Add OS to User-Agent

ts/test/util/getUserAgent_test.ts

@@ -0,0 +1,37 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import * as sinon from 'sinon';
+
+import { getUserAgent } from '../../util/getUserAgent';
+
+describe('getUserAgent', () => {
+  beforeEach(function beforeEach() {
+    this.sandbox = sinon.createSandbox();
+  });
+
+  afterEach(function afterEach() {
+    this.sandbox.restore();
+  });
+
+  it('returns the right User-Agent on Windows', function test() {
+    this.sandbox.stub(process, 'platform').get(() => 'win32');
+    assert.strictEqual(getUserAgent('1.2.3'), 'Signal-Desktop/1.2.3 Windows');
+  });
+
+  it('returns the right User-Agent on macOS', function test() {
+    this.sandbox.stub(process, 'platform').get(() => 'darwin');
+    assert.strictEqual(getUserAgent('1.2.3'), 'Signal-Desktop/1.2.3 macOS');
+  });
+
+  it('returns the right User-Agent on Linux', function test() {
+    this.sandbox.stub(process, 'platform').get(() => 'linux');
+    assert.strictEqual(getUserAgent('1.2.3'), 'Signal-Desktop/1.2.3 Linux');
+  });
+
+  it('omits the platform on unsupported platforms', function test() {
+    this.sandbox.stub(process, 'platform').get(() => 'freebsd');
+    assert.strictEqual(getUserAgent('1.2.3'), 'Signal-Desktop/1.2.3');
+  });
+});

ts/util/getUserAgent.ts

@@ -1,6 +1,20 @@
 // Copyright 2020 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+import { getOwn } from './getOwn';
+
+const PLATFORM_STRINGS: { [platform: string]: string } = {
+  win32: 'Windows',
+  darwin: 'macOS',
+  linux: 'Linux',
+};
+
 export function getUserAgent(appVersion: string): string {
-  return `Signal-Desktop/${appVersion}`;
+  // `process.platform` could be missing if someone figures out how to compile Signal on
+  //   an unsupported OS and forgets to update this file. We'd rather send nothing than
+  //   crash.
+  const platformString = getOwn(PLATFORM_STRINGS, process.platform);
+  const platformStringWithSpace = platformString ? ` ${platformString}` : '';
+
+  return `Signal-Desktop/${appVersion}${platformStringWithSpace}`;
 }