RECV(3SOCKET) 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_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, socklen_t *fromlen);


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


DESCRIPTION


The recv(), recvfrom(), and recvmsg() functions are used to receive
messages from another socket. The s socket is created with
socket(3SOCKET).


If from is a non-NULL pointer, the source address of the message is
filled in. The value-result parameter fromlen is initialized to the size
of the buffer associated with from and modified on return to indicate the
actual size of the address stored in the buffer. 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
from which the message is received. See socket(3SOCKET).


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


For processes on the same host, recvmsg() can be used to receive a file
descriptor from another process, but it cannot receive ancillary data.
See libxnet(3LIB).


If a zero-length buffer is specified for a message, an EOF condition
results that is indistinguishable from the successful transfer of a file
descriptor. For that reason, one or more bytes of data should be
provided when recvmsg() passes a file descriptor.


The select(3C) call can be used to determine when more data arrives.


The flags parameter is formed by an OR operation on 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 to allow a subsequent receive
operation to see the same data.


MSG_WAITALL
Messages are blocked until the full amount of data
requested is returned. The recv() function can return a
smaller amount of data if a signal is caught, the
connection is terminated, MSG_PEEK is specified, or if an
error is pending for the socket.


MSG_DONTWAIT
Pending messages received on the connection are returned.
If data is unavailable, the function does not block. This
behavior is the equivalent to specifying O_NONBLOCK on
the file descriptor of a socket, except that write
requests are unaffected.


The recvmsg() function call uses a msghdr structure defined in
<sys/socket.h> to minimize the number of directly supplied parameters.

RETURN VALUES


Upon successful completion, these functions return the number of bytes
received. Otherwise, they return -1 and set errno to indicate the error.

ERRORS


The recv(), recvfrom(), and recvmsg() functions return errors under the
following conditions:

EBADF
The s file descriptor is invalid.


ECONNRESET
The s argument refers to a connection oriented socket and
the connection was forcibly closed by the peer and is no
longer valid. I/O can no longer be performed to filedes.


EINVAL
The MSG_OOB flag is set and no out-of-band data is
available.


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


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


ENOMEM
Insufficient user memory is available to complete
operation.


ENOSR
Insufficient STREAMS resources are available for the
operation to complete.


ENOTSOCK
s is not a socket.


ESTALE
A stale NFS file handle exists.


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


ECONNREFUSED
The requested connection was refused by the peer. For
connected IPv4 and IPv6 datagram sockets, this indicates
that the system received an ICMP Destination Port
Unreachable message from the peer.


The recv() and recvfrom() functions fail under the following conditions:

EINVAL
The len argument overflows a ssize_t.


The recvmsg() function returns errors under the following conditions:

EINVAL
The msg_iovlen member of the msghdr structure pointed to by msg
is less than or equal to 0, or greater than [IOV_MAX}. See
Intro(2) for a definition of [IOV_MAX}.


EINVAL
One of the iov_len values in the msg_iov array member of the
msghdr structure pointed to by msg is negative, or the sum of
the iov_len values in the msg_iov array overflows a ssize_t.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+
|MT-Level | Safe |
+--------------------+-----------------+

SEE ALSO


fcntl(2), ioctl(2), read(2), connect(3SOCKET), getsockopt(3SOCKET),
libxnet(3LIB), select(3C), send(3SOCKET), sockaddr(3SOCKET),
socket(3SOCKET), socket.h(3HEAD), attributes(5)


December 3, 2014 RECV(3SOCKET)