RECV(3SOCKET)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 indi‐
cate 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 sup‐
plied 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 con‐
nection 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.
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 sig‐
nal 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 oper‐
ation.
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 indi‐
cates that the system received an ICMP Destination Port
Unreachable message from the peer.
The recv() and recvfrom() functions fail under the following condi‐
tions:
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 ALSOfcntl(2), ioctl(2), read(2), connect(3SOCKET), getsockopt(3SOCKET),
libxnet(3LIB), select(3C), send(3SOCKET), socket(3SOCKET),
socket.h(3HEAD), attributes(5)
Aug 20, 2007 RECV(3SOCKET)
