cocos2dx_CurlTest分析

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1.概述
Curl，是一套可以访问各种网络协议服务的API，
官方网站：http://curl.haxx.se

在cocos2d-x-3.10中，你可以在如下目录找到curl.h：
cocos2d-x-3.10/external/curl/include/android/curl
cocos2d-x-3.10/external/curl/include/ios/curl

注意：cocos2dx3.10中的Http连接的底层就是curl实现的，具体请看cocos2dx3.10 lua中的测试用例XMLHttpRequestTest。

2.实例
cocos2d-x提供了curl测试用例，在如下地址：
cocos2d-x-3.10/tests/cpp-tests/Classes/CurlTest

CurlTest.h---------------
#include "cocos2d.h"
#include "../BaseTest.h"

DEFINE_TEST_SUITE(CurlTests);

class CurlTest : public TestCase
{
public:
CREATE_FUNC(CurlTest);

CurlTest();
~CurlTest();

void onTouchesEnded(const std::vector<cocos2d::Touch*>& touches, cocos2d::Event *event);

private:
cocos2d::Label* _label;
};

CurlTest.cpp---------------
#include "platform/CCPlatformConfig.h"
#if (CC_TARGET_PLATFORM != CC_PLATFORM_IOS) && (CC_TARGET_PLATFORM != CC_PLATFORM_ANDROID)
#include "CurlTest.h"
#include "stdio.h"
#include "stdlib.h"
#include "curl/curl.h"

USING_NS_CC;

CurlTests::CurlTests(){
ADD_TEST_CASE(CurlTest);
}

CurlTest::CurlTest(){
auto label = Label::createWithTTF("Curl Test", "fonts/arial.ttf", 28);
addChild(label, 0);
label->setPosition(VisibleRect::center().x, VisibleRect::top().y-50);

auto listener = EventListenerTouchAllAtOnce::create();
listener->onTouchesEnded = CC_CALLBACK_2(CurlTest::onTouchesEnded, this);
_eventDispatcher->addEventListenerWithSceneGraphPriority(listener, this);

// create a label to display the tip string
_label = Label::createWithTTF("Touch the screen to connect", "fonts/arial.ttf", 22);
_label->setPosition(VisibleRect::center());
addChild(_label, 0);

_label->retain();
}

//用来保存要发送的数据的结构体
struct MemoryStruct {
char *memory;
size_t size;
};

//写数据
static size_t WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp){
size_t realsize = size * nmemb;
struct MemoryStruct *mem = (struct MemoryStruct *)userp;
if(mem != null){ //这里为了防止抛出异常，加了一个判断
mem->memory = (char*)realloc(mem->memory, mem->size + realsize + 1);
if(mem->memory == NULL) {
/* out of memory! */
printf("not enough memory (realloc returned NULL)\n");
return 0;
}

memcpy(&(mem->memory[mem->size]), contents, realsize);
mem->size += realsize;
mem->memory[mem->size] = 0;
}

return realsize;
}

// the test code is
// http://curl.haxx.se/mail/lib-2009-12/0071.html
void CurlTest::onTouchesEnded(const std::vector<Touch*>& touches, Event *event){
CURL *curl; //首先，使用CURL必须要创建一个CULR指针，它是CURL的全局句柄。
CURLcode res; //这里定义一个CURL库中API的返回值，用于取得API调用的结果。
char buffer[10]; //错误码的缓冲区

struct MemoryStruct chunk;
chunk.memory = (char*)malloc(1); /* will be grown as needed by the realloc above */
chunk.size = 0; /* no data at this point */

//第一步：初始化CURL，取得初始化成功后的CURL指针。
curl = curl_easy_init();
if (curl) {
//第二步，设定我们用此CURL指针来完成的动作。参数一为CURL指针，参数二为相应
//的动作类型枚举，这个枚举值在curl.h中定义，比如本例中的CURLOPT_URL，定义
//为CINIT(URL, OBJECTPOINT, 2),即联接一个网站的HTTP服务。参数三为动作对应
//的数据参数，这里是网站的URL地址。
curl_easy_setopt(curl, CURLOPT_URL, "http://webtest.cocos2d-x.org/curltest");
//code from http://curl.haxx.se/libcurl/c/getinmemory.html

/* we pass our 'chunk' struct to the callback function */
//保存回调函数得到的数据
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

//If we don't provide a write function for curl, it will recieve error code 23 on windows.
//将得到的数据传递到回调函数里
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);

//第三步，执行上面设定的动作处理。返回结果放在res中。
res = curl_easy_perform(curl);

/* always cleanup */
//最后一步，清除CURL指针，结束对CURL库的使用。
curl_easy_cleanup(curl);

if (res == 0){ //如果动作处理成功，则显示联结成功，但没有开始接收任何数据。
_label->setString(StringUtils::format("Connect successfully!\n%s", chunk.memory));
}else{ //如果动作处理失败，打印错误码。
sprintf(buffer,"code: %i",res);
_label->setString(buffer);
}
}else {
_label->setString("no curl");
}
}

CurlTest::~CurlTest(){
_label->release(); //对占用的标题文本标签计数器减一。不再继续占用以使它能够正常被释放。
}
#endif

3.函数分析
3.1.curl_easy_perform()
当你调用的时候，libcurl会执行所有的必要动作，当开始上传的时候，它会调用我的回调函数。
程序会尽可能多，尽可能快的的上传数据。回调函数返回写入缓冲区的数据的大小。
返回0的时候就表示上传结束了。

3.2.回调函数
如果你想自己处理得到的数据而不是直接显示在标准输出里，就需要自己写回调函数，如下：
size_t write_data(char *bufptr, size_t size, size_t nitems, void *userp);

bufptr 参数指向一段准备上传数据的缓冲区，nitem是这段缓冲区的大小，userp是一个用户自
定义指针，libcurl不对该指针作任何操作，它只是简单的传递该指针。
可以使用该指针在应用程序与libcurl之间传递信息。
以下函数的chunk就是该指针。
curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

3.3.
当你用字符串设置 curl_easy_setopt(），libcurl会复制这个字符串的一个副本，所以你在设
置后不用再保存那个字符串的内存。
使用 CURLOPT_WRITEDATA,libcurl不会处理你所传递的数据。

3.4.显示进度
通过将CURLOPT_NOPROGRESS设置为0开启进度支持。该选项默认值为1。对大多数应用程序，我们
需要提供一个进度显示回调。libcurl会不定期的将当前传输的进度通过回调函数告诉你的程序。

通过CURLOPT_PROGRESSFUNCTION注册该回调函数。
参数clientp是一个用户自定义指针，应用程序通过CURLOPT_PROCESSDATA
属性将该自定义指定传递给libcurl。libcurl对该参数不作任何处理，
只是简单将其传递给回调函数。

curl_easy_setopt(_curl, CURLOPT_PROGRESSFUNCTION, progress_callback);
curl_easy_setopt(_curl, CURLOPT_NOPROGRESS, 0L);

//回调函数原型
int progress_callback(void *clientp,double dltotal,double dlnow,double ultotal,double ulnow);

3.5.
每次执行完curl_easy_perform，licurl会继续保持与服务器的连接。接下来的请求可以使用这
个连接而不必创建新的连接（如果目标主机是同一个的话）。这样可以减少网络开销。
即使连接被释放了，libcurl也会缓存这些连接的会话信息，这样下次再连接到目标主机上时，
就可以使用这些信息，从而减少重新连接所需的时间。

4.curl_easy_perform()返回值说明
CURLE_OK = 0, /* 0 */ 0: no error
CURLE_UNSUPPORTED_PROTOCOL, /* 1 */ 1: unsupported protocol
CURLE_FAILED_INIT, /* 2 */ 2: failed init
CURLE_URL_MALFORMAT, /* 3 */ 3: URL using bad/illegal format or missing URL
CURLE_URL_MALFORMAT_USER, /* 4 - NOT USED */ 4: unknown error
CURLE_COULDNT_RESOLVE_PROXY, /* 5 */ 5: couldn't resolve proxy name
CURLE_COULDNT_RESOLVE_HOST, /* 6 */ 6: couldn't resolve host name
CURLE_COULDNT_CONNECT, /* 7 */ 7: couldn't connect to server
CURLE_FTP_WEIRD_SERVER_REPLY, /* 8 */ 8: FTP: weird server reply
CURLE_FTP_ACCESS_DENIED, /* 9 a service was denied by the FTP server 9: FTP: access denied
due to lack of access - when login fails
this is not returned. */
CURLE_FTP_USER_PASSWORD_INCORRECT, /* 10 - NOT USED */ 10: unknown error
CURLE_FTP_WEIRD_PASS_REPLY, /* 11 */ 11: FTP: unknown PASS reply
CURLE_FTP_WEIRD_USER_REPLY, /* 12 */ 12: FTP: unknown USER reply
CURLE_FTP_WEIRD_PASV_REPLY, /* 13 */ 13: FTP: unknown PASV reply
CURLE_FTP_WEIRD_227_FORMAT, /* 14 */ 14: FTP: unknown 227 response format
CURLE_FTP_CANT_GET_HOST, /* 15 */ 15: FTP: can't figure out the host in the PASV response
CURLE_FTP_CANT_RECONNECT, /* 16 */ 16: FTP: can't connect to server the response code is unknown
CURLE_FTP_COULDNT_SET_BINARY, /* 17 */ 17: FTP: couldn't set binary mode
CURLE_PARTIAL_FILE, /* 18 */ 18: Transferred a partial file
CURLE_FTP_COULDNT_RETR_FILE, /* 19 */ 19: FTP: couldn't retrieve (RETR failed) the specified file
CURLE_FTP_WRITE_ERROR, /* 20 */ 20: FTP: the post-transfer acknowledge response was not OK
CURLE_FTP_QUOTE_ERROR, /* 21 */ 21: FTP: a quote command returned error
CURLE_HTTP_RETURNED_ERROR, /* 22 */ 22: HTTP response code said error
CURLE_WRITE_ERROR, /* 23 */ 23: failed writing received data to disk/application
CURLE_MALFORMAT_USER, /* 24 - NOT USED */ 24: unknown error
CURLE_UPLOAD_FAILED, /* 25 - failed upload "command" */ 25: upload failed (at start/before it took off)
CURLE_READ_ERROR, /* 26 - could open/read from file */ 26: failed to open/read local data from file/application
CURLE_OUT_OF_MEMORY, /* 27 */ 27: out of memory
/* Note: CURLE_OUT_OF_MEMORY may sometimes indicate a conversion error
instead of a memory allocation error if CURL_DOES_CONVERSIONS
is defined
*/
CURLE_OPERATION_TIMEOUTED, /* 28 - the timeout time was reached */ 28: a timeout was reached
CURLE_FTP_COULDNT_SET_ASCII, /* 29 - TYPE A failed */ 29: FTP could not set ASCII mode (TYPE A)
CURLE_FTP_PORT_FAILED, /* 30 - FTP PORT operation failed */ 30: FTP command PORT failed
CURLE_FTP_COULDNT_USE_REST, /* 31 - the REST command failed */ 31: FTP command REST failed
CURLE_FTP_COULDNT_GET_SIZE, /* 32 - the SIZE command failed */ 32: FTP command SIZE failed
CURLE_HTTP_RANGE_ERROR, /* 33 - RANGE "command" didn't work */ 33: a range was requested but the server did not deliver it
CURLE_HTTP_POST_ERROR, /* 34 */ 34: internal problem setting up the POST
CURLE_SSL_CONNECT_ERROR, /* 35 - wrong when connecting with SSL */ 35: SSL connect error
CURLE_BAD_DOWNLOAD_RESUME, /* 36 - couldn't resume download */ 36: couldn't resume download
CURLE_FILE_COULDNT_READ_FILE, /* 37 */ 37: couldn't read a file:// file
CURLE_LDAP_CANNOT_BIND, /* 38 */ 38: LDAP: cannot bind
CURLE_LDAP_SEARCH_FAILED, /* 39 */ 39: LDAP: search failed
CURLE_LIBRARY_NOT_FOUND, /* 40 */ 40: a required shared library was not found
CURLE_FUNCTION_NOT_FOUND, /* 41 */ 41: a required function in the shared library was not found
CURLE_ABORTED_BY_CALLBACK, /* 42 */ 42: the operation was aborted by an application callback
CURLE_BAD_FUNCTION_ARGUMENT, /* 43 */ 43: a libcurl function was given a bad argument
CURLE_BAD_CALLING_ORDER, /* 44 - NOT USED */ 44: unknown error
CURLE_INTERFACE_FAILED, /* 45 - CURLOPT_INTERFACE failed */ 45: failed binding local connection end
CURLE_BAD_PASSWORD_ENTERED, /* 46 - NOT USED */ 46: unknown error
CURLE_TOO_MANY_REDIRECTS , /* 47 - catch endless re-direct loops */ 47: number of redirects hit maximum amount
CURLE_UNKNOWN_TELNET_OPTION, /* 48 - User specified an unknown option */ 48: User specified an unknown option
CURLE_TELNET_OPTION_SYNTAX , /* 49 - Malformed telnet option */ 49: Malformed telnet option
CURLE_OBSOLETE, /* 50 - NOT USED */ 50: unknown error
CURLE_SSL_PEER_CERTIFICATE, /* 51 - peer's certificate wasn't ok */ 51: SSL peer certificate was not ok
CURLE_GOT_NOTHING, /* 52 - when this is a specific error */ 52: server returned nothing (no headers, no data)
CURLE_SSL_ENGINE_NOTFOUND, /* 53 - SSL crypto engine not found */ 53: SSL crypto engine not found
CURLE_SSL_ENGINE_SETFAILED, /* 54 - can not set SSL crypto engine as 54: can not set SSL crypto engine as default
default */
CURLE_SEND_ERROR, /* 55 - failed sending network data */ 55: failed sending data to the peer
CURLE_RECV_ERROR, /* 56 - failure in receiving network data */ 56: failure when receiving data from the peer
CURLE_SHARE_IN_USE, /* 57 - share is in use */ 57: share is already in use
CURLE_SSL_CERTPROBLEM, /* 58 - problem with the local certificate */ 58: problem with the local SSL certificate
CURLE_SSL_CIPHER, /* 59 - couldn't use specified cipher */ 59: couldn't use specified SSL cipher
CURLE_SSL_CACERT, /* 60 - problem with the CA cert (path?) */ 60: peer certificate cannot be authenticated with known CA certificates
CURLE_BAD_CONTENT_ENCODING, /* 61 - Unrecognized transfer encoding */ 61: Unrecognized HTTP Content-Encoding
CURLE_LDAP_INVALID_URL, /* 62 - Invalid LDAP URL */ 62: Invalid LDAP URL
CURLE_FILESIZE_EXCEEDED, /* 63 - Maximum file size exceeded */ 63: Maximum file size exceeded
CURLE_FTP_SSL_FAILED, /* 64 - Requested FTP SSL level failed */ 64: Requested FTP SSL level failed
CURLE_SEND_FAIL_REWIND, /* 65 - Sending the data requires a rewind 65: Send failed since rewinding of the data stream failed
that failed */
CURLE_SSL_ENGINE_INITFAILED, /* 66 - failed to initialise ENGINE */ 66: failed to initialise SSL crypto engine
CURLE_LOGIN_DENIED, /* 67 - user, password or similar was not 67: FTP: login denied
accepted and we failed to login */
CURLE_TFTP_NOTFOUND, /* 68 - file not found on server */ 68: TFTP: File Not Found
CURLE_TFTP_PERM, /* 69 - permission problem on server */ 69: TFTP: Access Violation
CURLE_TFTP_DISKFULL, /* 70 - out of disk space on server */ 70: TFTP: Disk full or allocation exceeded
CURLE_TFTP_ILLEGAL, /* 71 - Illegal TFTP operation */ 71: TFTP: Illegal operation
CURLE_TFTP_UNKNOWNID, /* 72 - Unknown transfer ID */ 72: TFTP: Unknown transfer ID
CURLE_TFTP_EXISTS, /* 73 - File already exists */ 73: TFTP: File already exists
CURLE_TFTP_NOSUCHUSER, /* 74 - No such user */ 74: TFTP: No such user
CURLE_CONV_FAILED, /* 75 - conversion failed */ 75: conversion failed
CURLE_CONV_REQD, /* 76 - caller must register conversion 76: caller must register CURLOPT_CONV_ callback options
callbacks using curl_easy_setopt options
CURLOPT_CONV_FROM_NETWORK_FUNCTION,
CURLOPT_CONV_TO_NETWORK_FUNCTION, and
CURLOPT_CONV_FROM_UTF8_FUNCTION */
CURLE_SSL_CACERT_BADFILE, /* 77 - could not load CACERT file, missing 77: problem with the SSL CA cert (path? access rights?)
or wrong format */
CURLE_REMOTE_FILE_NOT_FOUND, /* 78 - remote file not found */ 78: Remote file not found
CURLE_SSH, /* 79 - error from the SSH layer, somewhat 79: Error in the SSH layer
generic so the error message will be of
interest when this has happened */
CURLE_SSL_SHUTDOWN_FAILED, /* 80 - Failed to shut down the SSL 80: Failed to shut down the SSL connection
connection */

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