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recv(3c)
recv(3C) Standard C Library Functions recv(3C)
NAME
recv, recvfrom, recvmsg - receive a message from a socket
SYNOPSIS
#include <sys/socket.h>
ssize_t recv(int s, void *buf, size_t len, int flags);
ssize_t recvfrom(int s, void *restrict buf, size_t len, int flags,
struct sockaddr *restrict from, socklen_t *restrict 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(3C).
If from is a non-NULL pointer, the source address of the message is
filled in. The value-result parameter fromlen is initialized by the
caller 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(3C).
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 socket.h(3HEAD).
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 poll(2) or select(3C) calls 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 re‐
turn 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 re‐
turned. If data is unavailable, the function does
not block. This behavior is the equivalent to spec‐
ifying O_NONBLOCK on the file descriptor of a
socket, except that write requests are unaffected.
MSG_CMSG_CLOEXEC Set the close-on-exec flag for file descriptors re‐
ceived using SCM_RIGHTS message.
MSG_CMSG_CLOFORK Set the close-on-fork flag for file descriptors re‐
ceived using SCM_RIGHTS message.
The recvmsg() function call uses a msghdr structure defined in
socket.h(3HEAD) to minimize the number of directly supplied parameters.
recvmmsg(3C) is an extension of the recvmsg() function that allows re‐
ceiving multiple messages in a single call.
The contents of the msghdr structure differ depending on whether or not
__USE_SUNOS_SOCKETS__ is defined before including the <sys/socket.h>
header. All source files accessing msghdr structures or calling the
recvmsg() function must be compiled with either __USE_SUNOS_SOCKETS__
defined or all with it undefined — mixing and matching will not work.
See the socket.h(3HEAD) manual page for details.
RETURN VALUES
Upon successful completion, these functions return the number of bytes
received. Otherwise, they return -1 and set errno to indicate the er‐
ror.
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 op‐
eration would block. EWOULDBLOCK is also set when
socket option SO_RCVTIMEO is set and the requested op‐
eration failed to transfer data before the timeout ex‐
pired. For more information, see the getsockopt(3C) man
page.
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:
EFAULT buf points to an illegal address.
EINVAL The len argument overflows a ssize_t.
The recvmsg() function returns errors under the following conditions:
EFAULT msg points to an illegal address.
EMSGSIZE 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(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
fcntl(2), ioctl(2), poll(2), read(2), connect(3C), getsockopt(3C),
recvmmsg(3C), select(3C), send(3C), socket(3C), socket.h(3HEAD), at‐
tributes(7)
HISTORY
These functions have been present since the initial release of Solaris.
Support for the following flags is available in Oracle Solaris starting
with the listed release:
tab() box; cw(4.71i) |cw(0.79i) lw(4.71i) |lw(0.79i) FLAGRELEASE _
MSG_CMSG_CLOFORK11.4.24 _ MSG_CMSG_CLOEXEC11.4.17 _ MSG_WAITALL,
MSG_DONTWAIT2.6 _ MSG_OOB, MSG_PEEK1.0
Oracle Solaris 11.4 13 Sep 2024 recv(3C)