? ? ? ?回顯就是服務端將接收到的任何內(nèi)容回發(fā)給客戶端顯示，然后關閉客戶端的連接。這個服務端可以處理任何數(shù)量的客戶端。每個客戶端連接之后發(fā)送一個消息，服務端接收到消息后把它發(fā)送回去。在那之后，服務端關閉連接。具體流程如下圖所示。

? ? ? ?對于TCP而言，我們需要一個額外的保證：每一個消息以換行符結(jié)束(‘n’)。編寫一個同步回顯服務端/客戶端非常簡單。下面我們分別實現(xiàn)同步客戶端，同步服務端，異步客戶端和異步服務端。

一.TCP同步客戶端

#ifdef?WIN32
#define?_WIN32_WINNT?0x0501
#include#endif

#include#include#include#include#includeusing?namespace?boost::asio;
using?boost::system::error_code;
io_service?service;

size_t?read_complete(char?*?buf,?const?error_code?&?err,?size_t?bytes)?{
	if?(err)?return?0;
	bool?found?=?std::find(buf,?buf?+?bytes,?'n')?<?buf?+?bytes;
	//?一個一個字符的讀取，直到回車,?不緩存
	return?found???0?:?1;
}

ip::tcp::endpoint?ep(ip::address::from_string("127.0.0.1"),?8001);
void?sync_echo(std::string?msg)?{
	msg?+=?"n";
	ip::tcp::socket?sock(service);
	sock.connect(ep);
	sock.write_some(buffer(msg));
	char?buf[1024];
	int?bytes?=?read(sock,?buffer(buf),?boost::bind(read_complete,?buf,?_1,?_2));
	std::string?copy(buf,?bytes?-?1);
	msg?=?msg.substr(0,?msg.size()?-?1);
	std::cout?<<?"server?echoed?our?"?<<?msg?<<?":?"
		<<?(copy?==?msg???"OK"?:?"FAIL")?<<?std::endl;
	sock.close();
}

int?main(int?argc,?char*?argv[])?{
	//?連接多個客戶端
	char*?messages[]?=?{?"Can",?"ge",?"ge",?"blog!",?0?};
	boost::thread_group?threads;
	for?(char?**?message?=?messages;?*message;?++message)?{
		threads.create_thread(boost::bind(sync_echo,?*message));
		boost::this_thread::sleep(boost::posix_time::millisec(100));
	}
	threads.join_all();

	system("pause");
}

? ? ? ?你會發(fā)現(xiàn)，在讀取時，我使用了自由函數(shù)（不屬于socket類，屬于命名空間asio）read()，因為我想要讀‘n’之前的所有內(nèi)容。sock.read_some()方法滿足不了這個要求，因為它只會讀可用的，不一定是整個的消息。
? ? ? ?read(stream, buffer [, completion])這個方法同步地從一個流中讀取數(shù)據(jù)。你可以選擇指定一個完成處理方法。完成處理方法會在每次read操作調(diào)用成功之后調(diào)用，然后告訴read操作是否完成（如果沒有完成，它會繼續(xù)讀?。?。它的格式是：size_t completion(const boost::system::error_code& err, size_t bytes_transfered) 。當這個完成處理方法返回0時，我們認為read操作完成；如果它返回一個非0值，它表示了下一次sock.read_some操作需要從流中讀取的字節(jié)數(shù)。

? ? ? ?read_complete一個個的讀取字符，直到回車，這是通過std::find方法控制的，std::find的行為大概如下。

templateInputIterator?find?(InputIterator?first,?InputIterator?last,?const?T&?val)
{
??while?(first!=last)?{
????if?(*first==val)?return?first;
????++first;
??}
??return?last;
}

? ? ? ?結(jié)合到上面客戶端代碼就是，如果沒有找到回車'n'，std::find始終返回buf+bytes，否則返回'n'的地址，也就是buf+bytes-1，此時'n'是已讀取內(nèi)容的最后一個字符。
? ? ? ?注意：因為我們是同步的，所以不需要調(diào)用service.run()。

二.TCP同步服務端

#ifdef?WIN32
#define?_WIN32_WINNT?0x0501
#include#endif

#include#include#include#includeusing?namespace?boost::asio;
using?namespace?boost::posix_time;
using?boost::system::error_code;


io_service?service;
size_t?read_complete(char?*?buff,?const?error_code?&?err,?size_t?bytes)?{
????if?(?err)?return?0;
????bool?found?=?std::find(buff,?buff?+?bytes,?'n')?<?buff?+?bytes;
????//?we?read?one-by-one?until?we?get?to?enter,?no?buffering
????return?found???0?:?1;
}


void?handle_connections()?{
????ip::tcp::acceptor?acceptor(service,?ip::tcp::endpoint(ip::tcp::v4(),8001));
????char?buff[1024];
????while?(?true)?{
????????ip::tcp::socket?sock(service);
????????acceptor.accept(sock);
????????int?bytes?=?read(sock,?buffer(buff),?
????????????????????boost::bind(read_complete,buff,_1,_2));
????????std::string?msg(buff,?bytes);
????????sock.write_some(buffer(msg));
????????sock.close();
????}
}


int?main(int?argc,?char*?argv[])?{
????handle_connections();
}

? ? ? ?服務端的邏輯主要在handle_connections()。因為是單線程，它接受一個客戶端請求，讀取客戶端發(fā)送的消息，然后回發(fā)給客戶端，接著等待下一個連接?？梢源_定，當兩個客戶端同時連接時，第二個客戶端需要等待服務端處理完第一個客戶端的請求。

? ? ? ?還是要注意因為我們是同步的，所以不需要調(diào)用service.run()。

? ? ? ?下面是客戶端回顯的結(jié)果，當然要先啟動服務端。

三.TCP異步客戶端

#ifdef?WIN32
#define?_WIN32_WINNT?0x0501
#include#endif

#include#include#include#include#includeusing?namespace?boost::asio;
io_service?service;

#define?MEM_FN(x)???????boost::bind(&self_type::x,?shared_from_this())
#define?MEM_FN1(x,y)????boost::bind(&self_type::x,?shared_from_this(),y)
#define?MEM_FN2(x,y,z)??boost::bind(&self_type::x,?shared_from_this(),y,z)

class?talk_to_svr?:?public?boost::enable_shared_from_this
	,?boost::noncopyable?{
	typedef?talk_to_svr?self_type;
	talk_to_svr(const?std::string?&?message)
		:?sock_(service),?started_(true),?message_(message)?{}
	void?start(ip::tcp::endpoint?ep)?{
		sock_.async_connect(ep,?MEM_FN1(on_connect,?_1));
	}
public:
	typedef?boost::system::error_code?error_code;
	typedef?boost::shared_ptrptr;

	static?ptr?start(ip::tcp::endpoint?ep,?const?std::string?&?message)?{
		ptr?new_(new?talk_to_svr(message));
		new_->start(ep);
		return?new_;
	}
	void?stop()?{
		if?(!started_)?return;
		started_?=?false;
		sock_.close();
	}
	bool?started()?{?return?started_;?}
private:
	void?on_connect(const?error_code?&?err)?{
		if?(!err)??????do_write(message_?+?"n");
		else????????????stop();
	}
	void?on_read(const?error_code?&?err,?size_t?bytes)?{
		if?(!err)?{
			std::string?copy(read_buffer_,?bytes?-?1);
			std::cout?<<?"server?echoed?our?"?<<?message_?<<?":?"
				<<?(copy?==?message_???"OK"?:?"FAIL")?<<?std::endl;
		}
		stop();
	}

	void?on_write(const?error_code?&?err,?size_t?bytes)?{
		do_read();
	}
	void?do_read()?{
		async_read(sock_,?buffer(read_buffer_),
			MEM_FN2(read_complete,?_1,?_2),?MEM_FN2(on_read,?_1,?_2));
	}
	void?do_write(const?std::string?&?msg)?{
		if?(!started())?return;
		std::copy(msg.begin(),?msg.end(),?write_buffer_);
		sock_.async_write_some(buffer(write_buffer_,?msg.size()),
			MEM_FN2(on_write,?_1,?_2));
	}
	size_t?read_complete(const?boost::system::error_code?&?err,?size_t?bytes)?{
		if?(err)?return?0;
		bool?found?=?std::find(read_buffer_,?read_buffer_?+?bytes,?'n')?<?read_buffer_?+?bytes;
		return?found???0?:?1;
	}

private:
	ip::tcp::socket?sock_;
	enum?{?max_msg?=?1024?};
	char?read_buffer_[max_msg];
	char?write_buffer_[max_msg];
	bool?started_;
	std::string?message_;
};

int?main(int?argc,?char*?argv[])?{
	ip::tcp::endpoint?ep(ip::address::from_string("127.0.0.1"),?8001);
	char*?messages[]?=?{?"Can",?"ge",?"ge",?"blog",?0?};
	for?(char?**?message?=?messages;?*message;?++message)?{
		talk_to_svr::start(ep,?*message);
		boost::this_thread::sleep(boost::posix_time::millisec(100));
	}
	service.run();
	system("pause");
}

四.TCP異步服務端

#ifdef?WIN32
#define?_WIN32_WINNT?0x0501
#include#endif

#include#include#include#includeusing?namespace?boost::asio;
using?namespace?boost::posix_time;
io_service?service;

#define?MEM_FN(x)???????boost::bind(&self_type::x,?shared_from_this())
#define?MEM_FN1(x,y)????boost::bind(&self_type::x,?shared_from_this(),y)
#define?MEM_FN2(x,y,z)??boost::bind(&self_type::x,?shared_from_this(),y,z)


class?talk_to_client?:?public?boost::enable_shared_from_this,?boost::noncopyable?{
	typedef?talk_to_client?self_type;
	talk_to_client()?:?sock_(service),?started_(false)?{}
public:
	typedef?boost::system::error_code?error_code;
	typedef?boost::shared_ptrptr;

	void?start()?{
		started_?=?true;
		do_read();
	}
	static?ptr?new_()?{
		ptr?new_(new?talk_to_client);
		return?new_;
	}
	void?stop()?{
		if?(!started_)?return;
		started_?=?false;
		sock_.close();
	}
	ip::tcp::socket?&?sock()?{?return?sock_;?}
private:
	void?on_read(const?error_code?&?err,?size_t?bytes)?{
		if?(!err)?{
			std::string?msg(read_buffer_,?bytes);
			//?echo?message?back,?and?then?stop
			do_write(msg?+?"n");
		}
		stop();
	}

	void?on_write(const?error_code?&?err,?size_t?bytes)?{
		do_read();
	}
	void?do_read()?{
		async_read(sock_,?buffer(read_buffer_),
			MEM_FN2(read_complete,?_1,?_2),?MEM_FN2(on_read,?_1,?_2));
	}
	void?do_write(const?std::string?&?msg)?{
		std::copy(msg.begin(),?msg.end(),?write_buffer_);
		sock_.async_write_some(buffer(write_buffer_,?msg.size()),
			MEM_FN2(on_write,?_1,?_2));
	}
	size_t?read_complete(const?boost::system::error_code?&?err,?size_t?bytes)?{
		if?(err)?return?0;
		bool?found?=?std::find(read_buffer_,?read_buffer_?+?bytes,?'n')?<?read_buffer_?+?bytes;
		//?we?read?one-by-one?until?we?get?to?enter,?no?buffering
		return?found???0?:?1;
	}
private:
	ip::tcp::socket?sock_;
	enum?{?max_msg?=?1024?};
	char?read_buffer_[max_msg];
	char?write_buffer_[max_msg];
	bool?started_;
};

ip::tcp::acceptor?acceptor(service,?ip::tcp::endpoint(ip::tcp::v4(),?8001));

void?handle_accept(talk_to_client::ptr?client,?const?boost::system::error_code?&?err)?{
	client->start();
	talk_to_client::ptr?new_client?=?talk_to_client::new_();
	acceptor.async_accept(new_client->sock(),?boost::bind(handle_accept,?new_client,?_1));
}


int?main(int?argc,?char*?argv[])?{
	talk_to_client::ptr?client?=?talk_to_client::new_();
	acceptor.async_accept(client->sock(),?boost::bind(handle_accept,?client,?_1));
	service.run();
}

? ? ? TCP異步客戶端和異步服務端的關鍵是enable_shared_from_this模板類的使用，關于enable_shared_from_this詳見：C++11新特性之十一：enable_shared_from_this，C++11和boost的enable_shared_from_this功能和原理一樣。

? ? ? ?客戶端回顯結(jié)果和同步時的一樣，如下：