Chromium 如何查找已经定义好的mojom函数实现c++

进程通信定义通常都是用.mojom文件或者idl文件格式

以content\common\frame.mojom里面的BeginNavigation函数为例。

一、如何查找BeginNavigation函数定义，在vscode里面直接搜索BeginNavigation，过滤条件

*.idl,*.mojom,*.cc

效果：

这样定义mojom找到了。

content\common\frame.mojom定义如下（截取部分）：

  // Sent by the renderer to request a navigation.// |blob_url_token| should be non-null when this is a navigation to a blob:// URL. The token will then be used to look up the blob associated with the// blob URL. Without this by the time the navigation code starts fetching// the URL the blob URL might no longer be valid. |blob_url_token| is// not part of BeginNavigationParams because that struct needs to be// cloneable, and thus can't contain mojo interfaces.// If an invalid BlobURLToken is passed in, or if the token doesn't match the// url in |common_params|, the navigation will result in a network error.// |navigation_client| is passed to the renderer to allow for further control// of the navigation. Allows for Commit and Cancels/Aborts.// Passing the |initiator_policy_container_keep_alive_handle| is just a means// to ensure that the PolicyContainerHost of the initiator RenderFrameHost is// kept alive, even if the RenderFrameHost itself has already been deleted in// the meantime. If this can be ensured in other ways, it is safe to pass a// mojo::NullRemote. In particular, if the initiator LocalFrame is alive when// issuing this mojo call, there is no need to pass// |initiator_policy_container_keep_alive_handle|, since the initiator// PolicyContainerHost is kept alive by LocalFrame's PolicyContainer.// TODO(https://crbug.com/1467502): |navigation_client| should not be// optional. Make it mandatory.// |renderer_cancellation_listener| is a per-navigation interface used to// listen to the end of the renderer-initiated navigation cancelation window// for this navigation. See comment for NavigationRendererCancellationListener// for more details.BeginNavigation(blink.mojom.CommonNavigationParams common_params,blink.mojom.BeginNavigationParams begin_params,pending_remote<blink.mojom.BlobURLToken>? blob_url_token,pending_associated_remote<NavigationClient>? navigation_client,pending_remote<blink.mojom.PolicyContainerHostKeepAliveHandle>?initiator_policy_container_keep_alive_handle,pending_receiver<NavigationRendererCancellationListener>renderer_cancellation_listener);

注意mojom文件编译时候会自动生成以下两个文件

out\Debug\gen\content\common\frame.mojom.cc

out\Debug\gen\content\common\frame.mojom.h

二、在vscode搜索BeginNavigation实现代码

第一部分、out\Debug\gen\+对应mojom文件相对目录.h这样存放

 例子：  out\Debug\gen\content\common\frame.mojom.h

              out\Debug\gen\content\common\frame.mojom.cc

    1）、发送方会调用在 ::mojo::internal::SendMojoMessage前设置好message.set_method_name("BeginNavigation");

知道此处打断点即可，可以不用想继续搜索发送方是谁了。

   看下规律frame.mojom.cc

void FrameHostProxy::BeginNavigation(::blink::mojom::CommonNavigationParamsPtr in_common_params, ::blink::mojom::BeginNavigationParamsPtr in_begin_params, ::mojo::PendingRemote<::blink::mojom::BlobURLToken> in_blob_url_token, ::mojo::PendingAssociatedRemote<::content::mojom::NavigationClient> in_navigation_client, ::mojo::PendingRemote<::blink::mojom::PolicyContainerHostKeepAliveHandle> in_initiator_policy_container_keep_alive_handle, ::mojo::PendingReceiver<NavigationRendererCancellationListener> in_renderer_cancellation_listener) {
#if BUILDFLAG(MOJO_TRACE_ENABLED)TRACE_EVENT1("mojom", "Send content::mojom::FrameHost::BeginNavigation", "input_parameters",[&](perfetto::TracedValue context){auto dict = std::move(context).WriteDictionary();perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("common_params"), in_common_params,"<value of type ::blink::mojom::CommonNavigationParamsPtr>");perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("begin_params"), in_begin_params,"<value of type ::blink::mojom::BeginNavigationParamsPtr>");perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("blob_url_token"), in_blob_url_token,"<value of type ::mojo::PendingRemote<::blink::mojom::BlobURLToken>>");perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("navigation_client"), in_navigation_client,"<value of type ::mojo::PendingAssociatedRemote<::content::mojom::NavigationClient>>");perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("initiator_policy_container_keep_alive_handle"), in_initiator_policy_container_keep_alive_handle,"<value of type ::mojo::PendingRemote<::blink::mojom::PolicyContainerHostKeepAliveHandle>>");perfetto::WriteIntoTracedValueWithFallback(dict.AddItem("renderer_cancellation_listener"), in_renderer_cancellation_listener,"<value of type ::mojo::PendingReceiver<NavigationRendererCancellationListener>>");});
#endifconst bool kExpectsResponse = false;const bool kIsSync = false;const bool kAllowInterrupt = true;const bool is_urgent = false;const uint32_t kFlags =((kExpectsResponse) ? mojo::Message::kFlagExpectsResponse : 0) |((kIsSync) ? mojo::Message::kFlagIsSync : 0) |((kAllowInterrupt) ? 0 : mojo::Message::kFlagNoInterrupt) |((is_urgent) ? mojo::Message::kFlagIsUrgent : 0);mojo::Message message(internal::kFrameHost_BeginNavigation_Name, kFlags, 0, 0, nullptr);mojo::internal::MessageFragment<::content::mojom::internal::FrameHost_BeginNavigation_Params_Data> params(message);params.Allocate();mojo::internal::MessageFragment<typename decltype(params->common_params)::BaseType> common_params_fragment(params.message());mojo::internal::Serialize<::blink::mojom::CommonNavigationParamsDataView>(in_common_params, common_params_fragment);params->common_params.Set(common_params_fragment.is_null() ? nullptr : common_params_fragment.data());MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(params->common_params.is_null(),mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,"null common_params in FrameHost.BeginNavigation request");mojo::internal::MessageFragment<typename decltype(params->begin_params)::BaseType> begin_params_fragment(params.message());mojo::internal::Serialize<::blink::mojom::BeginNavigationParamsDataView>(in_begin_params, begin_params_fragment);params->begin_params.Set(begin_params_fragment.is_null() ? nullptr : begin_params_fragment.data());MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(params->begin_params.is_null(),mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,"null begin_params in FrameHost.BeginNavigation request");mojo::internal::Serialize<mojo::InterfacePtrDataView<::blink::mojom::BlobURLTokenInterfaceBase>>(in_blob_url_token, &params->blob_url_token, &params.message());mojo::internal::Serialize<::content::mojom::NavigationClientAssociatedPtrInfoDataView>(in_navigation_client, &params->navigation_client, &params.message());mojo::internal::Serialize<mojo::InterfacePtrDataView<::blink::mojom::PolicyContainerHostKeepAliveHandleInterfaceBase>>(in_initiator_policy_container_keep_alive_handle, &params->initiator_policy_container_keep_alive_handle, &params.message());mojo::internal::Serialize<mojo::InterfaceRequestDataView<::content::mojom::NavigationRendererCancellationListenerInterfaceBase>>(in_renderer_cancellation_listener, &params->renderer_cancellation_listener, &params.message());MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(!mojo::internal::IsHandleOrInterfaceValid(params->renderer_cancellation_listener),mojo::internal::VALIDATION_ERROR_UNEXPECTED_INVALID_HANDLE,"invalid renderer_cancellation_listener in FrameHost.BeginNavigation request");#if defined(ENABLE_IPC_FUZZER)message.set_interface_name(FrameHost::Name_);message.set_method_name("BeginNavigation");
#endif// This return value may be ignored as false implies the Connector has// encountered an error, which will be visible through other means.::mojo::internal::SendMojoMessage(*receiver_, message);
}

2）、接收方BeginNavigation 定义如下out\Debug\gen\content\common\frame.mojom.cc

  有类似这样的字样就是实现方 impl->BeginNavigation

    case internal::kFrameHost_BeginNavigation_Name: {DCHECK(message->is_serialized());internal::FrameHost_BeginNavigation_Params_Data* params =reinterpret_cast<internal::FrameHost_BeginNavigation_Params_Data*>(message->mutable_payload());bool success = true;::blink::mojom::CommonNavigationParamsPtr p_common_params{};::blink::mojom::BeginNavigationParamsPtr p_begin_params{};::mojo::PendingRemote<::blink::mojom::BlobURLToken> p_blob_url_token{};::mojo::PendingAssociatedRemote<::content::mojom::NavigationClient> p_navigation_client{};::mojo::PendingRemote<::blink::mojom::PolicyContainerHostKeepAliveHandle> p_initiator_policy_container_keep_alive_handle{};::mojo::PendingReceiver<NavigationRendererCancellationListener> p_renderer_cancellation_listener{};FrameHost_BeginNavigation_ParamsDataView input_data_view(params, message);if (success && !input_data_view.ReadCommonParams(&p_common_params))success = false;if (success && !input_data_view.ReadBeginParams(&p_begin_params))success = false;if (success) {p_blob_url_token =input_data_view.TakeBlobUrlToken<decltype(p_blob_url_token)>();}if (success) {p_navigation_client =input_data_view.TakeNavigationClient<decltype(p_navigation_client)>();}if (success) {p_initiator_policy_container_keep_alive_handle =input_data_view.TakeInitiatorPolicyContainerKeepAliveHandle<decltype(p_initiator_policy_container_keep_alive_handle)>();}if (success) {p_renderer_cancellation_listener =input_data_view.TakeRendererCancellationListener<decltype(p_renderer_cancellation_listener)>();}if (!success) {ReportValidationErrorForMessage(message,mojo::internal::VALIDATION_ERROR_DESERIALIZATION_FAILED,FrameHost::Name_, 5, false);return false;}// A null |impl| means no implementation was bound.DCHECK(impl);impl->BeginNavigation(
std::move(p_common_params), 
std::move(p_begin_params), 
std::move(p_blob_url_token), 
std::move(p_navigation_client), 
std::move(p_initiator_policy_container_keep_alive_handle), 
std::move(p_renderer_cancellation_listener));return true;}

  第二部分、子进程定义

                   content\renderer\render_frame_impl.cc

  GetFrameHost()->BeginNavigation(MakeCommonNavigationParams(frame_->GetSecurityOrigin(), std::move(info),load_flags, has_download_sandbox_flag, from_ad,is_history_navigation_in_new_child_frame,request_destination),std::move(begin_navigation_params), std::move(blob_url_token),std::move(navigation_client_remote),std::move(initiator_policy_container_keep_alive_handle),std::move(renderer_cancellation_listener_receiver));

其中GetFrameHost()和FrameHostProxy对应关系很是巧妙。

mojom::FrameHost* RenderFrameImpl::GetFrameHost() {

  if (!frame_host_remote_.is_bound())

    GetRemoteAssociatedInterfaces()->GetInterface(&frame_host_remote_);

  return frame_host_remote_.get();

}

FrameHost和FrameHostProxy是同一个类吗？

先看mojo::AssociatedRemote<mojom::FrameHost> frame_host_remote_;定义

其中用模板对象AssociatedRemote初始化，那么看下定义

template <typename Interface>class AssociatedRemote {public:using InterfaceType = Interface;using PendingType = PendingAssociatedRemote<Interface>;using Proxy = typename Interface::Proxy_;

mojo::AssociatedRemote类的Proxy替换完之后是mojom::FrameHost::Proxy_;

那么在看FrameHost定义

class CONTENT_EXPORT FrameHost: public FrameHostInterfaceBase {public:using IPCStableHashFunction = uint32_t(*)();static const char Name_[];static IPCStableHashFunction MessageToMethodInfo_(mojo::Message& message);static const char* MessageToMethodName_(mojo::Message& message);static constexpr uint32_t Version_ = 0;static constexpr bool PassesAssociatedKinds_ = true;static inline constexpr uint32_t kSyncMethodOrdinals[] = {0};static constexpr bool HasUninterruptableMethods_ = false;using Base_ = FrameHostInterfaceBase;using Proxy_ = FrameHostProxy;

其中将using Proxy_ = FrameHostProxy;

至此FrameHost和FrameHostProxy完成了关联 其实是一个巧妙的用了模板和using。

这样在mojo::AssociatedRemote类带哦用get函数时候直接获取的是FrameHostProxy。

  typename Interface::Proxy_* get() const {

    DCHECK(is_bound())

        << "Cannot issue Interface method calls on an unbound AssociatedRemote";

    return internal_state_.instance();

  }

  第三部分、主进程定义

content\browser\renderer_host\render_frame_host_impl.cc

void RenderFrameHostImpl::BeginNavigation(blink::mojom::CommonNavigationParamsPtr unvalidated_common_params,blink::mojom::BeginNavigationParamsPtr begin_params,mojo::PendingRemote<blink::mojom::BlobURLToken> blob_url_token,mojo::PendingAssociatedRemote<mojom::NavigationClient> navigation_client,mojo::PendingRemote<blink::mojom::PolicyContainerHostKeepAliveHandle>initiator_policy_container_host_keep_alive_handle,mojo::PendingReceiver<mojom::NavigationRendererCancellationListener>renderer_cancellation_listener) {TRACE_EVENT("navigation", "RenderFrameHostImpl::BeginNavigation",ChromeTrackEvent::kRenderFrameHost, this, "url",unvalidated_common_params->url.possibly_invalid_spec());// Only active and prerendered documents are allowed to start navigation in// their frame.if (lifecycle_state() != LifecycleStateImpl::kPrerendering) {// If this is reached in case the RenderFrameHost is in BackForwardCache// evict the document from BackForwardCache.if (IsInactiveAndDisallowActivation(DisallowActivationReasonId::kBeginNavigation)) {return;}}

     

总结：搜索其他模块也是类似，debug/gen目录是mojom文件具体实现，其他的是发送和接收实现，找到对应参数定义函数即可。