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Cocos2d-x 网络Http篇

谈到Cocos2d-x中的Http网络编程，它的基本流程是:

  1. 创建HttpRequest
  2. 创建setResponseCallback()回调函数来设置如何对请求回复后的信息进行操作
  3. 通过HttpClient发送HttpRequest请求

因此，你首先要知道3个类:

  • HttpRequest
  • HttpResponse
  • HttpClient

了解了它们之后再来看引擎cpp-test中的cpp-test/Classes/ExtensionsTest/NetworkTest/HttpClientTest，就能对Cocos2d-x中Http的用法基本了解了。

HttpRequest

顾名思义，它将处理向Http的发出请求，即将用户的请求内容信息给封装到HttpRequest对象当中。目前的话，支持以下几种类型的HttpRequest

/** Use this enum type as param in setReqeustType(param) */
enum class Type
{
    GET,
    POST,
    PUT,
    DELETE,
    UNKNOWN,
};

其中UNKNOWN类型是它的初始化默认类型，这个在它的构造函数中可以看到，需要注意的是，由于线程不安全的问题，不要将HttpRequest放到自动回收池当中去，这可能会导致崩溃。

/** Constructor
    Because HttpRequest object will be used between UI thead and network thread,
    requestObj->autorelease() is forbidden to avoid crashes in AutoreleasePool
    new/retain/release still works, which means you need to release it manually
    Please refer to HttpRequestTest.cpp to find its usage
 */
HttpRequest()
{
    _requestType = Type::UNKNOWN;
    _url.clear();
    _requestData.clear();
    _tag.clear();
    _pTarget = nullptr;
    _pSelector = nullptr;
    _pCallback = nullptr;
    _pUserData = nullptr;
};

通过这个构造函数，我们也可以看到HttpRequest的一些属性，这些protected的属性在HttpRequest中的定义如下，可以通过注释来简单的了解下它们的作用。

protected:
 // properties
    Type                        _requestType;    /// kHttpRequestGet, kHttpRequestPost or other enums
    std::string                 _url;            /// target url that this request is sent to
    std::vector<char>           _requestData;    /// used for POST
    std::string                 _tag;            /// user defined tag, to identify different requests in response callback
    Ref*                        _pTarget;        /// callback target of pSelector function
    SEL_HttpResponse            _pSelector;      /// callback function, e.g. MyLayer::onHttpResponse(HttpClient *sender, HttpResponse * response)
    ccHttpRequestCallback       _pCallback;      /// C++11 style callbacks
    void*                       _pUserData;      /// You can add your customed data here 
    std::vector<std::string>    _headers;             /// custom http headers

这些属性中，_requestType，_url，_requestData，_tag，_pTarget，_headers都有get/set方法可以找到，这些也是比较常用到的属性。

_pSelector指的是发送请求后的回调函数，_pTarget是它的回调函数的作用对象，如下所示：

CC_DEPRECATED_ATTRIBUTE inline void setResponseCallback(Ref* pTarget, SEL_HttpResponse pSelector)
{
    _pTarget = pTarget;
    _pSelector = pSelector;

    if (_pTarget)
    {
        _pTarget->retain();
    }
}

可以看到，目前旧的setResponseCallback已经被废弃了，这是现在由于我们有了新的支持C++11类型的回调函数，现在这个回调函数将指向_pCallback，它是一个ccHttpRequestCallback类，它的定义如下：

typedef std::function<void(HttpClient* client, HttpResponse* response)> ccHttpRequestCallback;

_pCallback在HttpRequest类中担任发送请求后接受的回调函数的责任，它仍然叫做setResponseCallback但是已经是C++11类型的回调函数了:

inline void setResponseCallback(const ccHttpRequestCallback& callback)
{
    _pCallback = callback;
}

OK!HttpRequest的类的属性和接口的用法和含义大致上就是这样。

HttpResponse

与HttpRequest相反，HttpResponse存储Http服务器返回的请求，因此它并不需要由用户创建，它将由HttpClient创建并返回，用户只需要知道如何去处理它返回的信息即可。

它的一些基本属性:

protected:
    bool initWithRequest(HttpRequest* request);

    // properties
    HttpRequest*        _pHttpRequest;  /// the corresponding HttpRequest pointer who leads to this response 
    bool                _succeed;       /// to indecate if the http reqeust is successful simply
    std::vector<char>   _responseData;  /// the returned raw data. You can also dump it as a string
    std::vector<char>   _responseHeader;  /// the returned raw header data. You can also dump it as a string
    long                _responseCode;    /// the status code returned from libcurl, e.g. 200, 404
    std::string         _errorBuffer;   /// if _responseCode != 200, please read _errorBuffer to find the reason

其中initWithRequest只在内部调用的时候需要用到，用户不需要关心。_pHttpRequest可以通过getHttpRequest()来获得它对用的HttpRequest请求对象，_succeed可以通过isSucceed接口来判定是否请求成功。其余的属性均有get/set方法来获得进行操作。

HttpClient

HttpClient是一个单例，它控制着HttpRequest和HttpResponse的收发传递。它有一些公共接口，其中最重要的可能就是对请求的发送了，当然在这之前你得先获得这个单例对象：

/** Return the shared instance **/
static HttpClient *getInstance();

/** Relase the shared instance **/
static void destroyInstance();
/**
 * Add a get request to task queue
 * @param request a HttpRequest object, which includes url, response callback etc.
                  please make sure request->_requestData is clear before calling "send" here.
 */
void send(HttpRequest* request);

/**
 * Immediate send a request
 * @param request a HttpRequest object, which includes url, response callback etc.
                  please make sure request->_requestData is clear before calling "sendImmediate" here.
 */
void sendImmediate(HttpRequest* request);

在这里，send和sendImmediate的区别在于，前者会将HttpRequest排到到request的队列线程的最后，后者则会立刻新建一个线程后发送。除此之外，它还有一些接口对应其它的用途。如get/setTimeoutForConnect可以get/set连接的超时时间，get/setTimeoutForRead可以get/set下载的超时时间。

HttpClientTest

在了解了相关的3个类之后，我相信现在大部分内容你应该已经了解了，现在来看一下cpp-test中的http流程是怎么写的，你就基本上大致了解它的使用过程了。更多的内容，可以在cpp-test/Classes/ExtensionsTest/NetworkTest/HttpClientTest看到

void HttpClientTest::onMenuDeleteTestClicked(Ref *sender, bool isImmediate)    // test 1
    {
        HttpRequest* request = new (std::nothrow) HttpRequest();
        request->setUrl("http://just-make-this-request-failed.com");
        request->setRequestType(HttpRequest::Type::GET);
        request->setResponseCallback(CC_CALLBACK_2(HttpClientTest::onHttpRequestCompleted, this));
        if (isImmediate)
        {
            request->setTag("GET immediate test1");
            HttpClient::getInstance()->sendImmediate(request);
        }else
        {
            request->setTag("GET test1");
            HttpClient::getInstance()->send(request);
        }
        request->release();
    }
    }

上面的代码，创建了一个HttpRequest的对象，设置了它的一些信息：Url，RequestType，ResponseCallback的回调和tag。接着通过HttpClient将这个请求发送出去，在这里它通过一个isImmediate来判断它是否是立刻发送。最后由于是new出来的对象，它又手动release了一遍。下面的代码展示了这个请求结束后的回调函数。

void HttpClientTest::onHttpRequestCompleted(HttpClient *sender, HttpResponse *response)
{
    if (!response)
    {
        return;
    }

    // You can get original request type from: response->request->reqType
    if (0 != strlen(response->getHttpRequest()->getTag())) 
    {
        log("%s completed", response->getHttpRequest()->getTag());
    }

    long statusCode = response->getResponseCode();
    char statusString[64] = {};
    sprintf(statusString, "HTTP Status Code: %ld, tag = %s", statusCode, response->getHttpRequest()->getTag());
    _labelStatusCode->setString(statusString);
    log("response code: %ld", statusCode);

    if (!response->isSucceed()) 
    {
        log("response failed");
        log("error buffer: %s", response->getErrorBuffer());
        return;
    }

    // dump data
    std::vector<char> *buffer = response->getResponseData();
    log("Http Test, dump data: ");
    for (unsigned int i = 0; i < buffer->size(); i++)
    {
        log("%c", (*buffer)[i]);
    }
    log("\n");
    if (response->getHttpRequest()->getReferenceCount() != 2)
    {
        log("request ref count not 2, is %d", response->getHttpRequest()->getReferenceCount());
    }
}

这段函数中，处理了请求之后返回的HttpReponse对象的数据，并将对应信息一一打印。

安卓

需要注意的是，如果你是Android环境，不要忘了在您的应用程序的Manifest中增加相应的权限：

<uses-permission android:name=”android.permission.INTERNET” />

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