RECVFROM(3XNET) X/Open Networking Services Library Functions RECVFROM(3XNET)


NAME


recvfrom - receive a message from a socket

SYNOPSIS


cc [ flag ... ] file ... -lxnet [ library ... ]
#include <sys/socket.h>

ssize_t recvfrom(int socket, void *restrict buffer, size_t length,
int flags, struct sockaddr *restrict address,
socklen_t *restrict address_len);


DESCRIPTION


The recvfrom() function receives a message from a connection-mode or
connectionless-mode socket. It is normally used with connectionless-mode
sockets because it permits the application to retrieve the source address
of received data.


The function takes the following arguments:

socket
Specifies the socket file descriptor.


buffer
Points to the buffer where the message should be stored.


length
Specifies the length in bytes of the buffer pointed to by
the buffer argument.


flags
Specifies the type of message reception. Values of this
argument are formed by logically OR'ing zero or more of
the following values:

MSG_PEEK
Peeks at an incoming message. The data is
treated as unread and the next recvfrom()
or similar function will still return this
data.


MSG_OOB
Requests out-of-band data. The significance
and semantics of out-of-band data are
protocol-specific.


MSG_WAITALL
Requests that the function block until the
full amount of data requested can be
returned. The function may return a
smaller amount of data if a signal is
caught, if the connection is terminated,
if MSG_PEEK was specified, or if an error
is pending for the socket.


address
A null pointer, or points to a sockaddr structure in which
the sending address is to be stored. The length and
format of the address depend on the address family of the
socket.


address_len
Specifies the length of the sockaddr structure pointed to
by the address argument.


The recvfrom() function returns the length of the message written to the
buffer pointed to by the buffer argument. For message-based sockets such
as SOCK_DGRAM and SOCK_SEQPACKET, the entire message must be read in a
single operation. If a message is too long to fit in the supplied
buffer, and MSG_PEEK is not set in the flags argument, the excess bytes
are discarded. For stream-based sockets such as SOCK_STREAM, message
boundaries are ignored. In this case, data is returned to the user as
soon as it becomes available, and no data is discarded.


If the MSG_WAITALL flag is not set, data will be returned only up to the
end of the first message.


Not all protocols provide the source address for messages. If the
address argument is not a null pointer and the protocol provides the
source address of messages, the source address of the received message is
stored in the sockaddr structure pointed to by the address argument, and
the length of this address is stored in the object pointed to by the
address_len argument.


If the actual length of the address is greater than the length of the
supplied sockaddr structure, the stored address will be truncated.


If the address argument is not a null pointer and the protocol does not
provide the source address of messages, then the value stored in the
object pointed to by address is unspecified.


If no messages are available at the socket and O_NONBLOCK is not set on
the socket's file descriptor, recvfrom() blocks until a message arrives.
If no messages are available at the socket and O_NONBLOCK is set on the
socket's file descriptor, recvfrom() fails and sets errno to EAGAIN or
EWOULDBLOCK.

USAGE


The select(3C) and poll(2) functions can be used to determine when data
is available to be received.

RETURN VALUES


Upon successful completion, recvfrom() returns the length of the message
in bytes. If no messages are available to be received and the peer has
performed an orderly shutdown, recvfrom() returns 0. Otherwise the
function returns -1 and sets errno to indicate the error.

ERRORS


The recvfrom() function will fail if:

EAGAIN
EWOULDBLOCK
The socket's file descriptor is marked 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's file
descriptor is marked O_NONBLOCK or the socket does not
support blocking to await out-of-band data.


EBADF
The socket argument is not a valid file descriptor.


ECONNRESET
A connection was forcibly closed by a peer.


EFAULT
The buffer, address or address_len parameter can not be
accessed or written.


EINTR
A signal interrupted recvfrom() before any data was
available.


EINVAL
The MSG_OOB flag is set and no out-of-band data is
available.


ENOTCONN
A receive is attempted on a connection-mode socket that is
not connected.


ENOTSOCK
The socket argument does not refer to a socket.


EOPNOTSUPP
The specified flags are not supported for this socket
type.


ETIMEDOUT
The connection timed out during connection establishment,
or due to a transmission timeout on active connection.


The recvfrom() function may fail if:

EIO
An I/O error occurred while reading from or writing to the
file system.


ENOBUFS
Insufficient resources were available in the system to perform
the operation.


ENOMEM
Insufficient memory was available to fulfill the request.


ENOSR
There were insufficient STREAMS resources available for the
operation to complete.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO


poll(2), sockaddr(3SOCKET), recv(3XNET), recvmsg(3XNET), select(3C)
send(3XNET), sendmsg(3XNET), sendto(3XNET), shutdown(3XNET),
socket(3XNET), attributes(5), standards(5)


April 9, 2016 RECVFROM(3XNET)