NAME

sendmsg − send a message on a socket using a message structure

SYNOPSIS

cc [ flag ... ] file ... −lxnet [ library ... ]

#include <sys/socket.h> ssize_t sendmsg(int socket, const struct msghdr ∗message, int flags);

DESCRIPTION

The sendmsg() function sends a message through a connection-mode or connectionless-mode socket. If the socket is connectionless-mode, the message will be sent to the address specified by msghdr. If the socket is connection-mode, the destination address in msghdr is ignored. 

The function takes the following arguments:

socket Specifies the socket file descriptor. 

message Points to a msghdr structure, containing both the destination address and the buffers for the outgoing message.  The length and format of the address depend on the address family of the socket.  The msg_flags member is ignored. 

flags Specifies the type of message transmission.  Values of this argument are formed by logically OR ’ing zero or more of the following flags:

MSG_EOR Terminates a record (if supported by the protocol)

MSG_OOB Sends out-of-band data on sockets that support out-of-bound data.  The significance and semantics of out-of-band data are protocol-specific. 

Successful completion of a call to sendmsg() does not guarantee delivery of the message.  A return value of −1 indicates only locally-detected errors. 

If space is not available at the sending socket to hold the message to be transmitted and the socket file descriptor does not have O_NONBLOCK set, sendmsg() function blocks until space is available.  If space is not available at the sending socket to hold the message to be transmitted and the socket file descriptor does have O_NONBLOCK set, sendmsg() function will fail. 

If the socket protocol supports broadcast and the specified address is a broadcast address for the socket protocol, sendmsg() will fail if the SO_BROADCAST option is not set for the socket. 

RETURN VALUES

Upon successful completion, sendmsg() function returns the number of bytes sent.  Otherwise, −1 is returned and errno is set to indicate the error. 

ERRORS

The sendmsg() function will fail if:

EAFNOSUPPORT
Addresses in the specified address family cannot be used with this socket.

EBADF The socket argument is not a valid file descriptor. 

ECONNRESET
A connection was forcibly closed by a peer.

EINTR A signal interrupted sendmsg() before any data was transmitted. 

EINVAL The sum of the iov_len values overflows an ssize_t . 

EMSGSIZE The message is too large to be sent all at once, as the socket requires. 

ENOTCONN The socket is connection-mode but is not connected. 

ENOTSOCK The socket argument does not refer a socket. 

EOPNOTSUPP
The socket argument is associated with a socket that does not support one or more of the values set in flags.

EPIPE The socket is shut down for writing, or the socket is connection-mode and the peer is closed or shut down for reading.  In the latter case, and if the socket is of type SOCK_STREAM , the SIGPIPE signal is generated to the calling process. 

EAGAIN The socket’s file descriptor is marked O_NONBLOCK and the requested operation would block. 

If the address family of the socket is AF_UNIX, then sendmsg() will fail if:

EACCES Search permission is denied for a component of the path prefix; or write access to the named socket is denied. 

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

ELOOP Too many symbolic links were encountered in translating the pathname in the socket address. 

ENAMETOOLONG
A component of a pathname exceeded NAME_MAX characters, or an entire pathname exceeded PATH_MAX characters. 

ENOENT A component of the pathname does not name an existing file or the pathname is an empty string. 

ENOTDIR A component of the path prefix of the pathname in the socket address is not a directory. 

The sendmsg() function may fail if:

EDESTADDRREQ
The socket is not connection-mode and does not have its peer address set, and no destination address was specified.

EHOSTUNREACH
The destination host cannot be reached (probably because the host is down or a remote router cannot reach it).

EINVAL The msg_iovlen member of the msghdr structure pointed to by msg is less than or equal to 0, or is greater than IOV_MAX. 

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

EISCONN A destination address was specified and the socket is connection-mode and is already connected. 

ENETDOWN The local interface used to reach the destination is down. 

ENETUNREACH
No route to the network is present.

ENOBUFS Insufficient resources were available in the system to perform the operation. 

ENOMEM Insufficient memory was available to fulfill the request. 

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

If the address family of the socket is AF_UNIX , then sendmsg() may fail if:

ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX. 

USAGE

The select(3C) and poll(2) functions can be used to determine when it is possible to send more data. 

ATTRIBUTES

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

SEE ALSO

poll(2) getsockopt(3XN), recv(3XN), recvfrom(3XN), recvmsg(3XN), select(3C), send(3XN), sendto(3XN), setsockopt(3XN), shutdown(3XN), socket(3XN), attributes(5), socket(5)

SunOS 5.6  —  Last change: 16 May 1997