好用的http client库CPP REST SDK

C++中http client库本身就少,好用的就更少了,在了解微软开源的 CPP REST SDK 库之前,我知道的C++ http client库有 libc

好用的http client库CPP REST SDK

C++中http client库本身就少,好用的就更少了,在了解微软开源的 CPP REST SDK 库之前,我知道的C++ http client库有 libcurl (这个是C语言的),Qt的 QNetworkAccessManager ,还有VC++ http client,Qt的QNetworkAccessManager库我在开发 CZPlayer 的时候用来下载过音乐、专辑图片和歌词,不得不说Qt提供的API还是比较好用的,如果不涉及界面开发,难道我们在linux上就只能用libcurl,在windows上就用VC++的http client?答案是否定的,在绝望之际CPP REST SDK出现在我的眼前,CPP REST SDK是微软开源的基于PPL的异步http client,网络层使用的是Boost.Asio,跨平台,并且支持json解析,在使用CPP REST SDK之前要确保你已经安装了boost和openssl,下面是微软官方提供的例子。

微软官方例子

#include<cpprest/http_client.h>#include<cpprest/filestream.h>usingnamespaceutility;// Common utilities like string conversionsusingnamespaceweb;// Common features like URIs.usingnamespaceweb::http;// Common HTTP functionalityusingnamespaceweb::http::client;// HTTP client featuresusingnamespaceconcurrency::streams;// Asynchronous streamsintmain(intargc,char* argv[]){autofileStream =std::make_shared<ostream>();// Open stream to output file. pplx::task<void> requestTask = fstream::open_ostream(U("results.html")).then([=](ostream outFile) { *fileStream = outFile;// Create http_client to send the request. http_client client(U("http://www.bing.com/"));// Build request URI and start the request. uri_builder builder(U("/search")); builder.append_query(U("q"), U("cpprestsdk github"));returnclient.request(methods::GET, builder.to_string()); })// Handle response headers arriving. .then([=](http_response response) {printf("Received response status code:%u/n", response.status_code());// Write response body into the file.returnresponse.body().read_to_end(fileStream->streambuf()); })// Close the file stream. .then([=](size_t) {returnfileStream->close(); });// Wait for all the outstanding I/O to complete and handle any exceptionstry { requestTask.wait(); }catch(conststd::exception &e) {printf("Error exception:%s/n", e.what()); }return0;}

上面的例子主要内容是访问一个网站并将该内容保存在results.html里面,这里用到了微软自家的PPL并行计算库(还有一个是英特尔的TBB),该例子使用lambda表达式作为异步回调的handler,打开文件流、请求、回应和关闭文件流都是异步的,为了方便起见,我们将该例子改为同步方式。

使用同步方式

auto fileStream = std::make_shared<ostream>();ostream outFile = fstream::open_ostream(U("results.html")).get();*fileStream = outFile;// Create http_client to send the request.http_client client(U("http://www.bing.com/"));// Build request URI and start the request.uri_builder builder(U("/search"));builder.append_query(U("q"), U("cpprestsdk github"));http_response response = client.request(methods::GET, builder.to_string()).get();// Write response body into the file.response.body().read_to_end(fileStream->streambuf()).get();fileStream->close().get();

使用同步方式的代码比较清晰,可以看到每一个函数调用后面都会调用get函数,因为CPP REST SDK是基于PPL的,所以在request、read_to_end、close等函数调用后都会返回一个Task对象,而Task里面的get和wait函数是等待任务执行完成。

实战

我之前在看别人博客的时候看到每一篇博客前都有一副图,看起来比较好看,听博主讲他是使用bing的每日一图,后来我也效仿,我在主题之家找到了自己比较喜欢的图片,最开始自己写博客的时候都是直接去主题之家一页一页的找看,然后再下载图片,写了几篇博客之后感觉每次都要去下载图片感觉有点low,所以我决定直接将主题之家的某类型的图片都下载下来,这样选图片就方便多了,下面是我在主题之家抓图的代码。

#include <iostream>#include <string>#include <vector>#include <fstream>#include <memory>#include <regex>#include <cpprest/http_client.h>#include <cpprest/filestream.h>#include <cpprest/containerstream.h>// 请求并解析urlbool get_result(const std::string& url, const std::string& pattern, std::vector<std::string>& vec){ try { web::http::client::http_client client(web::uri(utility::conversions::to_string_t(url))); web::http::http_response response = client.request(web::http::methods::GET).get(); concurrency::streams::stringstreambuf buffer; response.body().read_to_end(buffer).get(); std::string& str = buffer.collection(); // 使用C++11提供的正则表达式库 std::regex r(pattern); for (std::sregex_iterator iter(str.begin(), str.end(), r), end; iter != end; ++iter) { std::cout << iter->str() << std::endl; vec.emplace_back(iter->str()); } } catch (std::exception& e) { std::cout << "Exception: " << e.what() << std::endl; return false; } return true;}// 获取图片bool get_result(const std::string& url, std::string& picture){ try { web::http::client::http_client client(web::uri(utility::conversions::to_string_t(url))); web::http::http_response response = client.request(web::http::methods::GET).get(); concurrency::streams::stringstreambuf buffer; response.body().read_to_end(buffer).get(); picture = buffer.collection(); } catch (std::exception& e) { std::cout << "Exception: " << e.what() << std::endl; return false; } return true;}// 保存图片bool write_to_file(const std::string& file_path, const std::string& data){ try { std::ofstream file; file.open(file_path, std::ios::out | std::ios::binary); if (!file.good()) { return false; } file.write(data.c_str(), data.size()); file.close(); } catch (std::exception& e) { std::cout << "Exception: " << e.what() << std::endl; return false; } return true;}int main(){ // [1] 请求每一页,将子页面的url保存在sub_url_vec里面 std::vector<std::string> sub_url_vec; std::string pattern = "/desk/[0-9]+.htm"; for (int i = 1; i <= 32; ++i) { // 创意主题 std::string url = "http://www.51ztzj.com/dbizhi/category_27_" + std::to_string(i) + ".htm#content_anchor"; std::cout << "Start get " << i << " page, url: " << url << std::endl; // 请求并解析url if (!get_result(url, pattern, sub_url_vec)) { std::cout << "Get " << i << " page failed" << std::endl; } } // 最终的图片url:http://img.51ztzj.com//upload/image/20130220/2013022014_670x419.jpg // [2] 将子页面的图片url解析出来放入picture_url_vec std::vector<std::string> picture_url_vec; pattern = "http://img.51ztzj.com//upload/image/.+/.+_670x419.jpg"; for (std::size_t i = 0; i < sub_url_vec.size(); ++i) { std::string url = "http://www.51ztzj.com" + sub_url_vec[i]; std::cout << "Start get " << i + 1 << " sub page, url: " << url << std::endl; // 请求并解析url if (!get_result(url, pattern, picture_url_vec)) { std::cout << "Get " << i + 1 << " sub page failed" << std::endl; } } // [3] 最后遍历picture_url_vec,然后一个一个的下载图片 for (std::size_t i = 0; i < picture_url_vec.size(); ++i) { std::cout << "Start download " << i + 1 << " picture, url: " << picture_url_vec[i] << std::endl; std::string picture; // 获取图片 if (!get_result(picture_url_vec[i], picture)) { std::cout << "Download " << i + 1 << " picture failed" << std::endl; } std::string file_path = "./download/" + std::to_string(i) + ".jpg"; // 保存图片 if (!write_to_file(file_path, picture)) { std::cout << "Write to file failed: " << i + 1 << std::endl; } } return 0;}
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到底啦