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好用的http client库CPP REST SDK

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 conversions
usingnamespaceweb;// Common features like URIs.
usingnamespaceweb::http;// Common HTTP functionality
usingnamespaceweb::http::client;// HTTP client features
usingnamespaceconcurrency::streams;// Asynchronous streams

intmain(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 exceptions
try
 {
 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url
bool 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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