Rewrite all policies as policy modules

entrypoint.example.ts

@@ -0,0 +1,4 @@
+#!/bin/sh
+//bin/true; exec deno run -A "$0" "$@"
+
+// TODO

src/pipeline.ts

@@ -0,0 +1,3 @@
+import { readStdin } from './stdin.ts';
+
+console.log(await readStdin());

src/policies/anti-duplication-policy.ts

@@ -1,24 +1,16 @@
-#!/bin/sh
-//bin/true; exec deno run -A "$0" "$@"
-import { Keydb, readLines } from '../deps.ts';
+import { Keydb } from '../deps.ts';
 
-import type { InputMessage, OutputMessage } from '../types.ts';
+import type { Policy } from '../types.ts';
 
 const ANTI_DUPLICATION_TTL = Number(Deno.env.get('ANTI_DUPLICATION_TTL') || 60000);
 const ANTI_DUPLICATION_MIN_LENGTH = Number(Deno.env.get('ANTI_DUPLICATION_MIN_LENGTH') || 50);
 
-/** https://stackoverflow.com/a/8831937 */
-function hashCode(str: string): number {
-  let hash = 0;
-  for (let i = 0, len = str.length; i < len; i++) {
-    const chr = str.charCodeAt(i);
-    hash = (hash << 5) - hash + chr;
-    hash |= 0; // Convert to 32bit integer
-  }
-  return hash;
-}
-
-async function handleMessage(msg: InputMessage): Promise<OutputMessage> {
+/**
+ * Prevent messages with the exact same content from being submitted repeatedly.
+ * It stores a hashcode for each content in an SQLite database and rate-limits them.
+ * Only messages that meet the minimum length criteria are selected.
+ */
+const antiDuplicationPolicy: Policy = async (msg) => {
   const { kind, content } = msg.event;
 
   if (kind === 1 && content.length >= ANTI_DUPLICATION_MIN_LENGTH) {
@@ -42,8 +34,21 @@ async function handleMessage(msg: InputMessage): Promise<OutputMessage> {
     action: 'accept',
     msg: '',
   };
+};
+
+/**
+ * Get a "good enough" unique identifier for this content.
+ * This algorithm was chosen because it's very fast with a low chance of collisions.
+ * https://stackoverflow.com/a/8831937
+ */
+function hashCode(str: string): number {
+  let hash = 0;
+  for (let i = 0, len = str.length; i < len; i++) {
+    const chr = str.charCodeAt(i);
+    hash = (hash << 5) - hash + chr;
+    hash |= 0; // Convert to 32bit integer
+  }
+  return hash;
 }
 
-for await (const line of readLines(Deno.stdin)) {
-  console.log(JSON.stringify(await handleMessage(JSON.parse(line))));
-}
+export default antiDuplicationPolicy;

src/policies/hellthread-policy.ts

@@ -1,11 +1,9 @@
-#!/usr/bin/env -S deno run
-import { readLines } from '../deps.ts';
-
-import type { InputMessage, OutputMessage } from '../types.ts';
+import type { Policy } from '../types.ts';
 
 const HELLTHREAD_LIMIT = Number(Deno.env.get('HELLTHREAD_LIMIT') || 100);
 
-function handleMessage(msg: InputMessage): OutputMessage {
+/** Reject messages that tag too many participants. */
+const hellthreadPolicy: Policy = (msg) => {
   if (msg.event.kind === 1) {
     const p = msg.event.tags.filter((tag) => tag[0] === 'p');
 
@@ -23,8 +21,6 @@ function handleMessage(msg: InputMessage): OutputMessage {
     action: 'accept',
     msg: '',
   };
-}
+};
 
-for await (const line of readLines(Deno.stdin)) {
-  console.log(JSON.stringify(handleMessage(JSON.parse(line))));
-}
+export default hellthreadPolicy;

src/policies/noop-policy.ts

@@ -1,16 +1,13 @@
-#!/usr/bin/env -S deno run
-import { readLines } from '../deps.ts';
+import type { Policy } from '../types.ts';
 
-import type { InputMessage, OutputMessage } from '../types.ts';
+/**
+ * Minimal sample policy for demonstration purposes.
+ * Allows all events through.
+ */
+const noopPolicy: Policy = (msg) => ({
+  id: msg.event.id,
+  action: 'accept',
+  msg: '',
+});
 
-function handleMessage(msg: InputMessage): OutputMessage {
-  return {
-    id: msg.event.id,
-    action: 'accept',
-    msg: '',
-  };
-}
-
-for await (const line of readLines(Deno.stdin)) {
-  console.log(JSON.stringify(handleMessage(JSON.parse(line))));
-}
+export default noopPolicy;

src/policies/rate-limit-policy.ts

@@ -1,15 +1,18 @@
-#!/bin/sh
-//bin/true; exec deno run -A "$0" "$@"
-import { Keydb, readLines } from '../deps.ts';
+import { Keydb } from '../deps.ts';
 
-import type { InputMessage, OutputMessage } from '../types.ts';
+import type { Policy } from '../types.ts';
 
 const IP_WHITELIST = (Deno.env.get('IP_WHITELIST') || '').split(',');
 
 const RATE_LIMIT_INTERVAL = Number(Deno.env.get('RATE_LIMIT_INTERVAL') || 60000);
 const RATE_LIMIT_MAX = Number(Deno.env.get('RATE_LIMIT_MAX') || 10);
 
-async function handleMessage(msg: InputMessage): Promise<OutputMessage> {
+/**
+ * Rate-limits users by their IP address.
+ * IPs are stored in an SQLite database. If you are running internal services,
+ * it's a good idea to at least whitelist `127.0.0.1` etc.
+ */
+const rateLimitPolicy: Policy = async (msg) => {
   if ((msg.sourceType === 'IP4' || msg.sourceType === 'IP6') && !IP_WHITELIST.includes(msg.sourceInfo)) {
     const db = new Keydb('sqlite:///tmp/strfry-rate-limit-policy.sqlite3');
     const count = await db.get<number>(msg.sourceInfo) || 0;
@@ -29,8 +32,6 @@ async function handleMessage(msg: InputMessage): Promise<OutputMessage> {
     action: 'accept',
     msg: '',
   };
-}
+};
 
-for await (const line of readLines(Deno.stdin)) {
-  console.log(JSON.stringify(await handleMessage(JSON.parse(line))));
-}
+export default rateLimitPolicy;

src/policies/read-only-policy.ts

@@ -1,17 +1,10 @@
-#!/bin/sh
-//bin/true; exec deno run -A "$0" "$@"
-import { readLines } from '../deps.ts';
+import type { Policy } from '../types.ts';
 
-import type { InputMessage, OutputMessage } from '../types.ts';
+/** This policy rejects all messages. */
+const readOnlyPolicy: Policy = (msg) => ({
+  id: msg.event.id,
+  action: 'reject',
+  msg: 'The relay is read-only.',
+});
 
-function handleMessage(msg: InputMessage): OutputMessage {
-  return {
-    id: msg.event.id,
-    action: 'reject',
-    msg: 'The relay is set to read-only.',
-  };
-}
-
-for await (const line of readLines(Deno.stdin)) {
-  console.log(JSON.stringify(handleMessage(JSON.parse(line))));
-}
+export default readOnlyPolicy;

src/stdin.ts

@@ -0,0 +1,14 @@
+import { readLines } from './deps.ts';
+
+import type { InputMessage } from './types.ts';
+
+/**
+ * Get the first line from stdin.
+ * Can only be read ONCE, or else it returns undefined.
+ */
+async function readStdin(): Promise<InputMessage> {
+  const { value } = await readLines(Deno.stdin).next();
+  return JSON.parse(value);
+}
+
+export { readStdin };

src/types.ts

@@ -22,4 +22,6 @@ interface Event<K extends number = number> {
   created_at: number;
 }
 
-export type { Event, InputMessage, OutputMessage };
+type Policy = (msg: InputMessage) => Promise<OutputMessage> | OutputMessage;
+
+export type { Event, InputMessage, OutputMessage, Policy };