从本篇开始，我们会深入学习怎样使用boost.asio建立更加复杂的客户端和服务端应用。你可以运行并测试它们，而且在理解之后，你可以把它们做为框架来构造自己的应用。
在接下来的例子中：
1.客户端使用一个用户名（无密码）登录到服务端
2.所有的连接由客户端建立，当客户端请求时服务端回应
3.所有的请求和回复都以换行符结尾（’\n’）
4.对于5秒钟没有ping操作的客户端，服务端会自动断开其连接
客户端可以发送如下请求：
1.获得所有已连接客户端的列表
2.客户端可以ping，当它ping时，服务端返回ping ok或者pingclient_list_chaned
为了更有趣一点，我们增加了一些难度：
1.每个客户端登录6个用户连接，比如johon,james,lucy,tracy,frank和abby
2.每个客户端连接随机地ping服务端（随机7秒；这样的话，服务端会时不时关闭一个连接）
基于tcp的同步客户端
1.流程图
2.实现
#ifdef win32
#define _win32_winnt 0x0501
#include
#endif
#include
#include
#include
#include
#include
using namespace boost::asio;
io_service service;
/** simple connection to server:
- logs in just with username (no password)
- all connections are initiated by the client: client asks, server answers
- server disconnects any client that hasn't pinged for 5 seconds
possible requests:
- gets a list of all connected clients
- ping: the server answers either with "ping ok" or "ping client_list_changed"
*/
struct talk_to_svr {
talk_to_svr(const std::string & username)
: sock_(service), started_(true), username_(username) {}
void connect(ip::tcp::endpoint ep) {
sock_.connect(ep);
}
void loop() {
// read answer to our login
write("login " username_ "\n");
read_answer();
while (started_) {
// 循环发送ping请求
write_request();
read_answer();
int millis = rand() % 7000;
std::cout << username_ << " postpone ping "
<< millis << " ms" << std::endl;
boost::this_thread::sleep(boost::posix_time::millisec(millis));
}
}
std::string username() const { return username_; }
private:
void write_request() {
write("ping\n");
}
void read_answer() {
already_read_ = 0;
read(sock_, buffer(buff_),
boost::bind(&talk_to_svr::read_complete, this, _1, _2));
process_msg();
}
void process_msg() {
std::string msg(buff_, already_read_);
if (msg.find("login ") == 0) on_login();
else if (msg.find("ping") == 0) on_ping(msg);
else if (msg.find("clients ") == 0) on_clients(msg);
else std::cerr << "invalid msg " << msg << std::endl;
}
void on_login() {
std::cout << username_ << " logged in" << std::endl;
do_ask_clients();
}
void on_ping(const std::string & msg) {
std::istringstream in(msg);
std::string answer;
in >> answer >> answer;
if (answer == "client_list_changed")
do_ask_clients();
}
void on_clients(const std::string & msg) {
std::string clients = msg.substr(8);
std::cout << username_ << ", new client list:" << clients;
}
// 获得所有已连接客户端的列表
void do_ask_clients() {
write("ask_clients\n");
read_answer();
}
void write(const std::string & msg) {
sock_.write_some(buffer(msg));
}
size_t read_complete(const boost::system::error_code & err, size_t bytes) {
if (err) return 0;
already_read_ = bytes;
bool found = std::find(buff_, buff_ bytes, '\n') < buff_ bytes;
return found ? 0 : 1;
}
private:
ip::tcp::socket sock_;
enum { max_msg = 1024 };
int already_read_;
char buff_[max_msg];
bool started_;
std::string username_;
};
ip::tcp::endpoint ep(ip::address::from_string("127.0.0.1"), 8001);
void run_client(const std::string & client_name) {
talk_to_svr client(client_name);
try {
client.connect(ep);
client.loop();
}
catch (boost::system::system_error & err) {
// 捕获socket断开原因
std::cout << "client terminated " << client.username()
<< "——" << err.what() << std::endl;
}
}
int main(int argc, char* argv[]) {
boost::thread_group threads;
char* names[] = { "john", "james", "lucy", "tracy", "frank", "abby", 0 };
for (char ** name = names; *name; name) {
threads.create_thread(boost::bind(run_client, *name));
boost::this_thread::sleep(boost::posix_time::millisec(100));
}
threads.join_all();
system("pause");
}