linux C 网络编程基础
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TCP/IP基础
UDP提供无连接服务
UDP的数据格式:
#ifdef __FAVOR_BSDstruct udphdr { u_int16_t uh_sport; /* source port */ u_int16_t uh_dport; /* destination port */ u_int16_t uh_ulen; /* udp length */ u_int16_t uh_sum; /* udp checksum */};#elsestruct udphdr { u_int16_t source; u_int16_t dest; u_int16_t len; u_int16_t check;};#endif
TCP是面向连接的,切实全双工的。
TCP协议数据段:
struct tcphdr { WORD SourPort; WORD DestPort; DWORD SeqNo; DWORD AckNo; BYTE HLen; BYTE Flag; WORD Window; WORD ChkSum; WORD UrgPtr; /* Put options here. */};
TCP的time_wait:
执行主动关闭的那端进入这种状态。这个端点在该状态的持续时间是2MSL(最长分节生命周期)。
网络中的几类地址:
物理地址:即MAC地址 (数据链路层)
逻辑地址:即IP地址
端口地址:应用程序端口号
域名地址:取代IP地址记忆
IPv4的套接字地址:
/* Internet address. */typedef uint32_t in_addr_t;struct in_addr { in_addr_t s_addr; };/* Structure describing an Internet socket address. */struct sockaddr_in { __SOCKADDR_COMMON (sin_); in_port_t sin_port; /* Port number. */ struct in_addr sin_addr; /* Internet address. */ /* Pad to size of `struct sockaddr'. */ unsigned char sin_zero[sizeof (struct sockaddr) - __SOCKADDR_COMMON_SIZE - sizeof (in_port_t) - sizeof (struct in_addr)]; };
IPv6套接字地址:
struct in6_addr { union { uint8_t __u6_addr8[16];#ifdef __USE_MISC uint16_t __u6_addr16[8]; uint32_t __u6_addr32[4];#endif } __in6_u;#define s6_addr __in6_u.__u6_addr8#ifdef __USE_MISC# define s6_addr16 __in6_u.__u6_addr16# define s6_addr32 __in6_u.__u6_addr32#endif };/* Ditto, for IPv6. */struct sockaddr_in6 { __SOCKADDR_COMMON (sin6_); in_port_t sin6_port; /* Transport layer port # */ uint32_t sin6_flowinfo; /* IPv6 flow information */ struct in6_addr sin6_addr; /* IPv6 address */ uint32_t sin6_scope_id; /* IPv6 scope-id */ };
TCP套接字编程
tcp套接字网络编程的主要实现过程:
关于socket函数:
#include<sys/socket.h>int socket(int family,int type,int protocol)
family指明了协议族。例如:AF_INET(IPv4协议);AF_INET6(IPV6协议);AF_ROUTE(路由套接口)
type指明了套接字类型。例如:
SOCK_STREAM字节流套接口(TCP);
SOCK_DGRAM数据包套接口(UDP);
SOCK_RAW原始套接口
protocol指明协议标志
端口与套接字
端口:访问网络不同计算机程序的编号
IP地址标记了不同的电脑,而域名则是iP地址便于记忆的别名
edemon@ubuntu:~$ ping www.baidu.com
PING www.a.shifen.com (119.75.218.70) 56(84) bytes of data.
socket的本义是插座。描述计算机之间不同程序之间的通信方式。TCP和UDP会遇到同时为多个应用程序同时并发进行通信的问题,为了区分不同的应用进程的应用和连接,需要使用应用程序与TCP/IP协议交互的套接字接口。
套接字:传输层协议+端口号+IP地址
域名和IP的相互转换
IP地址和网络地址:
网络地址很大一部分是由地址掩码决定的。
IP 转 domain:
#include <stdio.h>#include <sys/socket.h>#include <netdb.h> #include <netinet/in.h>#include <arpa/inet.h> #include <errno.h> #include <string.h>int main(){ struct hostent *host; char addr[]="208.108.249.216"; //202.108.249.216 61.135.169.121 http://61.135.169.125/ struct in_addr in; struct sockaddr_in addr_in; host=gethostbyaddr(addr,sizeof(addr),AF_INET); if(host!=(struct hostent *)NULL) { memcpy(&addr_in.sin_addr.s_addr,host->h_addr,4); in.s_addr=addr_in.sin_addr.s_addr; printf("Domain name: %s \n",host->h_name); printf("IP length: %d\n",host->h_length); printf("Type: %d\n",host->h_addrtype); printf("IP : %s \n",inet_ntoa(in)); } else { char *buffer = strerror(errno); printf("%s\n",buffer); } }/*Domain name: 50-48-56-46.dr05.nrwc.ny.frontiernet.net IP length: 16Type: 2IP : 50.48.56.46 */
domain 转IP:
#include <stdio.h>#include <sys/socket.h>#include <netdb.h>#include <string.h>#include <netinet/in.h>#include <arpa/inet.h>int main(){ struct hostent *host; char hostname[]="www.baidu.com"; char hostname2[]="www.012www.com"; struct in_addr in; struct sockaddr_in sock_in; extern int h_errno; if((host=gethostbyname(hostname))!=NULL){ //printf("%s\n",host->h_addr); memcpy(&sock_in.sin_addr.s_addr, host->h_addr, 4); in.s_addr=sock_in.sin_addr.s_addr; printf("Domain name: %s \n",hostname); printf("IP length: %d\n",host->h_length); printf("Type: %d\n",host->h_addrtype); /*inet_ntoa()用来将参数in所指的网络二进制的数字转换成网络地址, 然后将指向此网络地址字符串的指针返回。*/ printf("IP : %s \n",inet_ntoa(in)); } else{ printf("Domain name: %s \n",hostname); printf("error: %d\n",h_errno); printf("%s\n",hstrerror(h_errno)); } if((host=gethostbyname(hostname2))!=NULL){ memcpy(&sock_in.sin_addr.s_addr,host->h_addr,4); in.s_addr=sock_in.sin_addr.s_addr; printf("Domain name: %s \n",hostname2); printf("IP : %s \n",inet_ntoa(in)); printf("IP length: %d\n",host->h_length); printf("Type: %d\n",host->h_addrtype); } else{ printf("Domain name: %s \n",hostname2); printf("error: %d\n",h_errno); printf("%s\n",hstrerror(h_errno)); }}/*Domain name: www.baidu.com IP length: 4Type: 2IP : 61.135.169.121 Domain name: www.012www.com error: 1Unknown host*/
网络地址转换
对于不同的socket domain定义了一个通用的数据结构——套接字结构:
struct sockaddr{unsigned short int sa_family;char sa_data[14];};
sa_family 为调用socket()时的domain参数,即AF_xxxx值。
sa_data 最多使用14个字符长度。
此sockaddr结构会因使用不同的socket domain而有不同结构定义,例如使用AF_INET domain,其
socketaddr结构定义便为
struct socketaddr_in{unsigned short int sin_family;uint16_t sin_port;struct in_addr sin_addr;unsigned char sin_zero[8];};struct in_addr{uint32_t s_addr;};
sin_family 即为sa_family
sin_port 为使用的port编号
sin_addr.s_addr 为IP 地址
sin_zero 未使用。
struct hostent{char * h_name;char ** h_aliases;short h_addrtype;short h_length;char ** h_addr_list;};
主机字节序和网络字节序的转换:
unsigned long int htonl(unsigned long int hostlong);
将32位主机字符顺序转换成网络字符顺序
unsigned short int htons(unsigned short int hostshort);
将16位主机字符顺序转换成网络字符顺序
unsigned long int ntohl(unsigned long int netlong);
将32位网络字符顺序转换成主机字符顺序
unsigned short int ntohs(unsigned short int netshort);
将16位网络字符顺序转换成主机字符顺序
#include <stdio.h>#include <arpa/inet.h>int main(){ long local; int port; local =123456; port=123456; printf("host 32 %ld -> net 32: %d\n",local,htonl(local)); printf("host 16 %d -> net 16: %d\n",port,htons(port)); printf("net 32 %d -> host 32: %d\n",htonl(local),ntohl(htonl(local))); printf("net 16 %d -> host 16: %d\n",htons(port),ntohs(htons(port))); return 0;}/*host 32 123456 -> net 32: 1088553216host 16 123456 -> net 16: 16610net 32 1088553216 -> host 32: 123456net 16 16610 -> host 16: 57920*/
long inet_addr(char *str)
将网络IP地址转化成10进制长整型数
头文件:
#include<sys/socket.h>#include<netinet/in.h>#include<arpa/inet.h>
char *inet_ntoa(struct in_addr in);
将整数型地址转化成点分十进制地址(在计算机中经常使用长整型数表示IP地址)
表头文件
#include<sys/socket.h>#include<netinet/in.h>#include<arpa/inet.h>
例子:
#include <stdio.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>int main(){ struct in_addr ip; ip.s_addr=16885952; char *str=inet_ntoa(ip); printf("%s\n",str); printf("%u\n", inet_addr(str));}/*192.168.1.116885952*/
系统支持的网络服务
cat /etc/protocols……daytime 13/tcpdaytime 13/udpnetstat 15/tcp qotd 17/tcp quotemsp 18/tcp # message send protocolmsp 18/udpchargen 19/tcp ttytst sourcechargen 19/udp ttytst sourceftp-data 20/tcpftp 21/tcp……
获取服务信息:
#include <stdio.h>#include <netdb.h> int main(){ struct servent *ser; if( ser=getservbyname("http","tcp")) //通过名字获取网络服务 { printf("name : %s\n",ser->s_name); printf("net port: %d ", ser->s_port); printf("host port : %d\n",ntohs(ser->s_port)); //将16位网络字符顺序转换成主机字符顺序 printf("protocol:%s\n",ser->s_proto); printf("alias: %s\n",ser->s_aliases[0]); } else { printf("there is no such a service.\n"); } puts("---------------------------------------------"); if( ser=getservbyname("hehe","tcp")) { printf("name : %s\n",ser->s_name); printf("net port: %d ", ser->s_port); printf("host port : %d\n",ntohs(ser->s_port)); printf("protocol:%s\n",ser->s_proto); printf("alias: %s\n",ser->s_aliases[0]); } else { printf("there is no such a service.\n"); } puts("---------------------------------------------"); //通过端口号获取网络服务 if( ser=getservbyport(htons(21),"tcp")) //将16位主机字符顺序转换成网络字符顺序 { printf("name : %s\n",ser->s_name); printf("net port: %d ", ser->s_port); printf("host port : %d\n",ntohs(ser->s_port)); printf("protocol:%s\n",ser->s_proto); printf("alias: %s\n",ser->s_aliases[0]); } else { printf("there is no such a service.\n"); }}/*name : httpnet port: 20480 host port : 80protocol:tcpalias: www---------------------------------------------there is no such a service.---------------------------------------------name : ftpnet port: 5376 host port : 21protocol:tcpalias: (null)*/
捕获错误
void herror(const char *s);
可以显示网络函数上出现的错误。先输出这个字符串,然后输出错误信息。
extern int h_errno
可以捕获错误编号。
char *hstrerror(int err)
返回错误编码对应的错误信息。
三个和错误相关的函数或变量都与头文件netdb.h相关
#include <stdio.h>#include <netdb.h>int main(){ herror("result : "); extern int h_errno; printf("%s\n", hstrerror(h_errno));}
获取协议数据
系统支持的协议:
ip 0 IP # internet protocol, pseudo protocol numberhopopt 0 HOPOPT # IPv6 Hop-by-Hop Option [RFC1883]icmp 1 ICMP # internet control message protocoligmp 2 IGMP # Internet Group Managementggp 3 GGP # gateway-gateway protocolipencap 4 IP-ENCAP # IP encapsulated in IP (officially ``IP'')st 5 ST # ST datagram modetcp 6 TCP # transmission control protocolegp 8 EGP # exterior gateway protocoligp 9 IGP # any private interior gateway (Cisco)pup 12 PUP # PARC universal packet protocoludp 17 UDP # user datagram protocolhmp 20 HMP # host monitoring protocolxns-idp 22 XNS-IDP # Xerox NS IDPrdp 27 RDP # "reliable datagram" protocoliso-tp4 29 ISO-TP4 # ISO Transport Protocol class 4 [RFC905]dccp 33 DCCP # Datagram Congestion Control Prot. [RFC4340]xtp 36 XTP # Xpress Transfer Protocolddp 37 DDP # Datagram Delivery Protocolidpr-cmtp 38 IDPR-CMTP # IDPR Control Message Transportipv6 41 IPv6 # Internet Protocol, version 6ipv6-route 43 IPv6-Route # Routing Header for IPv6ipv6-frag 44 IPv6-Frag # Fragment Header for IPv6idrp 45 IDRP # Inter-Domain Routing Protocolrsvp 46 RSVP # Reservation Protocolgre 47 GRE # General Routing Encapsulationesp 50 IPSEC-ESP # Encap Security Payload [RFC2406]ah 51 IPSEC-AH # Authentication Header [RFC2402]skip 57 SKIP # SKIPipv6-icmp 58 IPv6-ICMP # ICMP for IPv6ipv6-nonxt 59 IPv6-NoNxt # No Next Header for IPv6ipv6-opts 60 IPv6-Opts # Destination Options for IPv6rspf 73 RSPF CPHB # Radio Shortest Path First (officially CPHB)vmtp 81 VMTP # Versatile Message Transporteigrp 88 EIGRP # Enhanced Interior Routing Protocol (Cisco)ospf 89 OSPFIGP # Open Shortest Path First IGPax.25 93 AX.25 # AX.25 framesipip 94 IPIP # IP-within-IP Encapsulation Protocoletherip 97 ETHERIP # Ethernet-within-IP Encapsulation [RFC3378]encap 98 ENCAP # Yet Another IP encapsulation [RFC1241]# 99 # any private encryption schemepim 103 PIM # Protocol Independent Multicastipcomp 108 IPCOMP # IP Payload Compression Protocolvrrp 112 VRRP # Virtual Router Redundancy Protocol [RFC5798]l2tp 115 L2TP # Layer Two Tunneling Protocol [RFC2661]isis 124 ISIS # IS-IS over IPv4sctp 132 SCTP # Stream Control Transmission Protocolfc 133 FC # Fibre Channelmobility-header 135 Mobility-Header # Mobility Support for IPv6 [RFC3775]udplite 136 UDPLite # UDP-Lite [RFC3828]mpls-in-ip 137 MPLS-in-IP # MPLS-in-IP [RFC4023]manet 138 # MANET Protocols [RFC5498]hip 139 HIP # Host Identity Protocolshim6 140 Shim6 # Shim6 Protocol [RFC5533]wesp 141 WESP # Wrapped Encapsulating Security Payloadrohc 142 ROHC # Robust Header Compression
获取协议信息的例子:
#include <stdio.h>#include <netdb.h> int main(){ struct protoent *pro; pro=getprotobyname("tcp"); // by protocol name printf("protocol name : %s\n",pro->p_name); printf("protocol number : %d\n",pro->p_proto); printf("protocol alias: %s\n",pro->p_aliases[0]); puts("------------------------------"); pro=getprotobynumber(2); // by protocol number printf("protocol name : %s\n",pro->p_name); printf("protocol number : %d\n",pro->p_proto); printf("protocol alias: %s\n",pro->p_aliases[0]);}protocol name : tcpprotocol number : 6protocol alias: TCP------------------------------protocol name : igmpprotocol number : 2protocol alias: IGMP
其他的套接字函数
自己的主机IP地址:
ifconfig
下面是ANSI C 中的字节操作函数:
1.
void *memset(void *s, int c, size_t n);
memset()会将参数s所指的内存区域前n个字节以参数c填入,然后返回指向s的指针。
2.
void *memcpy(void *dest, const void *src, size_t n);
memcpy()用来拷贝src所指的内存内容前n个字节到dest所指的内存地址上。与strcpy()不同的是,
memcpy()会完整的复制n个字节,不会因为遇到字符串结束’\0’而结束。
3.
int memcmp(const void *s1, const void *s2, size_t n);
memcmp()用来比较s1和s2所指的内存区间前n个字符。
字符串IP和二进制IP的相互转换(仅能处理IPv4):
int inet_aton(const char *cp, struct in_addr *inp);
函数说明
inet_aton()用来将参数cp所指的网络地址字符串转换成网络使用的二进制的数字,然后存于参数inp所
指的in_addr结构中。
返回值
成功则返回非0值,失败则返回0。
#include <stdio.h>#include<sys/socket.h>#include<netinet/in.h>#include<arpa/inet.h>int main(){ struct in_addr numstr; char IP[20]="192.160.8.60"; if(inet_aton(IP,&numstr)){ printf("0x%x\n",numstr.s_addr); } return 0;}/*0x3c08a0c0*/
inet_pton
int inet_pton(int af, const char *src, void *dst);
用于点分十进制转成二进制整数(16进制)。
成功返回1,af无效返回0,出错返回-1,指针dst存储得到的IP地址。
inet_ntop
const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt);
二进制整数(16进制)转换成点分十进制。
两者可以同时处理IPv4, IPv6.
AF_INET 是一个IPv4 网络协议的套接字类型
#include <stdio.h>#include <arpa/inet.h>int main (){ char IPstr1[20]="192.18.0.9"; char IPstr2[20]; struct in_addr s; // IPv4地址结构体 printf("%d\n",AF_INET); inet_pton(AF_INET, IPstr1, (void *)&s); printf("inet_pton: 0x%x\n", s.s_addr); //二进制整数(16进制)字节序 inet_ntop(AF_INET, (void *)&s, IPstr2, sizeof(IPstr2)); printf("inet_ntop: %s\n", IPstr2); //点分十进制 return 0;}/*2inet_pton: 0x90012c0inet_ntop: 192.18.0.9*/
从进程到内核传递套接字地址结构的函数常有3个——bind, connect, sendto
从内核到进程传递套接字地址结构的函数常有四个accept, recvfrom, getsockname, getpeername
bind()对socket定位
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