Socket structs

addrinfo

-----------
addrinfo
-----------
|
sockaddr
|

struct addrinfo 
{
  int ai_flags;          // AI_PASSIVE, AI_CANONNAME, etc.
  int ai_family;         // AF_INET, AF_INET6, AF_UNSPEC
  int ai_socktype;       // SOCK_STREAM, SOCK_DGRAM
  int ai_protocol;       // use 0 for "any"
  size_t ai_addrlen;     // size of ai_addr in bytes
  struct sockaddr *ai_addr; // struct sockaddr_in or _in6
  char *ai_canonname;    // full canonical hostname
  struct addrinfo *ai_next; // linked list, next node
};

Адреси

struct sockaddr {
  unsigned short sa_family;   // address family, AF_xxx
  char           sa_data[14]; // 14 bytes of protocol address
};

където

• sa_family е най-често - AF_INET за IPv4 или AF_INET6 за IPv6
• sa_data е дестинация и порт сокета

или

за IPv4

struct sockaddr_in {
    short int          sin_family;  // Address family, AF_INET
    unsigned short int sin_port;    // Port number
    struct in_addr     sin_addr;    // Internet address
    unsigned char      sin_zero[8]; // Same size as struct sockaddr
};

където

struct in_addr {
    uint32_t s_addr; // that's a 32-bit int (4 bytes)
};

за IPv6

struct sockaddr_in6 {
  u_int16_t       sin6_family;   // address family, AF_INET6
  u_int16_t       sin6_port;     // port number, Network Byte Order
  u_int32_t       sin6_flowinfo; // IPv6 flow information
  struct in6_addr sin6_addr;     // IPv6 address
  u_int32_t       sin6_scope_id; // Scope ID
};

struct in6_addr {
    unsigned char   s6_addr[16];   // IPv6 address
};

struct sockaddr_storage {
    sa_family_t ss_family;      // address family
    // all this is padding, implementation specific, ignore it:
    char      __ss_pad1[_SS_PAD1SIZE];
    int64_t   __ss_align;
    char      __ss_pad2[_SS_PAD2SIZE];
};