linux-socket編程（五）recv,getsockname，gethostname等函數學習

1：read與recv函數

recv首先查看一下幫助：

recv的功能和read的一樣，都可以從套接口當中獲取數據，但是recv只能用於套接口I/O不能用於文件I/O，以及其他的I/O，read函數可以用於任何I/O。
recv相比於read多了一個flags選項，通過這個選項可以指定接受的行爲。主要有兩個重要的選項：
MSG_OOB:可以接收帶外數據，通過緊急指針發送的數據。帶外數據被認爲具有比普通數據更高的優先級
MSG_PEEK:可以接收緩存區的數據但是並不將緩存區中的數據清除，read函數一旦讀取數據就會將數據從緩存區中清除。

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
        while(1)
        {
            int ret = recv(sockfd, buf, len, MSG_PEEK);
            //只接受數據不將數據從緩存區中清除
            if(ret == -1 && errno == EINTR) //信號中斷
            {
                continue;
            }
            return ret;
        }
}

2：readline實現（按行讀取）

ssize_t readline(int sockfd, void* buf, size_t maxline)
{
        int ret;
        int nread;
        char *bufp = buf;
        int nleft = maxline;
        while(1)
        {
            ret = recv_peek(sockfd, buf, nleft);
            if(ret < 0)
                return ret;
            else if(ret == 0) //對方關閉了套接口
                return ret;
            nread = ret;
            int i = 0;
            for(i = 0; i < nread; i++)
            {
                if(buf[i] == '\n')
                {
                    ret = readn(sockfd, bufp, i+1);
                    if(ret != i+1)
                        exit(EXIT_FAILURE);
                    return ret;
                }
            }
            if(nread > nleft)
                exit(EXIT_FAILURE);
            nleft -= nread;
            ret = readn(sockfd, bufp, nread);
            //將緩存區中的數據刪除
            if(ret != nread)
                exit(EXIT_FAILURE);
            bufp += nread;
            nleft -= nread;
        }
        return -1;
}

服務器端程序：

#include <iostream>
#include <stdio.h>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>


using namespace std;

struct packet
{
    int len;
    char buf[1024];
};

#define ERR_EXIT(m) \
        do  \
        {   \
            perror(m);  \
            exit(EXIT_FAILURE); \
        } while(0);

ssize_t readn(int fd, void *buf, size_t count)
{
    size_t nleft = count;   // 剩餘字節數
    ssize_t nread;
    char *bufp = (char*) buf;

    while (nleft > 0)
    {
        nread = read(fd, bufp, nleft);
        if (nread < 0)
        {
            if (errno == EINTR)
            {
                continue;
            }
            return  -1;
        } else if (nread == 0)
        {
            return count - nleft;
        }

        bufp += nread;
        nleft -= nread;
    }
    return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
    size_t nleft = count;
    ssize_t nwritten;
    char* bufp = (char*)buf;

    while (nleft > 0)
    {
        if ((nwritten = write(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)
            {
                continue;
            }
            return -1;
        }
        else if (nwritten == 0)
        {
            continue;
        }
        bufp += nwritten;
        nleft -= nwritten;
    }
    return count;
}

ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
    while (1)
    {
        int ret = recv(sockfd, buf, len, MSG_PEEK); // 查看傳入消息
        if (ret == -1 && errno == EINTR)
        {
            continue;
        }
        return ret;
    }
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
    int ret;
    int nread;
    char *bufp = (char*)buf;    // 當前指針位置
    int nleft = maxline;
    while (1)
    {
        ret = recv_peek(sockfd, buf, nleft);
        if (ret < 0)
        {
            return ret;
        }
        else if (ret == 0)
        {
            return ret;
        }
        nread = ret;
        int i;
        for (i = 0; i < nread; i++)
        {
            if (bufp[i] == '\n')
            {
                ret = readn(sockfd, bufp, i+1);
                if (ret != i+1)
                {
                    exit(EXIT_FAILURE);
                }
                return ret;
            }
        }
        if (nread > nleft)
        {
            exit(EXIT_FAILURE);
        }
        nleft -= nread;
        ret = readn(sockfd, bufp, nread);
        if (ret != nread)
        {
            exit(EXIT_FAILURE);
        }
        bufp += nread;
    }
    return -1;
}

void echo_srv(int connfd)
{
    char recvbuf[1024];
    // struct packet recvbuf;
    int n;
    while (1)
    {
        memset(recvbuf, 0, sizeof recvbuf);
        int ret = readline(connfd, recvbuf, 1024);
        if (ret == -1)
        {
            ERR_EXIT("readline");
        }
        if (ret == 0)
        {
            printf("client close\n");
            break;
        }

        fputs(recvbuf, stdout);
        writen(connfd, recvbuf, strlen(recvbuf));
    }

}

int main(int argc, char** argv) {
    // 1. 創建套接字
    int listenfd;
    if ((listenfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
        ERR_EXIT("socket");
    }

    // 2. 分配套接字地址
    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof servaddr);
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(6666);
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    // servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    // inet_aton("127.0.0.1", &servaddr.sin_addr);

    int on = 1;
    // 確保time_wait狀態下同一端口仍可使用
    if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof on) < 0) {
        ERR_EXIT("setsockopt");
    }

    // 3. 綁定套接字地址
    if (bind(listenfd, (struct sockaddr *) &servaddr, sizeof servaddr) < 0) {
        ERR_EXIT("bind");
    }
    // 4. 等待連接請求狀態
    if (listen(listenfd, SOMAXCONN) < 0) {
        ERR_EXIT("listen");
    }
    // 5. 允許連接
    struct sockaddr_in peeraddr;
    socklen_t peerlen = sizeof peeraddr;


    // 6. 數據交換
    pid_t pid;
    while (1) {
        int connfd;
        if ((connfd = accept(listenfd, (struct sockaddr *) &peeraddr, &peerlen)) < 0) {
            ERR_EXIT("accept");
        }

        printf("id = %s, ", inet_ntoa(peeraddr.sin_addr));
        printf("port = %d\n", ntohs(peeraddr.sin_port));

        pid = fork();

        if (pid == -1) {
            ERR_EXIT("fork");
        }
        if (pid == 0)   // 子進程
        {
            close(listenfd);
            echo_srv(connfd);
            //printf("child exit\n");
            exit(EXIT_SUCCESS);
        } else {
            //printf("parent exit\n");
            close(connfd);
        }


    }
    // 7. 斷開連接
    close(listenfd);


    return 0;
}

客戶端程序：

#include <iostream>
#include <stdio.h>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>


using namespace std;

struct packet
{
    int len;
    char buf[1024];
};

#define ERR_EXIT(m) \
        do  \
        {   \
            perror(m);  \
            exit(EXIT_FAILURE); \
        } while(0);

ssize_t readn(int fd, void *buf, size_t count)
{
    size_t nleft = count;   // 剩餘字節數
    ssize_t nread;
    char *bufp = (char*) buf;

    while (nleft > 0)
    {
        nread = read(fd, bufp, nleft);
        if (nread < 0)
        {
            if (errno == EINTR)
            {
                continue;
            }
            return  -1;
        } else if (nread == 0)
        {
            return count - nleft;
        }

        bufp += nread;
        nleft -= nread;
    }
    return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
    size_t nleft = count;
    ssize_t nwritten;
    char* bufp = (char*)buf;

    while (nleft > 0)
    {
        if ((nwritten = write(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)
            {
                continue;
            }
            return -1;
        }
        else if (nwritten == 0)
        {
            continue;
        }
        bufp += nwritten;
        nleft -= nwritten;
    }
    return count;
}


ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
    while (1)
    {
        int ret = recv(sockfd, buf, len, MSG_PEEK); // 查看傳入消息
        if (ret == -1 && errno == EINTR)
        {
            continue;
        }
        return ret;
    }
}

ssize_t readline(int sockfd, void *buf, size_t maxline)
{
    int ret;
    int nread;
    char *bufp = (char*)buf;    // 當前指針位置
    int nleft = maxline;
    while (1)
    {
        ret = recv_peek(sockfd, buf, nleft);
        if (ret < 0)
        {
            return ret;
        }
        else if (ret == 0)
        {
            return ret;
        }
        nread = ret;
        int i;
        for (i = 0; i < nread; i++)
        {
            if (bufp[i] == '\n')
            {
                ret = readn(sockfd, bufp, i+1);
                if (ret != i+1)
                {
                    exit(EXIT_FAILURE);
                }
                return ret;
            }
        }
        if (nread > nleft)
        {
            exit(EXIT_FAILURE);
        }
        nleft -= nread;
        ret = readn(sockfd, bufp, nread);
        if (ret != nread)
        {
            exit(EXIT_FAILURE);
        }
        bufp += nread;
    }
    return -1;
}

void ehco_cli(int sockfd)
{
    char recvbuf[1024];
    char sendbuf[1024];
    // struct packet recvbuf;
    // struct packet sendbuf;
    memset(recvbuf, 0, sizeof recvbuf);
    memset(sendbuf, 0, sizeof sendbuf);
    int n = 0;
    while (fgets(sendbuf, sizeof sendbuf, stdin) != NULL)   // 鍵盤輸入獲取
    {
        writen(sockfd, sendbuf, strlen(sendbuf)); // 寫入服務器

        int ret = readline(sockfd, recvbuf, sizeof recvbuf);    // 服務器讀取
        if (ret == -1)
        {
            ERR_EXIT("readline");
        }
        if (ret == 0)
        {
            printf("server close\n");
            break;
        }

        fputs(recvbuf, stdout); // 服務器返回數據輸出

        // 清空
        memset(recvbuf, 0, sizeof recvbuf);
        memset(sendbuf, 0, sizeof sendbuf);
    }
}

void handle_sigchld(int sig)
{
    // wait(NULL);
    while (waitpid(-1, NULL, WNOHANG) > 0);
}

int main(int argc, char** argv) {
    // signal(SIGCHLD, SIG_IGN);
    signal(SIGCHLD, handle_sigchld);
    // 1. 創建套接字
    int sockfd[5];
    int i;
    for (i = 0; i < 5; ++i)
    {
        if ((sockfd[i] = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
            ERR_EXIT("socket");
        }

        // 2. 分配套接字地址
        struct sockaddr_in servaddr;
        memset(&servaddr, 0, sizeof servaddr);
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(6666);
        // servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
        servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
        // inet_aton("127.0.0.1", &servaddr.sin_addr);

        // 3. 請求鏈接
        if (connect(sockfd[i], (struct sockaddr *) &servaddr, sizeof servaddr) < 0) {
            ERR_EXIT("connect");
        }

        struct sockaddr_in localaddr;
        socklen_t addrlen = sizeof localaddr;
        if (getsockname(sockfd[i], (struct sockaddr*)&localaddr, &addrlen) < 0)
        {
            ERR_EXIT("getsockname");
        }
        printf("id = %s, ", inet_ntoa(localaddr.sin_addr));
        printf("port = %d\n", ntohs(localaddr.sin_port));

    }
    // 4. 數據交換
    ehco_cli(sockfd[0]);

    // 5. 斷開連接
    close(sockfd[0]);


    return 0;
}

3：getsockname， getpeername，gethostname，gethostbyname，gethostbyaddr

函數原型：

getsocket函數獲取本地的地址
使用方式：
struct sockaddr_in localaddr;
        socklen_t addrlen = sizeof localaddr;
        if (getsockname(sockfd[i], (struct sockaddr*)&localaddr, &addrlen) < 0)
        {
            ERR_EXIT("getsockname");
        }
        printf("id = %s, ", inet_ntoa(localaddr.sin_addr));
        printf("port = %d\n", ntohs(localaddr.sin_port));

getpeername獲取對方的地址，與getsockname使用方法相同。但是套接字必須是連接成功之後的纔行。
gethostname獲取主機名稱，
gethostbyname通過主機名獲取主機上所有的IP地址

gethostname函數原型：

返回值

gethostbyname函數原型：

程序例子：

#include <iostream>
#include <stdio.h>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define ERR_EXIT(m) \
        do \
        { \
            perror(m); \
            exit(EXIT_FAILURE); \
        } while (0);

int getlocalip(char *ip)
{
    char host[100] = {0};
    if (gethostname(host, sizeof host) < 0)
    {
        ERR_EXIT("gethostname");
    }

    struct hostent *hp;
    if ((hp = gethostbyname(host)) == NULL)
    {
        ERR_EXIT("gethostbyname");
    }
    strcpy(ip, inet_ntoa(*(struct in_addr*)hp->h_addr_list[0]));
    return 0;
}

int main(void)
{
//    char host[100] = {0};
//    if (gethostname(host, sizeof host) < 0)
//    {
//        ERR_EXIT("gethostname");
//    }
//
//    struct hostent *hp;
//    if ((hp = gethostbyname(host)) == NULL)
//    {
//        ERR_EXIT("gethostbyname");
//    }
//    int i = 0;
//    while (hp->h_addr_list[i] != NULL)
//    {
//        printf("%s\n", inet_ntoa(*(struct in_addr*)hp->h_addr_list[i]));
//        ++i;
//    }

    char ip[16] = {0};
    getlocalip(ip); //獲取本機IP地址。
    printf("localip = %s\n", ip);

    return 0;
}

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