sendmsg.3p (8745B)
- '\" et
- .TH SENDMSG "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- sendmsg
- \(em send a message on a socket using a message structure
- .SH SYNOPSIS
- .LP
- .nf
- #include <sys/socket.h>
- .P
- ssize_t sendmsg(int \fIsocket\fP, const struct msghdr *\fImessage\fP, int \fIflags\fP);
- .fi
- .SH DESCRIPTION
- The
- \fIsendmsg\fR()
- 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
- .BR 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
- .BR msghdr
- (overriding the pre-specified peer address), or the function shall
- return \-1 and set
- .IR errno
- to
- .BR [EISCONN] .
- If the socket is connection-mode, the destination address in
- .BR msghdr
- shall be ignored.
- .P
- The
- \fIsendmsg\fR()
- function takes the following arguments:
- .IP "\fIsocket\fR" 12
- Specifies the socket file descriptor.
- .IP "\fImessage\fR" 12
- Points to a
- .BR 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
- .IR msg_flags
- member is ignored.
- .IP "\fIflags\fR" 12
- Specifies the type of message transmission. The application may
- specify 0 or the following flag:
- .RS 12
- .IP MSG_EOR 14
- Terminates a record (if supported by the protocol).
- .IP MSG_OOB 14
- 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.
- .IP MSG_NOSIGNAL 14
- 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
- .BR [EPIPE]
- error shall still be returned.
- .RE
- .P
- The
- .IR msg_iov
- and
- .IR msg_iovlen
- fields of
- .IR message
- specify zero or more buffers containing the data to be sent.
- .IR msg_iov
- points to an array of
- .BR iovec
- structures;
- .IR msg_iovlen
- shall be set to the dimension of this array. In each
- .BR iovec
- structure, the
- .IR iov_base
- field specifies a storage area and the
- .IR iov_len
- field gives its size in bytes. Some of these sizes can be zero. The
- data from each storage area indicated by
- .IR msg_iov
- is sent in turn.
- .P
- Successful completion of a call to
- \fIsendmsg\fR()
- does not guarantee delivery of the message. A return value of \-1
- indicates only locally-detected errors.
- .P
- 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
- \fIsendmsg\fR()
- 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
- \fIsendmsg\fR()
- function shall fail.
- .P
- If the socket protocol supports broadcast and the specified address is
- a broadcast address for the socket protocol,
- \fIsendmsg\fR()
- shall fail if the SO_BROADCAST option is not set for the socket.
- .P
- The socket in use may require the process to have appropriate
- privileges to use the
- \fIsendmsg\fR()
- function.
- .SH "RETURN VALUE"
- Upon successful completion,
- \fIsendmsg\fR()
- shall return the number of bytes sent. Otherwise, \-1 shall
- be returned and
- .IR errno
- set to indicate the error.
- .SH ERRORS
- The
- \fIsendmsg\fR()
- function shall fail if:
- .TP
- .BR EAGAIN " or " EWOULDBLOCK
- .br
- The socket's file descriptor is marked O_NONBLOCK and the requested
- operation would block.
- .TP
- .BR EAFNOSUPPORT
- .br
- Addresses in the specified address family cannot be used with this
- socket.
- .TP
- .BR EBADF
- The
- .IR socket
- argument is not a valid file descriptor.
- .TP
- .BR ECONNRESET
- A connection was forcibly closed by a peer.
- .TP
- .BR EINTR
- A signal interrupted
- \fIsendmsg\fR()
- before any data was transmitted.
- .TP
- .BR EINVAL
- The sum of the
- .IR iov_len
- values overflows an
- .BR ssize_t .
- .TP
- .BR EMSGSIZE
- The message is too large to be sent all at once (as the socket
- requires), or the
- .IR msg_iovlen
- member of the
- .BR msghdr
- structure pointed to by
- .IR message
- is less than or equal to 0 or is greater than
- {IOV_MAX}.
- .TP
- .BR ENOTCONN
- The socket is connection-mode but is not connected.
- .TP
- .BR ENOTSOCK
- The
- .IR socket
- argument does not refer to a socket.
- .TP
- .BR EOPNOTSUPP
- The
- .IR socket
- argument is associated with a socket that does not support one or more
- of the values set in
- .IR flags .
- .TP
- .BR 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.
- .P
- If the address family of the socket is AF_UNIX, then
- \fIsendmsg\fR()
- shall fail if:
- .TP
- .BR EIO
- An I/O error occurred while reading from or writing to the file
- system.
- .TP
- .BR ELOOP
- A loop exists in symbolic links encountered during resolution of the
- pathname in the socket address.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of a component of a pathname is longer than
- {NAME_MAX}.
- .TP
- .BR ENOENT
- A component of the pathname does not name an existing file or the path
- name is an empty string.
- .TP
- .BR 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-\c
- <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.
- .br
- .P
- The
- \fIsendmsg\fR()
- function may fail if:
- .TP
- .BR EACCES
- Search permission is denied for a component of the path prefix; or
- write access to the named socket is denied.
- .TP
- .BR EDESTADDRREQ
- .br
- The socket is not connection-mode and does not have its peer address
- set, and no destination address was specified.
- .TP
- .BR EHOSTUNREACH
- .br
- The destination host cannot be reached (probably because the host is
- down or a remote router cannot reach it).
- .TP
- .BR EIO
- An I/O error occurred while reading from or writing to the file system.
- .TP
- .BR EISCONN
- A destination address was specified and the socket is already
- connected.
- .TP
- .BR ENETDOWN
- The local network interface used to reach the destination is down.
- .TP
- .BR ENETUNREACH
- .br
- No route to the network is present.
- .TP
- .BR ENOBUFS
- Insufficient resources were available in the system to perform the
- operation.
- .TP
- .BR ENOMEM
- Insufficient memory was available to fulfill the request.
- .P
- If the address family of the socket is AF_UNIX, then
- \fIsendmsg\fR()
- may fail if:
- .TP
- .BR ELOOP
- More than
- {SYMLOOP_MAX}
- symbolic links were encountered during resolution of the pathname in
- the socket address.
- .TP
- .BR ENAMETOOLONG
- .br
- 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}.
- .LP
- .IR "The following sections are informative."
- .SH "EXAMPLES"
- Done.
- .SH "APPLICATION USAGE"
- The
- \fIselect\fR()
- and
- \fIpoll\fR()
- functions can be used to determine when it is possible to send more
- data.
- .SH "RATIONALE"
- None.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIgetsockopt\fR\^(\|)",
- .IR "\fIpoll\fR\^(\|)",
- .IR "\fIpselect\fR\^(\|)",
- .IR "\fIrecv\fR\^(\|)",
- .IR "\fIrecvfrom\fR\^(\|)",
- .IR "\fIrecvmsg\fR\^(\|)",
- .IR "\fIsend\fR\^(\|)",
- .IR "\fIsendto\fR\^(\|)",
- .IR "\fIsetsockopt\fR\^(\|)",
- .IR "\fIshutdown\fR\^(\|)",
- .IR "\fIsocket\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<sys_socket.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 by the Institute of
- Electrical and Electronics Engineers, Inc and The Open Group.
- In the event of any discrepancy between this version and the original IEEE and
- The Open Group Standard, the original IEEE and The Open Group Standard
- is the referee document. The original Standard can be obtained online at
- http://www.opengroup.org/unix/online.html .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .