This guide is intended for anyone building and distributing AOSP (e.g. Android device manufacturers or maintainers of custom ROM images) who wishes to rebuild, update, modify, or replace WebView in the system image for their Android device. This is not intended for Chromium developers who simply wish to run their local build of Chromium on a device.
Originally WebView was part of the Android framework, but since Android 5.0 (Lollipop) the WebView implementation has been provided by a separate APK. This APK is preinstalled on the device and can be updated in the same ways as an ordinary application.
The source code for the WebView implementation APK is maintained here, as part of the Chromium project. Building WebView from the AOSP source tree (as earlier versions of Android did) is no longer supported.
AOSP contains a prebuilt WebView APK for each supported CPU architecture, and the appropriate APK will be included in the system image by default. These APKs can be found in the external/chromium-webview directory in an AOSP checkout.
The prebuilt is provided in order to ensure that AOSP has a functional WebView for development and testing purposes. It is not currently updated on a regular schedule, and may have known security issues. It is strongly recommended that AOSP system images which are being shipped to end user devices include a recent stable version of WebView built following this guide, instead of the potentially outdated prebuilt version.
If you are not already familiar with building the Chromium browser for Android, we recommend that you first follow the general guide for Chromium on Android to ensure that your computer and Chromium checkout are properly configured.
Make sure that you can build
chrome_public_apk, install it on your device, and use it before continuing, as troubleshooting issues with WebView can be more difficult.
You will need to make several decisions before building WebView for AOSP:
There are currently three different variants of WebView that you can build, and you will need to decide which one is appropriate for your device. All three have the exact same features and app-facing behaviour, but are packaged in different ways that can provide advantages in certain configurations.
More detailed background and technical information about the different variants of WebView is available here, but here's a summary:
Most AOSP devices will use this variant. It is compatible with Android 5.0 (Lollipop) and later, and is the only variant which can be used on Android 5.x (Lollipop) and 6.x (Marshmallow).
The standalone WebView is a single APK which contains the entire WebView implementation. The prebuilt APK provided in AOSP is a standalone WebView APK.
The build target is called
system_webview_apk and the resulting output file is called
SystemWebView.apk. The prebuilt APK provided in AOSP has been renamed to
AndroidWebview.apk for historical reasons, and the filename used in AOSP is not significant; only the package name matters.
If your AOSP device will include a default web browser based on Chromium, it may be beneficial to use Monochrome as the WebView implementation. Monochrome is compatible with Android 7.x (Nougat), 8.x (Oreo) and 9.x (Pie), but not with Android Q and later due to changes made to support Trichrome.
Monochrome is a single APK which contains both the entire WebView implementation, and also an entire Chromium-based web browser. Since WebView and the Chromium browser share a lot of common source code, the Monochrome APK is much smaller than having a separate WebView APK and browser APK.
However, Monochrome can make it more difficult for you to allow the user to freely choose their own web browser and can have other downsides: see this section for more information.
The build target is called
monochrome_public_apk and the resulting output file is called
Trichrome is only compatible with Android Q and later.
Trichrome is composed of three APKs:
TrichromeWebView contains WebView-specific code and data, and provides Android apps with the WebView implementation.
TrichromeChrome contains browser-specific code and data, and provides the user with a Chromium-based web browser.
TrichromeLibrary contains the shared code and data, and is only used as an internal implementation detail of TrichromeWebView and TrichromeChrome.
The three Trichrome APKs together are roughly the same size as Monochrome, providing the same benefits, but many of the downsides and complexities of Monochrome don't apply to Trichrome.
The build targets are called
trichrome_library_apk respectively, and the resulting output files are called
WebView follows the same branching and release model as the rest of the Chromium project: a beta version is branched from the master branch approximately every six weeks, and after approximately six weeks of beta testing it is released to stable. If critical security or functionality issues are discovered after the stable release, a new version may be released from the same stable branch at any time (depending on urgency).
If you are intending to release your WebView build to users, you should generally use a stable release tag - ideally the most recent stable release, which includes the latest security and stability fixes. You can check the current stable and beta version numbers using the Chromium dashboard. See the “Syncing and building a release tag” section on this page to check out the desired release tag.
If you‘re intending to build WebView just in order to develop, modify, or customise it, it’s usually best to work directly on the latest version of the master branch. Chromium's master branch is covered by a large number of automated build and test systems that ensure it is sufficiently stable for development purposes at almost all times.
If you want to build WebView for a version of Android which was recently released or currently in development, you may find that the current stable version in the public repository is not yet compatible with that version of Android.
If this happens, you‘re likely to see errors referring to the
targetSdkVersion of the WebView APK, or about a class called
WebViewChromiumFactoryProviderFor<version> being missing. You can’t fix these problems by changing the
targetSdkVersion or adding the missing class: this will just cause difficult-to-diagnose issues later when the WebView is actually used by applications that rely on newly introduced APIs.
At present, the changes required in WebView to support a new version of Android are developed in a non-public repository, and we only release the WebView changes after the source code for the new version of Android has been released.
For development and testing purposes, you can try a newer version of WebView which may be compatible, but since newer versions have not yet been qualified as stable they shouldn't generally be used in a shipping device. You can contact the WebView team via the android-webview-dev Google group for guidance.
WebView is configured at build time using GN arguments. The most important GN arguments to build a release WebView suitable for end users are:
target_os = "android" target_cpu = "arm64" # or "arm", "x86", or "x64"; see below # Create an official release build. Only official builds should be distributed # to users, as non-official builds are intended for development and may not # be configured appropriately for production. is_debug = false is_official_build = true # WebView's efficient native library loading mechanism is not compatible with # component builds of Chromium. is_component_build = false # Disable Google-specific branding/features is_chrome_branded = false use_official_google_api_keys = false # Significantly reduces binary size at the cost of preventing Android's native # crash handler from being able to produce useful stack unwindings. exclude_unwind_tables = true
target_cpu option must be set to the CPU architecture which corresponds to your Android build. 64-bit builds of WebView (for
x64) include the code for both the 64-bit and corresponding 32-bit architecture, to support both 64-bit and 32-bit applications. Any Android device which is able to run 64-bit applications must use a 64-bit build: a WebView built for
arm will not function correctly on an
target_cpumay not be the actual CPU architecture of the hardware. Some Android devices have a 64-bit CPU but run a 32-bit version of Android and are not compatible with 64-bit applications. On these devices you should use a 32-bit version of WebView.
android_sdk_release option should always be left as the default setting for the version of the Chromium code you are using; do not specify a different version. It is not necessary or beneficial to use an older SDK even if you are building a WebView for an older Android version - the built WebView is fully backward compatible, and building with older SDKs is not tested or supported.
By default the WebView APK will be signed with an insecure test key provided as part of the public Chromium source code. For distribution to users, it should be signed with a private key you control instead. Follow the general Android documentation to create a keystore, and copy the keystore file into your Chromium checkout. Configure the build to use this keystore with the following GN arguments:
# Paths which begin with // are relative to the "src" directory. default_android_keystore_path = "//my-keystore.keystore" default_android_keystore_name = "my-key-alias" default_android_keystore_password = "my-password"
The default Android package name for the standalone WebView is
com.android.webview, which AOSP is configured to use by default. If you plan to distribute updates to your WebView via an app store or other update mechanism outside of a system OTA update, then you may need to change this package name to one of your own choosing, to avoid conflicting with other versions of WebView. You can set a custom package name for the standalone WebView with the following GN argument:
# This is used as the Android package name and should follow normal Java/Android # naming conventions. system_webview_package_name = "com.mycompany.webview"
If you change the package name, you will need to reconfigure your Android build to use the new package name.
In addition, you may want to include support for proprietary audio and video codecs, as Google's WebView does. These codecs may be covered by patents or licensing agreements, and you should seek legal advice before distributing a build of WebView which includes them. You can enable them with the following GN arguments:
ffmpeg_branding = "Chrome" proprietary_codecs = true
Other build options may be used but are not supported by the WebView team and may cause build failures or problems at runtime. Many of the Chromium build options do not affect WebView at all, so you should investigate the implementation of any option you wish to change before assuming that it does what you expect.
See the general WebView build instructions.
The simplest way to add your own version of standalone WebView to the system image is to copy the APK into the
external/chromium-webview directory in your AOSP checkout, replacing the existing prebuilt APK. If you configured your own signing key when building WebView, you should edit
external/chromium-webview/Android.mk as follows:
# replace the line: # LOCAL_CERTIFICATE := $(DEFAULT_SYSTEM_DEV_CERTIFICATE) # with: LOCAL_CERTIFICATE := PRESIGNED
This will prevent the Android build system from resigning the APK with the default platform key.
For Monochrome or Trichrome APKs you will need to define your own prebuilt modules in a new
Android.mk file. You may need to contact the WebView team via the android-webview-dev Google group for help creating the correct build files.
The permitted WebView implementations are configured using an XML file in the framework. The default configuration file is located at
frameworks/base/core/res/res/xml/config_webview_packages.xml - you can either edit this file in place, or create a new configuration file for your product and include it as a resource overlay using the
PRODUCT_PACKAGE_OVERLAYS build variable.
There must be at least one provider defined in the configuration. If more than one provider is defined, they will be considered in the order listed in the file, and the first valid provider chosen by default. A menu is provided in the Android developer settings UI to allow the user to choose a different provider.
engbuilds of Android, the WebView's signature, preinstallation, and version code checks are not performed, to simplify development. Make sure to test your configuration using a
userbuild of Android to ensure that it will work as intended for users.
Here's a commented example XML file:
<?xml version="1.0" encoding="utf-8"?> <webviewproviders> <!-- Each webviewprovider tag has the following attributes: packageName (required): The Android package name of the APK. description (required): The name shown to the user in the developer settings menu. availableByDefault (default false): If true, this provider can be automatically selected by the framework, if it's the first valid choice. If false, this provider will only be used if the user selects it themselves from the developer settings menu. isFallback (default false): If true, this provider will be automatically disabled by the framework, preventing it from being used or updated by app stores, unless there is no other valid provider available. Only one provider can be a fallback. See "Special requirements for Monochrome" to understand one possible use case. Each webviewprovider tag can also contain zero or more signature tags as children. If the provider has no signature tags, then the provider must be preinstalled (or be an installed update to a preinstalled provider) to be considered valid. If at least one signature tag is specified, then the provider is considered valid if it is signed with any one of the given signatures. Each signature tag contains the entire public certificate corresponding to the private key used to sign the APK, encoded as base64. --> <!-- This provider is listed first and has "availableByDefault" set to true, so will be used as the default if it's valid. Because it does not have a signature specified, it must be preinstalled. --> <webviewprovider packageName="com.android.webview" description="AOSP WebView" availableByDefault="true"> </webviewprovider> <!-- This provider will not be used unless the user chooses it from the developer settings menu. It must be signed with the correct key but does not have to be preinstalled. --> <webviewprovider packageName="com.android.webview.beta" description="Beta WebView"> <signature>MIIFxzCCA6+gAw ... FdCQ==</signature> </webviewprovider> <!-- This provider will be disabled automatically, and will not receive updates from app stores, unless no other provider is valid. --> <webviewprovider packageName="com.android.webview.fallback" description="Fallback WebView" isFallback="true"> </webviewprovider> </webviewproviders>
The name of the WebView package is specified as a string resource in the framework. The default value is located in
frameworks/base/core/res/res/values/config.xml under the resource name
config_webViewPackageName - you can either edit this file in place, or create a new configuration file for your product and include it as a resource overlay using the
PRODUCT_PACKAGE_OVERLAYS build variable.
In order to allow your WebView implementation to be updated without requiring a full system OTA update, you need several things:
Secure signing keys. Your WebView APK must be signed with a key that you generated and keep safe, as described above. If this key were to be compromised, an attacker could potentially trick users into installing a malicious version of WebView on their device, affecting all apps which use WebView.
A unique package name. Your APK should have a package name which refers to your company/organisation, to differentiate it from other versions of WebView. You should follow the usual Java package naming conventions, using a domain name you control in reverse order.
A distribution mechanism. WebView is a normal APK, so can be installed onto a device by any mechanism that can install APKs. You might distribute updates by publishing them in an Android app store, by using a custom updater specific to your Android build which downloads the APK directly, or by allowing users to download the APK themselves and install it via sideloading (though this probably should only be used for development/test versions). Ideally, your distribution mechanism should update WebView automatically without user intervention, to ensure that users receive the latest security updates.
Standalone WebView is not generally visible to the user unless they go looking for it, since it‘s a system app with no UI. In contrast, Monochrome is a web browser as well as a WebView implementation, which makes it much more visible, since it’s a normal app with a launcher icon.
This means that the user may wish to be able to disable Monochrome in some circumstances; for example, if they prefer to use a different web browser. Allowing the user to do this without breaking applications which use WebView can be difficult - on current versions of Android, WebView cannot function correctly if the package is disabled, and app stores generally do not update disabled apps, so the user would not receive security updates. An alternate WebView implementation must be provided on the device to allow users to disable Monochrome without unwanted side effects.
The simplest option is to also preinstall the standalone WebView, and mark it as
isFallback="true" in the framework WebView configuration. The framework will then automatically disable the standalone WebView in most cases, and will only re-enable it if the user does in fact disable Monochrome. This will allow the implementation that the user is using to receive updates, while blocking unnecessary updates of the implementation that is not being used.
However, preinstalling both Monochrome and the standalone WebView takes up a lot of space, as they‘re both quite large. To avoid this, it’s possible to preinstall a “stub” version of the standalone WebView instead, which is much smaller, but still performs the function of a full WebView APK by using a special codepath in the framework: it loads its actual implementation from the preinstalled Monochrome APK at runtime. The stub and Monochrome must be matching versions for this to work - they should be built together in a single build, and any time you build a new version of Monochrome you should also rebuild the stub.
Currently, the public Chromium source code does not contain a suitable stub WebView implementation. Please contact the WebView team for assistance if you're planning to ship a configuration based on Monochrome.
When an application uses WebView, the WebView implementation code is loaded directly into that app‘s process. This means that the WebView code has access to all of that app’s data, both in memory and on disk, and can make use of any of that app's Android permissions. A malicious WebView implementation APK would therefore be able to compromise the security of any app on the device which uses WebView.
To mitigate this risk, the AOSP framework code only allows the WebView implementation APK(s) specified by the AOSP system integrator to be used.