#Socket簡介

是一個編程接口是一種特殊的文件描述符(everything in Unix is a file)并不僅限于TCPip協(xié)議面向連接(Transmission Control PRotocol - TCPIP)無連接(User Datagram Protocol-UDP 和 Inter-Network Packet Exchange-IPX)

#Socket類型流式套接字(SOCK_STREAM)提供了一個面向連接，可靠的數(shù)據(jù)傳輸服務，數(shù)據(jù)無差錯，無重復的發(fā)送且按發(fā)送順序接收。內設置流量控制，避免數(shù)據(jù)流淹沒慢的接收方。數(shù)據(jù)被看作是字節(jié)流，無長度限制數(shù)據(jù)報套接字(SOCK_DGRAM)提供無連接服務。數(shù)據(jù)包以獨立數(shù)據(jù)包的形式被發(fā)送，不提供無差錯保證，數(shù)據(jù)可能丟失或重復，順序發(fā)送，可能亂序接收原始套接字(SOCK_RAW)可以對較低層次協(xié)議如IP，ICMP直接訪問

#IP地址IP地址是Internet中主機的標識Internet中的主機要與別的機器通信必須具有一個IP地址IP地址為32位(IPV4)或者128位(IPV6)每個數(shù)據(jù)包都必須攜帶目的IP地址和源IP地址，路由器依靠此信息為數(shù)據(jù)包選擇路由表示形式：常用點分形式，如202.38.64.10,最后都會轉換為一個32位的無符號整數(shù)。

#IP地址的轉換inet_aton()將strptr所指的字符串轉換成32位的網(wǎng)絡字節(jié)序二進制值int inet_aton(const char *strptr, struct in_addr *addrptr);inet_addr()功能同上，返回轉換后的地址in_addr_t inet_addr(const char *strptr);inet_ntoa()將32位網(wǎng)絡字節(jié)序二進制地址轉換成點分十進制的字符串。char *inet_ntoa(struct in_addr inaddr);

#端口號為了區(qū)分一臺主機接收到的數(shù)據(jù)包應該轉交給哪個進程來進行處理，使用端口號來區(qū)分TCP端口號與UDP端口號獨立(協(xié)議不同可以使用同一個端口)三無組：協(xié)議，IP，端口端口號一般由IANA(Internet Assigned Numbers Authority)管理眾所周知端口：1~1023(1~255之間為眾所周知端口，256~1023端口通常由UNIX系統(tǒng)占用已登記端口：1024~49151動態(tài)或私有端口：49152~65535

#字節(jié)序不同類型CPU的主機中，內存存儲多字節(jié)整數(shù)序列有兩種方法，稱為主機字節(jié)序(HBO):小端序(little-endian)-低字節(jié)存儲在低地址將低字節(jié)存儲在起始地址，稱為"Little-Endian"字節(jié)序，Intel,AMD等采用的是這種方式大端序(big-endian)-高序字節(jié)存儲在低地址將高字節(jié)存儲在起始地址，稱為"Big-Endian"字節(jié)序，由ARM，Motorola等所采用網(wǎng)絡中傳輸?shù)臄?shù)據(jù)必須按網(wǎng)絡字節(jié)序，即大端字節(jié)序在大部分PC機上，當應用進程將整數(shù)送入socket前，需要轉化成網(wǎng)絡字節(jié)序；當應用進程從socket取出整數(shù)后，要轉化成小端字節(jié)序

#字節(jié)序轉換函數(shù)把給定系統(tǒng)所采用的字節(jié)序稱為主機字節(jié)序，為了避免不同類別主機之間在數(shù)據(jù)交換時由于對于字節(jié)序的不用而導致的差錯，引入了網(wǎng)絡字節(jié)序主機字節(jié)序到網(wǎng)絡字節(jié)序：u_long htonl(u_long hostlong);u_short htons(u_short short);網(wǎng)絡字節(jié)序到主機字節(jié)序u_long ntohl(u_long hostlong);u_short ntohs(u_short short);

#網(wǎng)絡編程相關APIint Socket(int domain, int type, int protocol);int bind(int Sockfd, struct sockaddr *my_addr, int addrlen);int listen(int sockfd, in backlog);int accept(int sockfd, struct sockaddr *addr, Socklen_t *addrlen);int connect(int sockfd, const struct sockaddr *addr, Socklen_t addrlen);ssize_t send(int sockfd, const void *buf, size_t len, int flags);ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,　　　　　　　　const struct sockaddr *dest_addr, Socklen_t addrlen);ssize_t recv(int sockfd, void *buf, size_t len, int flags);ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,　　　　　　　　struct sockaddr *src_addr, Socklen_t *addrlen);int shutdown(int sockfd, int how);

#command:netstat -anpt

#地址結構的一般用法1.定義一個struct sockaddr_in類型的變量并清空struct sockaddr_in myaddr;memset(&myaddr, 0, sizeof(myaddr));2.填充地址信息myaddr.sin_family = PF_INET;myaddr.sin_port = htons(8888);myaddr.sin_addr.s_addr = inet_addr("192.168.1.100");3.將該變量強制轉換為struct sockaddr類型在函數(shù)中使用bind(listenfd,(struct sockaddr *)&myaddr, sizeof(myaddr));

#地址轉換函數(shù)unsigned long inet_addr(const char *address);int inet_aton(const char *cp, struct in_addr *inp);char *inet_ntoa(struct in_addr in);

socket流程圖：

附：代碼

client.c

//int socket(int domain, int type, int protocol);//int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);//int listen(int sockfd, int backlog);//int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);//uint16_t htons(uint16_t hostshort);//int atoi(const char *nptr);//in_addr_t inet_addr(const char *cp);//void bzero(void *s, size_t n);//int listen(int sockfd, int backlog);//int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);//int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);#include <stdio.h>#include <sys/types.h>//socket():bind();listen():accept();listen();accept();connect();#include <sys/socket.h>//socket():bind();listen():accept();inet_addr();listen():accept();connect();#include <arpa/inet.h>//htons();inet_addr():#include <netinet/in.h>//inet_addr():#include <strings.h>//bzero();#include <stdlib.h>//atoi();exit();#include <unistd.h>//close():#include <string.h>#define N 64int main(int argc, char *argv[]){    if(argc < 3)    {        printf("Using: %s ip port/n",argv[0]);        exit(-1);    }    int sockfd;    struct sockaddr_in myaddr,peeraddr;    char buf[N] = {0};    size_t n;    socklen_t mylen,peerlen;    mylen = sizeof(myaddr);    peerlen = sizeof(peeraddr);    /*  creat socket  */    if(-1 == (sockfd = socket(AF_INET,SOCK_DGRAM,0)))    {        perror("socket");        exit(-1);    }    /* bind initialization */    bzero(&myaddr,sizeof(myaddr));    myaddr.sin_family = AF_INET;    myaddr.sin_port = htons(atoi(argv[2])+1);    myaddr.sin_addr.s_addr = inet_addr(argv[1]);    /*      bind      */    if(-1 == bind(sockfd, (struct sockaddr *)&myaddr, mylen))    {        perror("bind");        exit(-1);    }    /*    connect    */    bzero(&peeraddr, sizeof(peeraddr));    peeraddr.sin_family = AF_INET;    peeraddr.sin_port = htons(atoi(argv[2]));    peeraddr.sin_addr.s_addr = inet_addr(argv[1]);    //connect(sockfd,(struct sockaddr *)&peeraddr, peerlen);    while(1){    fgets(buf, N, stdin);    printf("buf:%s",buf);    if(-1 == (n = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *)&peeraddr, peerlen)))    {        perror("sendto");        exit(-1);    }    if(strncmp(buf, "quit", 4) == 0)            break;    printf("n = %d/n",n);    }    close(sockfd);    exit(0);}復制代碼server.c復制代碼#include <stdio.h>#include <sys/types.h>//socket():bind();listen():accept();listen();accept();connect();#include <sys/socket.h>//socket():bind();listen():accept();inet_addr();listen():accept();connect();#include <arpa/inet.h>//htons();inet_addr():#include <netinet/in.h>//inet_addr():#include <strings.h>//bzero();#include <stdlib.h>//atoi();exit();#include <unistd.h>//close():#include <string.h>#define N 64typedef struct sockaddr SA;int main(int argc, char *argv[]){    if(argc < 3)    {        printf("Using: %s ip port/n",argv[0]);        exit(-1);    }    int listenfd, connfd;    struct sockaddr_in myaddr, peeraddr;    char buf[N] = {0};    size_t n;    socklen_t mylen, peerlen;    mylen = sizeof(myaddr);    peerlen = sizeof(peeraddr);    /*    create    socket    */    if ((listenfd = (socket(PF_INET, SOCK_DGRAM, 0))) < 0)    {        perror("socket");        exit(-1);    }    /*    bind initialization    */    bzero(&myaddr, mylen);    myaddr.sin_family = PF_INET;    myaddr.sin_port = htons(atoi(argv[2]));    inet_aton(argv[1], &myaddr.sin_addr);        if(bind(listenfd,(SA *)&myaddr, sizeof(myaddr)) < 0)    {        perror("bind");        exit(-1);    }    /*    listen        */    listen(listenfd, 5);    /*    accept        */    if(-1 == (connfd = accept(listenfd, (SA *)&peeraddr, &peerlen)))    {        perror("accept");        exit(-1);    }    printf("connect from %s: %d/n",inet_ntoa(peeraddr.sin_addr), ntohs(peeraddr.sin_port));    /*    recv-send    */    while(1){    n = recv(connfd, buf, N, 0);    buf[n] = 0;    printf("n = %d---%s/n",n,buf);    if(0 == strncmp(buf,"quit",4))　　　　break;    send(connfd, buf, strlen(buf), 0);    }    close(connfd);    close(listenfd);    exit(0);}
原文鏈接：http://m.survivalescaperooms.com/lr-ting/archive/2012/08/24/2652482.html