Create a policy for filtering messages by size, excluding contact lists.

deno.lock

@@ -1,5 +1,16 @@
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   "version": "3",
+  "packages": {
+    "specifiers": {
+      "npm:@types/node": "npm:@types/node@18.16.19"
+    },
+    "npm": {
+      "@types/node@18.16.19": {
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+        "dependencies": {}
+      }
+    }
+  },
   "remote": {
     "https://deno.land/std@0.181.0/_util/asserts.ts": "178dfc49a464aee693a7e285567b3d0b555dc805ff490505a8aae34f9cfb1462",
     "https://deno.land/std@0.181.0/bytes/bytes_list.ts": "b4cbdfd2c263a13e8a904b12d082f6177ea97d9297274a4be134e989450dfa6a",

src/policies/size-limit-policy.test.ts

@@ -0,0 +1,20 @@
+import { assertEquals } from '../deps.ts';
+import { buildEvent, buildInputMessage } from '../test.ts';
+
+import sizeLimitPolicy from './size-limit-policy.ts';
+
+Deno.test('Size limit policy test', async () => {
+  // Create a message under 12KB
+  const smallContent = 'Hello'.repeat(100); // Well under 12KB
+  const smallMessage = buildInputMessage({ event: buildEvent({ content: smallContent }) });
+
+  // Create a message over 12KB
+  const largeContent = 'Hello'.repeat(2500); // Over 12KB
+  const largeMessage = buildInputMessage({ event: buildEvent({ content: largeContent }) });
+
+  // Test that a small message is accepted
+  assertEquals((await sizeLimitPolicy(smallMessage)).action, 'accept', 'Small message should be accepted');
+
+  // Test that a large message is rejected
+  assertEquals((await sizeLimitPolicy(largeMessage)).action, 'reject', 'Large message should be rejected');
+});

src/policies/size-limit-policy.ts

@@ -0,0 +1,50 @@
+import { Policy } from '../types.ts';
+
+/** Policy options for `sizeLimitPolicy`. */
+interface SizeLimitOptions {
+  /** Maximum size of the message content in bytes. Default: 12KB (12288 bytes) */
+  maxContentSize?: number;
+  /** List of excluded event kinds */
+  excludeKinds?: number[];
+}
+
+/**
+ * Reject events larger than a specified size.
+ *
+ * @example
+ * ```ts
+ * // Reject events larger than a custom size (15KB) and exclude event kinds [1, 2].
+ * sizeLimitPolicy(msg, { maxContentSize: 15000, excludeKinds: [1, 2] });
+ * // Reject events larger than the default size (12KB) and exclude event kinds [3].
+ * sizeLimitPolicy(msg, { excludeKinds: [3] });
+ * ```
+ */
+const sizeLimitPolicy: Policy<SizeLimitOptions> = ({ event: { id, content, kind } }, opts = {}) => {
+  const {
+    excludeKinds = [3], // Exclude large events such as contact lists
+    maxContentSize = 12 * 1024  // Default size limit is 12KB
+  } = opts;
+
+  // Convert the content into bytes and check its size
+  const contentSize = new TextEncoder().encode(content).length;
+
+  if (contentSize > maxContentSize && !excludeKinds.includes(kind)) {
+    const timestamp = new Date().toISOString();
+    const logMessage = `${timestamp}: ID: ${id}, Kind: ${kind} rejected, ${contentSize} > max content size (${maxContentSize})\n`;
+    Deno.writeTextFileSync('./size-limit-policy.log', logMessage, { append: true });
+    return {
+      id,
+      action: 'reject',
+      msg: `blocked: message is too large.`,
+      //msg: `blocked: ${timestamp}: ID: ${id}, Kind: ${kind} rejected, ${contentSize} > max content size (${maxContentSize})\n`,
+    };
+  }
+
+  return {
+    id,
+    action: 'accept',
+    msg: '',
+  };
+};
+
+export default sizeLimitPolicy;