HeadlessDevToolsClientImpl::DispatchEvent to post a task

headless/lib/browser/headless_devtools_client_impl.cc

Index: headless/lib/browser/headless_devtools_client_impl.cc
diff --git a/headless/lib/browser/headless_devtools_client_impl.cc b/headless/lib/browser/headless_devtools_client_impl.cc
index 7179071b68d23da09b60b6c6fa3178df66106b13..166c47b5e4450c6cd533c8723866fbb0fdb016ca 100644
--- a/headless/lib/browser/headless_devtools_client_impl.cc
+++ b/headless/lib/browser/headless_devtools_client_impl.cc
@@ -6,10 +6,12 @@
 
 #include <memory>
 
+#include "base/bind.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/memory/ptr_util.h"
 #include "base/values.h"
+#include "content/public/browser/browser_thread.h"
 #include "content/public/browser/devtools_agent_host.h"
 
 namespace headless {
@@ -60,7 +62,10 @@ HeadlessDevToolsClientImpl::HeadlessDevToolsClientImpl()
       security_domain_(this),
       service_worker_domain_(this),
       tracing_domain_(this),
-      worker_domain_(this) {}
+      worker_domain_(this),
+      browser_main_thread_(content::BrowserThread::GetTaskRunnerForThread(
+          content::BrowserThread::UI)),
+      weak_ptr_factory_(this) {}
 
 HeadlessDevToolsClientImpl::~HeadlessDevToolsClientImpl() {}
 
@@ -90,8 +95,10 @@ void HeadlessDevToolsClientImpl::DispatchProtocolMessage(
     NOTREACHED() << "Badly formed reply";
     return;
   }
-  if (!DispatchMessageReply(*message_dict) && !DispatchEvent(*message_dict))
+  if (!DispatchMessageReply(*message_dict) &&
+      !DispatchEvent(std::move(message), *message_dict)) {
     DLOG(ERROR) << "Unhandled protocol message: " << json_message;
+  }
 }
 
 bool HeadlessDevToolsClientImpl::DispatchMessageReply(
@@ -120,6 +127,7 @@ bool HeadlessDevToolsClientImpl::DispatchMessageReply(
 }
 
 bool HeadlessDevToolsClientImpl::DispatchEvent(
+    std::unique_ptr<base::Value> owning_message,
     const base::DictionaryValue& message_dict) {
   std::string method;
   if (!message_dict.GetString("method", &method))
@@ -135,11 +143,24 @@ bool HeadlessDevToolsClientImpl::DispatchEvent(
       NOTREACHED() << "Badly formed event parameters";
       return false;
     }
-    it->second.Run(*result_dict);
+    // DevTools assumes event handling is async so we must post a task here or
+    // we risk breaking things.
+    browser_main_thread_->PostTask(
+        FROM_HERE, base::Bind(&HeadlessDevToolsClientImpl::DispatchEventTask,
+                              weak_ptr_factory_.GetWeakPtr(),
+                              base::Passed(std::move(owning_message)),
+                              &it->second, result_dict));

[Sami, 2016/08/01 11:05:02]

Might need to change the "auto it" above to "const auto& it" to make sure this
isn't pointing to a stack value.

[alex clarke (OOO till 29th), 2016/08/01 15:37:02]

As discussed offline I did something similar to nail down the type.

   }
   return true;
 }
 
+void HeadlessDevToolsClientImpl::DispatchEventTask(
+    std::unique_ptr<base::Value> owning_message,
+    base::Callback<void(const base::Value&)>* callback,
+    const base::DictionaryValue* result_dict) {
+  callback->Run(*result_dict);
+}
+
 void HeadlessDevToolsClientImpl::AgentHostClosed(
     content::DevToolsAgentHost* agent_host,
     bool replaced_with_another_client) {