strfry policies

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

For more information about installing these policies and how they work, see 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';

const msg = await 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.

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
@@ -9,6 +9,7 @@ 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';
 
 const msg = await readStdin();
 
@@ -17,6 +18,7 @@ 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.

Available policies

Please look directly at src/policies in this repo. The files include detailed JSDoc comments and it has good type support.

License

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

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