strfry policies

A collection of policies for the strfry Nostr relay, built in Deno.

For more information about policy plugins, see strfry: Write policy plugins.

This library introduces a model for writing policies and composing them in a pipeline. Policies are fully configurable and it's easy to add your own or install more from anywhere on the net.

Getting started

To get up and running, you will need to install Deno on the same machine as strfry:

sudo apt install -y unzip
curl -fsSL https://deno.land/x/install/install.sh | sudo DENO_INSTALL=/usr/local sh

Create an entrypoint file somewhere and make it executable:

sudo touch /opt/strfry-policy.ts
sudo chmod +x /opt/strfry-policy.ts

Now you can write your policy. Here's a good starting point:

#!/bin/sh
//bin/true; exec deno run -A "$0" "$@"
import {
  antiDuplicationPolicy,
  hellthreadPolicy,
  pipeline,
  rateLimitPolicy,
  readStdin,
  writeStdout,
} from 'https://gitlab.com/soapbox-pub/strfry-policies/-/raw/develop/mod.ts';

for await (const msg of readStdin()) {
  const result = await pipeline(msg, [
    [hellthreadPolicy, { limit: 100 }],
    [antiDuplicationPolicy, { ttl: 60000, minLength: 50 }],
    [rateLimitPolicy, { whitelist: ['127.0.0.1'] }],
  ]);

  writeStdout(result);
}

Finally, edit strfry.conf and enable the policy:

     writePolicy {
         # If non-empty, path to an executable script that implements the writePolicy plugin logic
-        plugin = ""
+        plugin = "/opt/strfry-policy.ts"
 
         # Number of seconds to search backwards for lookback events when starting the writePolicy plugin (0 for no lookback)
         lookbackSeconds = 0

That's it! 🎉 Now you should check strfry logs to ensure everything is working okay.

Available policies

For complete documentation of policies, see:

• https://doc.deno.land/https://gitlab.com/soapbox-pub/strfry-policies/-/raw/develop/mod.ts

Writing your own policies

You can write a policy in TypeScript and host it anywhere. Deno allows importing modules by URL, making it easy to share policies.

Here is a basic sample policy:

import type { Policy } from 'https://gitlab.com/soapbox-pub/strfry-policies/-/raw/develop/mod.ts';

/** Only American English is allowed. */
const americanPolicy: Policy<void> = (msg) => {
  const { content } = msg.event;

  const words = [
    'armour',
    'behaviour',
    'colour',
    'favourite',
    'flavour',
    'honour',
    'humour',
    'rumour',
  ];

  const isBritish = words.some((word) => content.toLowerCase().includes(word));

  if (isBritish) {
    return {
      id: msg.event.id,
      action: 'reject',
      msg: 'Sorry, only American English is allowed on this server!',
    };
  } else {
    return {
      id: msg.event.id,
      action: 'accept',
      msg: '',
    };
  }
};

export default americanPolicy;

Once you're done, you can either upload the file somewhere online or directly to your server. Then, update your pipeline:

--- a/strfry-policy.ts
+++ b/strfry-policy.ts
@@ -8,12 +8,14 @@ import {
   readStdin,
   writeStdout,
 } from 'https://gitlab.com/soapbox-pub/strfry-policies/-/raw/develop/mod.ts';
+import { americanPolicy } from 'https://gist.githubusercontent.com/alexgleason/5c2d084434fa0875397f44da198f4352/raw/3d3ce71c7ed9cef726f17c3a102c378b81760a45/american-policy.ts';
 
 for await (const msg of readStdin()) {
   const result = await pipeline(msg, [
     [hellthreadPolicy, { limit: 100 }],
     [antiDuplicationPolicy, { ttl: 60000, minLength: 50 }],
     [rateLimitPolicy, { whitelist: ['127.0.0.1'] }],
+    americanPolicy,
   ]);
 
   writeStdout(result);

Policy options

The Policy<Opts> type is a generic that accepts options of any type. With opts, the policy above could be rewritten as:

--- a/american-policy.ts
+++ b/american-policy.ts
@@ -1,7 +1,11 @@
 import type { Policy } from 'https://gitlab.com/soapbox-pub/strfry-policies/-/raw/develop/mod.ts';
 
+interface American {
+  withGrey?: boolean;
+}
+
 /** Only American English is allowed. */
-const americanPolicy: Policy<void> = (msg) => {
+const americanPolicy: Policy<American> = (msg, opts) => {
   const { content } = msg.event;
 
   const words = [
@@ -15,6 +19,10 @@
     'rumour',
   ];
 
+  if (opts?.withGrey) {
+    words.push('grey');
+  }
+
   const isBritish = words.some((word) => content.toLowerCase().includes(word));
 
   if (isBritish) {

Then, in the pipeline:

-  americanPolicy,
+  [americanPolicy, { withGrey: true }],

Caveats

• You should not use console.log anywhere in your policies, as strfry expects stdout to be the strfry output message.

Filtering jsonl events with your policy

It is not currently possible to retroactively filter events on your strfry relay. You can however export the events with strfry export, filter them locally, and then import them into a fresh database. You can also use this command to filter Nostr events from any source, not just strfry.

To do so, run:

cat [EVENTS_FILE] | deno task filter [POLICY_CMD] > [OUT_FILE]

For example:

cat events.jsonl | deno task filter ./my-policy.ts > filtered.jsonl

Accepted messages will be written to stdout, while rejected messages will be skipped. Also, [POLICY_CMD] can be any strfry policy, not just one created from this repo.

The command wraps each event in a strfry message of type new, with an IP4 source of 127.0.0.1, and a timestamp of the current UTC time. Therefore you may want to avoid certain policies such as the rateLimitPolicy that don't makes sense in this context.

License

This is free and unencumbered software released into the public domain.