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 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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