.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved .TH "SENDMSG" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual" .\" sendmsg .SH NAME sendmsg \- send a message on a socket using a message structure .SH SYNOPSIS .LP \fB#include .br .sp ssize_t sendmsg(int\fP \fIsocket\fP\fB, const struct msghdr *\fP\fImessage\fP\fB, int\fP \fIflags\fP\fB); .br \fP .SH DESCRIPTION .LP The \fIsendmsg\fP() function shall send a message through a connection-mode or connectionless-mode socket. If the socket is connectionless-mode, the message shall be sent to the address specified by \fBmsghdr\fP. If the socket is connection-mode, the destination address in \fBmsghdr\fP shall be ignored. .LP The \fIsendmsg\fP() function takes the following arguments: .TP 7 \fIsocket\fP Specifies the socket file descriptor. .TP 7 \fImessage\fP Points to a \fBmsghdr\fP 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 \fImsg_flags\fP member is ignored. .TP 7 \fIflags\fP Specifies the type of message transmission. The application may specify 0 or the following flag: .TP 7 MSG_EOR .RS Terminates a record (if supported by the protocol). .RE .TP 7 MSG_OOB .RS 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. .RE .sp .sp .LP The \fImsg_iov\fP and \fImsg_iovlen\fP fields of \fImessage\fP specify zero or more buffers containing the data to be sent. \fImsg_iov\fP points to an array of \fBiovec\fP structures; \fImsg_iovlen\fP shall be set to the dimension of this array. In each \fBiovec\fP structure, the \fIiov_base\fP field specifies a storage area and the \fIiov_len\fP field gives its size in bytes. Some of these sizes can be zero. The data from each storage area indicated by \fImsg_iov\fP is sent in turn. .LP Successful completion of a call to \fIsendmsg\fP() does not guarantee delivery of the message. A return value of -1 indicates only locally-detected errors. .LP 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\fP() 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\fP() function shall fail. .LP If the socket protocol supports broadcast and the specified address is a broadcast address for the socket protocol, \fIsendmsg\fP() shall fail if the SO_BROADCAST option is not set for the socket. .LP The socket in use may require the process to have appropriate privileges to use the \fIsendmsg\fP() function. .SH RETURN VALUE .LP Upon successful completion, \fIsendmsg\fP() shall return the number of bytes sent. Otherwise, -1 shall be returned and \fIerrno\fP set to indicate the error. .SH ERRORS .LP The \fIsendmsg\fP() function shall fail if: .TP 7 .B EAGAIN \fRor\fP EWOULDBLOCK The socket's file descriptor is marked O_NONBLOCK and the requested operation would block. .TP 7 .B EAFNOSUPPORT Addresses in the specified address family cannot be used with this socket. .TP 7 .B EBADF The \fIsocket\fP argument is not a valid file descriptor. .TP 7 .B ECONNRESET A connection was forcibly closed by a peer. .TP 7 .B EINTR A signal interrupted \fIsendmsg\fP() before any data was transmitted. .TP 7 .B EINVAL The sum of the \fIiov_len\fP values overflows an \fBssize_t\fP. .TP 7 .B EMSGSIZE The message is too large to be sent all at once (as the socket requires), or the \fImsg_iovlen\fP member of the \fBmsghdr\fP structure pointed to by \fImessage\fP is less than or equal to 0 or is greater than {IOV_MAX}. .TP 7 .B ENOTCONN The socket is connection-mode but is not connected. .TP 7 .B ENOTSOCK The \fIsocket\fP argument does not refer to a socket. .TP 7 .B EOPNOTSUPP The \fIsocket\fP argument is associated with a socket that does not support one or more of the values set in \fIflags\fP. .TP 7 .B 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, the SIGPIPE signal is generated to the calling thread. .sp .LP If the address family of the socket is AF_UNIX, then \fIsendmsg\fP() shall fail if: .TP 7 .B EIO An I/O error occurred while reading from or writing to the file system. .TP 7 .B ELOOP A loop exists in symbolic links encountered during resolution of the pathname in the socket address. .TP 7 .B ENAMETOOLONG A component of a pathname exceeded {NAME_MAX} characters, or an entire pathname exceeded {PATH_MAX} characters. .TP 7 .B ENOENT A component of the pathname does not name an existing file or the path name is an empty string. .TP 7 .B ENOTDIR A component of the path prefix of the pathname in the socket address is not a directory. .sp .LP The \fIsendmsg\fP() function may fail if: .TP 7 .B EACCES Search permission is denied for a component of the path prefix; or write access to the named socket is denied. .TP 7 .B EDESTADDRREQ The socket is not connection-mode and does not have its peer address set, and no destination address was specified. .TP 7 .B EHOSTUNREACH The destination host cannot be reached (probably because the host is down or a remote router cannot reach it). .TP 7 .B EIO An I/O error occurred while reading from or writing to the file system. .TP 7 .B EISCONN A destination address was specified and the socket is already connected. .TP 7 .B ENETDOWN The local network interface used to reach the destination is down. .TP 7 .B ENETUNREACH No route to the network is present. .TP 7 .B ENOBUFS Insufficient resources were available in the system to perform the operation. .TP 7 .B ENOMEM Insufficient memory was available to fulfill the request. .sp .LP If the address family of the socket is AF_UNIX, then \fIsendmsg\fP() may fail if: .TP 7 .B ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the pathname in the socket address. .TP 7 .B ENAMETOOLONG Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}. .sp .LP \fIThe following sections are informative.\fP .SH EXAMPLES .LP Done. .SH APPLICATION USAGE .LP The \fIselect\fP() and \fIpoll\fP() functions can be used to determine when it is possible to send more data. .SH RATIONALE .LP None. .SH FUTURE DIRECTIONS .LP None. .SH SEE ALSO .LP \fIgetsockopt\fP() , \fIpoll\fP() , \fIrecv\fP() , \fIrecvfrom\fP() , \fIrecvmsg\fP() , \fIselect\fP() , \fIsend\fP() , \fIsendto\fP() , \fIsetsockopt\fP() , \fIshutdown\fP() , \fIsocket\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI\fP .SH COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .