Ubuntu 22.04 下 CURL（C++） 实现分块上传/下载文件源码

为了帮助大家理解代码，先介绍文件上传/下载流程：

上传文件流程说明：首先向服务器 restful api 接口 /common发送 Post 请求 ，服务器端返回 project guid。读取本地文件，按照给定 chunk_size（例如 10240 byte），不断循环向服务器 restful api 接口 /upload_chunk 发送数据，直到文件传输完成。

视频上传后，在服务器端做 3D 建模，耗时1-2小时，故拆分步骤，首先向服务器发送请求生成 project_guid, “刷新”按钮不停获取服务器状态。这些步骤不是必须，使用者按照自己项目需求取舍。发送请求的 header, body_json 等格式，同样按照自己的项目需求设计即可。

这是创建 project 的接口说明： 

下载文件：同样采取分块下载。

CMakeList.txt:

# 查找libcurl组件
find_package(CURL REQUIRED)

include_directories(
  include
  ${PYTHON_INCLUDE_DIRS}
  ${CURL_INCLUDE_DIRS}
)

target_link_libraries(${PROJECT_NAME} PRIVATE "${CURL_LIBRARY}")
target_include_directories(${PROJECT_NAME} PRIVATE "${CURL_INCLUDE_DIR}")

upload调用代码：

void test_restapi_upload_chunk(){std::string project_id = "bee8400e-1f13-11ef-818a-7d68b3e42070";std::string file_path = "/home/coco/Documents/IMG_02391.MOV";std::string url = "http://192.168.1.87:8200/upload_chunk";try {upload_chunk(url, project_id, file_path);std::cout << "Chunk upload completed successfully." << std::endl;} catch (const std::exception& e) {std::cerr << "An error occurred: " << e.what() << std::endl;}
}

 upload_chunk() 函数实现代码：

void upload_chunk(const std::string& url, const std::string& project_id, const std::string& file_path, size_t chunkSize) {// curl初始化CURL* curl = curl_easy_init();if (!curl) {std::cerr << "CURL initialization failed." << std::endl;return;}// 初始化表单和头部curl_httppost* formpost = NULL;curl_httppost* lastptr = NULL;struct curl_slist* headers = NULL;// 设置 URL 和 HTTP POST 选项std::cout << "url.c_str(): " + url << std::endl;curl_easy_setopt(curl, CURLOPT_URL, url.c_str());curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);// 打开文件和读取逻辑std::ifstream file(file_path, std::ios::binary);if (!file.is_open()) {std::cerr << "Failed to open file: " << file_path << std::endl;return;}std::filesystem::path path(file_path);std::string file_name = path.filename();size_t totalSize = std::filesystem::file_size(file_path);size_t offset = 0;size_t start = 0;std::cout << "totalSize: " + std::to_string(totalSize) << std::endl;// 循环读取文件并发送std::vector<char> buffer(chunkSize);while (!file.eof()) {// 读取文件内容到bufferfile.read(buffer.data(), chunkSize);size_t bytesRead = file.gcount();if (bytesRead == 0) {break; // 没有更多数据可读，退出循环}// 构建project表单数据CURLFORMcode form_result = curl_formadd(&formpost,&lastptr,CURLFORM_COPYNAME, "project", // 表单字段名称CURLFORM_COPYCONTENTS, project_id.c_str(), // 表单字段值CURLFORM_END);// 为每个文件块创建一个新的表单form_result = curl_formadd(&formpost,&lastptr,CURLFORM_COPYNAME, "file", // 表单字段名称CURLFORM_BUFFERPTR, buffer.data(), // 缓冲区指针CURLFORM_BUFFERLENGTH, static_cast<long>(bytesRead), // 缓冲区长度CURLFORM_FILENAME, file_name.c_str(), // 文件名CURLFORM_CONTENTTYPE, "application/octet-stream", // 内容类型CURLFORM_END);if (form_result != CURL_FORMADD_OK) {std::cerr << "Error building file form." << std::endl;break;}// 设置请求头和POST数据std::string contentRange = std::to_string(start) + "-" + std::to_string(start + bytesRead - 1) + "/" + std::to_string(totalSize);std::cout << "contentRange: " + contentRange << std::endl;headers = curl_slist_append(headers, ("Content-Range: " + contentRange).c_str());curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);// 设置回调函数和数据std::string responseContent;curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, UploadWriteCallback);curl_easy_setopt(curl, CURLOPT_WRITEDATA, &responseContent);// 执行请求CURLcode res = curl_easy_perform(curl);if (res != CURLE_OK) {std::cerr << "CURL error: " << curl_easy_strerror(res) << std::endl;break;}// 更新下一个块的起始位置start += bytesRead;// 处理响应数据if (!responseContent.empty()) {std::cout << responseContent << std::endl;}// 清理headers和表单curl_slist_free_all(headers);headers = nullptr;curl_formfree(formpost);formpost = NULL;lastptr = NULL;}// 清理资源curl_formfree(formpost);curl_easy_cleanup(curl);file.close();
}

download 调用代码：

void test_restapi_download_chunk(){char cwd[PATH_MAX];if (getcwd(cwd, sizeof(cwd)) != NULL) {std::cout << "getcwd(): " << cwd << std::endl;} else {perror("getcwd() error");}QString currentPath = QDir::currentPath();std::cout << "Current working directory: " << currentPath.toStdString() << std::endl;std::string url = "http://192.168.1.87:8200/download_chunk"; // 替换为实际的Flask服务器URLstd::string project = "85c9c7cc-18d6-11ef-818a-7d68b3e42070"; // 替换为实际项目名称std::string output_path = "/home/coco/Downloads/point_cloud.ply"; // 替换为实际保存文件的路径size_t start = 0; // 替换为实际起始字节size_t end = 1024; // 替换为实际结束字节，这里假设DOWNLOAD_RANGE的值为102400try {if (FileSystemUtils::exists(output_path)) {std::cout << output_path + "already exists." << std::endl;return ;}download_chunk(url, project, output_path, start, end);std::cout << "Chunk download completed successfully." << std::endl;} catch (const std::exception& e) {std::cerr << "An error occurred: " << e.what() << std::endl;}
}

 download_chunk()函数代码实现：

int download_chunk(const std::string& url, const std::string& project_id, const std::string& output_path, size_t start, size_t end=10240) {// 创建 curl 句柄CURL *curl = curl_easy_init();if (!curl) {std::cerr << "CURL initialization failed." << std::endl;return 1;}// 保存文件，确保以追加模式打开std::ofstream outfile(output_path, std::ios::binary | std::ios::app);if (!outfile.is_open()) {std::cerr << "Cannot open file: " << output_path << std::endl;return 1;}// 设置请求的URLcurl_easy_setopt(curl, CURLOPT_URL, url.c_str());curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "GET");//curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);//curl_easy_setopt(curl, CURLOPT_HTTPHEADER, nullptr);// 设置请求body: project_idstd::string json_data = nlohmann::json{{"project", project_id}}.dump();curl_easy_setopt(curl, CURLOPT_POSTFIELDS, json_data.c_str());CURLcode res;size_t total_size = -1;size_t content_length;bool is_total_size_calculated = false;std::string response_content;std::string response_headers;std::string range_header = "Range: " + std::to_string(start) + "-" + std::to_string(end);std::cout << "first range_header: " << range_header << std::endl << std::endl;int i = 1;struct curl_slist *headers = nullptr;try {do {std::cout << "第" << std::to_string(i)  <<"次循环：" << std::endl;i = i + 1;// 设置请求头, 包括Range和Content-Typeheaders = curl_slist_append(headers, "Content-Type: application/json");headers = curl_slist_append(headers, range_header.c_str());curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);// 设置响应头回调函数curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, HeaderCallback);curl_easy_setopt(curl, CURLOPT_HEADERDATA, &response_headers);// 设置写入回调函数curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, DownloadWriteCallback);curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response_content);// 执行请求res = curl_easy_perform(curl);if (res != CURLE_OK) {std::cerr << "Download error: " << curl_easy_strerror(res) << std::endl;curl_slist_free_all(headers);curl_easy_cleanup(curl);//curl_global_cleanup();if (outfile.is_open()) {outfile.close(); // 关闭文件}return 1;} else {// 响应头存储在response_header中,解析response_header来获取需要的信息std::cout << "Response headers: "<< std::endl << response_headers << std::endl;// 解析响应头, Content-Range, Content-Lengthstd::istringstream header_stream(response_headers);std::string header_line;while (getline(header_stream, header_line)) {if (header_line.find("Content-Range:") == 0) {std::cout << "header_line: " << header_line << std::endl;if (!is_total_size_calculated ) {size_t pos = header_line.find('/');std::string total_size_str = header_line.substr(pos + 1);total_size = std::stoull(total_size_str);std::cout << "total_size: " << total_size << std::endl;is_total_size_calculated = true;}} else if (header_line.find("Content-Length:") == 0) {size_t pos = header_line.find(':');content_length = std::stoul(header_line.substr(pos + 2));std::cout << "content_length: " << content_length << std::endl;// 更新下一次请求的范围start += content_length;end = std::min(end + content_length, total_size);// 更新range_headerrange_header = "Range: bytes=" + std::to_string(start) + "-" + std::to_string(end);std::cout << "request range_header: " << range_header << std::endl;std::cout << "start: " << start << std::endl;std::cout << "end: " << end << std::endl << std::endl;}}// 将 responseContent 写入到文件outfile.write(response_content.c_str(), response_content.length());curl_slist_free_all(headers);headers = nullptr;response_headers.clear();response_content.clear();}} while (start < total_size);}catch (const std::bad_alloc& e) {std::cerr << "Memory allocation failed: " << e.what() << std::endl;if (headers) {curl_slist_free_all(headers);}curl_easy_cleanup(curl);if (outfile.is_open()) {outfile.close();}return 1;}curl_easy_cleanup(curl);if (outfile.is_open()) {outfile.close(); // 关闭文件}return 0;
}