DOM Distiller

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

The current efforts that will be powered by DOM Distiller:

• Reader mode: a mobile-friendly viewing mode for Chrome mobile

How to use Reader mode on mobile Chrome

• Open Chrome on your mobile device
• Navigate to chrome://flags and search for "Reader mode" (Menu -> Find in page -> Enable Reader Mode Toolbar Icon), or directly go to chrome://flags#enable-reader-mode-toolbar-icon
• Click Enable to turn on Reader mode
• Click "Relaunch Now" at the bottom of the page
• Next time you're trying to read a page, tap on the "Reader mode" icon in the toolbar to try it out!

Continuous integration

• 
• drone.io waterfall

Get the code

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

git clone https://github.com/chromium/dom-distiller.git

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.

Developing on Linux

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

sudo ./install-build-deps.sh

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 (chromedriver_mac32.zip) from the Download page
• Unzip the chromedriver_mac32.zip 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.

Tools for contributing

The DOM Distiller project uses the Chromium tools for collaboration. For code reviews, the Chromium Rietveld code review tool 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 https://chromium.googlesource.com/chromium/tools/depot_tools
export PATH="/path/to/depot_tools:$PATH"

You must also setup your local checkout needs to point to the Chromium Rietveld server. This is a one-time setup for your checkout, so from your dom-distiller checkout folder, run:

git cl config

• Rietveld server: https://codereview.chromium.org
• You can leave the rest of the fields blank.

Building

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] (https://code.google.com/p/googletest/wiki/AdvancedGuide#Running_a_Subset_of_the_Tests). 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 package Copies the main build artifacts into the out/package folder, typically the extracted JS and protocol buffer files.

Contributing

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 @chromium.org. account.
• For password, get it from GoogleCode.com settings page when logged into your @chromium.org account, and add the full machine code.google.com login line to your ~/.netrc file.

Committing a CL

• Change upstream to remote master, push cl, then revert upstream to local:

git branch -u origin/master
git cl land
git branch -u master

• For username, use your GitHub account name (the username, not the full e-mail).
• For password, use your GitHub password.
  • If you have two-factor authentication enabled, create a personal access token at your application settings page and use that as your password.

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 GYP to setup ninja build files using

build/gyp_chromium

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/isolate.py 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=http://www.example.com \
  > ./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=2

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:

distill http://example.com/article.html

Debug Code

Interactive debugging

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

• Update the test JavaScript by running ant gwtc.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:

org.chromium.distiller.JsTestEntry.run()

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

org.chromium.distiller.JsTestEntry.runWithFilter('MyTestClass.testSomething')

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.

Features

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.

Logging

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

• ant test: Terminal
• 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.

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

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.