feat: add support for instance banlist

[bentasker]

There are a lot of potentially undesirable instances in the fediverse, including some known for

• carrying content that's illegal
• running harassment campaigns against those who catch their attention

Users probably aren't going to want to show up in the logs of these instances or receive copies of their content.

This PR allows the user to specify a list of instances which FF should never connect to

find_posts.py \
--instance-blocklist "bad.example.com, verybad.example.com , badness.example"  \
--home-timeline-length 10

The list can also be exposed via env var instead:

export FF_INSTANCE_BLOCKLIST="bad.example.com,verybad.example.com,badness.example"

(it doesn't matter whether there are spaces around commas, excess whitespace will be stripped)

Or in the config file

{
    "instance-blocklist":"jsond-list,foo.bar"
    "home-timeline-length": 200,
}

When a URL matches the blocklist, the following exception will be thrown/logged

Connecting to {parsed_uri.netloc} is prohibited by the configured blocklist

[bentasker]

Note: although not implemented here you could probably expand this to support fetching a centralised blocklist and merging that in.

That would open up two possibilities:

• You could host an in-repo list of instances that have asked you to opt them out
• Admin co-operatives could build and host a shared list of blocked instances (much like already happens with fediblocks)

(not that either are without their own issues)

[nanos]

This is pretty cool. Thanks!

I’ll merge it after my holiday.

[bentasker]

No hurry, enjoy your break :)