FediBlockHole

A tool for keeping a Mastodon instance blocklist synchronised with remote lists.

Features

• Read block lists from multiple remote instances
• Read block lists from multiple URLs, including local files
• Write a unified block list to a local CSV file
• Push unified blocklist updates to multiple remote instances
• Control import and export fields

Installing

Instance admins who want to use this tool will need to add an Application at https://<instance-domain>/settings/applications/ so they can authorize the tool to create and update domain blocks with an OAuth token.

Reading remote instance blocklists

If a remote instance makes its domain blocks public, you don't need a token to read them.

If a remote instance only shows its domain blocks to local accounts you'll need to have a token with read:blocks authorization set up. If you have an account on that instance, you can get a token by setting up a new Application at https://<instance-domain>/settings/applications/.

To read admin blocks from a remote instance, you'll need to ask the instance admin to add a new Application at https://<instance-domain>/settings/applications/ and then tell you the access token.

The application needs the admin:read:domain_blocks OAuth scope, but unfortunately this scope isn't available in the current application screen (v4.0.2 of Mastodon at time of writing). There is a way to do it with scopes, but it's really dangerous, so I'm not going to tell you what it is here.

A better way is to ask the instance admin to connect to the PostgreSQL database and add the scope there, like this:

UPDATE oauth_access_tokens
    SET scopes='admin:read:domain_blocks'
    WHERE token='<your_app_token>';

When that's done, FediBlockHole should be able to use its token to authorise adding or updating domain blocks via the API.

Writing instance blocklists

To write domain blocks into an instance requires both the admin:read:domain_blocks and admin:write:domain_blocks OAuth scopes. The read scope is used to read the current list of domain blocks so we update ones that already exist, rather than trying to add all new ones and clutter up the instance.

Again, there's no way to do this (yet) on the application admin screen so we need to ask our destination admins to update the application permissions similar to reading domain blocks:

UPDATE oauth_access_tokens
    SET scopes='admin:read:domain_blocks admin:write:domain_blocks'
    WHERE token='<your_app_token>';

When that's done, FediBlockHole should be able to use its token to authorise adding or updating domain blocks via the API.

Configuring

Once you have your applications and tokens and scopes set up, create a configuration file for FediBlockHole to use. You can put it anywhere and use the -c <configfile> commandline parameter to tell FediBlockHole where it is.

Or you can use the default location of /etc/default/fediblockhole.conf.toml.

As the filename suggests, FediBlockHole uses TOML syntax.

There are 3 key sections:

1. blocklist_urls_sources: A list of URLS to read CSV formatted blocklists from
2. blocklist_instance_sources: A list of instances to read blocklists from via API
3. blocklist_instance_destinations: A list of instances to write blocklists to via API

URL sources

The URL sources is a list of URLs to fetch a CSV formatted blocklist from.

The required fields are domain and severity.

Optional fields that the tool understands are public_comment, private_comment, obfuscate, reject_media and reject_reports.

Instance sources

The tool can also read domain_blocks from instances directly.

The configuration is a list of dictionaries of the form:

{ domain = '<domain_name>', token = '<BearerToken>', admin = false }

The domain is the fully-qualified domain name of the API host for an instance you want to read or write domain blocks to/from.

The token is an optional OAuth token for the application that's configured in the instance to allow you to read/write domain blocks, as discussed above.

admin is an optional field that tells the tool to use the more detailed admin API endpoint for domain_blocks, rather than the more public API endpoint that doesn't provide as much detail. You will need a token that's been configured to permit access to the admin domain_blocks scope, as detailed above.

Instance destinations

The tool supports pushing a unified blocklist to multiple instances.

Configure the list of instances you want to push your blocklist to in the blocklist_instance_detinations list. Each entry is of the form:

{ domain = '<domain_name>', token = '<BearerToken>', max_followed_severity = 'silence' }

The fields domain and token are required. max_followed_severity is optional.

The domain is the hostname of the instance you want to push to. The token is an application token with both admin:read:domain_blocks and admin:write:domain_blocks authorization.

The optional max_followed_severity setting sets a per-instance limit on the severity of a domain_block if there are accounts on the instance that follow accounts on the domain to be blocked. If max_followed_severity isn't set, it defaults to 'silence'.

This setting exists to give people time to move off an instance that is about to be defederated and bring their followers from your instance with them. Without it, if a new Suspend block appears in any of the blocklists you subscribe to (or a block level increases from Silence to Suspend) and you're using the default max mergeplan, the tool would immediately suspend the instance, cutting everyone on the blocked instance off from their existing followers on your instance, even if they move to a new instance. If you actually want that outcome, you can set max_followed_severity = 'suspend' and use the max mergeplan.

Once the follow count drops to 0, the tool will automatically use the highest severity it finds again (if you're using the max mergeplan).

Using the tool

Once you've configured the tool, run it like this:

fediblock_sync.py -c <configfile_path>

If you put the config file in /etc/default/fediblockhole.conf.toml you don't need to pass in the config file path.

More advanced configuration

For a list of possible configuration options, check the --help and read the sample configuration file in etc/sample.fediblockhole.conf.toml.

save_intermediate

This option tells the tool to save the unmerged blocklists it fetches from remote instances and URLs into separate files. This is handy for debugging, or just to have a non-unified set of blocklist files.

Works with the savedir setting to control where to save the files.

These are parsed blocklists, not the raw data, and so will be affected by import_fields.

The filename is based on the URL or domain used so you can tell where each list came from.

savedir

Sets where to save intermediate blocklist files. Defaults to /tmp.

no_push_instance

Defaults to False.

When set, the tool won't actually try to push the unified blocklist to any configured instances.

If you want to see what the tool would try to do, but not actually apply any updates, use --dryrun.

no_fetch_url

Skip the fetching of blocklists from any URLs that are configured.

no_fetch_instance

Skip the fetching of blocklists from any remote instances that are configured.

mergeplan

If two (or more) blocklists define blocks for the same domain, but they're different, mergeplan tells the tool how to resolve the conflict.

max is the default. It uses the highest severity block it finds as the one that should be used in the unified blocklist.

min does the opposite. It uses the lowest severity block it finds as the one to use in the unified blocklist.

A full discussion of severities is beyond the scope of this README, but here is a quick overview of how it works for this tool.

The severities are:

• noop, level 0: This is essentially an 'unblock' but you can include a comment.
• silence, level 1: A silence adds friction to federation with an instance.
• suspend, level 2: A full defederation with the instance.

With mergeplan set to max, silence would take precedence over noop, and suspend would take precedence over both.

With mergeplan set to min, silence would take precedence over suspend, and noop would take precedence over both.

You would want to use max to ensure that you always block with whichever your harshest fellow admin thinks should happen.

You would want to use min to ensure that your blocks do what your most lenient fellow admin thinks should happen.

import_fields

import_fields controls which fields will be imported from remote instances and URL blocklists, and which fields are pushed to instances from the unified blocklist.

The fields domain and severity are always included, so only define extra fields, if you want them.

You can't export fields you haven't imported, so export_fields should be a subset of import_fields, but you can run the tool multiple times. You could, for example, include lots of fields for an initial import to build up a comprehensive list for export, combined with the --no-push-instances option so you don't actually apply the full list to anywhere.

Then you could use a different set of options when importing so you have all the detail in a file, but only push public_comment to instances.

export_fields

export_fields controls which fields will get saved to the unified blocklist file, if you export one.

The fields domain and severity are always included, so only define extra fields, if you want them.