Socket#recvfrom

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_addrinfo, contains protocol-specific address information of the sender.

Parameters

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

• flags - zero or more of the MSG_ options

Example

# 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_addrinfo = socket.accept
data = client.recvfrom( 20 )[0].chomp
puts "I only received 20 bytes '#{data}'"
sleep 1
socket.close

# 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!"
socket.close

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 interrupted 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 accommodate 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 connection 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.