Introduce --disable-ipv6 CLI option

app/main.ts

@@ -207,6 +207,8 @@ const defaultWebPrefs = {
 const DISABLE_GPU =
   OS.isLinux() && !process.argv.some(arg => arg === '--enable-gpu');
 
+const DISABLE_IPV6 = process.argv.some(arg => arg === '--disable-ipv6');
+
 const CLI_LANG = cliOptions.lang as string | undefined;
 
 setupCrashReports(getLogger, showDebugLogWindow);
@@ -1719,6 +1721,9 @@ if (DISABLE_GPU) {
 let ready = false;
 app.on('ready', async () => {
   dns.setFallback(await getDNSFallback());
+  if (DISABLE_IPV6) {
+    dns.setIPv6Enabled(false);
+  }
 
   const [userDataPath, crashDumpsPath, installPath] = await Promise.all([
     realpath(app.getPath('userData')),
@@ -2448,6 +2453,7 @@ ipc.on('get-config', async event => {
     ciMode,
     // Should be already computed and cached at this point
     dnsFallback: await getDNSFallback(),
+    disableIPv6: DISABLE_IPV6,
     ciBackupPath: config.get<string | null>('ciBackupPath') || undefined,
     nodeVersion: process.versions.node,
     hostname: os.hostname(),

ts/types/RendererConfig.ts

@@ -41,6 +41,7 @@ export const rendererConfigSchema = z.object({
   contentProxyUrl: configRequiredStringSchema,
   crashDumpsPath: configRequiredStringSchema,
   ciMode: z.enum(['full', 'benchmark']).or(z.literal(false)),
+  disableIPv6: z.boolean(),
   dnsFallback: DNSFallbackSchema,
   ciBackupPath: configOptionalStringSchema,
   environment: environmentSchema,

ts/util/dns.ts

@@ -26,6 +26,12 @@ export function setFallback(dnsFallback: DNSFallbackType): void {
   }
 }
 
+let ipv6Enabled = true;
+
+export function setIPv6Enabled(value: boolean): void {
+  ipv6Enabled = value;
+}
+
 function lookupAll(
   hostname: string,
   opts: LookupOneOptions | LookupAllOptions,
@@ -77,7 +83,7 @@ function lookupAll(
       }
     }
 
-    const addresses = result.endpoints.map(({ address, family }) => {
+    let addresses = result.endpoints.map(({ address, family }) => {
       let numericFamily = -1;
       if (family === 'ipv4') {
         numericFamily = 4;
@@ -90,6 +96,13 @@ function lookupAll(
       };
     });
 
+    if (!ipv6Enabled) {
+      const ipv4Only = addresses.filter(({ family }) => family !== 6);
+      if (ipv4Only.length !== 0) {
+        addresses = ipv4Only;
+      }
+    }
+
     if (!opts.all) {
       const random = addresses.at(Math.floor(Math.random() * addresses.length));
       if (random === undefined) {

ts/windows/main/phase2-dependencies.ts

@@ -74,6 +74,9 @@ if (config.crashDumpsPath) {
   addSensitivePath(config.crashDumpsPath);
 }
 
+if (SignalContext.config.disableIPv6) {
+  dns.setIPv6Enabled(false);
+}
 dns.setFallback(SignalContext.config.dnsFallback);
 
 window.Signal = setup({