Tribblix: manual page: recvfrom.3xnet

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

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