отправить сообщение в сокет, используя структуру сообщения (send a message on a socket using a message structure)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
sendmsg — send a message on a socket using a message structure
Синопсис (Synopsis)
#include <sys/socket.h>
ssize_t sendmsg(int socket, const struct msghdr *message, int flags);
Описание (Description)
The sendmsg() function shall send a message through a connection-
mode or connectionless-mode socket. If the socket is a
connectionless-mode socket, the message shall be sent to the
address specified by msghdr if no pre-specified peer address has
been set. If a peer address has been pre-specified, either the
message shall be sent to the address specified in msghdr
(overriding the pre-specified peer address), or the function
shall return -1 and set errno to [EISCONN]. If the socket is
connection-mode, the destination address in msghdr shall be
ignored.
The sendmsg() 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. The
application may specify 0 or the following flag:
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.
MSG_NOSIGNAL Requests not to send the SIGPIPE signal
if an attempt to send is made on a
stream-oriented socket that is no
longer connected. The [EPIPE] error
shall still be returned.
The msg_iov and msg_iovlen fields of message specify zero or more
buffers containing the data to be sent. msg_iov points to an
array of iovec structures; msg_iovlen shall be set to the
dimension of this array. In each iovec structure, the iov_base
field specifies a storage area and the iov_len field gives its
size in bytes. Some of these sizes can be zero. The data from
each storage area indicated by msg_iov is sent in turn.
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, the sendmsg() function shall block 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, the sendmsg() function shall
fail.
If the socket protocol supports broadcast and the specified
address is a broadcast address for the socket protocol, sendmsg()
shall fail if the SO_BROADCAST option is not set for the socket.
The socket in use may require the process to have appropriate
privileges to use the sendmsg() function.
Возвращаемое значение (Return value)
Upon successful completion, sendmsg() shall return the number of
bytes sent. Otherwise, -1 shall be returned and errno set to
indicate the error.
Ошибки (Error)
The sendmsg() function shall fail if:
EAGAIN or EWOULDBLOCK
The socket's file descriptor is marked O_NONBLOCK and the
requested operation would block.
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), or the msg_iovlen member of the msghdr
structure pointed to by message is less than or equal to 0
or is greater than {IOV_MAX}.
ENOTCONN
The socket is connection-mode but is not connected.
ENOTSOCK
The socket argument does not refer to 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 is no longer connected. In the latter
case, and if the socket is of type SOCK_STREAM or
SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set, the
SIGPIPE signal is generated to the calling thread.
If the address family of the socket is AF_UNIX, then sendmsg()
shall fail if:
EIO An I/O error occurred while reading from or writing to the
file system.
ELOOP A loop exists in symbolic links encountered during
resolution of the pathname in the socket address.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of the pathname does not name an existing file
or the path name is an empty string.
ENOTDIR
A component of the path prefix of the pathname in the
socket address names an existing file that is neither a
directory nor a symbolic link to a directory, or the
pathname in the socket address contains at least one
non-<slash> character and ends with one or more trailing
<slash> characters and the last pathname component names
an existing file that is neither a directory nor a
symbolic link to a directory.
The sendmsg() function may fail if:
EACCES Search permission is denied for a component of the path
prefix; or write access to the named socket is denied.
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).
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
already connected.
ENETDOWN
The local network 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.
If the address family of the socket is AF_UNIX, then sendmsg()
may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the pathname in the socket address.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
The following sections are informative.
Примеры (Examples)
Done.
Использование в приложениях (Application usage)
The select() and poll() functions can be used to determine when
it is possible to send more data.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
getsockopt(3p), poll(3p), pselect(3p), recv(3p), recvfrom(3p),
recvmsg(3p), send(3p), sendto(3p), setsockopt(3p), shutdown(3p),
socket(3p)
The Base Definitions volume of POSIX.1‐2017, sys_socket.h(0p)
