Embed a mojo ApplicationManager in content/browser

content/browser/mojo/mojo_shell_context.cc

+// Copyright 2015 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.
+
+#include "content/browser/mojo/mojo_shell_context.h"
+
+#include "base/lazy_instance.h"
+#include "base/macros.h"
+#include "base/single_thread_task_runner.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/thread_task_runner_handle.h"
+#include "content/common/process_control.mojom.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/content_browser_client.h"
+#include "content/public/browser/utility_process_host.h"
+#include "content/public/browser/utility_process_host_client.h"
+#include "content/public/common/content_client.h"
+#include "content/public/common/service_registry.h"
+#include "mojo/application/public/cpp/application_delegate.h"
+#include "mojo/common/url_type_converters.h"
+#include "mojo/services/network/public/interfaces/url_loader.mojom.h"
+#include "mojo/shell/application_loader.h"
+#include "mojo/shell/static_application_loader.h"
+#include "third_party/mojo/src/mojo/public/cpp/bindings/interface_request.h"
+#include "third_party/mojo/src/mojo/public/cpp/bindings/string.h"
+
+namespace content {
+
+namespace {
+
+// Virtual app URL to use as the requestor identity when connecting from browser
+// code to a Mojo app via the shell proxy.
+const char kBrowserAppUrl[] = "system:content_browser";
+
+// An extra set of apps to register on initialization, if set by a test.
+const MojoShellContext::StaticApplicationMap* g_applications_for_test;

[Lei Zhang, 2015/08/25 03:16:03]

Should this be explicitly initialized to nullptr?

[Ken Rockot(use gerrit already), 2015/08/25 03:54:51]

There's no need to do this as C++ guarantees zero-initialization for static
storage:

http://en.cppreference.com/w/cpp/language/zero_initialization

+
+void StartProcessOnIOThread(mojo::InterfaceRequest<ProcessControl> request) {
+  UtilityProcessHost* process_host =
+      UtilityProcessHost::Create(nullptr, nullptr);
+  // TODO(rockot): Make it possible for the embedder to associate app URLs with
+  // app names so we can have more meaningful process names here.
+  process_host->SetName(base::UTF8ToUTF16("Mojo Application"));

[Lei Zhang, 2015/08/25 03:16:04]

I'm assuming because this is in mojo_shell, it doesn't matter that this isn't
translated, since we are not shipping it to users?

[Ken Rockot(use gerrit already), 2015/08/25 03:54:51]

This is not in Mojo shell. This code is shipping to users but there are no
production code paths which trigger it in practice yet. We do need to fix it.

+  process_host->StartMojoMode();
+  ServiceRegistry* services = process_host->GetServiceRegistry();
+  services->ConnectToRemoteService(request.Pass());
+}
+
+void OnApplicationLoaded(const GURL& url, bool success) {
+  if (!success)
+    LOG(ERROR) << "Failed to launch Mojo application for " << url.spec();
+}
+
+// The default loader to use for all applications. This launches a utility
+// process and forwards the Load request the ProcessControl service there.
+class UtilityProcessLoader : public mojo::shell::ApplicationLoader {
+ public:
+  UtilityProcessLoader() {}
+  ~UtilityProcessLoader() override {}
+
+ private:
+  // mojo::shell::ApplicationLoader:
+  void Load(
+      const GURL& url,
+      mojo::InterfaceRequest<mojo::Application> application_request) override {
+    ProcessControlPtr process_control;
+    auto process_request = mojo::GetProxy(&process_control);
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&StartProcessOnIOThread, base::Passed(&process_request)));
+    process_control->LoadApplication(url.spec(), application_request.Pass(),
+                                     base::Bind(&OnApplicationLoaded, url));
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(UtilityProcessLoader);
+};
+
+}  // namespace
+
+// Thread-safe proxy providing access to the shell context from any thread.
+class MojoShellContext::Proxy {
+ public:
+  Proxy(MojoShellContext* shell_context)

[Lei Zhang, 2015/08/25 03:16:04]

nit: explicit

[Ken Rockot(use gerrit already), 2015/08/25 03:54:51]

Acknowledged.

+      : shell_context_(shell_context),
+        task_runner_(base::ThreadTaskRunnerHandle::Get()) {}
+
+  ~Proxy() {}
+
+  void ConnectToApplication(
+      const GURL& url,
+      mojo::InterfaceRequest<mojo::ServiceProvider> request) {
+    if (task_runner_ == base::ThreadTaskRunnerHandle::Get()) {
+      if (shell_context_)

[Lei Zhang, 2015/08/25 03:16:04]

Here you are checking for |shell_context_|, but in the else block, you pass it
as the object. Couldn't that crash if |shell_context_| is NULL?

[Ken Rockot(use gerrit already), 2015/08/25 03:54:51]

This is a pretty subtle thing, but I believe it's safe. shell_context_ lives on
task_runner_'s thread. If we're currently on that thread in this method, we can
test shell_context_ and call ConnectToApplicationOnOwnThread.

If we're not on task_runner_'s thread we post a task there to run the same
function. Because shell_context_'s lifetime is bound to that of task_runner_'s
MessageLoop, we know that if the task runs at all, the ShellContext is still
valid. Conversely if the ShellContext is no longer valid it means the
MessageLoop was destroyed and the task posted here will never run.

In fact I think the null test here could be replaced with a DCHECK.

+        shell_context_->ConnectToApplicationOnOwnThread(url, request.Pass());
+    } else {
+      // |shell_context_| outlives the main MessageLoop, so it's safe for it to
+      // be unretained here.
+      task_runner_->PostTask(
+          FROM_HERE,
+          base::Bind(&MojoShellContext::ConnectToApplicationOnOwnThread,
+                     base::Unretained(shell_context_), url,
+                     base::Passed(&request)));
+    }
+  }
+
+ private:
+  MojoShellContext* shell_context_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(Proxy);
+};
+
+// static
+base::LazyInstance<scoped_ptr<MojoShellContext::Proxy>>
+    MojoShellContext::proxy_ = LAZY_INSTANCE_INITIALIZER;
+
+void MojoShellContext::SetApplicationsForTest(
+    const StaticApplicationMap* apps) {
+  g_applications_for_test = apps;
+}
+
+MojoShellContext::MojoShellContext()
+    : application_manager_(new mojo::shell::ApplicationManager(this)) {
+  proxy_.Get().reset(new Proxy(this));
+  application_manager_->set_default_loader(
+      scoped_ptr<mojo::shell::ApplicationLoader>(new UtilityProcessLoader));
+
+  StaticApplicationMap apps;
+  GetContentClient()->browser()->RegisterMojoApplications(&apps);
+  if (g_applications_for_test) {
+    // Add testing apps to the map, potentially overwriting whatever the
+    // browser client registered.
+    for (const auto& entry : *g_applications_for_test)
+      apps[entry.first] = entry.second;
+  }
+  for (const auto& entry : apps) {
+    application_manager_->SetLoaderForURL(
+        scoped_ptr<mojo::shell::ApplicationLoader>(
+            new mojo::shell::StaticApplicationLoader(entry.second)),
+        entry.first);
+  }
+}
+
+MojoShellContext::~MojoShellContext() {
+}
+
+// static
+void MojoShellContext::ConnectToApplication(
+    const GURL& url,
+    mojo::InterfaceRequest<mojo::ServiceProvider> request) {
+  proxy_.Get()->ConnectToApplication(url, request.Pass());
+}
+
+void MojoShellContext::ConnectToApplicationOnOwnThread(
+    const GURL& url,
+    mojo::InterfaceRequest<mojo::ServiceProvider> request) {
+  mojo::URLRequestPtr url_request = mojo::URLRequest::New();
+  url_request->url = mojo::String::From(url);
+  application_manager_->ConnectToApplication(
+      url_request.Pass(), GURL(kBrowserAppUrl), request.Pass(),
+      mojo::ServiceProviderPtr(), base::Bind(&base::DoNothing));
+}
+
+GURL MojoShellContext::ResolveMappings(const GURL& url) {
+  return url;
+}
+
+GURL MojoShellContext::ResolveMojoURL(const GURL& url) {
+  return url;
+}
+
+bool MojoShellContext::CreateFetcher(
+    const GURL& url,
+    const mojo::shell::Fetcher::FetchCallback& loader_callback) {
+  return false;
+}
+
+}  // namespace content