNEY_DNS_CONF=X
• An environmental variable can be used to not set ServerDNSResolvConfFile
  • This can be used to implement --dns-conf-default: CHUTNEY_DNS_CONF=""

To fix the crash on SETCONF in #21900 (moved), the user needs to supply a DNS conf with at least one nameserver.

To provide a conf that simultaneously:

• works offline: CHUTNEY_DNS_CONF=/path/to/empty/or/working/conf
• and doesn't crash on SETCONF: CHUTNEY_DNS_CONF=/path/to/conf/with/a/dns/server

The user must supply a local DNS server that gives the right answers to tor (#19573 (moved)). Or we can fix #21900 (moved), and just say /dev/null. (We should document this in the chutney README.)

In #21989 (moved), arma suggests chutney uses ServerDNSDetectHijacking 0. That might solve some of these issues, but it certainly won't solve the eventdns breakage.

Rebased onto master as no-dns-rebased-v2. Still need to add ServerDNSDetectHijacking 0 and implement --offline/--dns-auto/--dns-conf=path.

Implemented and merged to master as c889534.

Replying to teor:

Here's a design for this:

• If the default ServerDNSResolvConfFile is missing, or is a symlink with a missing target (thanks, Apple!), chutney applies a workaround ServerDNSResolvConfFile /dev/null
• An environmental variable can be used to set ServerDNSResolvConfFile
  • This can be used to implement --offline: CHUTNEY_DNS_CONF=/dev/null
  • This can be used to implement --dns-conf=X: CHUTNEY_DNS_CONF=X
• An environmental variable can be used to not set ServerDNSResolvConfFile
  • This can be used to implement --dns-conf-default: CHUTNEY_DNS_CONF=""

This is implemented.

To fix the crash on SETCONF in #21900 (moved), the user needs to supply a DNS conf with at least one nameserver.

This is documented, and a local resolv.conf is provided by chutney.

To provide a conf that simultaneously:

• works offline: CHUTNEY_DNS_CONF=/path/to/empty/or/working/conf
• and doesn't crash on SETCONF: CHUTNEY_DNS_CONF=/path/to/conf/with/a/dns/server

The user must supply a local DNS server that gives the right answers to tor (#19573 (moved)). Or we can fix #21900 (moved), and just say /dev/null. (We should document this in the chutney README.)

This is documented, but providing the right DNS answers is out of scope for chutney.

Trac:
Status: needs_revision to closed
Resolution: N/A to fixed

closed

changed time estimate to 4h

mentioned in issue #21989 (moved)

mentioned in issue #22133 (moved)

mentioned in issue #22152 (moved)

moved to tpo/core/chutney#21903 (closed)

mentioned in issue tpo/core/chutney#22133 (closed)