Browser与Render进程

从cefsimple开始吧，cefsimple_win.cc中的wWinMain函数中调用了CefExecuteProcess()方法来检测是否要启动其它的子进程。此处的CefExecuteProcess是在libcef_dll_wrapper.cc中的，它内部又调用了cef_execute_process方法（libcef_dll.cc），cef_execute_process又调用了libcef/browser/context.cc文件内实现的CefExecuteProcess方法。这个方法代码如下：

int CefExecuteProcess(const CefMainArgs& args,
                      CefRefPtr<CefApp> application,
                      void* windows_sandbox_info) {
  base::CommandLine command_line(base::CommandLine::NO_PROGRAM);
#if defined(OS_WIN)
  command_line.ParseFromString(::GetCommandLineW());
#else
  command_line.InitFromArgv(args.argc, args.argv);
#endif

  // Wait for the debugger as early in process initialization as possible.
  if (command_line.HasSwitch(switches::kWaitForDebugger))
    base::debug::WaitForDebugger(60, true);

  // If no process type is specified then it represents the browser process and
  // we do nothing.
  std::string process_type =
      command_line.GetSwitchValueASCII(switches::kProcessType);
  if (process_type.empty())
    return -1;

  CefMainDelegate main_delegate(application);

  // Execute the secondary process.
#if defined(OS_WIN)
  sandbox::SandboxInterfaceInfo sandbox_info = {0};
  if (windows_sandbox_info == NULL) {
    content::InitializeSandboxInfo(&sandbox_info);
    windows_sandbox_info = &sandbox_info;
  }

  content::ContentMainParams params(&main_delegate);
  params.instance = args.instance;
  params.sandbox_info =
      static_cast<sandbox::SandboxInterfaceInfo*>(windows_sandbox_info);

  return content::ContentMain(params);
#else
  content::ContentMainParams params(&main_delegate);
  params.argc = args.argc;
  params.argv = const_cast<const char**>(args.argv);

  return content::ContentMain(params);
#endif

它分析了命令行参数，提取”type”参数，如果为空，说明是Browser进程，返回-1，这样一路回溯到wWinMain方法里，然后开始创建Browser进程相关的内容。

如果”type”参数不为空，做一些判断，最后调用了content::ContentMain方法，直到这个方法结束，子进程随之结束。

content::ContentMain方法再追溯下去，就到了chromium的代码里了，在chromium/src/content/app/content_main.cc文件中。具体我们不分析了，感兴趣的可以去看看。

分析了CefExecuteProcess方法我们知道，Browser进程在cefsimple_win.cc内调用了CefExecuteProcess之后做了进一步的配置，这个是在simple_app.cc内完成的，具体就是SimpleApp::OnContextInitialized()这个方法，代码如下：

void SimpleApp::OnContextInitialized() {
  CEF_REQUIRE_UI_THREAD();

  CefWindowInfo window_info;

  window_info.SetAsPopup(NULL, "cefsimple");

  // SimpleHandler implements browser-level callbacks.
  CefRefPtr<SimpleHandler> handler(new SimpleHandler());

  // Specify CEF browser settings here.
  CefBrowserSettings browser_settings;

  std::string url;

  CefRefPtr<CefCommandLine> command_line =
      CefCommandLine::GetGlobalCommandLine();
  url = command_line->GetSwitchValue("url");
  if (url.empty())
    url = "http://www.google.com";

  CefBrowserHost::CreateBrowser(window_info, handler.get(), url,
                                browser_settings, NULL);
}

可以看到，这里创建SimpleHandler，并传递给CefBrowserHost::CreateBrowser去使用。

现在我们清楚了，Browser进程，需要CefApp（SimpleApp实现了这个接口）和CefClient（SimpleHandler实现了这个接口）。而Renderer进程只要CefApp。

另外，CEF还定义了CefBrowserProcessHandler和CefRenderProcessHandler两个接口，分别来处理Browser进程和Render进程的个性化的通知。因此，Browser进程的App一般还需要实现CefBrowserProcessHandler接口，Renderer进程的App一般还需要实现CefRenderProcessHandler接口。这里https://bitbucket.org/chromiumembedded/cef/wiki/GeneralUsage有详细说明。

像cefsimple这个示例中的SimpeApp，没有实现CefRenderProcessHandler接口，没有针对Renderer进程做特别处理，所以当它作为Render进程时，会缺失一部分功能。比如JS与Native代码交互，这正是我们想要的。

如果要实现JS与Native代码交互，最好分开实现Browser进程需要的CefApp和Render进程需要的CefApp。像下面这样：

class ClientAppRenderer : public CefApp,
    public CefRenderProcessHandler 
{
    ...
}

class ClientAppBrowser : public CefApp, 
    public CefBrowserProcessHandler
{
    ...
}

当我们实现了CefRenderProcessHandler接口，就可以在其OnContextCreated()方法中获取到CefFrame对应的window对象，在它上面绑定一些JS函数或对象，然后JS代码里就可以通过window对象访问，如果是函数，就会调用到我们实现的CefV8Handler接口的Execute方法。

另外一种实现JS与Native交互的方式，是在实现CefRenderProcessHandler的OnWebKitInitialized()方法时导出JS扩展，具体参考https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration.md，有详细说明。

cef_js_integration项目

cef_js_integration是非常简单的示例，用来演示JS与Native的交互。它在一个项目内实现了ClientAppBrowser、ClientAppRenderer、ClientAppOther三种CefApp，分别对应Browser、Render及其它类别的三种进程。

JS和Native代码的交互发生在Render进程，App需要继承CefRenderProcessHandler来整合JS相关功能。因此在应用在启动时做了进程类型判断，根据不同的进程类型创建不同的CefApp。

这个示例演示了三种JS交互方式（参见https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration.md）：
- 在native代码中通过CefFrame::ExecuteJavaScript()来执行JavaScript代码
- 将函数或对象绑定到CefFrame对应的window对象上，JS代码通过window对象访问native代码导出的函数或对象
- 使用CefRegisterExtension()注册JS扩展，JS直接访问注册到JS Context中的对象

这个项目参考了cefsimple、cefclient，还有https://github.com/acristoffers/CEF3SimpleSample，最终它比cefsimple复杂一点，比cefclient简单很多。

好啦，背景差不多，上源码。

cef_js_integration.cpp：

#include <windows.h>
#include <tchar.h>
#include "cef_js_integration.h"
#include <string>
#include <algorithm>
#include "include/cef_app.h"
#include "include/cef_browser.h"
#include "ClientAppBrowser.h"
#include "ClientAppRenderer.h"
#include "ClientAppOther.h"
#include "include/cef_command_line.h"
#include "include/cef_sandbox_win.h"

//#define CEF_USE_SANDBOX 1

#if defined(CEF_USE_SANDBOX)
#pragma comment(lib, "cef_sandbox.lib")
#endif


int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPTSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    // Enable High-DPI support on Windows 7 or newer.
    CefEnableHighDPISupport();

    CefMainArgs main_args(hInstance);

    void* sandbox_info = NULL;

#if defined(CEF_USE_SANDBOX)
    CefScopedSandboxInfo scoped_sandbox;
    sandbox_info = scoped_sandbox.sandbox_info();
#endif

    // Parse command-line arguments.
    CefRefPtr<CefCommandLine> command_line = CefCommandLine::CreateCommandLine();
    command_line->InitFromString(::GetCommandLineW());

    // Create a ClientApp of the correct type.
    CefRefPtr<CefApp> app;
    // The command-line flag won't be specified for the browser process.
    if (!command_line->HasSwitch("type"))
    {
        app = new ClientAppBrowser();
    }
    else
    {
        const std::string& processType = command_line->GetSwitchValue("type");
        if (processType == "renderer")
        {
            app = new ClientAppRenderer();
        }
        else
        {
            app = new ClientAppOther();
        }
    }

    // Execute the secondary process, if any.
    int exit_code = CefExecuteProcess(main_args, app, sandbox_info);
    if (exit_code >= 0)
        return exit_code;


    // Specify CEF global settings here.
    CefSettings settings;

#if !defined(CEF_USE_SANDBOX)
    settings.no_sandbox = true;
#endif

    // Initialize CEF.
    CefInitialize(main_args, settings, app.get(), sandbox_info);

    // Run the CEF message loop. This will block until CefQuitMessageLoop() is
    // called.
    CefRunMessageLoop();

    // Shut down CEF.
    CefShutdown();

    return 0;
}

可以看到，_tWinMain方法中解析了命令行参数，根据进程类型创建了不同的CefApp。这是它与cefsimple的区别。

ClientAppBrowser类与cefsimple示例中的SimpleApp基本一致，略过。

ClientAppRender类在ClientAppRender.h和ClientAppRender.cpp中实现。先是ClientAppRender.h：

#ifndef CEF3_CLIENT_APP_RENDERER_H
#define CEF3_CLIENT_APP_RENDERER_H

#include "include/cef_app.h"
#include "include/cef_client.h"
#include "V8handler.h"

class ClientAppRenderer : public CefApp,
    public CefRenderProcessHandler 
{
public:
    ClientAppRenderer();

    CefRefPtr<CefRenderProcessHandler> GetRenderProcessHandler() OVERRIDE
    {
        return this;
    }

    void OnContextCreated(
        CefRefPtr<CefBrowser> browser,
        CefRefPtr<CefFrame> frame,
        CefRefPtr<CefV8Context> context);

    void OnWebKitInitialized() OVERRIDE;

private:
    CefRefPtr<ClientV8Handler> m_v8Handler;

    IMPLEMENT_REFCOUNTING(ClientAppRenderer);
};

#endif

ClientAppRender聚合了ClientV8Handler类的实例，回头再说。先来看ClientAppRender的OnContextCreated和OnWebKitInitialized，它们是实现JS与Native交互的关键。代码如下：

#include "ClientAppRenderer.h"
#include "V8handler.h"
#include <Windows.h>
#include <tchar.h>

ClientAppRenderer::ClientAppRenderer()
    : m_v8Handler(new ClientV8Handler)
{
}

void ClientAppRenderer::OnContextCreated(CefRefPtr<CefBrowser> browser,
    CefRefPtr<CefFrame> frame,
    CefRefPtr<CefV8Context> context)
{
    OutputDebugString(_T("ClientAppRenderer::OnContextCreated, create window binding\r\n"));

    // Retrieve the context's window object.
    CefRefPtr<CefV8Value> object = context->GetGlobal();


    // Create the "NativeLogin" function.
    CefRefPtr<CefV8Value> func = CefV8Value::CreateFunction("NativeLogin", m_v8Handler);

    // Add the "NativeLogin" function to the "window" object.
    object->SetValue("NativeLogin", func, V8_PROPERTY_ATTRIBUTE_NONE);
}

void ClientAppRenderer::OnWebKitInitialized()
{
    OutputDebugString(_T("ClientAppRenderer::OnWebKitInitialized, create js extensions\r\n"));
    std::string app_code =
        "var app;"
        "if (!app)"
        "    app = {};"
        "(function() {"
        "    app.GetId = function() {"
        "        native function GetId();"
        "        return GetId();"
        "    };"
        "})();";

    CefRegisterExtension("v8/app", app_code, m_v8Handler);
}

OnContextCreated给window对象绑定了一个NativeLogin函数，这个函数将由ClientV8Handler类来处理，当HTML中的JS代码调用window.NativeLogin时，ClientV8Handler的Execute方法会被调用。

OnWebKitInitialized注册了一个名为app的JS扩展，在这个扩展里为app定义了GetId方法，app.GetId内部调用了native版本的GetId()。HTML中的JS代码可能如下：

alert(app.GetId());

当浏览器执行上面的代码时，ClientV8Handler的Execute方法会被调用。

好啦，现在来看ClientV8Handler的实现（V8Handler.cpp）：

#include "V8handler.h"
#include <Windows.h>
#include <tchar.h>

bool ClientV8Handler::Execute(const CefString& name,
    CefRefPtr<CefV8Value> object,
    const CefV8ValueList& arguments,
    CefRefPtr<CefV8Value>& retval,
    CefString& exception) 
{
    if (name == "NativeLogin") 
    {
        if (arguments.size() == 2)
        {
            CefString strUser = arguments.at(0)->GetStringValue();
            CefString strPassword = arguments.at(1)->GetStringValue();

            TCHAR szLog[256] = { 0 };
            _stprintf_s(szLog, 256, _T("user - %s, password - %s\r\n"), strUser.c_str(), strPassword.c_str());
            OutputDebugString(szLog);

            //TODO: doSomething() in native way

            retval = CefV8Value::CreateInt(0);
        }
        else
        {
            retval = CefV8Value::CreateInt(2);
        }
        return true;
    }
    else if (name == "GetId") 
    {
        if (arguments.size() == 0) 
        {
            // execute javascript 
            // just for test
            CefRefPtr<CefFrame> frame = CefV8Context::GetCurrentContext()->GetBrowser()->GetMainFrame();
            frame->ExecuteJavaScript("alert('Hello, I came from native world.')", frame->GetURL(), 0);

            // return to JS
            retval = CefV8Value::CreateString("72395678");
            return true;
        }
    }
    // Function does not exist.
    return false;
}

Execute在处理GetId方法时，还使用CefFrame::ExecuteJavaScript演示了如何在native代码中执行JS代码。

最后，来看一下html代码：

<!DOCTYPE html>
<html>
  <!--
  Copyright (c) 2016 foruok. All rights reserved.
  欢迎关注foruok的微信订阅好“程序视界”。
  -->
<head>
    <script type="text/javascript">
      function Login(){
        window.NativeLogin(document.getElementById("userName").value, document.getElementById("password").value);
      }
      function GetId(){
        alert("get id from native by extensions: " + app.GetId());
      }
    </script>
  <title>CEF JS Integration</title>
</head>

<body>
<h3>Call into native by Window bindings:</h3>
<form>
UserName: <input type="text" id="userName" />&nbsp;&nbsp;Password: 
<input type="text" id="password" />&nbsp;&nbsp;<input  type="button" value="Login" onclick="Login()"/>
</form>
<hr>
<h3>Call into native by js extensions:</h3>
<input  type="button" value="GetId" onclick="GetId()"/>

</html>

通过下面的命令可以测试：

cef_js_integration.exe --url=file:///cef_js_integration.html

CEF中JavaScript与C++交互

Browser与Render进程

cef_js_integration项目

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