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getaddrinfo (3)
  • getaddrinfo (3) ( Solaris man: Библиотечные вызовы )
  • >> getaddrinfo (3) ( FreeBSD man: Библиотечные вызовы )
  • getaddrinfo (3) ( Русские man: Библиотечные вызовы )
  • getaddrinfo (3) ( Linux man: Библиотечные вызовы )
  • getaddrinfo (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    getaddrinfo
    
     
    freeaddrinfo
    
     - socket address structure to host and service name
    
     
    

    SYNOPSIS

    Fd #include <sys/types.h> Fd #include <sys/socket.h> Fd #include <netdb.h> int Fo getaddrinfo Fa const char *hostname const char *servname Fa const struct addrinfo *hints struct addrinfo **res Fc Ft void freeaddrinfo (struct addrinfo *ai);
     

    DESCRIPTION

    The getaddrinfo ();
    function is used to get a list of IP addresses and port numbers for host Fa hostname and service Fa servname . It is a replacement for and provides more flexibility than the gethostbyname(3) and getservbyname(3) functions.

    The Fa hostname and Fa servname arguments are either pointers to NUL-terminated strings or the null pointer. An acceptable value for Fa hostname is either a valid host name or a numeric host address string consisting of a dotted decimal IPv4 address or an IPv6 address. The Fa servname is either a decimal port number or a service name listed in services(5). At least one of Fa hostname and Fa servname must be non-null.

    Fa hints is an optional pointer to a struct addrinfo as defined by Aq Pa netdb.h :

    struct addrinfo {
            int ai_flags;           /* input flags */
            int ai_family;          /* protocol family for socket */
            int ai_socktype;        /* socket type */
            int ai_protocol;        /* protocol for socket */
            socklen_t ai_addrlen;   /* length of socket-address */
            struct sockaddr *ai_addr; /* socket-address for socket */
            char *ai_canonname;     /* canonical name for service location */
            struct addrinfo *ai_next; /* pointer to next in list */
    };
    

    This structure can be used to provide hints concerning the type of socket that the caller supports or wishes to use. The caller can supply the following structure elements in Fa hints :

    Fa ai_family
    The protocol family that should be used. When Fa ai_family is set to PF_UNSPEC it means the caller will accept any protocol family supported by the operating system.
    Fa ai_socktype
    Denotes the type of socket that is wanted: SOCK_STREAM SOCK_DGRAM or SOCK_RAW When Fa ai_socktype is zero the caller will accept any socket type.
    Fa ai_protocol
    Indicates which transport protocol is desired, IPPROTO_UDP or IPPROTO_TCP If Fa ai_protocol is zero the caller will accept any protocol.
    Fa ai_flags
    The Fa ai_flags field to which the Fa hints parameter points shall be set to zero or be the bitwise-inclusive OR of one or more of the values AI_ADDRCONFIG AI_ALL AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV AI_PASSIVE and AI_V4MAPPED

    AI_ADDRCONFIG
    If the AI_ADDRCONFIG bit is set, IPv4 addresses shall be returned only if an IPv4 address is configured on the local system, and IPv6 addresses shall be returned only if an IPv6 address is configured on the local system.
    AI_ALL
    If the AI_ALL bit is set with the AI_V4MAPPED bit, then getaddrinfo ();
    shall return all matching IPv6 and IPv4 addresses. The AI_ALL bit without the AI_V4MAPPED bit is ignored.
    AI_CANONNAME
    If the AI_CANONNAME bit is set, a successful call to getaddrinfo ();
    will return a NUL-terminated string containing the canonical name of the specified hostname in the Fa ai_canonname element of the first addrinfo structure returned.
    AI_NUMERICHOST
    If the AI_NUMERICHOST bit is set, it indicates that Fa hostname should be treated as a numeric string defining an IPv4 or IPv6 address and no name resolution should be attempted.
    AI_NUMERICSERV
    If the AI_NUMERICSERV bit is set, then a non-null Fa servname string supplied shall be a numeric port string. Otherwise, an EAI_NONAME error shall be returned. This bit shall prevent any type of name resolution service (for example, NIS+) from being invoked.
    AI_PASSIVE
    If the AI_PASSIVE bit is set it indicates that the returned socket address structure is intended for use in a call to bind(2). In this case, if the Fa hostname argument is the null pointer, then the IP address portion of the socket address structure will be set to INADDR_ANY for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6 address.

    If the AI_PASSIVE bit is not set, the returned socket address structure will be ready for use in a call to connect(2) for a connection-oriented protocol or connect(2), sendto(2), or sendmsg(2) if a connectionless protocol was chosen. The IP address portion of the socket address structure will be set to the loopback address if Fa hostname is the null pointer and AI_PASSIVE is not set.

    AI_V4MAPPED
    If the AI_V4MAPPED flag is specified along with an Fa ai_family of AF_INET6 then getaddrinfo ();
    shall return IPv4-mapped IPv6 addresses on finding no matching IPv6 addresses ( Fa ai_addrlen shall be 16). The AI_V4MAPPED flag shall be ignored unless Fa ai_family equals AF_INET6

    All other elements of the addrinfo structure passed via Fa hints must be zero or the null pointer.

    If Fa hints is the null pointer, getaddrinfo ();
    behaves as if the caller provided a struct addrinfo with Fa ai_family set to PF_UNSPEC and all other elements set to zero or NULL

    After a successful call to getaddrinfo (,);
    Fa *res is a pointer to a linked list of one or more addrinfo structures. The list can be traversed by following the Fa ai_next pointer in each addrinfo structure until a null pointer is encountered. The three members Fa ai_family, Fa ai_socktype, and Fa ai_protocol in each returned addrinfo structure are suitable for a call to socket(2). For each addrinfo structure in the list, the Fa ai_addr member points to a filled-in socket address structure of length Fa ai_addrlen .

    This implementation of getaddrinfo ();
    allows numeric IPv6 address notation with scope identifier, as documented in chapter 11 of draft-ietf-ipv6-scoping-arch-02.txt. By appending the percent character and scope identifier to addresses, one can fill the sin6_scope_id field for addresses. This would make management of scoped addresses easier and allows cut-and-paste input of scoped addresses.

    At this moment the code supports only link-local addresses with the format. The scope identifier is hardcoded to the name of the hardware interface associated with the link Po such as ne0 Pc . An example is ``fe80::1%ne0 '' which means Do fe80::1 on the link associated with the ne0 interface Dc .

    The current implementation assumes a one-to-one relationship between the interface and link, which is not necessarily true from the specification.

    All of the information returned by getaddrinfo ();
    is dynamically allocated: the addrinfo structures themselves as well as the socket address structures and the canonical host name strings included in the addrinfo structures.

    Memory allocated for the dynamically allocated structures created by a successful call to getaddrinfo ();
    is released by the freeaddrinfo ();
    function. The Fa ai pointer should be a addrinfo structure created by a call to getaddrinfo (.);
     

    RETURN VALUES

    getaddrinfo ();
    returns zero on success or one of the error codes listed in gai_strerror3 if an error occurs.  

    EXAMPLES

    The following code tries to connect to ``www.kame.net '' service ``http '' via a stream socket. It loops through all the addresses available, regardless of address family. If the destination resolves to an IPv4 address, it will use an AF_INET socket. Similarly, if it resolves to IPv6, an AF_INET6 socket is used. Observe that there is no hardcoded reference to a particular address family. The code works even if getaddrinfo ();
    returns addresses that are not IPv4/v6.
    struct addrinfo hints, *res, *res0;
    int error;
    int s;
    const char *cause = NULL;
    
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = PF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    error = getaddrinfo("www.kame.net", "http", &hints, &res0);
    if (error) {
            errx(1, "%s", gai_strerror(error));
            /*NOTREACHED*/
    }
    s = -1;
    for (res = res0; res; res = res->ai_next) {
            s = socket(res->ai_family, res->ai_socktype,
                res->ai_protocol);
            if (s < 0) {
                    cause = "socket";
                    continue;
            }
    
            if (connect(s, res->ai_addr, res->ai_addrlen) < 0) {
                    cause = "connect";
                    close(s);
                    s = -1;
                    continue;
            }
    
            break;  /* okay we got one */
    }
    if (s < 0) {
            err(1, "%s", cause);
            /*NOTREACHED*/
    }
    freeaddrinfo(res0);
    

    The following example tries to open a wildcard listening socket onto service ``http '' for all the address families available.

    struct addrinfo hints, *res, *res0;
    int error;
    int s[MAXSOCK];
    int nsock;
    const char *cause = NULL;
    
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = PF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    error = getaddrinfo(NULL, "http", &hints, &res0);
    if (error) {
            errx(1, "%s", gai_strerror(error));
            /*NOTREACHED*/
    }
    nsock = 0;
    for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
            s[nsock] = socket(res->ai_family, res->ai_socktype,
                res->ai_protocol);
            if (s[nsock] < 0) {
                    cause = "socket";
                    continue;
            }
    
            if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) {
                    cause = "bind";
                    close(s[nsock]);
                    continue;
            }
            (void) listen(s[nsock], 5);
    
            nsock++;
    }
    if (nsock == 0) {
            err(1, "%s", cause);
            /*NOTREACHED*/
    }
    freeaddrinfo(res0);
    
     

    SEE ALSO

    bind(2), connect(2), send(2), socket(2), gai_strerror3, gethostbyname(3), getnameinfo(3), getservbyname(3), resolver(3), hosts(5), resolv.conf5, services(5), hostname(7), named(8)
    R. Gilligan S. Thomson J. Bound J. McCann W. Stevens Basic Socket Interface Extensions for IPv6 RFC 3493 February 2003
    S. Deering B. Haberman T. Jinmei E. Nordmark B. Zill "IPv6 Scoped Address Architecture" internet draft draft-ietf-ipv6-scoping-arch-02.txt work in progress material
    Craig Metz Protocol Independence Using the Sockets API "Proceedings of the freenix track: 2000 USENIX annual technical conference" June 2000
     

    STANDARDS

    The getaddrinfo ();
    function is defined by the St -p1003.1-2004 specification and documented in RFC 3493 ``Basic Socket Interface Extensions for IPv6''


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    EXAMPLES
    SEE ALSO
    STANDARDS


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