Sockets Library Functions recv(3SOCKET)



NAME
recv, recvfrom, recvmsg - receive a message from a socket

SYNOPSIS
cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>

ssize recv(int s, void *buf, size len, int flags);

ssize recvfrom(int s, void *buf, size len, int flags,
struct sockaddr *from, int *fromlen);

ssize recvmsg(int s, struct msghdr *msg, int flags);

DESCRIPTION
recv(), recvfrom(), and recvmsg() are used to receive mes-
sages from another socket. recv() may be used only on a con-
nected socket (see connect(3SOCKET)), while recvfrom() and
recvmsg() may be used to receive data on a socket whether it
is in a connected state or not. s is a socket created with
socket(3SOCKET).

If from is not a NULL pointer, the source address of the
message is filled in. fromlen is a value-result parameter,
initialized to the size of the buffer associated with from,
and modified on return to indicate the actual size of the
address stored there. The length of the message is returned.
If a message is too long to fit in the supplied buffer,
excess bytes may be discarded depending on the type of
socket the message is received from (see socket(3SOCKET)).

If no messages are available at the socket, the receive call
waits for a message to arrive, unless the socket is non-
blocking (see fcntl(2)) in which case -1 is returned with
the external variable errno set to EWOULDBLOCK.

The select() call may be used to determine when more data
arrives.

The flags parameter is formed by ORing one or more of the
following:

MSGOB
Read any "out-of-band" data present on the socket
rather than the regular "in-band" data.

MSGEEK
"Peek" at the data present on the socket; the data is
returned, but not consumed, so that a subsequent
receive operation will see the same data.



SunOS 5.8 Last change: 8 Nov 1999 1






Sockets Library Functions recv(3SOCKET)



The recvmsg() call uses a msghdr structure to minimize the
number of directly supplied parameters. This structure is
defined in <sys/socket.h> and includes the following
members:


caddr msgame; /* optional address */
int msgamelen; /* size of address */
struct iovec *msgov; /* scatter/gather array */
int msgovlen; /* # elements in msgov */
caddr msgccrights; /* access rights sent/received */
int msgccrightslen;

Here msgame and msgamelen specify the destination
address if the socket is unconnected; msgame may be
given as a NULL pointer if no names are desired or
required. The msgov and msgovlen describe the
scatter-gather locations, as described in read(2). A
buffer to receive any access rights sent along with the
message is specified in msgccrights, which has length
msgccrightslen.


RETURN VALUES
These calls return the number of bytes received, or -1 if an
error occurred.

ERRORS
The calls fail if:

EBADF s is an invalid file descriptor.

EINTR The operation was interrupted by delivery of a signal
before any data was available to be received.

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

ENOMEM
There was insufficient user memory available for the
operation to complete.

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

ENOTSOCK
s is not a socket.

ESTALE
A stale NFS file handle exists.

EWOULDBLOCK



SunOS 5.8 Last change: 8 Nov 1999 2






Sockets Library Functions recv(3SOCKET)



The socket is marked non-blocking and the requested
operation would block.

ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:


| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|||
| MT-Level | Safe |
|||


SEE ALSO
fcntl(2), ioctl(2), read(2), connect(3SOCKET),
getsockopt(3SOCKET), send(3SOCKET), socket(3SOCKET), attri-
butes(5), socket(3HEAD)





































SunOS 5.8 Last change: 8 Nov 1999 3