headless: Implement DevTools events

headless/lib/browser/domain_cc.template

 // This file is generated
 
 // Copyright 2016 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 "headless/public/domains/{{domain.domain | camelcase_to_hacker_style}}.h"
 
 #include "base/bind.h"
 
 namespace headless {
 
 namespace {{domain.domain | camelcase_to_hacker_style}} {
 
-Domain::Domain(internal::MessageDispatcher* dispatcher) : dispatcher_(dispatcher) {}
+Domain::Domain(internal::MessageDispatcher* dispatcher)
+    : dispatcher_(dispatcher) {
+  {% if "events" in domain %}
+    {# Register all events in this domain. #}
+    {% for event in domain.events %}
+  dispatcher_->RegisterEventHandler(
+      "{{domain.domain}}.{{event.name}}",
+      base::Bind(&Domain::Dispatch{{event.name | to_title_case}}Event,
+                 base::Unretained(this)));
+    {% endfor %}
+  {% endif %}
+}
+
+  {% if "events" in domain %}
+void Domain::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void Domain::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+  {% endif %}
 
 Domain::~Domain() {}
   {% for command in domain.commands %}
     {# Skip redirected commands. #}
     {% if "redirect" in command %}{% continue %}{% endif %}
 
     {% set method_name = command.name | to_title_case %}
     {% if "parameters" in command and "returns" in command %}
 void Domain::{{method_name}}(std::unique_ptr<{{method_name}}Params> params, base::Callback<void(std::unique_ptr<{{method_name}}Result>)> callback) {
   dispatcher_->SendMessage("{{domain.domain}}.{{command.name}}", params->Serialize(), base::Bind(&Domain::Handle{{method_name}}Response, callback));
@@ skipping 47 matching lines @@
 // static
 void Domain::Handle{{method_name}}Response(base::Callback<void(std::unique_ptr<{{method_name}}Result>)> callback, const base::Value& response) {
   if (callback.is_null())
     return;
   ErrorReporter errors;
   std::unique_ptr<{{method_name}}Result> result = {{method_name}}Result::Parse(response, &errors);
   DCHECK(!errors.HasErrors());
   callback.Run(std::move(result));
 }
 {% endfor %}
+{% if "events" in domain %}
+  {% for event in domain.events %}
+
+{# Generate dispatchers which call registered observers for an event. #}
+void Domain::Dispatch{{event.name | to_title_case}}Event({# -#}
+    {% if "parameters" in event %}{# -#}
+    const base::Value& params{# -#}
+    {% endif %}) {
+    {% if "parameters" in event %}
+  ErrorReporter errors;
+  std::unique_ptr<{{event.name | to_title_case}}Params> parsed_params({{event.name | to_title_case}}Params::Parse(params, &errors));
+  DCHECK(!errors.HasErrors());
+  FOR_EACH_OBSERVER(Observer, observers_, On{{event.name | to_title_case}}(*parsed_params));
+    {% else %}
+  FOR_EACH_OBSERVER(Observer, observers_, On{{event.name | to_title_case}}());

[dgozman, 2016/04/21 17:21:36]

It could be easier for clients to roll new versions of protocol if every event
has params. This makes signature of event method stable and adding (yet unused)
parameter to event won't break existing code.


Similar idea applies to generated shorthands for protocol methods. If domain or
method is hidden, it could make sense to only supply signature with a params
object to make it stable.

[Sami, 2016/04/22 10:36:22]

Great points, I didn't consider that we might add new parameters to events that
currently don't have any. I'll implement your second suggestion in the patch
that adds experimental commands.

+    {% endif %}
+}
+  {% endfor %}
+{% endif %}
 
 }  // namespace {{domain.domain | camelcase_to_hacker_style}}
 
 } // namespace headless