解决方案

将

curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

换成

 curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "PUT");  

原因

在项目中对方要求使用PUT来发送控制指令，于是直接使用Libcurl来实现。原本是一个非常简单的事情，确怎么都没发送出控制指令，单步执行发现curl_easy_perform阻塞了，网上查了各种原因，发现都不适用，最后对比Postman发送数据，发现上述问题。最终实现代码如下：

size_t write_callback(void* contents, size_t size, size_t nmemb, void* userp) {// 处理响应数据  char* pData = (char*)contents;cout << "contents == " << pData << endl;return size * nmemb; // 返回接收到的字节数，以便libcurl知道数据已经被接收  
}
static bool initPutUpPlat(const char* url,  string strUser, string strPsd,  string& strRes)
{string strke = strUser + ":" + strPsd;curl_global_init(CURL_GLOBAL_ALL);CURLcode code;CURL* conn;conn = curl_easy_init();if (NULL == conn){std::cout << stderr << " Failed to create CURL connection" << std::endl;exit(EXIT_FAILURE);}code = curl_easy_setopt(conn, CURLOPT_URL, url);if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}code = curl_easy_setopt(conn, CURLOPT_USERPWD, strke.c_str());if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}code = curl_easy_setopt(conn, CURLOPT_HTTPAUTH, CURLAUTH_DIGEST);if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}code = curl_easy_setopt(conn, CURLOPT_CUSTOMREQUEST, "PUT");if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}struct curl_slist* headers = NULL;headers = curl_slist_append(headers, "Content-Type: text/plain");code = curl_easy_setopt(conn, CURLOPT_HTTPHEADER, headers);if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}const char* data = "指令....";code = curl_easy_setopt(conn, CURLOPT_POSTFIELDS, data);if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}code = curl_easy_setopt(conn, CURLOPT_WRITEFUNCTION, write_callback); // 设置回调函数以处理上传的数据if (code != CURLE_OK){std::cout << stderr << " Failed to set error buffer " << code << std::endl;return false;}code = curl_easy_perform(conn);if (code != CURLE_OK){return false;}curl_slist_free_all(headers);//记得释放return true;
}

为何阻塞

注意：如果使用CURLOPT_PUT一定要记得添加传输大小CURLOPT_INFILESIZE_LARGE

 通过put上传文件
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
curl_easy_setopt(curl, CURLOPT_PUT, 1L);
curl_easy_setopt(curl, CURLOPT_READDATA, fp);   // FILE *fp = fopen("/path/filename");
curl_easy_setopt(curl, CURLOPT_INFILESIZE_LARGE, fsize);  // fsize = sizeof /path/filename