没有人逼你学C语言,但它在复杂的计算世界中,曲径通幽。
socket相关的数据结构
sockaddr_in
sockaddr_in结构体定义在/usr/include/netinet/in.h中,它的定义是这样的:1
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13/* 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) -
truetruetrue __SOCKADDR_COMMON_SIZE -
truetruetrue sizeof (in_port_t) -
truetruetrue sizeof (struct in_addr)];
};
这个结构体中又涉及到另外几个类型和宏定义,包括__SOCKADDR_COMMON、in_port_t、in_addr。
__SOCKADDR_COMMON
__SOCKADDR_COMMON定义在bits/sockaddr.h当中,它的作用是将sin_和family参数拼接为对应的sa_family_t类型的地址家族。
1 | /* POSIX.1g specifies this type name for the `sa_family' member. */ |
也就是说这个预处理宏定义的意思是将sin_和family拼接在一起构成sa_family_t类型的sin_family。
sa_family_t就是短整形,长度16 bits的整数。
所以sockaddr_in结构体的第一个元素其实是sa_family_t类型的sin_family参数。
in_port_t
in_port_t实际上是uint16_t,16位的无符号整数。
1 | typedef uint16_t in_port_t; |
uint16_t其实就是__uint16_t,表示unsigned short int,它的长度是2个字节,能表示的范围是0-65535。
in_addr
这个显而易见,就是表示一个IPv4的地址:1
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6/* Internet address. */
typedef uint32_t in_addr_t;
struct in_addr
{
in_addr_t s_addr;
};
而uint32_t也就是__uint32_t,表示unsigned int,一共4个字节。IP地址一般是拆成点分十进制看的,一个字节能表示的范围是0-255,所以的in_addr也就是能表示成0.0.0.0 ~ 255.255.255.255。
sin_zero
sin_zero的相关定义:
1 | /* Structure describing an Internet (IP) socket address. */ |
__pad声明了一个长素为8个字节的字符数组。
1 | __SOCK_SIZE__ - sizeof(short int) - sizeof(unsigned short int) - sizeof(struct in_addr) |
sin_family的类型
在C语言实现网络通信中,最开始需要做的就是声明并且初始化sockaddr_in结构体。
其中sin_family的类型有这些:1
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100/* Protocol families. */
#define PF_UNSPEC 0 /* Unspecified. */
#define PF_LOCAL 1 /* Local to host (pipes and file-domain). */
#define PF_UNIX PF_LOCAL /* POSIX name for PF_LOCAL. */
#define PF_FILE PF_LOCAL /* Another non-standard name for PF_LOCAL. */
#define PF_INET 2 /* IP protocol family. */
#define PF_AX25 3 /* Amateur Radio AX.25. */
#define PF_IPX 4 /* Novell Internet Protocol. */
#define PF_APPLETALK 5 /* Appletalk DDP. */
#define PF_NETROM 6 /* Amateur radio NetROM. */
#define PF_BRIDGE 7 /* Multiprotocol bridge. */
#define PF_ATMPVC 8 /* ATM PVCs. */
#define PF_X25 9 /* Reserved for X.25 project. */
#define PF_INET6 10 /* IP version 6. */
#define PF_ROSE 11 /* Amateur Radio X.25 PLP. */
#define PF_DECnet 12 /* Reserved for DECnet project. */
#define PF_NETBEUI 13 /* Reserved for 802.2LLC project. */
#define PF_SECURITY 14 /* Security callback pseudo AF. */
#define PF_KEY 15 /* PF_KEY key management API. */
#define PF_NETLINK 16
#define PF_ROUTE PF_NETLINK /* Alias to emulate 4.4BSD. */
#define PF_PACKET 17 /* Packet family. */
#define PF_ASH 18 /* Ash. */
#define PF_ECONET 19 /* Acorn Econet. */
#define PF_ATMSVC 20 /* ATM SVCs. */
#define PF_RDS 21 /* RDS sockets. */
#define PF_SNA 22 /* Linux SNA Project */
#define PF_IRDA 23 /* IRDA sockets. */
#define PF_PPPOX 24 /* PPPoX sockets. */
#define PF_WANPIPE 25 /* Wanpipe API sockets. */
#define PF_LLC 26 /* Linux LLC. */
#define PF_IB 27 /* Native InfiniBand address. */
#define PF_MPLS 28 /* MPLS. */
#define PF_CAN 29 /* Controller Area Network. */
#define PF_TIPC 30 /* TIPC sockets. */
#define PF_BLUETOOTH 31 /* Bluetooth sockets. */
#define PF_IUCV 32 /* IUCV sockets. */
#define PF_RXRPC 33 /* RxRPC sockets. */
#define PF_ISDN 34 /* mISDN sockets. */
#define PF_PHONET 35 /* Phonet sockets. */
#define PF_IEEE802154 36 /* IEEE 802.15.4 sockets. */
#define PF_CAIF 37 /* CAIF sockets. */
#define PF_ALG 38 /* Algorithm sockets. */
#define PF_NFC 39 /* NFC sockets. */
#define PF_VSOCK 40 /* vSockets. */
#define PF_KCM 41 /* Kernel Connection Multiplexor. */
#define PF_QIPCRTR 42 /* Qualcomm IPC Router. */
#define PF_SMC 43 /* SMC sockets. */
#define PF_MAX 44 /* For now.. */
/* Address families. */
#define AF_UNSPEC PF_UNSPEC
#define AF_LOCAL PF_LOCAL
#define AF_UNIX PF_UNIX
#define AF_FILE PF_FILE
#define AF_INET PF_INET
#define AF_AX25 PF_AX25
#define AF_IPX PF_IPX
#define AF_APPLETALK PF_APPLETALK
#define AF_NETROM PF_NETROM
#define AF_BRIDGE PF_BRIDGE
#define AF_ATMPVC PF_ATMPVC
#define AF_X25 PF_X25
#define AF_INET6 PF_INET6
#define AF_ROSE PF_ROSE
#define AF_DECnet PF_DECnet
#define AF_NETBEUI PF_NETBEUI
#define AF_SECURITY PF_SECURITY
#define AF_KEY PF_KEY
#define AF_NETLINK PF_NETLINK
#define AF_ROUTE PF_ROUTE
#define AF_PACKET PF_PACKET
#define AF_ASH PF_ASH
#define AF_ECONET PF_ECONET
#define AF_ATMSVC PF_ATMSVC
#define AF_RDS PF_RDS
#define AF_SNA PF_SNA
#define AF_IRDA PF_IRDA
#define AF_PPPOX PF_PPPOX
#define AF_WANPIPE PF_WANPIPE
#define AF_LLC PF_LLC
#define AF_IB PF_IB
#define AF_MPLS PF_MPLS
#define AF_CAN PF_CAN
#define AF_TIPC PF_TIPC
#define AF_BLUETOOTH PF_BLUETOOTH
#define AF_IUCV PF_IUCV
#define AF_RXRPC PF_RXRPC
#define AF_ISDN PF_ISDN
#define AF_PHONET PF_PHONET
#define AF_IEEE802154 PF_IEEE802154
#define AF_CAIF PF_CAIF
#define AF_ALG PF_ALG
#define AF_NFC PF_NFC
#define AF_VSOCK PF_VSOCK
#define AF_KCM PF_KCM
#define AF_QIPCRTR PF_QIPCRTR
#define AF_SMC PF_SMC
#define AF_MAX PF_MAX
其中最常用的AF_INET就是PF_INET,也就2所代表的IP协议家族。
sin_addr的赋值
sin_addr需要一个IPv4的地址作为值,in.h中定义了这样几个常用值,其中包括本地地址、多拨地址等:
写服务端socket最常用的INADDR_ANY地址就是((unsigned long int) 0x00000000)
,即 0.0.0.0:1
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/* Address to accept any incoming messages. */
#define INADDR_ANY ((unsigned long int) 0x00000000)
/* Address to send to all hosts. */
#define INADDR_BROADCAST ((unsigned long int) 0xffffffff)
/* Address indicating an error return. */
#define INADDR_NONE ((unsigned long int) 0xffffffff)
/* Network number for local host loopback. */
#define IN_LOOPBACKNET 127
/* Address to loopback in software to local host. */
#define INADDR_LOOPBACK 0x7f000001 /* 127.0.0.1 */
#define IN_LOOPBACK(a) ((((long int) (a)) & 0xff000000) == 0x7f000000)
/* Defines for Multicast INADDR */
#define INADDR_UNSPEC_GROUP 0xe0000000U /* 224.0.0.0 */
#define INADDR_ALLHOSTS_GROUP 0xe0000001U /* 224.0.0.1 */
#define INADDR_ALLRTRS_GROUP 0xe0000002U /* 224.0.0.2 */
#define INADDR_MAX_LOCAL_GROUP 0xe00000ffU /* 224.0.0.255 */
#endif
socket的类型
关于socket的类型,在bits/socket_type.h中定义:
1 | /* Types of sockets. */ |
socket相关的函数
主要是定义在sys/socket.h中的以下函数:
- socket
- bind
- listen
- accept
- connect
关于这些函数的介绍暂不赘述,sys/socket.h里写的很详细。这里用一个socket基础的例子来演示其用法:
服务端server.c:
1 | /* |
客户端client.c:
1 | /* |