recv(3N) recv(3N)
NAME
recv, recvfrom, recvmsg - receive a message from a socket
SYNOPSIS
cc [options] file -lsocket -lnsl
#include <sys/types.h>
#include <sys/socket.h>
ssize_t recv(int s, void *buf, size_t len, int flags);
ssize_t recvfrom(int s, void *buf, size_t len, int flags,
struct sockaddr *from, size_t *fromlen);
ssize_t recvmsg(int s, struct msghdr *msg, int flags);
DESCRIPTION
s is a socket created with socket. recv, recvfrom, and
recvmsg are used to receive messages from another socket.
recv may be used only on a connected socket [see connect(3N)],
while recvfrom and recvmsg may be used to receive data on a
socket whether it is in a connected state or not.
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(3N)].
If no messages are available at the socket, the receive call
waits for a message to arrive, unless the socket is
nonblocking [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:
MSG_OOB Read any out-of-band data present on the socket
rather than the regular in-band data.
MSG_PEEK 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.
Copyright 1994 Novell, Inc. Page 1
recv(3N) recv(3N)
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_t msg_name; /* optional address */
int msg_namelen; /* size of address */
struct iovec *msg_iov; /* scatter/gather array */
int msg_iovlen; /* # elements in msg_iov */
caddr_t msg_accrights; /* access rights sent/received */
int msg_accrightslen;
Here msg_name and msg_namelen specify the destination address
if the socket is unconnected; msg_name may be given as a NULL
pointer if no names are desired or required. The msg_iov and
msg_iovlen describe the scatter-gather locations, as described
in read. A buffer to receive any access rights sent along
with the message is specified in msg_accrights, which has
length msg_accrightslen.
Files
/usr/lib/locale/locale/LC_MESSAGES/uxnsl
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 descriptor.
ENOTSOCK s is a descriptor for a file, not a
socket.
EINTR The operation was interrupted by delivery
of a signal before any data was available
to be received.
EWOULDBLOCK The socket is marked non-blocking and the
requested operation would block.
ENOMEM There was insufficient user memory
available for the operation to complete.
Copyright 1994 Novell, Inc. Page 2
recv(3N) recv(3N)
ENOSR There were insufficient STREAMS resources
available for the operation to complete.
REFERENCES
connect(3N), fcntl(2), getsockopt(3N), ioctl(2), read(2)
send(3N), socket(3N)
NOTICES
The type of address structure passed to recv depends on the
address family. UNIX domain sockets (address family AF_UNIX)
require a sockaddr_un structure as defined in sys/un.h;
Internet domain sockets (address family AF_INET) require a
struct sockaddr_in structure as defined in netinet/in.h.
Other address families may require other structures. Use the
structure appropriate to the address family; cast the
structure address to a struct sockaddr* in the call to recv
and pass the size of the structure in the fromlen argument.
Copyright 1994 Novell, Inc. Page 3