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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// A small example application showing the use of the C++ Headless Chrome
// library. It navigates to a web site given on the command line, waits for it
// to load and prints out the DOM.
// Tip: start reading from the main() function below.
#include "base/bind.h"
#include "base/command_line.h"
#include "base/memory/weak_ptr.h"
#include "headless/public/devtools/domains/page.h"
#include "headless/public/devtools/domains/runtime.h"
#include "headless/public/headless_browser.h"
#include "headless/public/headless_devtools_client.h"
#include "headless/public/headless_devtools_target.h"
#include "headless/public/headless_web_contents.h"
#include "ui/gfx/geometry/size.h"
// This class contains the main application logic, i.e., waiting for a page to
// load and printing its DOM. Note that browser initialization happens outside
// this class.
class HeadlessExample : public headless::HeadlessWebContents::Observer,
public headless::page::Observer {
HeadlessExample(headless::HeadlessBrowser* browser,
headless::HeadlessWebContents* web_contents);
~HeadlessExample() override;
// headless::HeadlessWebContents::Observer implementation:
void DevToolsTargetReady() override;
// headless::page::Observer implementation:
void OnLoadEventFired(
const headless::page::LoadEventFiredParams& params) override;
// Tip: Observe headless::inspector::ExperimentalObserver::OnTargetCrashed to
// be notified of renderer crashes.
void OnDomFetched(std::unique_ptr<headless::runtime::EvaluateResult> result);
// The headless browser instance. Owned by the headless library. See main().
headless::HeadlessBrowser* browser_;
// Our tab. Owned by |browser_|.
headless::HeadlessWebContents* web_contents_;
// The DevTools client used to control the tab.
std::unique_ptr<headless::HeadlessDevToolsClient> devtools_client_;
// A helper for creating weak pointers to this class.
base::WeakPtrFactory<HeadlessExample> weak_factory_;
namespace {
HeadlessExample* g_example;
HeadlessExample::HeadlessExample(headless::HeadlessBrowser* browser,
headless::HeadlessWebContents* web_contents)
: browser_(browser),
weak_factory_(this) {
HeadlessExample::~HeadlessExample() {
// Note that we shut down the browser last, because it owns objects such as
// the web contents which can no longer be accessed after the browser is gone.
// This method is called when the tab is ready for DevTools inspection.
void HeadlessExample::DevToolsTargetReady() {
// Attach our DevTools client to the tab so that we can send commands to it
// and observe events.
// Start observing events from DevTools's page domain. This lets us get
// notified when the page has finished loading. Note that it is possible
// the page has already finished loading by now. See
// HeadlessShell::DevToolTargetReady for how to handle that case correctly.
void HeadlessExample::OnLoadEventFired(
const headless::page::LoadEventFiredParams& params) {
// The page has now finished loading. Let's grab a snapshot of the DOM by
// evaluating the outerHTML property on the body element.
base::Bind(&HeadlessExample::OnDomFetched, weak_factory_.GetWeakPtr()));
void HeadlessExample::OnDomFetched(
std::unique_ptr<headless::runtime::EvaluateResult> result) {
std::string dom;
// Make sure the evaluation succeeded before reading the result.
if (result->HasExceptionDetails()) {
LOG(ERROR) << "Failed to evaluate document.body.outerHTML: "
<< result->GetExceptionDetails()->GetText();
} else if (result->GetResult()->GetValue()->GetAsString(&dom)) {
printf("%s\n", dom.c_str());
// Shut down the browser (see ~HeadlessExample).
delete g_example;
g_example = nullptr;
// This function is called by the headless library after the browser has been
// initialized. It runs on the UI thread.
void OnHeadlessBrowserStarted(headless::HeadlessBrowser* browser) {
// In order to open tabs, we first need a browser context. It corresponds to a
// user profile and contains things like the user's cookies, local storage,
// cache, etc.
headless::HeadlessBrowserContext::Builder context_builder =
// Here we can set options for the browser context. As an example we enable
// incognito mode, which makes sure profile data is not written to disk.
// Construct the context and set it as the default. The default browser
// context is used by the Target.createTarget() DevTools command when no other
// context is given.
headless::HeadlessBrowserContext* browser_context = context_builder.Build();
// Get the URL from the command line.
base::CommandLine::StringVector args =
if (args.empty()) {
LOG(ERROR) << "No URL to load";
GURL url(args[0]);
// Open a tab (i.e., HeadlessWebContents) in the newly created browser
// context.
headless::HeadlessWebContents::Builder tab_builder(
// We can set options for the opened tab here. In this example we are just
// setting the initial URL to navigate to.
// Create an instance of the example app, which will wait for the page to load
// and print its DOM.
headless::HeadlessWebContents* web_contents = tab_builder.Build();
g_example = new HeadlessExample(browser, web_contents);
int main(int argc, const char** argv) {
// This function must be the first thing we call to make sure child processes
// such as the renderer are started properly. The headless library starts
// child processes by forking and exec'ing the main application.
headless::RunChildProcessIfNeeded(argc, argv);
// Create a headless browser instance. There can be one of these per process
// and it can only be initialized once.
headless::HeadlessBrowser::Options::Builder builder(argc, argv);
// Here you can customize browser options. As an example we set the window
// size.
builder.SetWindowSize(gfx::Size(800, 600));
// Pass control to the headless library. It will bring up the browser and
// invoke the given callback on the browser UI thread. Note: if you need to
// pass more parameters to the callback, you can add them to the Bind() call
// below.
return headless::HeadlessBrowserMain(builder.Build(),