Boost.Asio翻译（三）--DayTime1 A synchronous TCP daytime client

A synchronous TCP daytime client

一个同步的TCP daytime客户端

// client.cpp // // Copyright (c) 2003-2008 Christopher M. Kohlhoff (chris at kohlhoff dot com) // // Distributed under the Boost Software License, Version 1.0. (See accompanying // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) #include <iostream> #include <boost/array.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; int main(int argc, char* argv[]) { try { if (argc != 2) { std::cerr << "Usage: client <host>" << std::endl; return 1; } boost::asio::io_service io_service; tcp::resolver resolver(io_service); tcp::resolver::query query(argv[1], "daytime"); tcp::resolver::iterator endpoint_iterator = resolver.resolve(query); tcp::resolver::iterator end; tcp::socket socket(io_service); boost::system::error_code error = boost::asio::error::host_not_found; while (error && endpoint_iterator != end) { socket.close(); socket.connect(*endpoint_iterator++, error); } if (error) throw boost::system::system_error(error); for (;;) { boost::array<char, 128> buf; boost::system::error_code error; size_t len = socket.read_some(boost::asio::buffer(buf), error); if (error == boost::asio::error::eof) break; // Connection closed cleanly by peer. else if (error) throw boost::system::system_error(error); // Some other error. std::cout.write(buf.data(), len); } } catch (std::exception& e) { std::cerr << e.what() << std::endl; } return 0; }

说明：

我们需要把服务器的名称转化为TCP的节点，而该名称是通过应用程序的参数指定的。我们使用boost::asio::ip::tcp::resolver 对象来完成。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"><div style="font-size: 16px;"> <img alt="" style="border-top-style: none; border-right-style: none; border-bottom-style: none; border-left-style: none; border-color: initial;" src="http://images.csdn.net/syntaxhighlighting/OutliningIndicators/None.gif"><span style="color: rgb(0, 0, 0);">tcp::resolverresolver(io_service);</span> </div></div>

一个resolver对象获得一个query对象,并将其转换为节点列表.我们通过argv[1]中的服务器名称和服务名，在这里是daytime，构造一个query。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"> <div> <img alt="" style="border-top-style: none; border-right-style: none; border-bottom-style: none; border-left-style: none; border-color: initial;" src="http://images.csdn.net/syntaxhighlighting/OutliningIndicators/None.gif"><span style="color: rgb(0, 0, 0);">tcp::resolver::queryquery(argv[</span><span style="color: rgb(0, 0, 0);">1</span><span style="color: rgb(0, 0, 0);">],</span><span style="color: rgb(0, 0, 0);">"</span><span style="color: rgb(0, 0, 0);">daytime</span><span style="color: rgb(0, 0, 0);">"</span><span style="color: rgb(0, 0, 0);">);</span> </div> </div>

节点列表用boost::asio::ip::tcp::resolver::iterator类型的迭代器返回。返回的iterator将采用boost::asio::ip::tcp::resolver::iterator的默认构造函数来构造。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"><div> <span style="color: rgb(0, 0, 0);">tcp::resolver::iteratorendpoint_iterator</span><span style="color: rgb(0, 0, 0);">=</span><span style="color: rgb(0, 0, 0);">resolver.resolve(query);<br>tcp::resolver::iteratorend;</span> </div></div>

现在我们建立一个socket并连接之,由于获得的节点既有IPv4也有IPv6的。所以,我们需要依次尝试访问它们直到找到一个可以正常工作的。这样做可使得我们的程序独立于特定的IP版本。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"> <div> <span style="color: rgb(0, 0, 0);">tcp::socketsocket(io_service);<br>boost::system::error_codeerror</span><span style="color: rgb(0, 0, 0);">=</span><span style="color: rgb(0, 0, 0);">boost::asio::error::host_not_found;<br></span><span style="color: rgb(0, 0, 255);">while</span><span style="color: rgb(0, 0, 0);">(error</span><span style="color: rgb(0, 0, 0);">&&</span><span style="color: rgb(0, 0, 0);">endpoint_iterator</span><span style="color: rgb(0, 0, 0);">!=</span><span style="color: rgb(0, 0, 0);">end)<br>{<br>socket.close();<br>socket.connect(</span><span style="color: rgb(0, 0, 0);">*</span><span style="color: rgb(0, 0, 0);">endpoint_iterator</span><span style="color: rgb(0, 0, 0);">++</span><span style="color: rgb(0, 0, 0);">,error);<br>}<br></span><span style="color: rgb(0, 0, 255);">if</span><span style="color: rgb(0, 0, 0);">(error)<br></span><span style="color: rgb(0, 0, 255);">throw</span><span style="color: rgb(0, 0, 0);">boost::system::system_error(error);</span> </div> </div>

连接打开后，现在我们需要做的就是读取daytime服务器的响应。

我们使用boost::array来存放接收到的数据。boost::asio::buffer()函数会自动确定array的长度来防止缓冲区溢出。我们也可以使用char[]或std::vector来代替boost::array。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"> <div style="font-size: 16px;"> <span style="color: rgb(0, 0, 0);"></span><span style="color: rgb(0, 0, 255);">for</span><span style="color: rgb(0, 0, 0);">(;;)<br>{<br>boost::array</span><span style="color: rgb(0, 0, 0);"><</span><span style="color: rgb(0, 0, 255);">char</span><span style="color: rgb(0, 0, 0);">,</span><span style="color: rgb(0, 0, 0);">128</span><span style="color: rgb(0, 0, 0);">></span><span style="color: rgb(0, 0, 0);">buf;<br>boost::system::error_codeerror;<br><br>size_tlen</span><span style="color: rgb(0, 0, 0);">=</span><span style="color: rgb(0, 0, 0);">socket.read_some(boost::asio::buffer(buf),error);</span> </div> <span style="font-size: 16px;"> </span> </div>

当服务器关闭连接时,boost::asio::ip::tcp::socket::read_some()函数会以boost::asio::error::eof错误标志返回,通过该错误标志，我们知道应该退出循环了。

<div style="border-top-width: 0.5pt; border-right-width: 0.5pt; border-bottom-width: 0.5pt; border-left-width: 0.5pt; border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: windowtext; border-right-color: windowtext; border-bottom-color: windowtext; border-left-color: windowtext; padding-top: 4px; padding-right: 5.4pt; padding-bottom: 4px; padding-left: 5.4pt; background-image: none; background-color: rgb(230, 230, 230); width: 659px; background-position: 0% 0%;"><div> <span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;"></span></span><span style="color: rgb(0, 0, 255);"><span style="font-size: 16px;">if</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">(error</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">==</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">boost::asio::error::eof)<br></span></span><span style="color: rgb(0, 0, 255);"><span style="font-size: 16px;">break</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">;</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;">//</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;">Connectionclosedcleanlybypeer.</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;"><br></span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;"></span></span><span style="color: rgb(0, 0, 255);"><span style="font-size: 16px;">else</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;"></span></span><span style="color: rgb(0, 0, 255);"><span style="font-size: 16px;">if</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">(error)<br></span></span><span style="color: rgb(0, 0, 255);"><span style="font-size: 16px;">throw</span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;">boost::system::system_error(error);</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;">//</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;">Someothererror.</span></span><span style="color: rgb(0, 128, 0);"><span style="font-size: 16px;"><br></span></span><span style="color: rgb(0, 0, 0);"><span style="font-size: 16px;"><br>std::cout.write(buf.data(),len);<br>}</span></span> </div></div>