6.3.11.11. socket¶
socket函数的原型为 int socket(int domain, int type, int protocol); 。
其中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要使用一个绝对路径名作为地址。
支持的所有协议定义在 /include/linux/socket.h 中，具体内容如下：
/* Supported address families. */
#define AF_UNSPEC 0
#define AF_UNIX 1 /* Unix domain sockets */
#define AF_LOCAL 1 /* POSIX name for AF_UNIX */
#define AF_INET 2 /* Internet IP Protocol */
#define AF_AX25 3 /* Amateur Radio AX.25 */
#define AF_IPX 4 /* Novell IPX */
#define AF_APPLETALK 5 /* AppleTalk DDP */
#define AF_NETROM 6 /* Amateur Radio NET/ROM */
#define AF_BRIDGE 7 /* Multiprotocol bridge */
#define AF_ATMPVC 8 /* ATM PVCs */
#define AF_X25 9 /* Reserved for X.25 project */
#define AF_INET6 10 /* IP version 6 */
#define AF_ROSE 11 /* Amateur Radio X.25 PLP */
#define AF_DECnet 12 /* Reserved for DECnet project */
#define AF_NETBEUI 13 /* Reserved for 802.2LLC project*/
#define AF_SECURITY 14 /* Security callback pseudo AF */
#define AF_KEY 15 /* PF_KEY key management API */
#define AF_NETLINK 16
#define AF_ROUTE AF_NETLINK /* Alias to emulate 4.4BSD */
#define AF_PACKET 17 /* Packet family */
#define AF_ASH 18 /* Ash */
#define AF_ECONET 19 /* Acorn Econet */
#define AF_ATMSVC 20 /* ATM SVCs */
#define AF_RDS 21 /* RDS sockets */
#define AF_SNA 22 /* Linux SNA Project (nutters!) */
#define AF_IRDA 23 /* IRDA sockets */
#define AF_PPPOX 24 /* PPPoX sockets */
#define AF_WANPIPE 25 /* Wanpipe API Sockets */
#define AF_LLC 26 /* Linux LLC */
#define AF_IB 27 /* Native InfiniBand address */
#define AF_MPLS 28 /* MPLS */
#define AF_CAN 29 /* Controller Area Network */
#define AF_TIPC 30 /* TIPC sockets */
#define AF_BLUETOOTH 31 /* Bluetooth sockets */
#define AF_IUCV 32 /* IUCV sockets */
#define AF_RXRPC 33 /* RxRPC sockets */
#define AF_ISDN 34 /* mISDN sockets */
#define AF_PHONET 35 /* Phonet sockets */
#define AF_IEEE802154 36 /* IEEE802154 sockets */
#define AF_CAIF 37 /* CAIF sockets */
#define AF_ALG 38 /* Algorithm sockets */
#define AF_NFC 39 /* NFC sockets */
#define AF_VSOCK 40 /* vSockets */
#define AF_KCM 41 /* Kernel Connection Multiplexor*/
#define AF_QIPCRTR 42 /* Qualcomm IPC Router */
#define AF_SMC 43 /* smc sockets: reserve number for
* PF_SMC protocol family that
* reuses AF_INET address family
*/
#define AF_XDP 44 /* XDP sockets */
#define AF_MAX 45 /* For now.. */
type指定socket类型，常用的socket类型为:
enum sock_type {
SOCK_STREAM = 1, // 字节流套接字
SOCK_DGRAM = 2, // 数据报文套接字
SOCK_RAW = 3, // 原始套接字
SOCK_RDM = 4,
SOCK_SEQPACKET = 5, // 有序分组套接字
SOCK_DCCP = 6,
SOCK_PACKET = 10,
};
protocol指协议，常用的协议类型为:
/* Standard well-defined IP protocols. */
enum {
IPPROTO_IP = 0, /* Dummy protocol for TCP */
#define IPPROTO_IP IPPROTO_IP
IPPROTO_ICMP = 1, /* Internet Control Message Protocol */
#define IPPROTO_ICMP IPPROTO_ICMP
IPPROTO_IGMP = 2, /* Internet Group Management Protocol */
#define IPPROTO_IGMP IPPROTO_IGMP
IPPROTO_IPIP = 4, /* IPIP tunnels (older KA9Q tunnels use 94) */
#define IPPROTO_IPIP IPPROTO_IPIP
IPPROTO_TCP = 6, /* Transmission Control Protocol */
#define IPPROTO_TCP IPPROTO_TCP
IPPROTO_EGP = 8, /* Exterior Gateway Protocol */
#define IPPROTO_EGP IPPROTO_EGP
IPPROTO_PUP = 12, /* PUP protocol */
#define IPPROTO_PUP IPPROTO_PUP
IPPROTO_UDP = 17, /* User Datagram Protocol */
#define IPPROTO_UDP IPPROTO_UDP
IPPROTO_IDP = 22, /* XNS IDP protocol */
#define IPPROTO_IDP IPPROTO_IDP
IPPROTO_TP = 29, /* SO Transport Protocol Class 4 */
#define IPPROTO_TP IPPROTO_TP
IPPROTO_DCCP = 33, /* Datagram Congestion Control Protocol */
#define IPPROTO_DCCP IPPROTO_DCCP
IPPROTO_IPV6 = 41, /* IPv6-in-IPv4 tunnelling */
#define IPPROTO_IPV6 IPPROTO_IPV6
IPPROTO_RSVP = 46, /* RSVP Protocol */
#define IPPROTO_RSVP IPPROTO_RSVP
IPPROTO_GRE = 47, /* Cisco GRE tunnels (rfc 1701,1702) */
#define IPPROTO_GRE IPPROTO_GRE
IPPROTO_ESP = 50, /* Encapsulation Security Payload protocol */
#define IPPROTO_ESP IPPROTO_ESP
IPPROTO_AH = 51, /* Authentication Header protocol */
#define IPPROTO_AH IPPROTO_AH
IPPROTO_MTP = 92, /* Multicast Transport Protocol */
#define IPPROTO_MTP IPPROTO_MTP
IPPROTO_BEETPH = 94, /* IP option pseudo header for BEET */
#define IPPROTO_BEETPH IPPROTO_BEETPH
IPPROTO_ENCAP = 98, /* Encapsulation Header */
#define IPPROTO_ENCAP IPPROTO_ENCAP
IPPROTO_PIM = 103, /* Protocol Independent Multicast */
#define IPPROTO_PIM IPPROTO_PIM
IPPROTO_COMP = 108, /* Compression Header Protocol */
#define IPPROTO_COMP IPPROTO_COMP
IPPROTO_SCTP = 132, /* Stream Control Transport Protocol */
#define IPPROTO_SCTP IPPROTO_SCTP
IPPROTO_UDPLITE = 136, /* UDP-Lite (RFC 3828) */
#define IPPROTO_UDPLITE IPPROTO_UDPLITE
IPPROTO_MPLS = 137, /* MPLS in IP (RFC 4023) */
#define IPPROTO_MPLS IPPROTO_MPLS
IPPROTO_ETHERNET = 143, /* Ethernet-within-IPv6 Encapsulation */
#define IPPROTO_ETHERNET IPPROTO_ETHERNET
IPPROTO_RAW = 255, /* Raw IP packets */
#define IPPROTO_RAW IPPROTO_RAW
IPPROTO_MPTCP = 262, /* Multipath TCP connection */
#define IPPROTO_MPTCP IPPROTO_MPTCP
IPPROTO_MAX
};