PPAPI的插件，原本是能够使用JS与浏览器交互的，https://code.google.com/p/ppapi/wiki/InterfacingWithJavaScript。这里还提供了一个JS与plugin交互的文档，但如今说不支持了。如今应该通过PPB_Messaging接口来完毕Plugin和浏览器的交互，详细參考https://src.chromium.org/viewvc/chrome/trunk/src/ppapi/c/ppb_messaging.h?revision=92312&view=markup这里。
我实验了一下。通了。
Messaging接口非常好。传递的消息能够自已定义。类型也无限制。非常方便。
foruok原创。如需转载请关注foruok的微信订阅号“程序视界”联系foruok。
使用postMessage通信
Messaging接口与其他大多数接口一样，分PPB和PPP两側。
分开来说明一下要做的事情。
插件側
要做这么些事情：
- 实现PPP_Messaging接口。关键是void (*HandleMessage)(PP_Instance instance, struct PP_Var message)方法
- 在Get_Interface中返回名字是PPP_MESSAGING_INTERFACE的接口
- 在PPP_InitializeModule中获取 PPB_Messaging、PPB_Var、PPB_VarArray、PPB_VarDictionary等接口。
PPB_Messaging的PostMessage用于向浏览器发送消息。发送过去的消息，JS代码能够接收到。
PPB_Var能够用来构造String类型的Var。能够操作Var的引用计数
PPB_VarArray是数组接口，能够创建、訪问、设置数组
PPB_VarDictionary是字典（map）接口。能够创建字典Var，能够存取key-value对。 - PPP_Messaging的HandleMessage处理浏览器的消息，假设须要。调用PPB_Messaging的PostMessage发送消息.
注意，插件側调用PPB_Var接口的VarFromUtf8时，传入的len不包含’ ’在内。PPAPI的ppb_var.h的凝视里的演示样例代码片段有误，调用时传递的长度是sizeof(hello_world)。应该减去一。
另一点，插件和浏览器交互的数据。都是数据的拷贝哦，调用接口会发生复制行为。
浏览器側
浏览器側能够使用JavaScript来监听插件发送的message事件，也能够使用插件元素的postMessage发送消息给插件。
基本上做以下几件事就可以：
- 实现处理消息的JS函数，其參数是MessageEvent。data成员为插件发过来的信息，能够当做JS对象来訪问。
- 监听插件的message事件
- 在合适的时候调用插件的postMessage(object)方法发送消息给插件
代码
分插件代码和HTML代码。
插件代码
代码是在在PPAPI插件中创建本地窗体一文演示样例代码的基础上改的。加入了消息处理的部分。仅仅贴相关的部分了。
获取消息相关接口的代码
在PPP_InitializeModule中加入了获取PPB_Messaging接口以及其他可能用到的PP_Var类型的接口。有Array和Dictionary。
g_var_interface = (const PPB_Var*)get_browser_interface(PPB_VAR_INTERFACE);
g_dictionary_interface = (const PPB_VarDictionary*)get_browser_interface(PPB_VAR_DICTIONARY_INTERFACE);
g_array_interface = (const PPB_VarArray*)get_browser_interface(PPB_VAR_ARRAY_INTERFACE);
g_message_interface = (const PPB_Messaging*)get_browser_interface(PPB_MESSAGING_INTERFACE);PPP_Messaging接口的实现
PPP_Messaging接口的实现代码例如以下：
void Plugin_HandleMessage(PP_Instance instance, struct PP_Var message)
{
char szLog[256] = { 0 };
sprintf_s(szLog, 256, "Plugin_HandleMessage, type = %d
", message.type);
OutputDebugStringA(szLog);
if (message.type == PP_VARTYPE_DICTIONARY)
{
char command[] = "command";
struct PP_Var commandKey = g_var_interface->VarFromUtf8(command, sizeof(command) - 1);
struct PP_Var commandVar = g_dictionary_interface->Get(message, commandKey);
int len = 0;
const char *strCommand = g_var_interface->VarToUtf8(commandVar, &len);
g_var_interface->Release(commandKey);
sprintf_s(szLog, 256, "Plugin_HandleMessage, dict, command = %s, len = %d
", strCommand, len);
OutputDebugStringA(szLog);
if (len == 0)
{
OutputDebugString(_T("Tang_plugin, recv invalid command
"));
g_var_interface->Release(commandVar);
return;
}
if (strncmp(strCommand, "joinConf", len) == 0)
{
char confIdKey[] = "confId";
char userNameKey[] = "userName";
char *szConfId = 0;
char*szUserName = 0;
struct PP_Var idKey = g_var_interface->VarFromUtf8(confIdKey, sizeof(confIdKey) - 1);
struct PP_Var userKey = g_var_interface->VarFromUtf8(userNameKey, sizeof(userNameKey) - 1);
struct PP_Var var = g_dictionary_interface->Get(message, idKey);
const char *value = g_var_interface->VarToUtf8(var, &len);
if (len > 0)
{
szConfId = malloc(len + 1);
strncpy_s(szConfId, len+1, value, len);
szConfId[len] = 0;
}
g_var_interface->Release(var);
var = g_dictionary_interface->Get(message, userKey);
value = g_var_interface->VarToUtf8(var, &len);
if (len > 0)
{
szUserName = malloc(len + 1);
strncpy_s(szUserName, len+1, value, len);
szUserName[len] = 0;
}
g_var_interface->Release(var);
sprintf_s(szLog, 256, "Plugin_HandleMessage, dict, command = joinConf, user = %s, confId = %s
", szUserName, szConfId);
OutputDebugStringA(szLog);
if (szConfId && szUserName)
{
sprintf_s(szLog, 256, "plugin got confId - %s, user - %s
", szConfId, szUserName);
OutputDebugStringA(szLog);
joinConf(szConfId, szUserName);
}
else
{
OutputDebugString(_T("Invalid conference id or userName
"));
}
if (szConfId) free(szConfId);
if (szUserName) free(szUserName);
g_var_interface->Release(idKey);
g_var_interface->Release(userKey);
/* fake attendees*/
char szMsgTypeValue[] = "userlist";
char szTypeKey[] = "type";
struct PP_Var typeKey = g_var_interface->VarFromUtf8(szTypeKey, sizeof(szTypeKey) - 1);
struct PP_Var typeValue = g_var_interface->VarFromUtf8(szMsgTypeValue, sizeof(szMsgTypeValue) - 1);
struct PP_Var attendee = g_dictionary_interface->Create();
g_dictionary_interface->Set(attendee, typeKey, typeValue);
struct PP_Var userArray = g_array_interface->Create();
char szUser1[] = "ZhangSan";
char szUser2[] = "LiSi";
struct PP_Var user1 = g_var_interface->VarFromUtf8(szUser1, sizeof(szUser1) - 1);
struct PP_Var user2 = g_var_interface->VarFromUtf8(szUser2, sizeof(szUser2) - 1);
g_array_interface->Set(userArray, 0, user1);
g_array_interface->Set(userArray, 1, user2);
char szValueKey[] = "value";
struct PP_Var valueKey = g_var_interface->VarFromUtf8(szValueKey, sizeof(szValueKey) - 1);
g_dictionary_interface->Set(attendee, valueKey, userArray);
g_message_interface->PostMessage(instance, attendee);
OutputDebugString(_T("Post attendee to browser"));
g_var_interface->Release(typeKey);
g_var_interface->Release(typeValue);
g_var_interface->Release(user1);
g_var_interface->Release(user2);
g_var_interface->Release(valueKey);
g_var_interface->Release(userArray);
g_var_interface->Release(attendee);
}
else if (strncmp(strCommand, "viewVideo", len) == 0)
{
char userIdKey[] = "userId";
char *szUserId = 0;
struct PP_Var idKey = g_var_interface->VarFromUtf8(userIdKey, sizeof(userIdKey) - 1);
struct PP_Var var = g_dictionary_interface->Get(message, idKey);
const char *value = g_var_interface->VarToUtf8(var, &len);
if (len > 0)
{
szUserId = malloc(len + 1);
strncpy_s(szUserId, len + 1, value, len);
szUserId[len] = 0;
}
if (szUserId)
{
sprintf_s(szLog, 256, "plugin got userId - %s
", szUserId);
OutputDebugStringA(szLog);
viewVideo(szUserId, g_child_window);
}
else
{
OutputDebugString(_T("Invalid viewVideo command without userId
"));
}
if (szUserId) free(szUserId);
g_var_interface->Release(var);
g_var_interface->Release(idKey);
}
g_var_interface->Release(commandVar);
}
else if (message.type == PP_VARTYPE_STRING)
{
char hello_world[] = "Hello world!";
struct PP_Var var = g_var_interface->VarFromUtf8(hello_world, sizeof(hello_world) - 1);
g_message_interface->PostMessage(instance, var); // var will be copyed
g_var_interface->Release(var);
}
}
static PPP_Messaging message_interface = {
&Plugin_HandleMessage
};有点长，比較潦草。
返回PPP_Messaging的代码
完整的PPP_GetInterface函数例如以下：
PP_EXPORT const void* PPP_GetInterface(const char* interface_name) {
if (strcmp(interface_name, PPP_INSTANCE_INTERFACE) == 0)
{
OutputDebugString(_T("PPP_GetInterface, instance_interface
"));
return &instance_interface;
}
else if (strcmp(interface_name, PPP_INPUT_EVENT_INTERFACE) == 0)
{
OutputDebugString(_T("PPP_GetInterface, input_interface
"));
return &input_interface;
}
else if (strcmp(interface_name, PPP_MESSAGING_INTERFACE) == 0)
{
OutputDebugString(_T("PPP_GetInterface, message_interface
"));
return &message_interface;
}
return NULL;
}网页代码
网页代码例如以下：
<!DOCTYPE html>
<html>
<!--
Copyright (c) 2016 foruok@微信订阅号“程序视界”(programmer_sight).
All rights reserved.
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->
<head>
<style type="text/css">
#contacts
{
margin: 10px;
width: 300px;
height: 200px;
background-color: gray;
}
</style>
<script type="text/javascript">
function handleMessage(message) {
alert(message.data.type);
if(message.data.type.localeCompare("userlist") == 0){
var i = 0;
ul = document.getElementById("attendee");
for(; i < message.data.value.length; i++){
var li = document.createElement("li");
li.appendChild(document.createTextNode(message.data.value[i]));
ul.appendChild(li);
}
}
}
function joinConference(){
plugin = document.getElementById('tangplugin');
plugin.postMessage({
command:"joinConf",
confId: document.getElementById("confId").value,
userName: document.getElementById("userName").value
});
}
function viewSharedVideo(){
plugin = document.getElementById('tangplugin');
plugin.postMessage({
command:"viewVideo",
userId: document.getElementById("userId").value
});
}
function initialize() {
plugin = document.getElementById('tangplugin');
plugin.addEventListener('message', handleMessage, false);
}
document.addEventListener('DOMContentLoaded', initialize, false);
</script>
<title>Tang in Plugin</title>
</head>
<body>
<form>
ConferenceID: <input type="text" id="confId" /> User:
<input type="text" id="userName" /> <input type="button" value="Join" onclick="joinConference()"/>
</form>
<hr>
<div id="contacts">
<p>contacts:</p>
<ul id="attendee">
<!--
here will show attendee list, added by JS callback
-->
</ul>
UserId:<input type="text" id="userId" /> <button type="button" onclick="viewSharedVideo()">View Video</button>
</div>
<p>share video:</p>
<embed id="tangplugin" type="application/x-ppapi-tang-video" width="300px" height="200px" top="40px" left="20px">
</body>
</html>
Join按钮会获取它前面两个文本框的内容。发送给插件。插件返回一个用户列表，网页解析（HandleMessage方法）出来，动态改动用户列表。
执行效果
贴两幅图，点击Join按钮之前是酱紫的：
点击Join按钮后是酱紫的：
其他參考文章：