read、write 與recv、send區別 gethostname

時間 2019-11-15

標籤 read write recv send 區別 gethostname 简体版

原文原文鏈接

recv相對於read有什麼區別呢？html

其實它跟read函數功能同樣，均可以從套接口緩衝區sockfd中取數據到buf,可是recv僅僅只可以用於套接口IO，並不能用於文件IO以及其它的IO，而read函數能夠用於任何的IO；web

recv函數相比read函數多了一個flags參數，經過這個參數能夠指定接收的行爲，比較有用的兩個選項是：緩存

這個此次要學習的，它能夠接收緩衝區中的數據，可是並不從緩衝區中清除，這是跟read函數有區別的地方，read函數一旦讀取了，就會直接從緩衝區中清除。網絡

readline實現socket

也就是實現按行讀取，讀取直到\n字符，實際上，它也能解決上節中提到的粘包問題，回顧下上節的粘包問題解決方案：函數

包尾加\r\n(ftp)學習

咱們只要解釋\n爲止，表示前面是一個條合法的消息，對於readline的實現，能夠有三種方案：spa

①、最簡單的方案就是一個字符一個字符的讀取，而後作判斷是否有"\n"，可是這種效率比較低，由於會屢次掉用read或recv系統函數。code

②、用一個static變量保存接收到的數據進行緩存，在下次時從這個緩存變量中讀取而後估"\n"判斷。可是一旦用到了static變量，這意味着用到的函數是不可重錄函數【關於這個概念，能夠參考博文：http://www.cnblogs.com/webor2006/p/3744002.html】。server

③、偷窺的方法，也就是此次要採用的方案。下面就利用咱們封裝的recv_peek函數實現readline：

server.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

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

ssize_t readn(int fd, void *buf, size_t count)//讀取count個字節數，其中size_t是無符號
的整數，ssize_t是有符號的整數
{
    size_t nleft = count;//剩餘的字節數
    printf("nleft = %d\n",nleft);
    ssize_t nread;//已接收的字節數
    char *bufp = (char*)buf;

    while (nleft > 0)
    {//因爲不能保證一次讀操做可以返回字節數是多少，因此須要進行循環來接收
        if ((nread = read(fd, bufp, nleft)) < 0)
        {
            if (errno == EINTR)//被信號中斷了，則繼續執行，由於不是出錯
                continue;
            return -1;//表示讀取失敗了
        }
        else if (nread == 0)//對等方關閉了
            return count - nleft;//返回已經讀取的字節數

        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)//若是是這種狀況，則表示什麼都沒發生，繼續還得執行
                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);
                if(ret == -1 && errno == EINTR)
                        continue;
                return ret;
        }
}

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

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

int main(void)
{
        int listenfd;
        if((listenfd = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP)) < 0)
        {
                ERR_EXIT("socket");
        }
        struct sockaddr_in servaddr;
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(5188);
        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);*/

        //地址重用
        int on=1;
        if(setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)) < 0)
        {
                ERR_EXIT("setsockopt");
        }

        if(bind(listenfd,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
        {
                ERR_EXIT("bind");
        }

        if(listen(listenfd,SOMAXCONN) < 0)
        {
            ERR_EXIT("listen");
        }

        struct sockaddr_in peeraddr;
        socklen_t peerlen = sizeof(peeraddr);
        int confd;

        pid_t pid;
        while(1)
        {
                if((confd = accept(listenfd,(struct sockaddr*)&peeraddr, &peerlen)) < 0)
                {
                        ERR_EXIT("accept");
                }
                printf("ip = %s, port = %d\n",inet_ntoa(peeraddr.sin_addr),ntohs(peeraddr.sin_port));
                pid = fork();
                if(pid == -1)
                {
                        ERR_EXIT("fork");
                }
                if(pid == 0)
                {
                        close(listenfd);
                        do_service(confd);
                        exit(EXIT_SUCCESS);
                }
                else
                {
                        close(confd);
                }
        }

        return 0;
}

client.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

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

ssize_t readn(int fd, void *buf, size_t count)//須要將函數的定義也挪過來
{
    size_t nleft = count;
    ssize_t nread;
    char *bufp = (char*)buf;

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

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,bufp,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;
}

int main(void)
{
        int sockfd;
        if((sockfd = socket(PF_INET,SOCK_STREAM,IPPROTO_TCP)) < 0)
        {
                ERR_EXIT("socket");
        }
        struct sockaddr_in servaddr;
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(5188);
        servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
        /*inet_aton("127.0.0.1",&servaddr.sin_addr);*/

        if (connect(sockfd,(struct sockaddr*)&servaddr,sizeof(servaddr)) < 0)
        {
                ERR_EXIT("connect");
        }

        struct sockaddr_in localaddr;
        socklen_t addrlen = sizeof(localaddr);
        if(getsockname(sockfd,(struct sockaddr*)&localaddr,&addrlen) < 0)
                ERR_EXIT("getsockname");
        printf("ip = %s, port = %d\n",inet_ntoa(localaddr.sin_addr),ntohs(localaddr.s
in_port));

        char sendbuf[1024] = {0};
        char recvbuf[1024] = {0};
        //struct packet sendbuf;
        //struct packet recvbuf;
        //memset(&sendbuf,0,sizeof(sendbuf));
        //memset(&recvbuf,0,sizeof(recvbuf));

        int n;

        while(fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)
        {
                //writen(sockfd,sendbuf,sizeof(sendbuf));
                //readn(sockfd,recvbuf,sizeof(recvbuf));
                //n =strlen(sendbuf.buf);
                //sendbuf.len = htonl(n);//網絡字節序
                writen(sockfd,sendbuf,strlen(sendbuf));
                int ret = readline(sockfd,recvbuf,sizeof(recvbuf));
                //int ret = readn(sockfd,&recvbuf.len,4);
                if(ret == -1)
                {
                        ERR_EXIT("read");
                }
                else if(ret == 0)
                {
                        printf("client close\n");
                        break;
                }

                fputs(recvbuf,stdout);
                memset(sendbuf,0,sizeof(sendbuf));
                memset(recvbuf,0,sizeof(recvbuf));
        }
        close(sockfd);
        return 0;
}

Makefile

.PHONY: clean all
CC=gcc
CFLAGE= -G -Wall
BIN=client server getiplist
all:$(BIN)
%.o:%.c
        $(CC) $(cflags) -C $< -O $@
clean:
        rm -f *.o $(BIN)

getsockname:獲取套接口本地的地址

當客戶端成功與服務端鏈接以後，若是想知道客戶端的地址，就能夠經過它來獲取，

getpeername:獲取對等方的地址

因爲它的使用方法跟getsockname同樣，這裏就不說明了，注意：sockfd需是鏈接成功的套接口，另外對於服務端獲取客戶端ip，像這種狀況下也需用這個接口來得到：

gethostname:獲取主機的名稱

gethostbyname:經過主機名來獲取主機上全部的ip地址

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

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.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)
      return -1;
    struct hostent *hp;
    if ((hp = gethostbyname(host)) == NULL)
      return -1;
    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);
    printf("localip=%s\n", ip);
    return 0;
}

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