socket 网络编程

1. 基础socket库

socket.h:

/**
 * 网络套接字库
 */

#ifndef Socket_h
#define Socket_h

#include <stdio.h>
#include <string>

#ifdef WIN32
// windows
#include <winsock.h>

typedef int socklen_t;
#else
// linux, MacOS
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <errno.h>

#define INVALID_SOCKET -1
#define SOCKET_ERROR -1

typedef int SOCKET;
#endif

#define SOCKET_BACKLOG 100

namespace avalon {
    int socket_error();
    int socket_init();
    int socket_clean();
    void socket_debug(const char* message, ...);    

    class Socket {
    public:
        static Socket* create(SOCKET socket_fd);
        static Socket* create(int family, int type, int protocal = IPPROTO_IP);
        
    public:
        Socket(SOCKET socket_fd);
        Socket(int family, int type, int protocal = IPPROTO_IP);
        Socket& operator = (SOCKET socket_fd);
        virtual ~Socket();
        
        bool connect(const char* host, unsigned short port);
        bool bind(unsigned short port);
        bool listen(int backlog = SOCKET_BACKLOG);
        Socket* accept(char* client_host = nullptr);
        ssize_t send(const char* buffer, size_t len, int flag = 0);
        ssize_t recv(char* buffer, size_t len, int flag = 0);
        
        int close();
        
        SOCKET getSocketFD();
        
        void set_blocking(const bool blocking);
        
    private:
        SOCKET _socket_fd;
        
        int _family;
        int _type;
        int _protocal;
    };
}

#endif

socket.cpp

/**
 * 网络套接字库
 */

#include "AvalonSocket.h"

#ifdef WIN32
#pragma comment(lib, "wsock32")
#endif
#define SOCKET_DEBUG_LEVEL 0

namespace avalon {
    int socket_error() {
        int error = 0;
#ifdef WIN32
        error = WSAGetLastError();
#else
        error = errno;
#endif
        
        printf("Avalon socket error: %d %s 
", error, strerror(error));
        
        return error;
    }
    
    void socket_debug(const char* message, ...) {
        char buf[1024] = "";
        
        va_list args;
        va_start(args, message);
        vsnprintf(buf, 1024, message, args);
        va_end(args);
        
        std::string error = "Avalon sokcet: ";
        error.append(buf);
        error.append("
");
        
        printf(error.c_str());
        
        if (SOCKET_DEBUG_LEVEL) {
            int error_no = socket_error();
            if (error_no != -1) {
                throw error_no;
            }
        }
    }
    
    int socket_init() {
#ifdef WIN32
        WSADATA wsadata;
        WORD version = MAKEWORD(2, 0);
        
        int ret = WSAStartup(version,&wsadata);
        if (ret) {
            socket_debug("Initilize winsock error");
            return -1;
        }
#endif
        return 0;
    }
    
    int socket_clean() {
#ifdef WIN32
        return WSACleanup();
#endif
        return 0;
    }
    
    Socket* Socket::create(SOCKET socket_fd) {
        if (socket_fd < 0) {
            socket_debug("socket_fd(%d) is invailed.", socket_fd);
            return nullptr;
        }
        else {
            Socket* socket = new Socket(socket_fd);
            if (socket) {
                return socket;
            }
            else {
                socket_debug("Create avalon socket failed.");
                return nullptr;
            }
        }
    }
    
    Socket* Socket::create(int family, int type, int protocal) {
        Socket* socket = new Socket(family, type, protocal);
        if (socket) {
            if (socket->getSocketFD() == INVALID_SOCKET) {
                delete socket;
                socket_debug("Create socket failed.");
                return nullptr;
            }
            socket_debug("Create socket(%d) successfully.", socket->getSocketFD());
            return socket;
        }
        else {
            socket_debug("Create avalon socket failed.");
            return nullptr;
        }
    }
    
    Socket::Socket(SOCKET socket_fd)
    : _family(AF_INET)
    , _type(SOCK_STREAM)
    , _protocal(IPPROTO_IP) {
        _socket_fd = socket_fd;
    }
    
    Socket::Socket(int family, int type, int protocal)
    : _family(AF_INET)
    , _type(SOCK_STREAM)
    , _protocal(IPPROTO_IP) {
        _socket_fd = socket(family, type, protocal);
        if (_socket_fd != INVALID_SOCKET) {
            _family = family;
            _type = type;
            _protocal = protocal;
        }
    }
    
    Socket& Socket::operator = (SOCKET socket_fd) {
        _socket_fd = socket_fd;
        
        return *this;
    }
    
    Socket::~Socket() {
        if (_socket_fd != -1) {
            this->close();
        }
    }
    
    bool Socket::connect(const char* host, unsigned short port) {
        struct sockaddr_in remote_addr;
        remote_addr.sin_family = _family;
        remote_addr.sin_port = htons(port);
        inet_pton(_family, host, &remote_addr.sin_addr);
        if (errno == EAFNOSUPPORT) return false;
        
        int ret = ::connect(_socket_fd, (struct sockaddr*)(&remote_addr), sizeof(remote_addr));
        if (ret == SOCKET_ERROR) {
            socket_debug("Connect %s:%d failed.", host, port);
            socket_error();
            return false;
        }
        socket_debug("Connect %s:%d successfully.", host, port);
        return true;
    }
    
    bool Socket::bind(unsigned short port) {
        int opt = 1;
        if (setsockopt(_socket_fd, SOL_SOCKET, SO_REUSEADDR, (char*)&opt, sizeof(opt)) < 0)
            return false;
        
        struct sockaddr_in remote_addr;
        remote_addr.sin_family = _family;
        remote_addr.sin_addr.s_addr = INADDR_ANY;
        remote_addr.sin_port = htons(port);
        
        int ret = ::bind(_socket_fd, (struct sockaddr*)(&remote_addr), sizeof(remote_addr));
        if (ret == SOCKET_ERROR) {
            socket_debug("Socket(%d) bind port(%d) failed.", _socket_fd, port);
            return false;
        }
        socket_debug("Socket(%d) bind port(%d) successfully.", _socket_fd, port);
        return true;
    }
    
    bool Socket::listen(int backlog) {
        int ret = ::listen(_socket_fd, backlog);
        if (ret == SOCKET_ERROR) {
            socket_debug("Socket(%d) listen failed.", _socket_fd);
            return false;
        }
        socket_debug("Socket(%d) Listen successfully.", _socket_fd);
        return true;
    }
    
    Socket* Socket::accept(char* client_host) {
        struct sockaddr_in com_socket;
        socklen_t len = sizeof(com_socket);
        
        SOCKET ret = -1;
        do {
            ret = ::accept(_socket_fd, (struct sockaddr*)(&com_socket), &len);
            if (ret == SOCKET_ERROR) {
                if (errno == EINTR) continue;
                else {
                    socket_debug("Socket(%d) accept failed.", _socket_fd);
                    socket_error();
                    return nullptr;
                }
            }
            else break;
        } while (true);
        
        avalon::Socket* socket = avalon::Socket::create(ret);
        if (client_host) {
            sprintf(client_host, "%s", inet_ntoa(com_socket.sin_addr));
        }
        
        socket_debug("Socket(%d) accept successfully, client socket: %d ip: %s", _socket_fd, socket->getSocketFD(), inet_ntoa(com_socket.sin_addr));
        return socket;
    }
    
    ssize_t Socket::send(const char* buffer, size_t len, int flag) {
        ssize_t count = 0;
        
        while (count < len) {
            ssize_t bytes = ::send(_socket_fd, buffer + count, len - count, flag);
            count += bytes;
            
            if (bytes == -1 || bytes == 0) {
                socket_error();
                break;
            }
        }
        
        return count;
    }
    
    ssize_t Socket::recv(char* buffer, size_t len, int flag) {
        return ::recv(_socket_fd, buffer, len, flag);
    }
    
    ssize_t Socket::write(const char* buffer, size_t len) {
        ssize_t count = 0;
        
        while (count < len) {
            ssize_t bytes = ::write(_socket_fd, buffer + count, len - count);
            count += bytes;
            
            if (bytes == -1 || bytes == 0) {
                socket_error();
                break;
            }
        }
        
        return count;
    }
    
    ssize_t Socket::read(char* buffer, size_t len) {
        return ::read(_socket_fd, buffer, len);
    }
    
    void Socket::set_blocking(const bool blocking) {
        int opts;
        
        opts = fcntl(_socket_fd, F_GETFL);
        if (opts < 0) return;
        
        if (!blocking) opts = (opts | O_NONBLOCK);
        else opts = (opts & ~O_NONBLOCK);
        fcntl(_socket_fd, F_SETFL, opts);
    }
    
    int Socket::close() {
        int ret = -1;
#ifdef WIN32
        ret = closesocket(_socket_fd);
#else
        ret = ::close(_socket_fd);
#endif
        if (ret == SOCKET_ERROR) {
            socket_debug("Socket(%d) close failed.", _socket_fd);
        }
        _socket_fd = -1;
        
        return ret;
    }
    
    SOCKET Socket::getSocketFD() {
        return _socket_fd;
    }
}

2. 多线程的模型：

在accept成功之后，为每个通信socket创建新的进程和线程，单独用于处理服务器和客户端的通信。但是系统都会有创建进程数量的限制，在linux下，创建的线程也叫轻量级进程，所以即时创建的是线程也会受到系统的限制，通常这个默认限制是2048个，而且进程或者线程数量过多，也会导致进程或者线程切换的开销：

客户端：

    avalon::Socket* socket = avalon::Socket::create(AF_INET, SOCK_STREAM);
    if (socket) {
        if (!socket->connect("127.0.0.1", 6666)) continue;
            
            char buf[1024] = "";
            sprintf(buf, "%d I am a client socket!", i);
            ssize_t bytes = socket->send(buf, strlen(buf), 0);
            
            char recvBuf[1024];
            while (true) {
                memset(recvBuf, 0, 1024);
                bytes = socket->recv(recvBuf, 1024);
                if (bytes > 0) {
                    printf("%d recv data from remote: %d %s 
", i, bytes, recvBuf);
                }
                else if (bytes == 0) {
                    printf("remote socket %d cloese. 
", socket->getSocketFD());
                    
                    break;
                }
                else {
                    int error = avalon::socket_error();
                    printf("%d socket error: %d %s 
", i, error, strerror(error));
                    
                    break;
                }
            }
        }    

服务端：

void communiction_handler(avalon::Socket* socket) {
    char buffer[1024];
    
    while (true) {
        if (!socket) continue;
        
        printf("thread %ld 
", std::this_thread::get_id());
        
        ssize_t bytes = socket->recv(buffer, 1024, 0);
        if (bytes > 0) {
            buffer[bytes] = '';
        
            printf("recv msg from client: %s 
", buffer);
            
            const char* data = "I am remote.0123456789abcdefg!wwwwwer";
            ssize_t sendedBytes = socket->send(data, strlen(data), 0);
        }
        else if (bytes == 0) {
            printf("client socket(%d) closed. thread(%ld) 
", socket->getSocketFD(), std::this_thread::get_id());
            
            socket->close();
            
            break;
        }
        else {
            int error_no = avalon::socket_error();
            printf("recv msg from client failed %d %s 
", error_no, strerror(error_no));
            
            socket->close();
            
            break;
        }
    }
}

int main(int argc, const char * argv[]) {
    // 多线程
    std::vector<std::thread> threads;
  
     avalon::Socket* listen_socket = avalon::Socket::create(AF_INET, SOCK_STREAM);
    
    do {
        if (!listen_socket->bind(6666)) break;
        if (!listen_socket->listen(10)) break;
        
        while (true) {
            // 多线程
            avalon::Socket* clientSocket = listen_socket->accept();
            if (clientSocket) {
                threads.push_back(
                    std::move(
                        std::thread(communiction_handler, clientSocket)
                    )
                );
            }
        } while (false);

for(std::thread& thread : threads){
        thread.join();
    }
    
    delete listen_socket;
}

3. I/O多路复用

　　内核一旦检测到某个I/O的读取条件就绪，就通知用户进程进行响应；

　　多路复用一般用于需要同时处理多个文件描述符，多个套接字口，多种协议的情况；

　　相比使用多进程和多线程的机制，I/O多路复用具有系统开销小的优势；

（1）select模型：

最大的问题就是连接数限制，通常是1024或者2048个，不过可以修改内核配置达到更多的连接数。但是由于select模型需要线性遍历fd集合，因此如果连接数改的过大，例如10万个，会导致线性遍历的性能问题，最后的结果可能是导致超时。其次，就是内存拷贝问题，select模型在fd消息通知用户的时候，是采用的将内核中的数据拷贝到用户空间中：

服务端：

//
//  main.cpp
//  SocketServer
//
//  Created by avl-showell on 16/8/8.
//  Copyright © 2016年 avl-showell. All rights reserved.
//

#include <iostream>
#include "socket/AvalonSocket.h"
#include <mutex>
#include <condition_variable>
#include <chrono>
#include <thread>
#include <vector>
// select
#include <sys/select.h>
#include <sys/time.h>
#define MAX_CLIENT_SOCKET_COUNT 10000
#define RECV_BUFFER_LEN 10

int main(int argc, const char * argv[]) {
    std::vector<avalon::Socket*> socket_fds(MAX_CLIENT_SOCKET_COUNT, nullptr);
    fd_set read_fds, write_fds;
    struct timeval timeout;
    
    char recvBuf[RECV_BUFFER_LEN];
    
    avalon::Socket* listen_socket = avalon::Socket::create(AF_INET, SOCK_STREAM);
    
    do {
        if (!listen_socket->bind(6666)) break;
        if (!listen_socket->listen(10)) break;
        
        while (true) {
            // select
            int listen_socket_fd = listen_socket->getSocketFD();
            int max_socket_fd = listen_socket_fd;
            
            FD_ZERO(&read_fds);
            FD_SET(listen_socket_fd, &read_fds);
            
            for (int i = 0; i < MAX_CLIENT_SOCKET_COUNT; ++i) {
                avalon::Socket* socket = socket_fds[i];
                if (!socket) continue;
                
                SOCKET socket_fd = socket->getSocketFD();
                if (socket_fd > 0) {
                    FD_SET(socket_fd, &read_fds);
                    if (socket_fd > max_socket_fd)
                        max_socket_fd = socket_fd;
                }
            }
            
            timeout.tv_sec = 5;
            timeout.tv_usec = 0;
            
            int ret = select(max_socket_fd + 1, &read_fds, NULL, NULL, &timeout);
            if (ret == SOCKET_ERROR) {
                avalon::socket_error();
                break;
            }
            else if (ret == 0) {
                printf("select socket timeout. 
");
                continue;
            }
            else {
                printf("_______________ 
");
                
                for (int i = 0; i < MAX_CLIENT_SOCKET_COUNT; ++i) {
                    avalon::Socket* socket = socket_fds[i];
                    if (!socket) continue;
                    
                    SOCKET socket_fd = socket->getSocketFD();
                    if (socket_fd > 0 && FD_ISSET(socket_fd, &read_fds)) {
                        int recvedBytes = 0;
                        
                        while (true) {
                            memset(recvBuf, 0, RECV_BUFFER_LEN);
                            int bytes = socket->recv(recvBuf, RECV_BUFFER_LEN);
                            if (bytes > 0) {
                                recvedBytes += bytes;
                                socket->send(recvBuf, RECV_BUFFER_LEN);
                                break;
                            }
                            else {
                                avalon::socket_error();
                                
                                delete socket;
                                socket_fds[i] = nullptr;
                                
                                break;
                            }
                        }
                        
                        recvBuf[recvedBytes] = '';
                        printf("select: recv data from client: %s 
", recvBuf);

　　　　　　　　　　　　　　// 处理数据...
                    }
                }
                
                if (FD_ISSET(listen_socket_fd, &read_fds)) {
                    printf("select: new client connection. 
");
                    
                    bool found = false;
                    
                    for (int i = 0; i < MAX_CLIENT_SOCKET_COUNT; ++i) {
                        avalon::Socket* socket = socket_fds[i];
                        
                        if (!socket) {
                            avalon::Socket* clientSocket = listen_socket->accept();
                            if (clientSocket) {
//                                clientSocket->set_blocking(false);
                                socket_fds[i] = clientSocket;
                                found = true;
                                break;
                            }
                        }
                    }
                    
                    if (!found) {
                        printf("select: out of max sockets limit. 
");
                    }
                }
            }
        }
    } while (false);
    
    delete listen_socket;
    
    return 0;
}

(2) poll模型：

poll模型和select模型类似，但是poll没有最大文件数量的限制，不过依然存在将消息从内核空间拷贝到用户空间的问题：

服务端：

#include <poll.h>

#define MAX_CLIENT_SOCKET_COUNT 10
#define RECV_BUFFER_LEN 10

int main(int argc, const char * argv[]) {
    char recvBuf[RECV_BUFFER_LEN];
    
    avalon::Socket* listen_socket = avalon::Socket::create(AF_INET, SOCK_STREAM);
    
    // poll
    struct pollfd client_fds[MAX_CLIENT_SOCKET_COUNT];
    client_fds[0].fd = listen_socket->getSocketFD();
    client_fds[0].events = POLLIN;
    for (int i = 1; i < MAX_CLIENT_SOCKET_COUNT; ++i) {
        client_fds[i].fd = -1;
    }
    int max_socket = 0;
    
    do {
        if (!listen_socket->bind(6666)) break;
        if (!listen_socket->listen(10)) break;
        
        while (true) {
            int ready = poll(client_fds, max_socket + 1, 3000);
            if (ready == -1) {
                avalon::socket_error();
                break;
            }
            else if (ready == 0) {
                printf("select socket timeout. 
");
                continue;
            }
            
            printf("_______________ 
");
            
            if (client_fds[0].revents & POLLIN) {
                printf("select: new client connection. 
");
                
                bool found = false;
                
                int i = 0;
                for (i = 1; i < MAX_CLIENT_SOCKET_COUNT; ++i) {
                    avalon::Socket* socket = socket_fds[i];
                    
                    if (!socket) {
                        avalon::Socket* clientSocket = listen_socket->accept();
                        if (clientSocket) {
                            client_fds[i].fd = clientSocket->getSocketFD();
                            client_fds[i].events = POLLIN;
                            socket_fds[i] = clientSocket;
                            found = true;
                            break;
                        }
                    }
                }
                
                if (!found) {
                    printf("select: out of max sockets limit. 
");
                }
                else {
                    if (i > max_socket)
                        max_socket = i;
                }
            }
            
            for (int j = 1; j <= max_socket; ++j) {
                avalon::Socket* socket = socket_fds[j];
                if (!socket) continue;
                
                if (client_fds[j].revents & (POLLIN | POLLERR)) {
                    int recvedBytes = 0;

                    while (true) {
                        memset(recvBuf, 0, RECV_BUFFER_LEN);
                        int bytes = socket->read(recvBuf, RECV_BUFFER_LEN);
                        if (bytes > 0) {
                            recvedBytes += bytes;
                            int writedBytes = socket->write(recvBuf, RECV_BUFFER_LEN);
                            
                            recvBuf[bytes] = '';
                            printf("select: recv data from client: %s 
", recvBuf);
                            
                            if (bytes < RECV_BUFFER_LEN) break;
                        }
                        else {
                            avalon::socket_error();
                            
                            delete socket;
                            client_fds[j].fd = -1;
                            socket_fds[j] = nullptr;
                            
                            break;
                        }
                    }
                }
            }
        }
    } while (false);
    
    for(std::thread& thread : threads){
        thread.join();
    }
    
    delete listen_socket;
    
    return 0;
}

 (2) epoll模型

epoll模型是poll模型的改进版本，没有文件描述符的限制，epoll只处理活跃的文件描述符，不会遍历整个集合，而且epoll使用了内核中的“共享内存”，减少了内存的拷贝：

/* 实现功能：通过epoll, 处理多个socket
 * 监听一个端口,监听到有链接时,添加到epoll_event
 */
#include "select.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <poll.h>
#include <sys/epoll.h>
#include <sys/time.h>
#include <netinet/in.h>

typedef struct _CLIENT{
    int fd;
    struct sockaddr_in addr; /* client's address information */
} CLIENT;

#define MYPORT 59000

//最多处理的connect
#define MAX_EVENTS 500

//当前的连接数
int currentClient = 0; 

//数据接受 buf
#define REVLEN 10
char recvBuf[REVLEN];

//EPOLL相关 
//epoll描述符
int epollfd;
//事件数组
struct epoll_event eventList[MAX_EVENTS];

void AcceptConn(int srvfd);
void RecvData(int fd);

int main()
{
    int i, ret, sinSize;
    int recvLen = 0;
    fd_set readfds, writefds;
    int sockListen, sockSvr, sockMax;
    int timeout;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    
    //socket
    if((sockListen=socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf("socket error
");
        return -1;
    }
    
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family  =  AF_INET;
    server_addr.sin_port = htons(MYPORT);
    server_addr.sin_addr.s_addr  =  htonl(INADDR_ANY); 
    
    //bind
    if(bind(sockListen, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0)
    {
        printf("bind error
");
        return -1;
    }
    
    //listen
    if(listen(sockListen, 5) < 0)
    {
        printf("listen error
");
        return -1;
    }
    
    //1. epoll 初始化
    epollfd = epoll_create(MAX_EVENTS);
    struct epoll_event event;
    event.events = EPOLLIN|EPOLLET;
    event.data.fd = sockListen;
    
    //2. epoll_ctrl
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockListen, &event) < 0)
    {
        printf("epoll add fail : fd = %d
", sockListen);
        return -1;
    }
    
    //epoll
    while(1)
    {
        timeout=3000;                
        //3. epoll_wait
        int ret = epoll_wait(epollfd, eventList, MAX_EVENTS, timeout);
        
        if(ret < 0)
        {
            printf("epoll error
");
            break;
        }
        else if(ret == 0)
        {
            printf("timeout ...
");
            continue;
        }
        
        //直接获取了事件数量,给出了活动的流,这里是和poll区别的关键
        int n = 0;
        for(n=0; n<ret; n++)
        {
            //错误退出
            if ((eventList[n].events & EPOLLERR) ||
                (eventList[n].events & EPOLLHUP) ||
                !(eventList[n].events & EPOLLIN))
            {
              printf ( "epoll error
");
              close (eventList[n].data.fd);
              return -1;
            }
            
            if (eventList[n].data.fd == sockListen)
            {
                AcceptConn(sockListen);
        
            }else{
                RecvData(eventList[n].data.fd);
                //不删除
             //   epoll_ctl(epollfd, EPOLL_CTL_DEL, pEvent->data.fd, pEvent);
            }
        }
    }
    
    close(epollfd);
    close(sockListen);
    
    printf("test
");
    return 0;
}

/**************************************************
函数名：AcceptConn
功能：接受客户端的链接
参数：srvfd：监听SOCKET
***************************************************/
void AcceptConn(int srvfd)
{
    struct sockaddr_in sin;
    socklen_t len = sizeof(struct sockaddr_in);
    bzero(&sin, len);

    int confd = accept(srvfd, (struct sockaddr*)&sin, &len);

    if (confd < 0)
    {
       printf("bad accept
");
       return;
    }else
    {
        printf("Accept Connection: %d", confd);
    }

    //setnonblocking(confd);

    //4. epoll_wait
    //将新建立的连接添加到EPOLL的监听中
    struct epoll_event event;
    event.data.fd = confd;
    event.events =  EPOLLIN|EPOLLET;
    epoll_ctl(epollfd, EPOLL_CTL_ADD, confd, &event);
}

//读取数据
void RecvData(int fd)
{
    int ret;
    int recvLen = 0;
    
    memset(recvBuf, 0, REVLEN);
    printf("RecvData function
");
    
    if(recvLen != REVLEN)
    {
        while(1)
        {
            //recv数据
            ret = recv(fd, (char *)recvBuf+recvLen, REVLEN-recvLen, 0);
            if(ret == 0)
            {
                recvLen = 0;
                break;
            }
            else if(ret < 0)
            {
                recvLen = 0;
                break;
            }
            //数据接受正常
            recvLen = recvLen+ret;
            if(recvLen<REVLEN)
            {
                continue;
            }
            else
            {
                //数据接受完毕
                printf("buf = %s
",  recvBuf);
                recvLen = 0;
                break;
            }
        }
    }

    printf("content is %s", recvBuf);
}