C++使用libcurl做HttpClient

    当使用C++做HTTP客户端时，目前通用的做法就是使用libcurl。其官方网站的地址是http://curl.haxx.se/，该网站主要提供了Curl和libcurl。Curl是命令行工具，用于完成FTP, FTPS, HTTP, HTTPS, GOPHER, TELNET, DICT, FILE 以及 LDAP的命令的请求及接收回馈。libcurl提供给开发者，用于使用C++跨平台的开发各种网络协议的请求及响应。里面的文档非常齐全，不过都是英文的。

    本文提供最简单的demo使用libcurl开发HttpClient。主要包括同步的HTTP GET、HTTP POST、HTTPS GET、HTTPS POST。

    下载libcurl包，如果使用Linux平台，建议下载源文件编译；如果使用Windows平台，建议下载Win32 - MSVC，下载地址是：http://curl.haxx.se/download.html

 #ifndef __HTTP_CURL_H__
 #define __HTTP_CURL_H__

 #include <string>

 class CHttpClient
 {
 public:
     CHttpClient(void);
     ~CHttpClient(void);

 public:
     /**
     * @brief HTTP POST请求
     * @param strUrl 输入参数,请求的Url地址,如:http://www.baidu.com
     * @param strPost 输入参数,使用如下格式para1=val1¶2=val2&…
     * @param strResponse 输出参数,返回的内容
     * @return 返回是否Post成功
     */
     int Post(const std::string & strUrl, const std::string & strPost, std::string & strResponse);

     /**
     * @brief HTTP GET请求
     * @param strUrl 输入参数,请求的Url地址,如:http://www.baidu.com
     * @param strResponse 输出参数,返回的内容
     * @return 返回是否Post成功
     */
     int Get(const std::string & strUrl, std::string & strResponse);

     /**
     * @brief HTTPS POST请求,无证书版本
     * @param strUrl 输入参数,请求的Url地址,如:https://www.alipay.com
     * @param strPost 输入参数,使用如下格式para1=val1¶2=val2&…
     * @param strResponse 输出参数,返回的内容
     * @param pCaPath 输入参数,为CA证书的路径.如果输入为NULL,则不验证服务器端证书的有效性.
     * @return 返回是否Post成功
     */
     int Posts(const std::string & strUrl, const std::string & strPost, std::string & strResponse, const char * pCaPath = NULL);

     /**
     * @brief HTTPS GET请求,无证书版本
     * @param strUrl 输入参数,请求的Url地址,如:https://www.alipay.com
     * @param strResponse 输出参数,返回的内容
     * @param pCaPath 输入参数,为CA证书的路径.如果输入为NULL,则不验证服务器端证书的有效性.
     * @return 返回是否Post成功
     */
     int Gets(const std::string & strUrl, std::string & strResponse, const char * pCaPath = NULL);

 public:
     void SetDebug(bool bDebug);

 private:
     bool m_bDebug;
 };

 #endif

 #include "httpclient.h"
 #include "curl/curl.h"
 #include <string>

 CHttpClient::CHttpClient(void) :
 m_bDebug(false)
 {

 }

 CHttpClient::~CHttpClient(void)
 {

 }

 static int OnDebug(CURL *, curl_infotype itype, char * pData, size_t size, void *)
 {
     if(itype == CURLINFO_TEXT)
     {
         //printf("[TEXT]%s\n", pData);
     }
     else if(itype == CURLINFO_HEADER_IN)
     {
         printf("[HEADER_IN]%s\n", pData);
     }
     else if(itype == CURLINFO_HEADER_OUT)
     {
         printf("[HEADER_OUT]%s\n", pData);
     }
     else if(itype == CURLINFO_DATA_IN)
     {
         printf("[DATA_IN]%s\n", pData);
     }
     else if(itype == CURLINFO_DATA_OUT)
     {
         printf("[DATA_OUT]%s\n", pData);
     }
     return 0;
 }

 static size_t OnWriteData(void* buffer, size_t size, size_t nmemb, void* lpVoid)
 {
     std::string* str = dynamic_cast<std::string*>((std::string *)lpVoid);
     if( NULL == str || NULL == buffer )
     {
         return -1;
     }

     char* pData = (char*)buffer;
     str->append(pData, size * nmemb);
     return nmemb;
 }

 int CHttpClient::Post(const std::string & strUrl, const std::string & strPost, std::string & strResponse)
 {
     CURLcode res;
     CURL* curl = curl_easy_init();
     if(NULL == curl)
     {
         return CURLE_FAILED_INIT;
     }
     if(m_bDebug)
     {
         curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
         curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, OnDebug);
     }
     curl_easy_setopt(curl, CURLOPT_URL, strUrl.c_str());
     curl_easy_setopt(curl, CURLOPT_POST, 1);
     curl_easy_setopt(curl, CURLOPT_POSTFIELDS, strPost.c_str());
     curl_easy_setopt(curl, CURLOPT_READFUNCTION, NULL);
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, OnWriteData);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&strResponse);
     curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 3);
     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);
     res = curl_easy_perform(curl);
     curl_easy_cleanup(curl);
     return res;
 }

 int CHttpClient::Get(const std::string & strUrl, std::string & strResponse)
 {
     CURLcode res;
     CURL* curl = curl_easy_init();
     if(NULL == curl)
     {
         return CURLE_FAILED_INIT;
     }
     if(m_bDebug)
     {
         curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
         curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, OnDebug);
     }
 <pre name="code" class="cpp">   curl_easy_setopt(curl, CURLOPT_URL, strUrl.c_str());
     curl_easy_setopt(curl, CURLOPT_READFUNCTION, NULL);
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, OnWriteData);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&strResponse);
     /**
     * 当多个线程都使用超时处理的时候，同时主线程中有sleep或是wait等操作。
     * 如果不设置这个选项，libcurl将会发信号打断这个wait从而导致程序退出。
     */
     curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 3);
     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);
     res = curl_easy_perform(curl);
     curl_easy_cleanup(curl);
     return res;
 }

 int CHttpClient::Posts(const std::string & strUrl, const std::string & strPost, std::string & strResponse, const char * pCaPath)
 {
     CURLcode res;
     CURL* curl = curl_easy_init();
     if(NULL == curl)
     {
         return CURLE_FAILED_INIT;
     }
     if(m_bDebug)
     {
         curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
         curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, OnDebug);
     }
     curl_easy_setopt(curl, CURLOPT_URL, strUrl.c_str());
     curl_easy_setopt(curl, CURLOPT_POST, 1);
     curl_easy_setopt(curl, CURLOPT_POSTFIELDS, strPost.c_str());
     curl_easy_setopt(curl, CURLOPT_READFUNCTION, NULL);
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, OnWriteData);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&strResponse);
     curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);
     if(NULL == pCaPath)
     {
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, false);
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, false);
     }
     else
     {
         //缺省情况就是PEM，所以无需设置，另外支持DER
         //curl_easy_setopt(curl,CURLOPT_SSLCERTTYPE,"PEM");
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, true);
         curl_easy_setopt(curl, CURLOPT_CAINFO, pCaPath);
     }
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 3);
     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);
     res = curl_easy_perform(curl);
     curl_easy_cleanup(curl);
     return res;
 }

 int CHttpClient::Gets(const std::string & strUrl, std::string & strResponse, const char * pCaPath)
 {
     CURLcode res;
     CURL* curl = curl_easy_init();
     if(NULL == curl)
     {
         return CURLE_FAILED_INIT;
     }
     if(m_bDebug)
     {
         curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);
         curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, OnDebug);
     }
     curl_easy_setopt(curl, CURLOPT_URL, strUrl.c_str());
     curl_easy_setopt(curl, CURLOPT_READFUNCTION, NULL);
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, OnWriteData);
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&strResponse);
     curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);
     if(NULL == pCaPath)
     {
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, false);
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, false);
     }
     else
     {
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, true);
         curl_easy_setopt(curl, CURLOPT_CAINFO, pCaPath);
     }
     curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 3);
     curl_easy_setopt(curl, CURLOPT_TIMEOUT, 3);
     res = curl_easy_perform(curl);
     curl_easy_cleanup(curl);
     return res;
 }

 ///////////////////////////////////////////////////////////////////////////////////////////////

 void CHttpClient::SetDebug(bool bDebug)
 {
     m_bDebug = bDebug;
 }
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