Chore: sort Telegram DC Options

Build/lib/mtproto-dc-config.test.ts

@@ -3,6 +3,7 @@ import { expect } from 'earl';
 
 import {
   DC_OPTION_FLAG_IPV6,
+  DC_OPTION_FLAG_MEDIA_ONLY,
   DC_OPTION_FLAG_STATIC,
   mergeFallbackEndpoints,
   TELEGRAM_BOOTSTRAP_ENDPOINTS
@@ -69,6 +70,53 @@ describe('MTProto DC config', () => {
     expect(result.bootstrapAdded).toEqual(TELEGRAM_BOOTSTRAP_ENDPOINTS.length - 1);
   });
 
+  it('emits a deterministic option order regardless of input order', () => {
+    const options = [
+      { id: 2, ip: '149.154.167.222', port: 443, flags: DC_OPTION_FLAG_MEDIA_ONLY },
+      { id: 1, ip: '2001:0b28:f23d:f001:0000:0000:0000:000a', port: 443, flags: DC_OPTION_FLAG_IPV6 },
+      // Numerically before .222 but lexically after it.
+      { id: 2, ip: '149.154.167.41', port: 443, flags: DC_OPTION_FLAG_STATIC },
+      { id: 1, ip: '149.154.175.56', port: 443, flags: 0 }
+    ];
+
+    const build = (input: typeof options) => {
+      const config: MTProtoDCConfig = {
+        version: 1,
+        date: 1,
+        expires: 2,
+        this_dc: 1,
+        options: structuredClone(input)
+      };
+      mergeFallbackEndpoints(config, []);
+      return config.options;
+    };
+
+    const forward = build(options);
+    expect(build([...options].reverse())).toEqual(forward);
+
+    const ipsOfDc = (id: number) => forward.reduce<string[]>((acc, option) => {
+      if (option.id === id) acc.push(option.ip);
+      return acc;
+    }, []);
+
+    // IPv4 sorts numerically and precedes IPv6 within the same DC.
+    expect(ipsOfDc(1)).toEqual([
+      '149.154.175.50',
+      '149.154.175.56',
+      '2001:b28:f23d:f001::a'
+    ]);
+    expect(ipsOfDc(2)).toEqual([
+      '95.161.76.100',
+      '149.154.167.41',
+      '149.154.167.50',
+      '149.154.167.51',
+      '149.154.167.222',
+      '2001:67c:4e8:f002::a'
+    ]);
+    // DC ids are non-decreasing across the whole array.
+    expect(forward.every((option, i) => i === 0 || forward[i - 1].id <= option.id)).toEqual(true);
+  });
+
   it('keeps functional variants separate and preserves backup secrets', () => {
     const config: MTProtoDCConfig = {
       version: 1,

Build/lib/mtproto-dc-config.ts

@@ -7,6 +7,7 @@ import type { TelegramBackupEndpoint } from './get-telegram-backup-ip';
 import { setBit, getBit } from 'foxts/bitwise';
 import { bigint2ip, ip2bigint } from 'fast-cidr-tools';
 import { isProbablyIpv6 } from 'foxts/is-probably-ip';
+import { fastIpVersion } from 'foxts/fast-ip-version';
 
 export const DC_OPTION_FLAG_IPV6 = 1 << 0;
 export const DC_OPTION_FLAG_MEDIA_ONLY = 1 << 1;
@@ -148,6 +149,39 @@ function mergeEndpoint(config: MTProtoDCConfig, endpoint: MTProtoEndpoint) {
   return !matched;
 }
 
+/**
+ * The output order is otherwise a mix of whatever help.getConfig returned and
+ * the order the concurrent backup-endpoint lookups happened to resolve in, so
+ * two builds over identical upstream data can produce a spurious diff. Sort on
+ * the full option identity to keep the committed JSON reviewable.
+ */
+function sortOptions(config: MTProtoDCConfig) {
+  config.options.sort((a, b) => {
+    if (a.id !== b.id) return a.id - b.id;
+
+    // IPv4 before IPv6, each ordered numerically rather than lexically so
+    // 149.154.167.51 sorts before 149.154.167.222.
+    const aVersion = fastIpVersion(a.ip);
+    const bVersion = fastIpVersion(b.ip);
+    if (aVersion !== bVersion) return aVersion - bVersion;
+
+    if (aVersion === 0 || bVersion === 0) return 0; // how is invalid ip even here? just leave them in their original order
+
+    const aIp = ip2bigint(a.ip, aVersion);
+    const bIp = ip2bigint(b.ip, bVersion);
+    if (aIp !== bIp) return aIp < bIp ? -1 : 1;
+
+    if (a.port !== b.port) return a.port - b.port;
+    if (a.flags !== b.flags) return a.flags - b.flags;
+
+    // Secrets are base64, so a plain code-unit compare is stable and locale-free.
+    const aSecret = a.secret ?? '';
+    const bSecret = b.secret ?? '';
+    if (aSecret === bSecret) return 0;
+    return aSecret < bSecret ? -1 : 1;
+  });
+}
+
 function deduplicateOptions(config: MTProtoDCConfig) {
   const previousCount = config.options.length;
   const seen = new Set<string>();
@@ -186,9 +220,12 @@ export function mergeFallbackEndpoints(
     if (mergeEndpoint(config, endpoint)) bootstrapAdded++;
   }
 
+  const duplicatesRemoved = deduplicateOptions(config);
+  sortOptions(config);
+
   return {
     backupAdded,
     bootstrapAdded,
-    duplicatesRemoved: deduplicateOptions(config)
+    duplicatesRemoved
   };
 }