Boost Beast 异步休息客户端：async_resolve - 解决：找不到主机权威

问题描述

我有异步提升休息客户端代码。我能够在 Windows 上使用 Cygwin 编译和运行此代码。

#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/connect.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <memory>
#include <string>

using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>
namespace http = boost::beast::http;    // from <boost/beast/http.hpp>

void
fail(boost::system::error_code ec,char const* what)
{
    std::cerr << what << ": " << ec.message() << "\n";
}

// Performs an HTTP GET and prints the response
class session : public std::enable_shared_from_this<session>
{
    tcp::resolver resolver_;
    tcp::socket socket_;
    boost::beast::flat_buffer buffer_; // (Must persist between reads)
    http::request<http::empty_body> req_;
    http::response<http::string_body> res_;

public:
    // Resolver and socket require an io_context
    explicit
    session(boost::asio::io_context& ioc)
        : resolver_(ioc),socket_(ioc)
    {
    }

    // Start the asynchronous operation
    void
    run(char const* host,char const* port,char const* target,int version)
    {
        // Set up an HTTP GET request message
        req_.version(version);
        req_.method(http::verb::get);
        req_.target(target);
        req_.set(http::field::host,host);
        req_.set(http::field::user_agent,BOOST_BEAST_VERSION_STRING);

        // Look up the domain name
        resolver_.async_resolve(host,port,std::bind( &session::on_resolve,shared_from_this(),std::placeholders::_1,std::placeholders::_2));
    }

    void
    on_resolve( boost::system::error_code ec,tcp::resolver::results_type results)
    {
        if(ec) {
            return fail(ec,"resolve");
        }

        // Make the connection on the IP address we get from a lookup
        boost::asio::async_connect(socket_,results.begin(),results.end(),std::bind(&session::on_connect,std::placeholders::_1));
    }

    void
    on_connect(boost::system::error_code ec)
    {
        if(ec) {
            return fail(ec,"connect");
        }

        // Send the HTTP request to the remote host
        http::async_write(socket_,req_,std::bind(&session::on_write,std::placeholders::_2));
    }

    void
    on_write( boost::system::error_code ec,std::size_t bytes_transferred)
    {
        boost::ignore_unused(bytes_transferred);

        if(ec) {
            return fail(ec,"write");
        }

        // Receive the HTTP response
        http::async_read(socket_,buffer_,res_,std::bind( &session::on_read,std::placeholders::_2));
    }

    void
    on_read(boost::system::error_code ec,"read");
        }
        // Write the message to standard out
        std::cout << res_ << std::endl;

        // Gracefully close the socket
        socket_.shutdown(tcp::socket::shutdown_both,ec);

        // not_connected happens sometimes so don't bother reporting it.
        if(ec && ec != boost::system::errc::not_connected) {
            return fail(ec,"shutdown");
        }
        // If we get here then the connection is closed gracefully
    }
};



int main(int argc,char** argv)
{
    // Check command line arguments.
    if(argc != 4 && argc != 5)
    {
        std::cerr <<
                  "Usage: http-client-async <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
                  "Example:\n" <<
                  "    http-client-async www.example.com 80 /\n" <<
                  "    http-client-async www.example.com 80 / 1.0\n";
        return EXIT_FAILURE;
    }
    auto const host = argv[1];
    auto const port = argv[2];
    auto const target = argv[3];
    int version = argc == 5 && !std::strcmp("1.0",argv[4]) ? 10 : 11;

    // The io_context is required for all I/O
    boost::asio::io_context ioc;

    // Launch the asynchronous operation
    std::make_shared<session>(ioc)->run(host,target,version);

    // Run the I/O service. The call will return when
    // the get operation is complete.
    ioc.run();

    return EXIT_SUCCESS;
}

我有一个 python REST 服务器，它运行等待来自这个客户端的请求。

#!flask/bin/python
from flask import Flask,jsonify

app = Flask(__name__)

tasks = [
    {
        'id': 1,'title': u'Buy groceries','description': u'Milk,Cheese,Pizza,Fruit,Tylenol','done': False
    },{
        'id': 2,'title': u'Learn Python','description': u'Need to find a good Python tutorial on the web','done': False
    }
]

@app.route('/todo/api/v1.0/tasks',methods=['GET'])
def get_tasks():
    return jsonify({'tasks': tasks})

if __name__ == '__main__':
    app.run(host='0.0.0.0',debug=True)

我能够运行此服务器。输出如下所示。

 * Serving Flask app 'RESTServer' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployme
nt.
   Use a production Wsgi server instead.
 * Debug mode: on
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 409-562-797
 * Running on all addresses.
   WARNING: This is a development server. Do not use it in a production deployme
nt.
 * Running on http://192.168.1.104:5000/ (Press CTRL+C to quit)

但是当我运行 REST 客户端时，如下

rest_client.exe http://192.168.1.104 5000 /todo/api/v1.0/tasks

我收到以下错误

 resolve: Host not found (authoritative)

解决方法

程序需要单独的参数。它甚至会为您提供使用说明：

Usage: http-client-async <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]
Example:
    http-client-async www.example.com 80 /
    http-client-async www.example.com 80 / 1.0

所以看起来您至少要删除 http://