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flags: disable optimization guide and media router (#282)
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@paulirish
paulirish committed Nov 9, 2022
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60 changes: 37 additions & 23 deletions docs/chrome-flags-for-tools.md
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Expand Up @@ -17,15 +17,16 @@ All use cases are different, so you'll have to choose which flags are most appro
* `--use-fake-device-for-media-stream`: Use fake device for Media Stream to replace camera and microphone
* `--use-file-for-fake-video-capture=<path-to-file>`: Use file for fake video capture (.y4m or .mjpeg) Needs `--use-fake-device-for-media-stream`
* `--disable-external-intent-requests`: Disallow opening links in external applications
* `--disable-features=Translate`: Disables Chrome translation, both the manual option and the popup prompt when a page with differing language is detected.

## Performance & web platform behavior

* `--allow-running-insecure-content`
* `--autoplay-policy=user-gesture-required`: Don't render video
* `--disable-background-timer-throttling`: Disable timers being throttled in background pages/tabs
* `--disable-backgrounding-occluded-windows`
* `--disable-backgrounding-occluded-windows`: Normally, Chrome will treat a 'foreground' tab instead as _backgrounded_ if the surrounding window is occluded (aka visually covered) by another window. This flag disables that.
* `--disable-features=ScriptStreaming`: V8 script streaming
* `--disable-hang-monitor`
* `--disable-hang-monitor`: Suppresses hang monitor dialogs in renderer processes. This flag may allow slow unload handlers on a page to prevent the tab from closing.
* `--disable-ipc-flooding-protection`: Some javascript functions can be used to flood the browser process with IPC. By default, protection is on to limit the number of IPC sent to 10 per second per frame. This flag disables it. https://crrev.com/604305
* `--disable-notifications`: Disables the Web Notification and the Push APIs.
* `--disable-popup-blocking`: Disable popup blocking. `--block-new-web-contents` is the strict version of this.
Expand All @@ -35,19 +36,19 @@ All use cases are different, so you'll have to choose which flags are most appro

## Test & debugging flags

* `--disable-device-discovery-notifications`: Avoid messages like "New printer on your network"
* `--enable-automation`: Disable a few things considered not appropriate for automation. ([Original design doc](https://docs.google.com/a/google.com/document/d/1JYj9K61UyxIYavR8_HATYIglR9T_rDwAtLLsD3fbDQg/preview), though renamed [here](https://codereview.chromium.org/2564973002#msg24)) [codesearch](https://cs.chromium.org/search/?q=kEnableAutomation&type=cs). Note that some projects have chosen to **avoid** using this flag: [web-platform-tests/wpt/#6348](https://github.com/web-platform-tests/wpt/pull/6348)
- disables bubble notification about running development/unpacked extensions
- disables the password saving UI (which [covers](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/password_manager/chrome_password_manager_client.cc;l=295-298;drc=00053fb4d880a925c890193b74a8ff35e1cef2a0) the usecase of the [removed](https://bugs.chromium.org/p/chromedriver/issues/detail?id=1015) `--disable-save-password-bubble` flag)
- disables infobar animations
- disables auto-reloading on network errors ([source](https://cs.chromium.org/chromium/src/chrome/renderer/net/net_error_helper_core.cc?l=917&rcl=6eaf0af71262eb876764c6237ee2fe021a3e7a18))
- means the default browser check prompt isn't shown
- avoids showing these 3 infobars: ShowBadFlagsPrompt, GoogleApiKeysInfoBarDelegate, ObsoleteSystemInfoBarDelegate
- adds this infobar: ![image](https://user-images.githubusercontent.com/39191/30349667-92a7a086-97c8-11e7-86b2-1365e3d407e3.png)
* `--enable-automation`: Disable a few things considered not appropriate for automation. ([Original design doc](https://docs.google.com/a/google.com/document/d/1JYj9K61UyxIYavR8_HATYIglR9T_rDwAtLLsD3fbDQg/preview), though renamed [here](https://codereview.chromium.org/2564973002#msg24)) [codesearch](https://cs.chromium.org/search/?q=kEnableAutomation&type=cs). Note that some projects have chosen to **avoid** using this flag: [web-platform-tests/wpt/#6348](https://github.com/web-platform-tests/wpt/pull/6348), [crbug.com/1277272](https://crbug.com/1277272)
- sets `window.navigator.webdriver` to `true` within all JS contexts. This is also set [when using](https://source.chromium.org/chromium/chromium/src/+/main:content/child/runtime_features.cc;l=374-376;drc=4a843634b8b3006e431add55968f6f45ee54d35e) `--headless`, `--remote-debugging-pipe` and `--remote-debugging-port=0` (yes, [_specifically_ 0](https://source.chromium.org/chromium/chromium/src/+/main:content/child/runtime_features.cc;l=412-427;drc=4a843634b8b3006e431add55968f6f45ee54d35e)).
- disables bubble notification about running development/unpacked extensions ([source](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/extensions/extension_message_bubble_factory.cc;l=71-76;drc=1e6c1a39cbbc1dcad6e7828661d74d76463465ed))
- disables the password saving UI (which [covers](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/password_manager/chrome_password_manager_client.cc;l=301-308;drc=1e6c1a39cbbc1dcad6e7828661d74d76463465ed) the usecase of the [removed](https://bugs.chromium.org/p/chromedriver/issues/detail?id=1015) `--disable-save-password-bubble` flag)
- disables infobar animations ([source](https://source.chromium.org/chromium/chromium/src/+/main:components/infobars/content/content_infobar_manager.cc;l=48-52;drc=1e6c1a39cbbc1dcad6e7828661d74d76463465ed))
- disables auto-reloading on network errors ([source](https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/chrome_content_browser_client.cc;l=1328-1331;drc=1e6c1a39cbbc1dcad6e7828661d74d76463465ed))
- enables the CDP method [`Browser.getBrowserCommandLine`](https://chromedevtools.github.io/devtools-protocol/tot/Browser/#method-getBrowserCommandLine).
- avoids showing these 4 infobars: ShowBadFlagsPrompt, GoogleApiKeysInfoBarDelegate, ObsoleteSystemInfoBarDelegate, LacrosButterBar
- adds this infobar: ![image](https://user-images.githubusercontent.com/39191/30349667-92a7a086-97c8-11e7-86b2-1365e3d407e3.png) ... which is known to [adversely affect screenshots](https://bugs.chromium.org/p/chromium/issues/detail?id=1277272).
* `--enable-logging=stderr`: Logging behavior slightly more appropriate for a server-type process.
* `--log-level=0`: 0 means INFO and higher.
* `--password-store=basic`: Avoid potential instability of using Gnome Keyring or KDE wallet. [chromium/linux/password_storage.md](https://chromium.googlesource.com/chromium/src/+/main/docs/linux/password_storage.md) https://crbug.com/571003
* `--log-level=0`: 0 means INFO and higher. `2` is the most verbose. Protip: Use `--enable-logging=stderr --v=2` and you may spot additional components active that you may want to disable.
* `--remote-debugging-pipe`: more secure than using protocol over a websocket
* `--remote-debugging-port=...`: With a value of 0, Chrome will automatically select a useable port _and_ will set `navigator.webdriver` to `true`.
* `--silent-debugger-extension-api`: Does not show an infobar when a Chrome extension attaches to a page using `chrome.debugger` page. Required to attach to extension background pages.
* `--test-type`: Basically the 2014 version of `--enable-automation`. [codesearch](https://cs.chromium.org/search/?q=kTestType%5Cb&type=cs)
- It avoids creating application stubs in ~/Applications on mac.
Expand All @@ -57,9 +58,14 @@ All use cases are different, so you'll have to choose which flags are most appro
- disables initializing chromecast service
- "Component extensions with background pages are not enabled during tests because they generate a lot of background behavior that can interfere."
- when quitting the browser, it disables additional checks that may stop that quitting process. (like unsaved form modifications or unhandled profile notifications..)
* `--use-mock-keychain`: Use mock keychain on Mac to prevent blocking permissions dialogs. https://crbug.com/865247
* `--deny-permission-prompts`: Suppress all permission prompts by automatically denying them.

## Chromium Annoyances

* `--password-store=basic`: Avoid potential instability of using Gnome Keyring or KDE wallet. [chromium/linux/password_storage.md](https://chromium.googlesource.com/chromium/src/+/main/docs/linux/password_storage.md) https://crbug.com/571003
* `--use-mock-keychain`: Use mock keychain on Mac to prevent the blocking permissions dialog asking: _Do you want the application “Chromium.app” to accept incoming network connections?_
* `--disable-features=DialMediaRouteProvider`: Avoid the startup dialog for _Do you want the application “Chromium.app” to accept incoming network connections?_

## Background updates, networking, reporting

* `--disable-background-networking`: Disable various background network services, including extension updating,safe browsing service, upgrade detector, translate, UMA
Expand Down Expand Up @@ -105,6 +111,8 @@ All use cases are different, so you'll have to choose which flags are most appro

## Headless

* `--headless`
* `--headless=chrome`
* `--disable-dev-shm-usage`: Often used in Lambda, Cloud Functions scenarios. ([pptr issue](https://github.com/GoogleChrome/puppeteer/issues/1834), [crbug](https://bugs.chromium.org/p/chromium/issues/detail?id=736452))
* `--no-sandbox`: [Sometimes used](https://github.com/puppeteer/puppeteer/blob/main/docs/troubleshooting.md#setting-up-chrome-linux-sandbox) with headless, though not recommended.
* `--disable-gpu`: Was often [used](https://bugs.chromium.org/p/chromium/issues/detail?id=737678) along with `--headless`, but as of 2021, isn't needed.
Expand All @@ -113,9 +121,10 @@ All use cases are different, so you'll have to choose which flags are most appro

* `--disable-add-to-shelf`: [Removed June 2017](https://codereview.chromium.org/2944283002)
* `--disable-background-downloads`: [Removed Oct 2014](https://codereview.chromium.org/607843002).
* `--disable-browser-side-navigation` Disabled PlzNavigate.
* `--disable-datasaver-prompt`
* `--disable-desktop-notifications`
* `--disable-browser-side-navigation`: Disabled PlzNavigate.
* `--disable-datasaver-prompt`: Removed
* `--disable-desktop-notifications`: Removed
* `--disable-device-discovery-notifications`: Avoided messages like "New printer on your network". [Replaced](https://crbug.com/1020447#c1) with `--disable-features=MediaRouter`.
* `--disable-features=TranslateUI`: renamed `TranslateUI` to `Translate` in [Sept 2020](https://chromium-review.googlesource.com/c/chromium/src/+/2404484).
* `--disable-infobars`: [Removed April 2014](https://codereview.chromium.org/240193003)
* `--disable-save-password-bubble`: [Removed May 2016](https://codereview.chromium.org/1978563002)
Expand All @@ -127,17 +136,22 @@ All use cases are different, so you'll have to choose which flags are most appro

* [chrome-launcher's flags](https://github.com/GoogleChrome/chrome-launcher/blob/main/src/flags.ts)
* [Chromedriver's flags](https://cs.chromium.org/chromium/src/chrome/test/chromedriver/chrome_launcher.cc?type=cs&q=f:chrome_launcher++kDesktopSwitches&sq=package:chromium)
* [Puppeteer's flags](https://github.com/puppeteer/puppeteer/blob/main/src/node/Launcher.ts)
* [Puppeteer's flags](https://github.com/puppeteer/puppeteer/blob/3f2c0590f154aefd2ad3449a3f943ee79d1e33a9/packages/puppeteer-core/src/node/ChromeLauncher.ts#L159)
* [WebpageTest's flags](https://github.com/WPO-Foundation/wptagent/blob/master/internal/chrome_desktop.py)
* [Catapult's flags](https://source.chromium.org/search?q=f:catapult%20f:desktop%20symbol:GetBrowserStartupArgs&ss=chromium%2Fchromium%2Fsrc)
* [Catapult's flags](https://source.chromium.org/chromium/chromium/src/+/main:third_party/catapult/telemetry/telemetry/internal/backends/chrome/chrome_startup_args.py) and [here](https://source.chromium.org/chromium/chromium/src/+/main:third_party/catapult/telemetry/telemetry/internal/backends/chrome/desktop_browser_finder.py;l=218;drc=4a0e6f034e9756605cfc837c8526588d6c13436b)
* [Karma's flags](https://github.com/karma-runner/karma-chrome-launcher/blob/master/index.js)

# All Chrome flags
Here's a [Nov 2022 comparison of what flags all these tools use](https://docs.google.com/spreadsheets/d/1n-vw_PCPS45jX3Jt9jQaAhFqBY6Ge1vWF_Pa0k7dCk4/edit#gid=1265672696).

* [The canonical list of Chrome command-line switches on peter.sh](http://peter.sh/experiments/chromium-command-line-switches/) (maintained by the Chromium team)

FYI: (Probably) all flags are defined in files matching the pattern of [`*_switches.cc`](f:_switches\.cc).
[The canonical list of Chrome command-line switches on peter.sh](http://peter.sh/experiments/chromium-command-line-switches/) (maintained by the Chromium team)

FYI: (Probably) all flags are defined in files matching the pattern of [`*_switches.cc`](https://source.chromium.org/search?q=f:_switches%5C.cc&ss=chromium%2Fchromium%2Fsrc).
## Feature Flags FYI

Chromium and Blink use feature flags to disable/enable many features at runtime. Chromium has [~400 features](https://source.chromium.org/search?q=%22const%20base::Feature%22%20f:%5C.cc&sq=&ss=chromium%2Fchromium%2Fsrc) that can be toggled with `--enable-features` / `--disable-features`. Independently, Blink has [many features](https://source.chromium.org/chromium/chromium/src/+/main:out/Debug/gen/third_party/blink/renderer/platform/runtime_enabled_features.cc;l=1812;drc=77ab795d8fd2c0fe7ad7adb16478120fbf8c613e) that can be toggled [with commandline switches](https://chromium.googlesource.com/chromium/src/+/main/third_party/blink/renderer/platform/RuntimeEnabledFeatures.md#command_line-switches): `--enable-blink-features` / `--disable-blink-features`. For a complete overview of all available features, see https://niek.github.io/chrome-features/.
Chromium and Blink use feature flags to disable/enable many features at runtime. Chromium has [~400 features](https://source.chromium.org/search?q=%22const%20base::Feature%22%20f:%5C.cc&sq=&ss=chromium%2Fchromium%2Fsrc) that can be toggled with `--enable-features` / `--disable-features`. https://niek.github.io/chrome-features/ presents all of them very clearly.


Independently, Blink has [many features](https://source.chromium.org/chromium/chromium/src/+/main:out/Debug/gen/third_party/blink/renderer/platform/runtime_enabled_features.cc;l=1969;drc=d6e91a65ded605d8577f0651b3665c8206ae6ce3) that can be toggled [with commandline switches](https://chromium.googlesource.com/chromium/src/+/main/third_party/blink/renderer/platform/RuntimeEnabledFeatures.md#command_line-switches): `--enable-blink-features` / `--disable-blink-features`.


17 changes: 14 additions & 3 deletions src/flags.ts
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Expand Up @@ -5,11 +5,22 @@
*/
'use strict';

// https://github.com/GoogleChrome/chrome-launcher/blob/main/docs/chrome-flags-for-tools.md
/**
* See the following `chrome-flags-for-tools.md` for exhaustive coverage of these and related flags
* @url https://github.com/GoogleChrome/chrome-launcher/blob/main/docs/chrome-flags-for-tools.md
*/

export const DEFAULT_FLAGS: ReadonlyArray<string> = [
// Disable built-in Google Translate service
'--disable-features=Translate',
'--disable-features=' +
[
// Disable built-in Google Translate service
'Translate',
// Disable the Chrome Optimization Guide background networking
'OptimizationHints',
// Disable the Chrome Media Router (cast target discovery) background networking
'MediaRouter',
].join(','),

// Disable all chrome extensions
'--disable-extensions',
// Disable some extensions that aren't affected by --disable-extensions
Expand Down

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