Method: BasicSocket#recvmsg

Defined in:

lib/socket.rb

#recvmsg(dlen = nil, flags = 0, clen = nil, scm_rights: false) ⇒ Object

call-seq:

basicsocket.recvmsg(maxmesglen=nil, flags=0, maxcontrollen=nil, opts={}) => [mesg, sender_addrinfo, rflags, *controls]

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 'lib/socket.rb', line 431

def recvmsg(dlen = nil, flags = 0, clen = nil, scm_rights: false)
  __recvmsg(dlen, flags, clen, scm_rights)
end