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  1. ccfe233 Fix EmbedExtractorTest.testDivCaption by Wei-Yin Chen (陳威尹) · 10 months ago master
  2. 8825eaf In tests, render elements before getting their innerText by Wei-Yin Chen (陳威尹) · 10 months ago
  3. 8c9af2c Make generateOutput(textOnly=true) standard compliant by Wei-Yin Chen (陳威尹) · 10 months ago
  4. 9596033 Skip elements with zero area when finding article element by Wei-Yin Chen (陳威尹) · 1 year, 6 months ago
  5. 38037b3 Update docs after GoB/gerrit migration by Wei-Yin Chen (陳威尹) · 1 year, 8 months ago

DOM Distiller

DOM Distiller aims to provide a better reading experience by distilling the content of the web pages. This distilled content can then be used in a variety of ways.

Projects or features powered by DOM Distiller:

DOM Distiller is loosely based off of a research project called “Boilerpipe”. The original paper, the presentation, source, and more info can be found here:

Report a bug

We use the same bug tracking system Chromium uses, crbug, and the DOM distiller related bugs are filed under component:UI>Browser>ReaderMode component.

If the extracted contents have missing or extra text or images, it‘s considered a bug. If a long non-mobile-friendly article doesn’t trigger the infobar on Chrome on Android, you can also file a bug.

How to use Reader mode on Chrome on Android

This feature was already launched, so you should be able to use it on current version of Chrome on Android. If you would like to configure the triggering logic, follow these steps:

  • Open Chrome on your Android phone.
  • Navigate to chrome://flags and search for “Reader mode” (Menu -> Find in page -> Reader Mode triggering), or directly go to chrome://flags#reader-mode-heuristics.
  • Choose “Non-mobile-friendly article” to turn on Reader mode for non-mobile-friendly articles. This is the default behavior. You could choose “All articles” to turn on Reader mode for articles, or choose “Always” for debugging.
  • Click “Relaunch Now” at the bottom of the page.
  • Next time you're trying to read a page, tap on the “Make page mobile-friendly” infobar to try it out!

Continuous integration

Get the code

In a folder where you want the code (outside of the chromium checkout):

git clone

A dom-distiller folder will be created in the folder you run that command.

Environment setup

Before you build for the first time, you need to install the build dependencies.

For all platforms, it is require to download and install Google Chrome browser.

ChromeDriver requires Google Chrome to be installed at a specific location (the default location for the platform). See ChromeDriver documentation for details.

Also install the git hooks:


Developing on Ubuntu/Debian

Install the dependencies by entering the dom-distiller folder and running:

sudo ./

Ubuntu 14.04 64-bit is recommended.

Developing on Mac OS X

  • Install JDK 7 using either your organizations software management tool, or download it from Oracle.

  • Install Homebrew.

  • Install ant and python using Homebrew:

    brew install ant python
  • Since both the protocol buffer compiler and Python bindings are needed, install the protobuf package with the --with-python command line parameter:

    brew install protobuf --with-python
  • Create a folder named buildtools inside your DOM Distiller checkout

  • Download ChromeDriver ( from the Download page

  • Unzip the and ensure the binary ends up in your buildtools folder.

  • Install the PyPI package management tool pip by running:

    sudo easy_install pip
  • Install selenium using pip:

    pip install --user selenium

For the rest of this guide, there are sometimes references to a tool called xvfb and specifically when running shell commands using xvfb-run. When you develop using a Mac OS X, you can remove that part of the command. For example xvfb-run echo would just become echo.

Developing with Vagrant

This option could be useful if you want to develop on an unsupported system like Windows or Red Hat Linux. Even if you are on a supported system but would rather not touch the system too much, Vagrant is a viable alternative.

The Vagrant VM is based on Ubuntu 14.04.

  • Install Vagrant on your system. Version 1.7.2 or higher is recommended.

  • Launch the Vagrant VM instance

    vagrant up
  • SSH to the VM

    vagrant ssh

Tools for contributing

The DOM Distiller project uses the Chromium tools for collaboration. For code reviews, Chromium Gerrit is used and the set of tools found in depot_tools is also required.

To get depot_tools, follow the guide at Chrome infrastructure documentation for depot_tools.

The TL;DR of that is to run this from a folder where you install developer tools, for example in your $HOME folder:

git clone
export PATH="/path/to/depot_tools:$PATH"


Using ant

ant is the tool we use to build, and the available targets can be listed using ant -p, but the typical targets you might use when you work on this project is:

  • ant test Runs all tests.
  • ant test -Dtest.filter=$FILTER_PATTERN where $FILTER_PATTERN is a gtest_filter pattern. For example *.FilterTest.*:*Foo*-*Bar* would run all tests containing .FilterTest. and Foo, but not those with Bar.
  • ant gwtc compiles .class + .java files to JavaScript. Standalone JavaScript is available at war/domdistiller/domdistiller.nocache.js.
  • ant gwtc.jstests creates a standalone JavaScript for the tests.
  • ant extractjs creates standalone JavaScript from output of ant gwtc. The compiled JavaScript file is available at out/domdistiller.js.
  • ant extractjs.jstests creates a standalone JavaScript for the tests.
  • ant package Copies the main build artifacts into the out/package folder, typically the extracted JS and protocol buffer files.


You can use regular git command when developing in this project and use git cl for collaboration.

Uploading a CL for review

On your branch, run: git cl upload. The first time you do this, you will have to provide a username and password.

  • For username, use your account.
  • For password, get it from settings page when logged into your account, and add the full machine login line to your ~/.netrc file.

Landing a CL

  • After getting LGTM, you can land the CL in the code review system by clicking the “Submit” button.

Code formatting

Before uploading a CL it is recommended to run git cl format. However, this requires adding symbolic links to your chromium checkout.

Inside the buildtools folder of your checkout, add the following symbolic links:

  • clang_format/path/to/chromium/src/buildtools/clang_format/
  • linux64/path/to/chromium/src/buildtools/linux64/ (only for Linux 64-bit platform)
  • mac/path/to/chromium/mac/buildtools/linux64/ (only for Mac platform)

Doing this enables you to run the command git cl format to fix the formatting of your code.

Run in Chrome for desktop

In this section, the following shell variables and are assumed correctly set:

export CHROME_SRC=/path/to/chromium/src
export DOM_DISTILLER_DIR=/path/to/dom-distiller
  • Pull generated package (from ant package) into Chrome. You can use this handy bash-function to help with that:

    roll-distiller () {
        (cd $DOM_DISTILLER_DIR && ant package) && \
        rm -rf $CHROME_SRC/third_party/dom_distiller_js/dist/* && \
        cp -rf $DOM_DISTILLER_DIR/out/package/* $CHROME_SRC/third_party/dom_distiller_js/dist/ && \
        touch $CHROME_SRC/components/resources/dom_distiller_resources.grdp
  • From $CHROME_SRC run GN to setup ninja build files using

    gn args out/Debug

Running the Chrome browser with distiller support

  • For running Chrome, you need to build the chrome target:

    ninja -C out/Debug chrome
  • Run chrome with DOM Distiller enabled:

    out/Debug/chrome --enable-dom-distiller
  • This adds a menu item Distill page that you can use to distill web pages.

  • You can also go to chrome://dom-distiller to access the debug page.

  • To have a unique user profile every time you run Chrome, you can also add --user-data-dir=/tmp/$(mktemp -d) as a command line parameter. On Mac OS X, you can instead write --user-data-dir=$(mktemp -d 2>/dev/null || mktemp -d -t 'chromeprofile').

Running the automated tests in Chromium

  • For running the tests, you need to build the components_browsertests target:

    ninja -C out/Debug components_browsertests
  • Run the components_browsertests binary to execute the tests. You can prefix the command with xvfb-run to avoid pop-up windows:

    xvfb-run out/Debug/components_browsertests
  • To only run tests related to DOM Distiller, run:

    xvfb-run out/Debug/components_browsertests --gtest_filter=\*Distiller\*
  • For running tests as isolates, you need to build components_browsertests_run and execute them using the swarming tool:

    ninja -C out/Debug components_browsertests_run
    python tools/swarming_client/ run -s out/Debug/components_browsertests.isolated

Running the content extractor

To extract the content from a web page directly, you can run:

xvfb-run out/Debug/components_browsertests \
  --gtest_filter='*MANUAL_ExtractUrl' \
  --run-manual \
  --test-tiny-timeout=600000 \
  --output-file=./extract.out \
  --url= \
  > ./extract.log 2>&1

extract.out has the extracted HTML, extract.log has the console logging.

If you need more logging, you can add the following arguments to the command:

  • Chrome browser: --vmodule=*distiller*=2
  • Content extractor: --debug-level=99

If this is something you often do, you can put the following function in a bash file you include (for example ~/.bashrc) and use it for iterative development:

distill() {
    roll-distiller && \
    ninja -C out/Debug components_browsertests &&
    xvfb-run out/Debug/components_browsertests \
      --gtest_filter='*MANUAL_ExtractUrl' \
      --run-manual \
      --test-tiny-timeout=600000 \
      --output-file=./extract.out \
      --url=$1 \
      > ./extract.log 2>&1

Usage when running from $CHROME_SRC:


Debug Code

Interactive debugging

You can use the Chrome Developer Tools to debug DOM Distiller:

  • Update the test JavaScript by running ant extractjs.jstests or ant test.

  • Open war/test.html in Chrome desktop

  • Open the Console panel in Developer Tools (Ctrl-Shift-J). On Mac OS X you can use ⌥-⌘-I (uppercase I) as the shortcut.

  • Run all tests by calling:
  • To run only a subset of tests, you can use a regular expression that matches a single test or multiple tests:


The Sources panel contains both the extracted JavaScript and all the Java source files as long as you haven't disabled JavaScript source maps in Developer Tools. You can set breakpoints in the Java source files and then inspect all kinds of different interesting things when that breakpoint is hit.

When a test fails, you will see several stack traces. One of these contains clickable links to the corresponding Java source files for the stack frames.

Developer extension

After running ant package, the out/extension folder contains an unpacked Chrome extension. This can be added to Chrome and used for development.

  • Go to chrome://extensions
  • Enable developer mode
  • Select to load an unpacked extension and point to the out/extension folder.


The extension currently supports profiling the extraction code.

It also adds a panel to the Developer Tools which you can use to trigger extraction on the inspected page. This can be used to trigger and profile extraction on a mobile device which you are currently inspecting using chrome://inspect.


To add logging, you can use the LogUtil. You can use the Java function LogUtil.logToConsole(). Destination of logs:

  • ant test: Terminal. To get more verbose output, use ant test -Dtest.debug_level=99.
  • Chrome browser: the Chrome log file, as set by shell variable $CHROME_LOG_FILE. A release mode build of Chrome will log all JavaScript INFO there if you start Chrome with --enable-logging. You can add --enable-logging=stderr to have the log go to stderr instead of a file.
  • Content extractor: See [documentation about extract.log above] (#running-the-content-extractor).

For an example, see $DOM_DISTILLER_DIR/java/org/chromium/distiller/

Use ant package '-Dgwt.custom.args=-style PRETTY' for easier JavaScript debugging.

Mobile distillation from desktop

  1. In the tab with the interesting URL, bring up the Developer Tools emulation panel (the mobile device icon).
  2. Select the desired Device and reload the page. Verify that you get what you expect. For example a Nexus 4 might get a mobile site, whereas Nexus 7 might get the desktop site.
  3. The User-Agent can be copied directly out from the UA field. This field does not even require reload after changing device, but it is good practice to verify that you get what you expect. Copy this to the clipboard.
  4. (Re)start chrome with --user-agent="$USER_AGENT_FROM_CLIPBOARD". Remember to also add --enable-dom-distiller.
  5. Distill the same URL in viewer by either using the menu Distill page or by going to chrome://dom-distiller and using the input field there.
  6. Have fun scrutinizing the Chrome log file.

If you want you can copy some of these User-Agent aliases into normal bash aliases for easy access later. For example, Nexus 4 would be:

--user-agent="Mozilla/5.0 (Linux; Android 4.2.1; en-us; Nexus 4 Build/JOP40D) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166 Mobile Safari/535.19"

Steps 1-3 in the guide above can typically be done in a stable version of Chrome, whereas the rest of the steps is typically done in your own build of Chrome (hence the “(Re)” in step 4). Besides speed, this also facilitates side-by-side comparison.