class BasicSocket

Gets the global do_not_reverse_lookup flag.

BasicSocket.do_not_reverse_lookup  #=> false

static VALUE
bsock_do_not_rev_lookup(VALUE _)
{
    return rsock_do_not_reverse_lookup?Qtrue:Qfalse;
}

Sets the global do_not_reverse_lookup flag.

The flag is used for initial value of do_not_reverse_lookup for each socket.

s1 = TCPSocket.new("localhost", 80)
p s1.do_not_reverse_lookup                 #=> true
BasicSocket.do_not_reverse_lookup = false
s2 = TCPSocket.new("localhost", 80)
p s2.do_not_reverse_lookup                 #=> false
p s1.do_not_reverse_lookup                 #=> true

static VALUE
bsock_do_not_rev_lookup_set(VALUE self, VALUE val)
{
    rsock_do_not_reverse_lookup = RTEST(val);
    return val;
}

Returns a socket object which contains the file descriptor, fd.

# If invoked by inetd, STDIN/STDOUT/STDERR is a socket.
STDIN_SOCK = Socket.for_fd(STDIN.fileno)
p STDIN_SOCK.remote_address

static VALUE
bsock_s_for_fd(VALUE klass, VALUE _descriptor)
{
    rb_io_t *fptr;

    int descriptor = RB_NUM2INT(_descriptor);
    rsock_validate_descriptor(descriptor);

    VALUE sock = rsock_init_sock(rb_obj_alloc(klass), descriptor);

    GetOpenFile(sock, fptr);

    return sock;
}

Disallows further read using shutdown system call.

s1, s2 = UNIXSocket.pair
s1.close_read
s2.puts #=> Broken pipe (Errno::EPIPE)

static VALUE
bsock_close_read(VALUE sock)
{
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    shutdown(fptr->fd, 0);
    if (!(fptr->mode & FMODE_WRITABLE)) {
        return rb_io_close(sock);
    }
    fptr->mode &= ~FMODE_READABLE;

    return Qnil;
}

Disallows further write using shutdown system call.

UNIXSocket.pair {|s1, s2|
  s1.print "ping"
  s1.close_write
  p s2.read        #=> "ping"
  s2.print "pong"
  s2.close
  p s1.read        #=> "pong"
}

static VALUE
bsock_close_write(VALUE sock)
{
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (!(fptr->mode & FMODE_READABLE)) {
        return rb_io_close(sock);
    }
    shutdown(fptr->fd, 1);
    fptr->mode &= ~FMODE_WRITABLE;

    return Qnil;
}

Returns an address of the socket suitable for connect in the local machine.

This method returns self.local_address, except following condition.

• IPv4 unspecified address (0.0.0.0) is replaced by IPv4 loopback address (127.0.0.1).

• IPv6 unspecified address (::) is replaced by IPv6 loopback address (::1).

If the local address is not suitable for connect, SocketError is raised. IPv4 and IPv6 address which port is 0 is not suitable for connect. Unix domain socket which has no path is not suitable for connect.

Addrinfo.tcp("0.0.0.0", 0).listen {|serv|
  p serv.connect_address #=> #<Addrinfo: 127.0.0.1:53660 TCP>
  serv.connect_address.connect {|c|
    s, _ = serv.accept
    p [c, s] #=> [#<Socket:fd 4>, #<Socket:fd 6>]
  }
}

# File ext/socket/lib/socket.rb, line 255
def connect_address
  addr = local_address
  afamily = addr.afamily
  if afamily == Socket::AF_INET
    raise SocketError, "unbound IPv4 socket" if addr.ip_port == 0
    if addr.ip_address == "0.0.0.0"
      addr = Addrinfo.new(["AF_INET", addr.ip_port, nil, "127.0.0.1"], addr.pfamily, addr.socktype, addr.protocol)
    end
  elsif defined?(Socket::AF_INET6) && afamily == Socket::AF_INET6
    raise SocketError, "unbound IPv6 socket" if addr.ip_port == 0
    if addr.ip_address == "::"
      addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
    elsif addr.ip_address == "0.0.0.0" # MacOS X 10.4 returns "a.b.c.d" for IPv4-mapped IPv6 address.
      addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
    elsif addr.ip_address == "::ffff:0.0.0.0" # MacOS X 10.6 returns "::ffff:a.b.c.d" for IPv4-mapped IPv6 address.
      addr = Addrinfo.new(["AF_INET6", addr.ip_port, nil, "::1"], addr.pfamily, addr.socktype, addr.protocol)
    end
  elsif defined?(Socket::AF_UNIX) && afamily == Socket::AF_UNIX
    raise SocketError, "unbound Unix socket" if addr.unix_path == ""
  end
  addr
end

Gets the do_not_reverse_lookup flag of basicsocket.

require 'socket'

BasicSocket.do_not_reverse_lookup = false
TCPSocket.open("www.ruby-lang.org", 80) {|sock|
  p sock.do_not_reverse_lookup      #=> false
}
BasicSocket.do_not_reverse_lookup = true
TCPSocket.open("www.ruby-lang.org", 80) {|sock|
  p sock.do_not_reverse_lookup      #=> true
}

static VALUE
bsock_do_not_reverse_lookup(VALUE sock)
{
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    return (fptr->mode & FMODE_NOREVLOOKUP) ? Qtrue : Qfalse;
}

Sets the do_not_reverse_lookup flag of basicsocket.

TCPSocket.open("www.ruby-lang.org", 80) {|sock|
  p sock.do_not_reverse_lookup       #=> true
  p sock.peeraddr                    #=> ["AF_INET", 80, "221.186.184.68", "221.186.184.68"]
  sock.do_not_reverse_lookup = false
  p sock.peeraddr                    #=> ["AF_INET", 80, "carbon.ruby-lang.org", "54.163.249.195"]
}

static VALUE
bsock_do_not_reverse_lookup_set(VALUE sock, VALUE state)
{
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (RTEST(state)) {
        fptr->mode |= FMODE_NOREVLOOKUP;
    }
    else {
        fptr->mode &= ~FMODE_NOREVLOOKUP;
    }
    return sock;
}

Returns the user and group on the peer of the UNIX socket. The result is a two element array which contains the effective uid and the effective gid.

Socket.unix_server_loop("/tmp/sock") {|s|
  begin
    euid, egid = s.getpeereid

    # Check the connected client is myself or not.
    next if euid != Process.uid

    # do something about my resource.

  ensure
    s.close
  end
}

static VALUE
bsock_getpeereid(VALUE self)
{
#if defined(HAVE_GETPEEREID)
    rb_io_t *fptr;
    uid_t euid;
    gid_t egid;
    GetOpenFile(self, fptr);
    if (getpeereid(fptr->fd, &euid, &egid) == -1)
        rb_sys_fail("getpeereid(3)");
    return rb_assoc_new(UIDT2NUM(euid), GIDT2NUM(egid));
#elif defined(SO_PEERCRED) /* GNU/Linux */
    rb_io_t *fptr;
    struct ucred cred;
    socklen_t len = sizeof(cred);
    GetOpenFile(self, fptr);
    if (getsockopt(fptr->fd, SOL_SOCKET, SO_PEERCRED, &cred, &len) == -1)
        rb_sys_fail("getsockopt(SO_PEERCRED)");
    return rb_assoc_new(UIDT2NUM(cred.uid), GIDT2NUM(cred.gid));
#elif defined(HAVE_GETPEERUCRED) /* Solaris */
    rb_io_t *fptr;
    ucred_t *uc = NULL;
    VALUE ret;
    GetOpenFile(self, fptr);
    if (getpeerucred(fptr->fd, &uc) == -1)
        rb_sys_fail("getpeerucred(3C)");
    ret = rb_assoc_new(UIDT2NUM(ucred_geteuid(uc)), GIDT2NUM(ucred_getegid(uc)));
    ucred_free(uc);
    return ret;
#endif
}

Returns the remote address of the socket as a sockaddr string.

TCPServer.open("127.0.0.1", 1440) {|serv|
  c = TCPSocket.new("127.0.0.1", 1440)
  s = serv.accept
  p s.getpeername #=> "\x02\x00\x82u\x7F\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00"
}

If Addrinfo object is preferred over the binary string, use BasicSocket#remote_address.

static VALUE
bsock_getpeername(VALUE sock)
{
    union_sockaddr buf;
    socklen_t len = (socklen_t)sizeof buf;
    socklen_t len0 = len;
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (getpeername(fptr->fd, &buf.addr, &len) < 0)
        rb_sys_fail("getpeername(2)");
    if (len0 < len) len = len0;
    return rb_str_new((char*)&buf, len);
}

Returns the local address of the socket as a sockaddr string.

TCPServer.open("127.0.0.1", 15120) {|serv|
  p serv.getsockname #=> "\x02\x00;\x10\x7F\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00"
}

If Addrinfo object is preferred over the binary string, use BasicSocket#local_address.

static VALUE
bsock_getsockname(VALUE sock)
{
    union_sockaddr buf;
    socklen_t len = (socklen_t)sizeof buf;
    socklen_t len0 = len;
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (getsockname(fptr->fd, &buf.addr, &len) < 0)
        rb_sys_fail("getsockname(2)");
    if (len0 < len) len = len0;
    return rb_str_new((char*)&buf, len);
}

Gets a socket option. These are protocol and system specific, see your local system documentation for details. The option is returned as a Socket::Option object.

Parameters¶ ↑

• level is an integer, usually one of the SOL_ constants such as Socket::SOL_SOCKET, or a protocol level. A string or symbol of the name, possibly without prefix, is also accepted.

• optname is an integer, usually one of the SO_ constants, such as Socket::SO_REUSEADDR. A string or symbol of the name, possibly without prefix, is also accepted.

Examples¶ ↑

Some socket options are integers with boolean values, in this case getsockopt could be called like this:

reuseaddr = sock.getsockopt(:SOCKET, :REUSEADDR).bool

optval = sock.getsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR)
optval = optval.unpack "i"
reuseaddr = optval[0] == 0 ? false : true

Some socket options are integers with numeric values, in this case getsockopt could be called like this:

ipttl = sock.getsockopt(:IP, :TTL).int

optval = sock.getsockopt(Socket::IPPROTO_IP, Socket::IP_TTL)
ipttl = optval.unpack1("i")

Option values may be structs. Decoding them can be complex as it involves examining your system headers to determine the correct definition. An example is a +struct linger+, which may be defined in your system headers as:

struct linger {
  int l_onoff;
  int l_linger;
};

In this case getsockopt could be called like this:

# Socket::Option knows linger structure.
onoff, linger = sock.getsockopt(:SOCKET, :LINGER).linger

optval =  sock.getsockopt(Socket::SOL_SOCKET, Socket::SO_LINGER)
onoff, linger = optval.unpack "ii"
onoff = onoff == 0 ? false : true

static VALUE
bsock_getsockopt(VALUE sock, VALUE lev, VALUE optname)
{
    int level, option;
    socklen_t len;
    char *buf;
    rb_io_t *fptr;
    int family;

    GetOpenFile(sock, fptr);
    family = rsock_getfamily(fptr);
    level = rsock_level_arg(family, lev);
    option = rsock_optname_arg(family, level, optname);
    len = 256;
#ifdef _AIX
    switch (option) {
      case SO_DEBUG:
      case SO_REUSEADDR:
      case SO_KEEPALIVE:
      case SO_DONTROUTE:
      case SO_BROADCAST:
      case SO_OOBINLINE:
        /* AIX doesn't set len for boolean options */
        len = sizeof(int);
    }
#endif
    buf = ALLOCA_N(char,len);

    rb_io_check_closed(fptr);

    if (getsockopt(fptr->fd, level, option, buf, &len) < 0)
        rsock_sys_fail_path("getsockopt(2)", fptr->pathv);

    return rsock_sockopt_new(family, level, option, rb_str_new(buf, len));
}

Returns an Addrinfo object for local address obtained by getsockname.

Note that addrinfo.protocol is filled by 0.

TCPSocket.open("www.ruby-lang.org", 80) {|s|
  p s.local_address #=> #<Addrinfo: 192.168.0.129:36873 TCP>
}

TCPServer.open("127.0.0.1", 1512) {|serv|
  p serv.local_address #=> #<Addrinfo: 127.0.0.1:1512 TCP>
}

static VALUE
bsock_local_address(VALUE sock)
{
    union_sockaddr buf;
    socklen_t len = (socklen_t)sizeof buf;
    socklen_t len0 = len;
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (getsockname(fptr->fd, &buf.addr, &len) < 0)
        rb_sys_fail("getsockname(2)");
    if (len0 < len) len = len0;
    return rsock_fd_socket_addrinfo(fptr->fd, &buf.addr, len);
}

Receives a message.

maxlen is the maximum number of bytes to receive.

flags should be a bitwise OR of Socket::MSG_* constants.

outbuf will contain only the received data after the method call even if it is not empty at the beginning.

UNIXSocket.pair {|s1, s2|
  s1.puts "Hello World"
  p s2.recv(4)                     #=> "Hell"
  p s2.recv(4, Socket::MSG_PEEK)   #=> "o Wo"
  p s2.recv(4)                     #=> "o Wo"
  p s2.recv(10)                    #=> "rld\n"
}

static VALUE
bsock_recv(int argc, VALUE *argv, VALUE sock)
{
    return rsock_s_recvfrom(sock, argc, argv, RECV_RECV);
}

Receives up to maxlen bytes from socket using recvfrom(2) after O_NONBLOCK is set for the underlying file descriptor. flags is zero or more of the MSG_ options. The result, mesg, is the data received.

When recvfrom(2) returns 0, Socket#recv_nonblock returns nil. In most cases it means the connection was closed, but for UDP connections it may mean an empty packet was received, as the underlying API makes it impossible to distinguish these two cases.

Parameters¶ ↑

• maxlen - the number of bytes to receive from the socket

• flags - zero or more of the MSG_ options

• buf - destination String buffer

• options - keyword hash, supporting ‘exception: false`

Example¶ ↑

serv = TCPServer.new("127.0.0.1", 0)
af, port, host, addr = serv.addr
c = TCPSocket.new(addr, port)
s = serv.accept
c.send "aaa", 0
begin # emulate blocking recv.
  p s.recv_nonblock(10) #=> "aaa"
rescue IO::WaitReadable
  IO.select([s])
  retry
end

Refer to Socket#recvfrom for the exceptions that may be thrown if the call to recv_nonblock fails.

BasicSocket#recv_nonblock may raise any error corresponding to recvfrom(2) failure, including Errno::EWOULDBLOCK.

If the exception is Errno::EWOULDBLOCK or Errno::EAGAIN, it is extended by IO::WaitReadable. So IO::WaitReadable can be used to rescue the exceptions for retrying recv_nonblock.

By specifying a keyword argument exception to false, you can indicate that recv_nonblock should not raise an IO::WaitReadable exception, but return the symbol :wait_readable instead.

See¶ ↑

• Socket#recvfrom

# File ext/socket/lib/socket.rb, line 376
def recv_nonblock(len, flag = 0, str = nil, exception: true)
  __recv_nonblock(len, flag, str, exception)
end

recvmsg receives a message using recvmsg(2) system call in blocking manner.

maxmesglen is the maximum length of mesg to receive.

flags is bitwise OR of MSG_* constants such as Socket::MSG_PEEK.

maxcontrollen is the maximum length of controls (ancillary data) to receive.

opts is option hash. Currently :scm_rights=>bool is the only option.

:scm_rights option specifies that application expects SCM_RIGHTS control message. If the value is nil or false, application don’t expects SCM_RIGHTS control message. In this case, recvmsg closes the passed file descriptors immediately. This is the default behavior.

If :scm_rights value is neither nil nor false, application expects SCM_RIGHTS control message. In this case, recvmsg creates IO objects for each file descriptors for Socket::AncillaryData#unix_rights method.

The return value is 4-elements array.

mesg is a string of the received message.

sender_addrinfo is a sender socket address for connection-less socket. It is an Addrinfo object. For connection-oriented socket such as TCP, sender_addrinfo is platform dependent.

rflags is a flags on the received message which is bitwise OR of MSG_* constants such as Socket::MSG_TRUNC. It will be nil if the system uses 4.3BSD style old recvmsg system call.

controls is ancillary data which is an array of Socket::AncillaryData objects such as:

#<Socket::AncillaryData: AF_UNIX SOCKET RIGHTS 7>

maxmesglen and maxcontrollen can be nil. In that case, the buffer will be grown until the message is not truncated. Internally, MSG_PEEK is used. Buffer full and MSG_CTRUNC are checked for truncation.

recvmsg can be used to implement recv_io as follows:

mesg, sender_sockaddr, rflags, *controls = sock.recvmsg(:scm_rights=>true)
controls.each {|ancdata|
  if ancdata.cmsg_is?(:SOCKET, :RIGHTS)
    return ancdata.unix_rights[0]
  end
}

# File ext/socket/lib/socket.rb, line 431
def recvmsg(dlen = nil, flags = 0, clen = nil, scm_rights: false)
  __recvmsg(dlen, flags, clen, scm_rights)
end

recvmsg receives a message using recvmsg(2) system call in non-blocking manner.

It is similar to BasicSocket#recvmsg but non-blocking flag is set before the system call and it doesn’t retry the system call.

By specifying a keyword argument exception to false, you can indicate that recvmsg_nonblock should not raise an IO::WaitReadable exception, but return the symbol :wait_readable instead.

# File ext/socket/lib/socket.rb, line 447
def recvmsg_nonblock(dlen = nil, flags = 0, clen = nil,
                     scm_rights: false, exception: true)
  __recvmsg_nonblock(dlen, flags, clen, scm_rights, exception)
end

Returns an Addrinfo object for remote address obtained by getpeername.

Note that addrinfo.protocol is filled by 0.

TCPSocket.open("www.ruby-lang.org", 80) {|s|
  p s.remote_address #=> #<Addrinfo: 221.186.184.68:80 TCP>
}

TCPServer.open("127.0.0.1", 1728) {|serv|
  c = TCPSocket.new("127.0.0.1", 1728)
  s = serv.accept
  p s.remote_address #=> #<Addrinfo: 127.0.0.1:36504 TCP>
}

static VALUE
bsock_remote_address(VALUE sock)
{
    union_sockaddr buf;
    socklen_t len = (socklen_t)sizeof buf;
    socklen_t len0 = len;
    rb_io_t *fptr;

    GetOpenFile(sock, fptr);
    if (getpeername(fptr->fd, &buf.addr, &len) < 0)
        rb_sys_fail("getpeername(2)");
    if (len0 < len) len = len0;
    return rsock_fd_socket_addrinfo(fptr->fd, &buf.addr, len);
}

send mesg via basicsocket.

mesg should be a string.

flags should be a bitwise OR of Socket::MSG_* constants.

dest_sockaddr should be a packed sockaddr string or an addrinfo.

TCPSocket.open("localhost", 80) {|s|
  s.send "GET / HTTP/1.0\r\n\r\n", 0
  p s.read
}

VALUE
rsock_bsock_send(int argc, VALUE *argv, VALUE socket)
{
    struct rsock_send_arg arg;
    VALUE flags, to;
    rb_io_t *fptr;
    rb_blocking_function_t *func;
    const char *funcname;

    rb_scan_args(argc, argv, "21", &arg.mesg, &flags, &to);

    StringValue(arg.mesg);
    if (!NIL_P(to)) {
        SockAddrStringValue(to);
        to = rb_str_new4(to);
        arg.to = (struct sockaddr *)RSTRING_PTR(to);
        arg.tolen = RSTRING_SOCKLEN(to);
        func = rsock_sendto_blocking;
        funcname = "sendto(2)";
    }
    else {
        func = rsock_send_blocking;
        funcname = "send(2)";
    }

    RB_IO_POINTER(socket, fptr);

    arg.fd = fptr->fd;
    arg.flags = NUM2INT(flags);

    while (true) {
#ifdef RSOCK_WAIT_BEFORE_BLOCKING
        rb_io_wait(socket, RB_INT2NUM(RUBY_IO_WRITABLE), Qnil);
#endif

        ssize_t n = (ssize_t)BLOCKING_REGION_FD(func, &arg);

        if (n >= 0) return SSIZET2NUM(n);

        if (rb_io_maybe_wait_writable(errno, socket, RUBY_IO_TIMEOUT_DEFAULT)) {
            continue;
        }

        rb_sys_fail(funcname);
    }
}

sendmsg sends a message using sendmsg(2) system call in blocking manner.

mesg is a string to send.

flags is bitwise OR of MSG_* constants such as Socket::MSG_OOB.

dest_sockaddr is a destination socket address for connection-less socket. It should be a sockaddr such as a result of Socket.sockaddr_in. An Addrinfo object can be used too.

controls is a list of ancillary data. The element of controls should be Socket::AncillaryData or 3-elements array. The 3-element array should contains cmsg_level, cmsg_type and data.

The return value, numbytes_sent is an integer which is the number of bytes sent.

sendmsg can be used to implement send_io as follows:

# use Socket::AncillaryData.
ancdata = Socket::AncillaryData.int(:UNIX, :SOCKET, :RIGHTS, io.fileno)
sock.sendmsg("a", 0, nil, ancdata)

# use 3-element array.
ancdata = [:SOCKET, :RIGHTS, [io.fileno].pack("i!")]
sock.sendmsg("\0", 0, nil, ancdata)

# File ext/socket/lib/socket.rb, line 307
def sendmsg(mesg, flags = 0, dest_sockaddr = nil, *controls)
  __sendmsg(mesg, flags, dest_sockaddr, controls)
end

sendmsg_nonblock sends a message using sendmsg(2) system call in non-blocking manner.

It is similar to BasicSocket#sendmsg but the non-blocking flag is set before the system call and it doesn’t retry the system call.

By specifying a keyword argument exception to false, you can indicate that sendmsg_nonblock should not raise an IO::WaitWritable exception, but return the symbol :wait_writable instead.

# File ext/socket/lib/socket.rb, line 323
def sendmsg_nonblock(mesg, flags = 0, dest_sockaddr = nil, *controls,
                     exception: true)
  __sendmsg_nonblock(mesg, flags, dest_sockaddr, controls, exception)
end

Sets a socket option. These are protocol and system specific, see your local system documentation for details.

Parameters¶ ↑

• level is an integer, usually one of the SOL_ constants such as Socket::SOL_SOCKET, or a protocol level. A string or symbol of the name, possibly without prefix, is also accepted.

• optname is an integer, usually one of the SO_ constants, such as Socket::SO_REUSEADDR. A string or symbol of the name, possibly without prefix, is also accepted.

• optval is the value of the option, it is passed to the underlying setsockopt() as a pointer to a certain number of bytes. How this is done depends on the type:

  • Integer: value is assigned to an int, and a pointer to the int is passed, with length of sizeof(int).

  • true or false: 1 or 0 (respectively) is assigned to an int, and the int is passed as for an Integer. Note that false must be passed, not nil.

  • String: the string’s data and length is passed to the socket.

• socketoption is an instance of Socket::Option

Examples¶ ↑

Some socket options are integers with boolean values, in this case setsockopt could be called like this:

sock.setsockopt(:SOCKET, :REUSEADDR, true)
sock.setsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR, true)
sock.setsockopt(Socket::Option.bool(:INET, :SOCKET, :REUSEADDR, true))

Some socket options are integers with numeric values, in this case setsockopt could be called like this:

sock.setsockopt(:IP, :TTL, 255)
sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_TTL, 255)
sock.setsockopt(Socket::Option.int(:INET, :IP, :TTL, 255))

Option values may be structs. Passing them can be complex as it involves examining your system headers to determine the correct definition. An example is an ip_mreq, which may be defined in your system headers as:

struct ip_mreq {
  struct  in_addr imr_multiaddr;
  struct  in_addr imr_interface;
};

In this case setsockopt could be called like this:

optval = IPAddr.new("224.0.0.251").hton +
         IPAddr.new(Socket::INADDR_ANY, Socket::AF_INET).hton
sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, optval)

static VALUE
bsock_setsockopt(int argc, VALUE *argv, VALUE sock)
{
    VALUE lev, optname, val;
    int family, level, option;
    rb_io_t *fptr;
    int i;
    char *v;
    int vlen;

    if (argc == 1) {
        lev = rb_funcall(argv[0], rb_intern("level"), 0);
        optname = rb_funcall(argv[0], rb_intern("optname"), 0);
        val = rb_funcall(argv[0], rb_intern("data"), 0);
    }
    else {
        rb_scan_args(argc, argv, "30", &lev, &optname, &val);
    }

    GetOpenFile(sock, fptr);
    family = rsock_getfamily(fptr);
    level = rsock_level_arg(family, lev);
    option = rsock_optname_arg(family, level, optname);

    switch (TYPE(val)) {
      case T_FIXNUM:
        i = FIX2INT(val);
        goto numval;
      case T_FALSE:
        i = 0;
        goto numval;
      case T_TRUE:
        i = 1;
      numval:
        v = (char*)&i; vlen = (int)sizeof(i);
        break;
      default:
        StringValue(val);
        v = RSTRING_PTR(val);
        vlen = RSTRING_SOCKLEN(val);
        break;
    }

    rb_io_check_closed(fptr);
    if (setsockopt(fptr->fd, level, option, v, vlen) < 0)
        rsock_sys_fail_path("setsockopt(2)", fptr->pathv);

    return INT2FIX(0);
}

Calls shutdown(2) system call.

s.shutdown(Socket::SHUT_RD) disallows further read.

s.shutdown(Socket::SHUT_WR) disallows further write.

s.shutdown(Socket::SHUT_RDWR) disallows further read and write.

how can be symbol or string:

• :RD, :SHUT_RD, “RD” and “SHUT_RD” are accepted as Socket::SHUT_RD.

• :WR, :SHUT_WR, “WR” and “SHUT_WR” are accepted as Socket::SHUT_WR.

• :RDWR, :SHUT_RDWR, “RDWR” and “SHUT_RDWR” are accepted as Socket::SHUT_RDWR.

  UNIXSocket.pair {|s1, s2|

  s1.puts "ping"
  s1.shutdown(:WR)
  p s2.read          #=> "ping\n"
  s2.puts "pong"
  s2.close
  p s1.read          #=> "pong\n"
  

  }

static VALUE
bsock_shutdown(int argc, VALUE *argv, VALUE sock)
{
    VALUE howto;
    int how;
    rb_io_t *fptr;

    rb_scan_args(argc, argv, "01", &howto);
    if (howto == Qnil)
        how = SHUT_RDWR;
    else {
        how = rsock_shutdown_how_arg(howto);
        if (how != SHUT_WR && how != SHUT_RD && how != SHUT_RDWR) {
            rb_raise(rb_eArgError, "`how' should be either :SHUT_RD, :SHUT_WR, :SHUT_RDWR");
        }
    }
    GetOpenFile(sock, fptr);
    if (shutdown(fptr->fd, how) == -1)
        rb_sys_fail("shutdown(2)");

    return INT2FIX(0);
}