recvfrom(...) public

Receives up to maxlen bytes from socket. flags is zero or more of the MSG_ options. The first element of the results, mesg, is the data received. The second element, sender_sockaddr, contains protocol-specific information on the sender.


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

  • flags - zero or more of the MSG_ options


# In one file, start this first
require 'socket'
include Socket::Constants
socket = Socket.new( AF_INET, SOCK_STREAM, 0 )
sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
socket.bind( sockaddr )
socket.listen( 5 )
client, client_sockaddr = socket.accept
data = client.recvfrom( 20 )[0].chomp
puts "I only received 20 bytes '#{data}'"
sleep 1

# In another file, start this second
require 'socket'
include Socket::Constants
socket = Socket.new( AF_INET, SOCK_STREAM, 0 )
sockaddr = Socket.pack_sockaddr_in( 2200, 'localhost' )
socket.connect( sockaddr )
socket.puts "Watch this get cut short!"

Unix-based Exceptions

On unix-based based systems the following system exceptions may be raised if the call to recvfrom fails:

  • Errno::EAGAIN - the socket file descriptor is marked as O_NONBLOCK and no data is waiting to be received; or MSG_OOB is set and no out-of-band data is available and either the socket file descriptor is marked as O_NONBLOCK or the socket does not support blocking to wait for out-of-band-data

  • Errno::EWOULDBLOCK - see Errno::EAGAIN

  • Errno::EBADF - the socket is not a valid file descriptor

  • Errno::ECONNRESET - a connection was forcibly closed by a peer

  • Errno::EFAULT - the socket’s internal buffer, address or address length cannot be accessed or written

  • Errno::EINTR - a signal interupted recvfrom before any data was available

  • Errno::EINVAL - the MSG_OOB flag is set and no out-of-band data is available

  • Errno::EIO - an i/o error occurred while reading from or writing to the filesystem

  • Errno::ENOBUFS - insufficient resources were available in the system to perform the operation

  • Errno::ENOMEM - insufficient memory was available to fulfill the request

  • Errno::ENOSR - there were insufficient STREAMS resources available to complete the operation

  • Errno::ENOTCONN - a receive is attempted on a connection-mode socket that is not connected

  • Errno::ENOTSOCK - the socket does not refer to a socket

  • Errno::EOPNOTSUPP - the specified flags are not supported for this socket type

  • Errno::ETIMEDOUT - the connection timed out during connection establishment or due to a transmission timeout on an active connection

Windows Exceptions

On Windows systems the following system exceptions may be raised if the call to recvfrom fails:

  • Errno::ENETDOWN - the network is down

  • Errno::EFAULT - the internal buffer and from parameters on socket are not part of the user address space, or the internal fromlen parameter is too small to accomodate the peer address

  • Errno::EINTR - the (blocking) call was cancelled by an internal call to the WinSock function WSACancelBlockingCall

  • Errno::EINPROGRESS - a blocking Windows Sockets 1.1 call is in progress or the service provider is still processing a callback function

  • Errno::EINVAL - socket has not been bound with a call to bind, or an unknown flag was specified, or MSG_OOB was specified for a socket with SO_OOBINLINE enabled, or (for byte stream-style sockets only) the internal len parameter on socket was zero or negative

  • Errno::EISCONN - socket is already connected. The call to recvfrom is not permitted with a connected socket on a socket that is connetion oriented or connectionless.

  • Errno::ENETRESET - the connection has been broken due to the keep-alive activity detecting a failure while the operation was in progress.

  • Errno::EOPNOTSUPP - MSG_OOB was specified, but socket is not stream-style such as type SOCK_STREAM. OOB data is not supported in the communication domain associated with socket, or socket is unidirectional and supports only send operations

  • Errno::ESHUTDOWN - socket has been shutdown. It is not possible to call recvfrom on a socket after shutdown has been invoked.

  • Errno::EWOULDBLOCK - socket is marked as nonblocking and a call to recvfrom would block.

  • Errno::EMSGSIZE - the message was too large to fit into the specified buffer and was truncated.

  • Errno::ETIMEDOUT - the connection has been dropped, because of a network failure or because the system on the other end went down without notice

  • Errno::ECONNRESET - the virtual circuit was reset by the remote side executing a hard or abortive close. The application should close the socket; it is no longer usable. On a UDP-datagram socket this error indicates a previous send operation resulted in an ICMP Port Unreachable message.

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February 28, 2011
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from ‘man recvfrom’

The flags argument to a recv() function is formed by or'ing one or more of the values:

MSG_OOB        process out-of-band data
MSG_PEEK       peek at incoming message
MSG_WAITALL    wait for full request or error

The MSG_OOB flag requests receipt of out-of-band data that would not be received in the normal data stream.  Some protocols place expedited data at the head of the
normal data queue, and thus this flag cannot be used with such protocols.  The MSG_PEEK flag causes the receive operation to return data from the beginning of the
receive queue without removing that data from the queue.  Thus, a subsequent receive call will return the same data.  The MSG_WAITALL flag requests that the opera-
tion block until the full request is satisfied.  However, the call may still return less data than requested if a signal is caught, an error or disconnect occurs, or
the next data to be received is of a different type than that returned.