socket编程基础

Posted 2021-01-02 sunnypoem

参考：https://www.cnblogs.com/jikexianfeng/p/5729168.html

函数及参数意义

socket

int socket(int domain, int type, int protocol)

 

domain：即协议域，又称为协议族（family）。常用的协议族有，AF_INET、AF_INET6、AF_LOCAL（或称AF_UNIX，Unix域socket）、AF_ROUTE等等。协议族决定了socket的地址类型，在通信中必须采用对应的地址，如AF_INET决定了要用ipv4地址（32位的）与端口号（16位的）的组合、AF_UNIX决定了要用一个绝对路径名作为地址。

 

type：指定socket类型。常用的socket类型有，SOCK_STREAM、SOCK_DGRAM、SOCK_RAW、SOCK_PACKET、SOCK_SEQPACKET等等。

 

protocol：故名思意，就是指定协议。常用的协议有，IPPROTO_TCP、IPPTOTO_UDP、IPPROTO_SCTP、IPPROTO_TIPC等，它们分别对应TCP传输协议、UDP传输协议、STCP传输协议、TIPC传输协议。

sockaddr_in

struct sockaddr_in

{

short sin_family;/*Address family一般来说AF_INET（地址族）PF_INET（协议族）*/

 

unsigned short sin_port;/*Port number(必须要采用网络数据格式,普通数字可以用htons()函数转换成网络数据格式的数字)*/

 

struct in_addr sin_addr;/*IP address in network byte order（Internet address）*/

 

unsigned char sin_zero[8];/*Same size as struct sockaddr没有实际意义,只是为了跟SOCKADDR结构在内存中对齐*/

};

 

sockaddr_in 与 sockaddr :  https://blog.csdn.net/will130/article/details/53326740

in_addr

typedef uint32_t in_addr_t;

struct in_addr

{

    in_addr_t s_addr;

};

地址转换函数

UDP 发送

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <arpa/inet.h> #include <sys/socket.h>   #define  MAX_RCVBUF_LEN   60000 char dstIp[16] = "10.10.10.10"; unsigned short dstPort = 1083;   int main(int argc, char *argv[]) {     int sock_send;         unsigned char buf[MAX_RCVBUF_LEN];     int sendLen = 20;       struct sockaddr_in serv_adr;       sock_send = socket(PF_INET, SOCK_DGRAM, 0);     if(sock_send == -1)     {         exit(1);     }        memset(&serv_adr, 0, sizeof(serv_adr));        serv_adr.sin_family = AF_INET;        inet_pton(AF_INET, dstIp, &serv_adr.sin_addr);        serv_adr.sin_port = htons(dstPort);            sendto(sock_send, buf, sendLen, 0, (struct sockaddr*)&serv_adr, sizeof(serv_adr));        printf("send buf %d. ", sendLen);        close(sock_send);         return 0; }

 

UDP接收

void* udp_server(void *arg) {     struct sockaddr_in sin;     struct sockaddr_in rin;     int sock_fd;     int bindrt;     int address_size;     unsigned int i;     unsigned char rcvbuf[MAX_RCVBUF_LEN];     char str[MAX_RCVBUF_LEN];     unsigned short uwMsglen;         bzero(&sin, sizeof(sin));     bzero(rcvbuf, MAX_RCVBUF_LEN);     sin.sin_family = AF_INET;     sin.sin_addr.s_addr = INADDR_ANY;     sin.sin_port = htons(rcvPort);            sock_fd = socket(AF_INET, SOCK_DGRAM, 0);     bindrt = bind(sock_fd, (struct sockaddr *)&sin, sizeof(sin));       while(1)     {         address_size = sizeof(rin);         uwMsglen = recvfrom(sock_fd, rcvbuf, MAX_RCVBUF_LEN, 0, (struct sockaddr *)&rin, &address_size);         if(-1 == uwMsglen)         {             perror("call to recvfrom. ");             exit(1);         }                } }

 

RAW SOCKET

两种raw socket应用：http://blog.chinaunix.net/uid-21757287-id-194935.html

1.socket(AF_INET, SOCK_RAW, IPPROTO_TCP|IPPROTO_UDP|IPPROTO_ICMP)发送接收ip数据包

2.socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP|ETH_P_ARP|ETH_P_ALL))发送接收以太网数据帧

 

参考了以下文章的代码。

源码：https://blog.csdn.net/luchengtao11/article/details/73878760

 

#include <unistd.h> #include <stdio.h> #include <sys/socket.h> #include <netinet/ip.h> #include <netinet/udp.h> #include<memory.h> #include<stdlib.h> #include <linux/if_ether.h> #include <linux/if_packet.h> // sockaddr_ll #include<arpa/inet.h> #include<netinet/if_ether.h> #include<iomanip> #include<iostream>   // The packet length #define PCKT_LEN 100   //UDP的伪头部 struct UDP_PSD_Header {     u_int32_t src;     u_int32_t des;     u_int8_t  mbz;     u_int8_t ptcl;     u_int16_t len; }; //计算校验和 unsigned short csum(unsigned short *buf, int nwords) {     unsigned long sum;     for (sum = 0; nwords > 0; nwords--)     {         sum += *buf++;     }        while(sum>>16){               sum = (sum & 0xffff) + (sum >>16);        }    return (unsigned short)(~sum); }   // Source IP, source port, target IP, target port from the command line arguments int main(int argc, char *argv[]) {     int sd;     char buffer[PCKT_LEN] ;     //查询www.chongfer.cn的DNS报文 #if 1     unsigned char DNS[] = { 0xd8, 0xcb , 0x01, 0x00, 0x00, 0x01, 0x00 ,0x00,         0x00, 0x00, 0x00, 0x00, 0x03, 0x77, 0x77, 0x77,         0x08, 0x63, 0x68, 0x6f, 0x6e, 0x67, 0x66, 0x65,         0x72, 0x02, 0x63, 0x6e, 0x00, 0x00, 0x01, 0x00,         0x01 };   #endif     struct iphdr *ip = (struct iphdr *) buffer;     struct udphdr *udp = (struct udphdr *) (buffer + sizeof(struct iphdr));     // Source and destination addresses: IP and port     struct sockaddr_in sin, din;     int  one = 1;     const int *val = &one;     //缓存清零     memset(buffer, 0, PCKT_LEN);       if (argc != 5)     {         printf("- Invalid parameters!!! ");         printf("- Usage %s <source hostname/IP> <source port> <target hostname/IP> <target port> ", argv[0]);         exit(-1);     }       // Create a raw socket with UDP protocol     sd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);     if (sd < 0)     {         perror("socket() error");         // If something wrong just exit         exit(-1);     }     else         printf("socket() - Using SOCK_RAW socket and UDP protocol is OK. ");     //IPPROTO_TP说明用户自己填写IP报文     //IP_HDRINCL表示由内核来计算IP报文的头部校验和，和填充那个IP的id     if (setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(int)))     {         perror("setsockopt() error");         exit(-1);     }     else         printf("setsockopt() is OK. ");       // The source is redundant, may be used later if needed     // The address family     din.sin_family = AF_INET;     // Port numbers     din.sin_port = htons(atoi(argv[4]));     // IP addresses     din.sin_addr.s_addr = inet_addr(argv[3]);       // Fabricate the IP header or we can use the     // standard header structures but assign our own values.     ip->ihl = 5;     ip->version = 4;//报头长度，4*32=128bit=16B     ip->tos = 0; // 服务类型     ip->tot_len = htons ((sizeof(struct iphdr) + sizeof(struct udphdr)+sizeof(DNS)));     //ip->id = htons(54321);//可以不写     ip->ttl = 64; // hops生存周期     ip->protocol = 17; // UDP     ip->check = 0;     // Source IP address, can use spoofed address here!!!     ip->saddr = inet_addr(argv[1]);     // The destination IP address     ip->daddr = inet_addr(argv[3]);       // Fabricate the UDP header. Source port number, redundant     udp->source = htons(atoi(argv[2]));//源端口     // Destination port number     udp->dest = htons(atoi(argv[4]));//目的端口     udp->len = htons(sizeof(struct udphdr)+sizeof(DNS));//长度     //forUDPCheckSum用来计算UDP报文的校验和用     //UDP校验和需要计算 伪头部、UDP头部和数据部分     char * forUDPCheckSum = new char[sizeof(UDP_PSD_Header) + sizeof(udphdr)+sizeof(DNS) +1];     memset(forUDPCheckSum, 0, sizeof(UDP_PSD_Header) + sizeof(udphdr) + sizeof(DNS) +1 );     UDP_PSD_Header * udp_psd_Header = (UDP_PSD_Header *)forUDPCheckSum;     udp_psd_Header->src = inet_addr(argv[1]);     udp_psd_Header->des = inet_addr(argv[3]);     udp_psd_Header->mbz = 0;     udp_psd_Header->ptcl = 17;     udp_psd_Header->len = htons(sizeof(udphdr)+sizeof(DNS));     memcpy(forUDPCheckSum + sizeof(UDP_PSD_Header), udp, sizeof(udphdr));     memcpy(forUDPCheckSum + sizeof(UDP_PSD_Header) + sizeof(udphdr), DNS, sizeof(DNS));       ip->check = csum((unsigned short *)ip, sizeof(iphdr)/2);//可以不用算     //计算UDP的校验和，因为报文长度可能为单数，所以计算的时候要补0     udp->check = csum((unsigned short *)forUDPCheckSum,(sizeof(udphdr)+sizeof(UDP_PSD_Header)+sizeof(DNS) +1)/2);       setuid(getpid());//如果不是root用户，需要获取权限        printf("Using Source IP: %s port: %u, Target IP: %s port: %u. ", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));     std::cout << "Ip length:" << ip->tot_len << std::endl;     int count;     //将DNS报文拷贝进缓存区     memcpy(buffer + sizeof(iphdr) + sizeof(udphdr), DNS, sizeof(DNS));         if (sendto(sd, buffer, ip->tot_len, 0, (struct sockaddr *)&din, sizeof(din)) < 0)     {         perror("sendto() error");         exit(-1);     }     close(sd);     return 0; }

 

IP/UDP 头填充

 

IP、TCP、UDP头详解：https://blog.csdn.net/mrwangwang/article/details/8537775

 

/*IPv4 Header*/ struct IpHead {     unsigned char     verHeaderLen; /*version (0100 0110) and header len (4 bytes per unit)*/     unsigned char     typeOfService;/*type of service: PPP D T R M Rsvd*/     unsigned short     totalLen;     /*Total length: header + data*/     unsigned short     identifier;   /*Identifier*/     unsigned short     flagFragOff;  /*Flags and Fragment Offset*/     unsigned char     ttl;          /*TTL*/     unsigned char     protocol;     /*Protocol: 1-ICMP  6-TCP 17-UDP*/     unsigned short     checkSum;     /*Header Checksum*/     unsigned int    srcIp;       unsigned int    dstIp;     char pData[0]; };   /*UDP Header*/ struct UdpHead {     unsigned short   srcPort;     unsigned short   dstPort;     unsigned short   dataLen;     unsigned short   checkSum;     char pData[0]; };

 

 

IP头部校验和字段：

当发送 IP 包时，需要计算 IP 报头的校验和：

1 、把校验和字段置为 0 ；

2 、对 IP 头部中的每 16bit 进行二进制求和；

3 、 如果和的高 16bit 不为 0 ，则将和的高 16bit 和低 16bit 反复相加，直到和的高 16bit 为 0 ，从而获得一个 16bit 的值；

4 、将该 16bit 的值取反，存入校验和字段。

当接收 IP 包时，需要对报头进行确认，检查 IP 头是否有误，算法同上 2 、 3 步，然后判断取反的结果是否为 0 ，是则正确，否则有错。

unsigned short csum(unsigned short *buf, int nwords) {     unsigned long sum;     for (sum = 0; nwords > 0; nwords--)     {         sum += *buf++;     }          while(sum>>16){               sum = (sum & 0xffff) + (sum >>16);        }       return (unsigned short)(~sum); }

 

 

 

UDP头中校验和字段：占16比特。用来对UDP头部和UDP数据进行校验。和TCP不同的是，对UDP来说，此字段是可选项，而TCP数据段中的校验和字段是必须有的。UDP头中的校验和可以设置为0，表示发送端没有计算校验和。

 

文件系统、linux协议栈、系统调用与socket

牛人总结：https://www.cnblogs.com/kakawater/p/7085122.html