class Socket::AncillaryData

Socket::AncillaryData 表示 sendmsg 和 recvmsg 系统调用使用的辅助数据（控制信息）。它包含套接字的 family、控制消息 (cmsg) 的 level、cmsg 的 type 以及 cmsg 的 data。

公共类方法

Socket::AncillaryData.int(family, cmsg_level, cmsg_type, integer) → ancillarydata

源码

static VALUE
ancillary_s_int(VALUE klass, VALUE vfamily, VALUE vlevel, VALUE vtype, VALUE integer)
{
    int family = rsock_family_arg(vfamily);
    int level = rsock_level_arg(family, vlevel);
    int type = rsock_cmsg_type_arg(family, level, vtype);
    int i = NUM2INT(integer);
    return ancdata_new(family, level, type, rb_str_new((char*)&i, sizeof(i)));
}

创建一个新的 Socket::AncillaryData 对象，其中包含一个整数作为数据。

大小和字节序取决于主机。

require 'socket'

p Socket::AncillaryData.int(:UNIX, :SOCKET, :RIGHTS, STDERR.fileno)
#=> #<Socket::AncillaryData: UNIX SOCKET RIGHTS 2>

Socket::AncillaryData.ip_pktinfo(addr, ifindex) → ancdata

Socket::AncillaryData.ip_pktinfo(addr, ifindex, spec_dst) → ancdata

源码

static VALUE
ancillary_s_ip_pktinfo(int argc, VALUE *argv, VALUE self)
{
    VALUE v_addr, v_ifindex, v_spec_dst;
    unsigned int ifindex;
    struct sockaddr_in sa;
    struct in_pktinfo pktinfo;

    rb_scan_args(argc, argv, "21", &v_addr, &v_ifindex, &v_spec_dst);

    SockAddrStringValue(v_addr);
    ifindex = NUM2UINT(v_ifindex);
    if (NIL_P(v_spec_dst))
        v_spec_dst = v_addr;
    else
        SockAddrStringValue(v_spec_dst);

    memset(&pktinfo, 0, sizeof(pktinfo));

    memset(&sa, 0, sizeof(sa));
    if (RSTRING_LEN(v_addr) != sizeof(sa))
        rb_raise(rb_eArgError, "addr size different to AF_INET sockaddr");
    memcpy(&sa, RSTRING_PTR(v_addr), sizeof(sa));
    if (sa.sin_family != AF_INET)
        rb_raise(rb_eArgError, "addr is not AF_INET sockaddr");
    memcpy(&pktinfo.ipi_addr, &sa.sin_addr, sizeof(pktinfo.ipi_addr));

    pktinfo.ipi_ifindex = ifindex;

    memset(&sa, 0, sizeof(sa));
    if (RSTRING_LEN(v_spec_dst) != sizeof(sa))
        rb_raise(rb_eArgError, "spec_dat size different to AF_INET sockaddr");
    memcpy(&sa, RSTRING_PTR(v_spec_dst), sizeof(sa));
    if (sa.sin_family != AF_INET)
        rb_raise(rb_eArgError, "spec_dst is not AF_INET sockaddr");
    memcpy(&pktinfo.ipi_spec_dst, &sa.sin_addr, sizeof(pktinfo.ipi_spec_dst));

    return ancdata_new(AF_INET, IPPROTO_IP, IP_PKTINFO, rb_str_new((char *)&pktinfo, sizeof(pktinfo)));
}

返回 IP_PKTINFO 的新的辅助数据。

如果未给出 spec_dst，则使用 addr。

IP_PKTINFO 不是标准。

支持的平台：GNU/Linux

addr = Addrinfo.ip("127.0.0.1")
ifindex = 0
spec_dst = Addrinfo.ip("127.0.0.1")
p Socket::AncillaryData.ip_pktinfo(addr, ifindex, spec_dst)
#=> #<Socket::AncillaryData: INET IP PKTINFO 127.0.0.1 ifindex:0 spec_dst:127.0.0.1>

Socket::AncillaryData.ipv6_pktinfo(addr, ifindex) → ancdata

源码

static VALUE
ancillary_s_ipv6_pktinfo(VALUE self, VALUE v_addr, VALUE v_ifindex)
{
    unsigned int ifindex;
    struct sockaddr_in6 sa;
    struct in6_pktinfo pktinfo;

    SockAddrStringValue(v_addr);
    ifindex = NUM2UINT(v_ifindex);

    memset(&pktinfo, 0, sizeof(pktinfo));

    memset(&sa, 0, sizeof(sa));
    if (RSTRING_LEN(v_addr) != sizeof(sa))
        rb_raise(rb_eArgError, "addr size different to AF_INET6 sockaddr");
    memcpy(&sa, RSTRING_PTR(v_addr), sizeof(sa));
    if (sa.sin6_family != AF_INET6)
        rb_raise(rb_eArgError, "addr is not AF_INET6 sockaddr");
    memcpy(&pktinfo.ipi6_addr, &sa.sin6_addr, sizeof(pktinfo.ipi6_addr));

    pktinfo.ipi6_ifindex = ifindex;

    return ancdata_new(AF_INET6, IPPROTO_IPV6, IPV6_PKTINFO, rb_str_new((char *)&pktinfo, sizeof(pktinfo)));
}

返回 IPV6_PKTINFO 的新的辅助数据。

IPV6_PKTINFO 由 RFC 3542 定义。

addr = Addrinfo.ip("::1")
ifindex = 0
p Socket::AncillaryData.ipv6_pktinfo(addr, ifindex)
#=> #<Socket::AncillaryData: INET6 IPV6 PKTINFO ::1 ifindex:0>

Socket::AncillaryData.new(family, cmsg_level, cmsg_type, cmsg_data) → ancillarydata

源码

static VALUE
ancillary_initialize(VALUE self, VALUE vfamily, VALUE vlevel, VALUE vtype, VALUE data)
{
    int family = rsock_family_arg(vfamily);
    int level = rsock_level_arg(family, vlevel);
    int type = rsock_cmsg_type_arg(family, level, vtype);
    StringValue(data);
    rb_ivar_set(self, rb_intern("family"), INT2NUM(family));
    rb_ivar_set(self, rb_intern("level"), INT2NUM(level));
    rb_ivar_set(self, rb_intern("type"), INT2NUM(type));
    rb_ivar_set(self, rb_intern("data"), data);
    return self;
}

family 应该是一个整数、字符串或符号。

Socket::AF_INET, “AF_INET”, “INET”, :AF_INET, :INET
Socket::AF_UNIX, “AF_UNIX”, “UNIX”, :AF_UNIX, :UNIX
等等。

cmsg_level 应该是一个整数、字符串或符号。

Socket::SOL_SOCKET, “SOL_SOCKET”, “SOCKET”, :SOL_SOCKET 和 :SOCKET
Socket::IPPROTO_IP, “IP” 和 :IP
Socket::IPPROTO_IPV6, “IPV6” 和 :IPV6
Socket::IPPROTO_TCP, “TCP” 和 :TCP
等等。

cmsg_type 应该是一个整数、字符串或符号。如果指定了字符串/符号，则根据 cmsg_level 解释它。

Socket::SCM_RIGHTS, “SCM_RIGHTS”, “RIGHTS”, :SCM_RIGHTS, :RIGHTS for SOL_SOCKET
Socket::IP_RECVTTL, “RECVTTL” 和 :RECVTTL for IPPROTO_IP
Socket::IPV6_PKTINFO, “PKTINFO” 和 :PKTINFO for IPPROTO_IPV6
等等。

cmsg_data 应该是一个字符串。

p Socket::AncillaryData.new(:INET, :TCP, :NODELAY, "")
#=> #<Socket::AncillaryData: INET TCP NODELAY "">

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "")
#=> #<Socket::AncillaryData: INET6 IPV6 PKTINFO "">

Socket::AncillaryData.unix_rights(io1, io2, ...) → ancillarydata

源码

static VALUE
ancillary_s_unix_rights(int argc, VALUE *argv, VALUE klass)
{
    VALUE result, str, ary;
    int i;

    ary = rb_ary_new();

    for (i = 0 ; i < argc; i++) {
        VALUE obj = argv[i];
        if (!RB_TYPE_P(obj, T_FILE)) {
            rb_raise(rb_eTypeError, "IO expected");
        }
        rb_ary_push(ary, obj);
    }

    str = rb_str_buf_new(sizeof(int) * argc);

    for (i = 0 ; i < argc; i++) {
        VALUE obj = RARRAY_AREF(ary, i);
        rb_io_t *fptr;
        int fd;
        GetOpenFile(obj, fptr);
        fd = fptr->fd;
        rb_str_buf_cat(str, (char *)&fd, sizeof(int));
    }

    result = ancdata_new(AF_UNIX, SOL_SOCKET, SCM_RIGHTS, str);
    rb_ivar_set(result, rb_intern("unix_rights"), ary);
    return result;
}

创建一个新的 Socket::AncillaryData 对象，其中包含文件描述符作为数据。

p Socket::AncillaryData.unix_rights(STDERR)
#=> #<Socket::AncillaryData: UNIX SOCKET RIGHTS 2>

公共实例方法

cmsg_is?(level, type) → true or false

源码

static VALUE
ancillary_cmsg_is_p(VALUE self, VALUE vlevel, VALUE vtype)
{
    int family = ancillary_family(self);
    int level = rsock_level_arg(family, vlevel);
    int type = rsock_cmsg_type_arg(family, level, vtype);

    if (ancillary_level(self) == level &&
        ancillary_type(self) == type)
        return Qtrue;
    else
        return Qfalse;
}

测试 ancillarydata 的级别和类型。

ancdata = Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "")
ancdata.cmsg_is?(Socket::IPPROTO_IPV6, Socket::IPV6_PKTINFO) #=> true
ancdata.cmsg_is?(:IPV6, :PKTINFO)       #=> true
ancdata.cmsg_is?(:IP, :PKTINFO)         #=> false
ancdata.cmsg_is?(:SOCKET, :RIGHTS)      #=> false

data → string

源码

static VALUE
ancillary_data(VALUE self)
{
    VALUE v = rb_attr_get(self, rb_intern("data"));
    StringValue(v);
    return v;
}

返回 cmsg 数据作为字符串。

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "").data
#=> ""

family → integer

源码

static VALUE
ancillary_family_m(VALUE self)
{
    return INT2NUM(ancillary_family(self));
}

返回套接字族作为整数。

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "").family
#=> 10

inspect → string

源码

static VALUE
ancillary_inspect(VALUE self)
{
    VALUE ret;
    int family, level, type;
    VALUE data;
    ID family_id, level_id, type_id;
    VALUE vtype;
    int inspected;

    family = ancillary_family(self);
    level = ancillary_level(self);
    type = ancillary_type(self);
    data = ancillary_data(self);

    ret = rb_sprintf("#<%s:", rb_obj_classname(self));

    family_id = rsock_intern_family_noprefix(family);
    if (family_id)
        rb_str_catf(ret, " %s", rb_id2name(family_id));
    else
        rb_str_catf(ret, " family:%d", family);

    if (level == SOL_SOCKET) {
        rb_str_cat2(ret, " SOCKET");

        type_id = rsock_intern_scm_optname(type);
        if (type_id)
            rb_str_catf(ret, " %s", rb_id2name(type_id));
        else
            rb_str_catf(ret, " cmsg_type:%d", type);
    }
    else if (IS_IP_FAMILY(family)) {
        level_id = rsock_intern_iplevel(level);
        if (level_id)
            rb_str_catf(ret, " %s", rb_id2name(level_id));
        else
            rb_str_catf(ret, " cmsg_level:%d", level);

        vtype = ip_cmsg_type_to_sym(level, type);
        if (SYMBOL_P(vtype))
            rb_str_catf(ret, " %"PRIsVALUE, rb_sym2str(vtype));
        else
            rb_str_catf(ret, " cmsg_type:%d", type);
    }
    else {
        rb_str_catf(ret, " cmsg_level:%d", level);
        rb_str_catf(ret, " cmsg_type:%d", type);
    }

    inspected = 0;

    if (level == SOL_SOCKET)
        family = AF_UNSPEC;

    switch (family) {
      case AF_UNSPEC:
        switch (level) {
#        if defined(SOL_SOCKET)
          case SOL_SOCKET:
            switch (type) {
#            if defined(SCM_TIMESTAMP) /* GNU/Linux, FreeBSD, NetBSD, OpenBSD, MacOS X, Solaris */
              case SCM_TIMESTAMP: inspected = inspect_timeval_as_abstime(level, type, data, ret); break;
#            endif
#            if defined(SCM_TIMESTAMPNS) /* GNU/Linux */
              case SCM_TIMESTAMPNS: inspected = inspect_timespec_as_abstime(level, type, data, ret); break;
#            endif
#            if defined(SCM_BINTIME) /* FreeBSD */
              case SCM_BINTIME: inspected = inspect_bintime_as_abstime(level, type, data, ret); break;
#            endif
#            if defined(SCM_RIGHTS) /* 4.4BSD */
              case SCM_RIGHTS: inspected = anc_inspect_socket_rights(level, type, data, ret); break;
#            endif
#            if defined(SCM_CREDENTIALS) /* GNU/Linux */
              case SCM_CREDENTIALS: inspected = anc_inspect_passcred_credentials(level, type, data, ret); break;
#            endif
#            if defined(INSPECT_SCM_CREDS) /* NetBSD */
              case SCM_CREDS: inspected = anc_inspect_socket_creds(level, type, data, ret); break;
#            endif
            }
            break;
#        endif
        }
        break;

      case AF_INET:
#ifdef INET6
      case AF_INET6:
#endif
        switch (level) {
#        if defined(IPPROTO_IP)
          case IPPROTO_IP:
            switch (type) {
#            if defined(IP_RECVDSTADDR) /* 4.4BSD */
              case IP_RECVDSTADDR: inspected = anc_inspect_ip_recvdstaddr(level, type, data, ret); break;
#            endif
#            if defined(IP_PKTINFO) && defined(HAVE_STRUCT_IN_PKTINFO_IPI_SPEC_DST) /* GNU/Linux */
              case IP_PKTINFO: inspected = anc_inspect_ip_pktinfo(level, type, data, ret); break;
#            endif
            }
            break;
#        endif

#        if defined(IPPROTO_IPV6)
          case IPPROTO_IPV6:
            switch (type) {
#            if defined(IPV6_PKTINFO) && defined(HAVE_TYPE_STRUCT_IN6_PKTINFO) /* RFC 3542 */
              case IPV6_PKTINFO: inspected = anc_inspect_ipv6_pktinfo(level, type, data, ret); break;
#            endif
            }
            break;
#        endif
        }
        break;
    }

    if (!inspected) {
        rb_str_cat2(ret, " ");
        rb_str_append(ret, rb_str_dump(data));
    }

    rb_str_cat2(ret, ">");

    return ret;
}

返回一个以人类可读形式显示 ancillarydata 的字符串。

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "").inspect
#=> "#<Socket::AncillaryData: INET6 IPV6 PKTINFO \"\">"

int → integer

源码

static VALUE
ancillary_int(VALUE self)
{
    VALUE data;
    int i;
    data = ancillary_data(self);
    if (RSTRING_LEN(data) != sizeof(int))
        rb_raise(rb_eTypeError, "size differ.  expected as sizeof(int)=%d but %ld", (int)sizeof(int), (long)RSTRING_LEN(data));
    memcpy((char*)&i, RSTRING_PTR(data), sizeof(int));
    return INT2NUM(i);
}

以整数形式返回 ancillarydata 中的数据。

大小和字节序取决于主机。

ancdata = Socket::AncillaryData.int(:UNIX, :SOCKET, :RIGHTS, STDERR.fileno)
p ancdata.int #=> 2

ip_pktinfo → [addr, ifindex, spec_dst]

源码

static VALUE
ancillary_ip_pktinfo(VALUE self)
{
    int level, type;
    VALUE data;
    struct in_pktinfo pktinfo;
    struct sockaddr_in sa;
    VALUE v_spec_dst, v_addr;

    level = ancillary_level(self);
    type = ancillary_type(self);
    data = ancillary_data(self);

    if (level != IPPROTO_IP || type != IP_PKTINFO ||
        RSTRING_LEN(data) != sizeof(struct in_pktinfo)) {
        rb_raise(rb_eTypeError, "IP_PKTINFO ancillary data expected");
    }

    memcpy(&pktinfo, RSTRING_PTR(data), sizeof(struct in_pktinfo));
    memset(&sa, 0, sizeof(sa));

    sa.sin_family = AF_INET;
    memcpy(&sa.sin_addr, &pktinfo.ipi_addr, sizeof(sa.sin_addr));
    v_addr = rsock_addrinfo_new((struct sockaddr *)&sa, sizeof(sa), PF_INET, 0, 0, Qnil, Qnil);

    sa.sin_family = AF_INET;
    memcpy(&sa.sin_addr, &pktinfo.ipi_spec_dst, sizeof(sa.sin_addr));
    v_spec_dst = rsock_addrinfo_new((struct sockaddr *)&sa, sizeof(sa), PF_INET, 0, 0, Qnil, Qnil);

    return rb_ary_new3(3, v_addr, UINT2NUM(pktinfo.ipi_ifindex), v_spec_dst);
}

从 IP_PKTINFO 辅助数据中提取 addr、ifindex 和 spec_dst。

IP_PKTINFO 不是标准。

支持的平台：GNU/Linux

addr = Addrinfo.ip("127.0.0.1")
ifindex = 0
spec_dest = Addrinfo.ip("127.0.0.1")
ancdata = Socket::AncillaryData.ip_pktinfo(addr, ifindex, spec_dest)
p ancdata.ip_pktinfo
#=> [#<Addrinfo: 127.0.0.1>, 0, #<Addrinfo: 127.0.0.1>]

ipv6_pktinfo → [addr, ifindex]

源码

static VALUE
ancillary_ipv6_pktinfo(VALUE self)
{
    struct in6_pktinfo pktinfo;
    struct sockaddr_in6 sa;
    VALUE v_addr;

    extract_ipv6_pktinfo(self, &pktinfo, &sa);
    v_addr = rsock_addrinfo_new((struct sockaddr *)&sa, (socklen_t)sizeof(sa), PF_INET6, 0, 0, Qnil, Qnil);
    return rb_ary_new3(2, v_addr, UINT2NUM(pktinfo.ipi6_ifindex));
}

从 IPV6_PKTINFO 辅助数据中提取 addr 和 ifindex。

IPV6_PKTINFO 由 RFC 3542 定义。

addr = Addrinfo.ip("::1")
ifindex = 0
ancdata = Socket::AncillaryData.ipv6_pktinfo(addr, ifindex)
p ancdata.ipv6_pktinfo #=> [#<Addrinfo: ::1>, 0]

ipv6_pktinfo_addr → addr

源码

static VALUE
ancillary_ipv6_pktinfo_addr(VALUE self)
{
    struct in6_pktinfo pktinfo;
    struct sockaddr_in6 sa;
    extract_ipv6_pktinfo(self, &pktinfo, &sa);
    return rsock_addrinfo_new((struct sockaddr *)&sa, (socklen_t)sizeof(sa), PF_INET6, 0, 0, Qnil, Qnil);
}

从 IPV6_PKTINFO 辅助数据中提取 addr。

IPV6_PKTINFO 由 RFC 3542 定义。

addr = Addrinfo.ip("::1")
ifindex = 0
ancdata = Socket::AncillaryData.ipv6_pktinfo(addr, ifindex)
p ancdata.ipv6_pktinfo_addr #=> #<Addrinfo: ::1>

ipv6_pktinfo_ifindex → addr

源码

static VALUE
ancillary_ipv6_pktinfo_ifindex(VALUE self)
{
    struct in6_pktinfo pktinfo;
    struct sockaddr_in6 sa;
    extract_ipv6_pktinfo(self, &pktinfo, &sa);
    return UINT2NUM(pktinfo.ipi6_ifindex);
}

从 IPV6_PKTINFO 辅助数据中提取 ifindex。

IPV6_PKTINFO 由 RFC 3542 定义。

addr = Addrinfo.ip("::1")
ifindex = 0
ancdata = Socket::AncillaryData.ipv6_pktinfo(addr, ifindex)
p ancdata.ipv6_pktinfo_ifindex #=> 0

level → integer

源码

static VALUE
ancillary_level_m(VALUE self)
{
    return INT2NUM(ancillary_level(self));
}

返回 cmsg 级别作为整数。

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "").level
#=> 41

timestamp → time

源码

static VALUE
ancillary_timestamp(VALUE self)
{
    int level, type;
    VALUE data;
    VALUE result = Qnil;

    level = ancillary_level(self);
    type = ancillary_type(self);
    data = ancillary_data(self);

# ifdef SCM_TIMESTAMP
    if (level == SOL_SOCKET && type == SCM_TIMESTAMP &&
        RSTRING_LEN(data) == sizeof(struct timeval)) {
        struct timeval tv;
        memcpy((char*)&tv, RSTRING_PTR(data), sizeof(tv));
        result = rb_time_new(tv.tv_sec, tv.tv_usec);
    }
# endif

# ifdef SCM_TIMESTAMPNS
    if (level == SOL_SOCKET && type == SCM_TIMESTAMPNS &&
        RSTRING_LEN(data) == sizeof(struct timespec)) {
        struct timespec ts;
        memcpy((char*)&ts, RSTRING_PTR(data), sizeof(ts));
        result = rb_time_nano_new(ts.tv_sec, ts.tv_nsec);
    }
# endif

#define add(x,y) (rb_funcall((x), '+', 1, (y)))
#define mul(x,y) (rb_funcall((x), '*', 1, (y)))
#define quo(x,y) (rb_funcall((x), rb_intern("quo"), 1, (y)))

# ifdef SCM_BINTIME
    if (level == SOL_SOCKET && type == SCM_BINTIME &&
        RSTRING_LEN(data) == sizeof(struct bintime)) {
        struct bintime bt;
        VALUE d, timev;
        memcpy((char*)&bt, RSTRING_PTR(data), sizeof(bt));
        d = ULL2NUM(0x100000000ULL);
        d = mul(d,d);
        timev = add(TIMET2NUM(bt.sec), quo(ULL2NUM(bt.frac), d));
        result = rb_time_num_new(timev, Qnil);
    }
# endif

    if (result == Qnil)
        rb_raise(rb_eTypeError, "timestamp ancillary data expected");

    return result;
}

返回时间戳作为时间对象。

ancillarydata 应该是以下类型之一

SOL_SOCKET/SCM_TIMESTAMP (微秒) GNU/Linux, FreeBSD, NetBSD, OpenBSD, Solaris, MacOS X
SOL_SOCKET/SCM_TIMESTAMPNS (纳秒) GNU/Linux

SOL_SOCKET/SCM_BINTIME (2**(-64) 秒) FreeBSD

Addrinfo.udp(“127.0.0.1”, 0).bind {|s1|

Addrinfo.udp("127.0.0.1", 0).bind {|s2|
  s1.setsockopt(:SOCKET, :TIMESTAMP, true)
  s2.send "a", 0, s1.local_address
  ctl = s1.recvmsg.last
  p ctl    #=> #<Socket::AncillaryData: INET SOCKET TIMESTAMP 2009-02-24 17:35:46.775581>
  t = ctl.timestamp
  p t      #=> 2009-02-24 17:35:46 +0900
  p t.usec #=> 775581
  p t.nsec #=> 775581000
}

}

type → integer

源码

static VALUE
ancillary_type_m(VALUE self)
{
    return INT2NUM(ancillary_type(self));
}

返回 cmsg 类型作为整数。

p Socket::AncillaryData.new(:INET6, :IPV6, :PKTINFO, "").type
#=> 2

unix_rights → array-of-IOs or nil

源码

static VALUE
ancillary_unix_rights(VALUE self)
{
    int level, type;

    level = ancillary_level(self);
    type = ancillary_type(self);

    if (level != SOL_SOCKET || type != SCM_RIGHTS)
        rb_raise(rb_eTypeError, "SCM_RIGHTS ancillary data expected");

    return rb_attr_get(self, rb_intern("unix_rights"));
}

在 UNIX 域套接字中，返回 SCM_RIGHTS 控制消息的 IO 对象数组。

数组中 IO 对象的类是 IO 或 Socket。

该数组在 ancillarydata 实例化时附加到它。例如，当接收到 SCM_RIGHTS 控制消息并且给出了 :scm_rights=>true 选项时，BasicSocket#recvmsg 会附加该数组。

# recvmsg needs :scm_rights=>true for unix_rights
s1, s2 = UNIXSocket.pair
p s1                                         #=> #<UNIXSocket:fd 3>
s1.sendmsg "stdin and a socket", 0, nil, Socket::AncillaryData.unix_rights(STDIN, s1)
_, _, _, ctl = s2.recvmsg(:scm_rights=>true)
p ctl                                        #=> #<Socket::AncillaryData: UNIX SOCKET RIGHTS 6 7>
p ctl.unix_rights                            #=> [#<IO:fd 6>, #<Socket:fd 7>]
p File.identical?(STDIN, ctl.unix_rights[0]) #=> true
p File.identical?(s1, ctl.unix_rights[1])    #=> true

# If :scm_rights=>true is not given, unix_rights returns nil
s1, s2 = UNIXSocket.pair
s1.sendmsg "stdin and a socket", 0, nil, Socket::AncillaryData.unix_rights(STDIN, s1)
_, _, _, ctl = s2.recvmsg
p ctl #=> #<Socket::AncillaryData: UNIX SOCKET RIGHTS 6 7>
p ctl.unix_rights #=> nil