recvfrom(3XNET) X/Open Networking Services Library Functions recvfrom(3XNET)NAMErecvfrom - 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 sim‐
ilar 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 con‐
nection 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 sock‐
ets 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, the 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 mes‐
sage in bytes. If no messages are available to be received and the
peer has performed an orderly shutdown, recvfrom() returns 0. Other‐
wise the function returns −1 and sets errno to indicate the error.
ERRORS
The recvfrom() function will fail if:
EAGAIN The socket's file descriptor is marked O_NON‐
EWOULDBLOCK BLOCK 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 descrip‐
tor 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 ALSOpoll(2), recv(3XNET), recvmsg(3XNET), select(3C)send(3XNET),
sendmsg(3XNET), sendto(3XNET), shutdown(3XNET), socket(3XNET),
attributes(5), standards(5)SunOS 5.10 10 Jun 2002 recvfrom(3XNET)
