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
In addition to the errors documented below, an asynchronous error
generated by the underlying socket protocol may be returned. For the full
list of errors, please see the corresponding socket protocol manual page.
For example, for a list of TCP errors, please see
tcp(4P).
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(7) 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),
tcp(4P),
attributes(7),
standards(7) September 10, 2018
RECVFROM(3XNET)