Are network.dns.disablePrefetch/network.dns.disablePrefetchFromHTTPS master switches of dom.prefetch_dns_for_anchor_http_document/dom.prefetch_dns_for_anchor_https_document?

[Jee-Hex]

@mik0l commented in #1862 (comment)

network.dns.* main switches, they already cover dom.prefetch_dns_for_anchor_http(s)_document

So I used the following test case (inspired by bug 1596935 comment 28):

1. Start HTTP logging.
2. Open a new tab and open the Network Monitor beforehand.
3. Visit https://en.wikipedia.org/wiki/Main_Page. AFAICT the page do not request any resources from meta.wikimedia.org yet contains <link rel="dns-prefetch" href="//meta.wikimedia.org" /> in its source, so that's what we will be watching out for.
4. Stop HTTP logging.
5. Open about:networking#dns to confirm any resolved hostnames.
6. Check the Network Monitor to see if any resources were requested from these hostnames.
7. Check the HTTP logs for entries like D/nsHostResolver Resolving Host [meta.wikimedia.org]<^partitionKey=%28https%2Cwikipedia%2Corg%29> type 0. [this=blahblahblah]

Using a vanilla 127.0.2 (i.e. dom.prefetch_dns_for_anchor_https_document= false, network.dns.disablePrefetchFromHTTPS= false):

 I see DNS lookups for `meta.wikimedia.org` (Expected Behavior).

with dom.prefetch_dns_for_anchor_https_document= true, network.dns.disablePrefetchFromHTTPS= false:

In addition to `meta.wikimedia.org`, I also see DNS lookups for other Wikipedia editions (e.g. `ja.wikipedia.org`) (Expected Behavior).

with dom.prefetch_dns_for_anchor_https_document= true, network.dns.disablePrefetchFromHTTPS= true:

No DNS lookups for `meta.wikimedia.org` or other Wikipedia editions (Expected if `network.dns.disablePrefetchFromHTTPS` is the master switch for `dom.prefetch_dns_for_anchor_https_document`).

with dom.prefetch_dns_for_anchor_http_document= true, dom.prefetch_dns_for_anchor_https_document= true, network.dns.disablePrefetch= true, and network.dns.disablePrefetchFromHTTPS= false:

No DNS lookups for `meta.wikimedia.org` or other Wikipedia editions!

with dom.prefetch_dns_for_anchor_http_document= false, dom.prefetch_dns_for_anchor_https_document= true, network.dns.disablePrefetch= false, and network.dns.disablePrefetchFromHTTPS= false:

DNS lookups for `meta.wikimedia.org` and other Wikipedia editions (Expected Behavior).

with dom.prefetch_dns_for_anchor_http_document= false, dom.prefetch_dns_for_anchor_https_document= true, network.dns.disablePrefetch= true, and network.dns.disablePrefetchFromHTTPS= false:

No DNS lookups for `meta.wikimedia.org` or other Wikipedia editions!

with dom.prefetch_dns_for_anchor_http_document= false, dom.prefetch_dns_for_anchor_https_document= false, network.dns.disablePrefetch= true, and network.dns.disablePrefetchFromHTTPS= true:

No DNS lookups for `meta.wikimedia.org` or other Wikipedia editions (Expected Behavior).

Am I missing something or is there a bug somewhere?

[Jee-Hex]

So I ran the same test on 126.0.1.

network.dns.disablePrefetch=false, network.dns.disablePrefetchfromHTTPS=true (default):

no DNS lookups for meta.wikimedia.org

network.dns.disablePrefetch=true, network.dns.disablePrefetchfromHTTPS=false:

no DNS lookups for meta.wikimedia.org

network.dns.disablePrefetch=false, network.dns.disablePrefetchfromHTTPS=false:

DNS lookups for meta.wikimedia.org

Am I missing something

The answer is yes, because network.dns.disablePrefetch is also the master switch of network.dns.disablePrefetchfromHTTPS. I guess I always thought it meant something like network.dns.disablePrefetchfromHTTP.

In short

1. network.dns.disablePrefetchfromHTTPS is the master switch of dom.prefetch_dns_for_anchor_https_document,
2. network.dns.disablePrefetch is (presumably) the master switch of dom.prefetch_dns_for_anchor_http_document,
3. network.dns.disablePrefetch is also the master switch of network.dns.disablePrefetchfromHTTPS.

Sorry again for all the noise.

[Thorin-Oakenpants]

okie dokie - thanks for testing