From b95b3495157225f0c41c70617f892bd834390619 Mon Sep 17 00:00:00 2001
From: Brian Lee <blee@satstack.cloud>
Date: Sun, 7 Jan 2024 19:59:15 -0800
Subject: [PATCH] Create a policy for filtering messages by size, excluding
 contact lists.

---
 deno.lock                              | 11 ++++++
 src/policies/size-limit-policy.test.ts | 20 +++++++++++
 src/policies/size-limit-policy.ts      | 50 ++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 src/policies/size-limit-policy.test.ts
 create mode 100644 src/policies/size-limit-policy.ts

diff --git a/deno.lock b/deno.lock
index 459bfe5..1ca549c 100644
--- a/deno.lock
+++ b/deno.lock
@@ -1,5 +1,16 @@
 {
   "version": "3",
+  "packages": {
+    "specifiers": {
+      "npm:@types/node": "npm:@types/node@18.16.19"
+    },
+    "npm": {
+      "@types/node@18.16.19": {
+        "integrity": "sha512-IXl7o+R9iti9eBW4Wg2hx1xQDig183jj7YLn8F7udNceyfkbn1ZxmzZXuak20gR40D7pIkIY1kYGx5VIGbaHKA==",
+        "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",
diff --git a/src/policies/size-limit-policy.test.ts b/src/policies/size-limit-policy.test.ts
new file mode 100644
index 0000000..78bb9bb
--- /dev/null
+++ b/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');
+});
diff --git a/src/policies/size-limit-policy.ts b/src/policies/size-limit-policy.ts
new file mode 100644
index 0000000..fc036bf
--- /dev/null
+++ b/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;