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>Chapter 38. TCP/IP Library Reference</TD
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NAME="NET-COMMON-TCPIP-MANPAGES-SEND">send</H1
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>SEND(2) System Calls Manual SEND(2)
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NAME
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send, sendto, sendmsg - send a message from a socket
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SYNOPSIS
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#include <sys/types.h>
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#include <sys/socket.h>
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ssize_t
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send(int s, const void *msg, size_t len, int flags);
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ssize_t
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sendto(int s, const void *msg, size_t len, int flags,
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const struct sockaddr *to, socklen_t tolen);
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ssize_t
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sendmsg(int s, const struct msghdr *msg, int flags);
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DESCRIPTION
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send(), sendto(), and sendmsg() are used to transmit a message to another
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socket. send() may be used only when the socket is in a connected state,
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while sendto() and sendmsg() may be used at any time.
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The address of the target is given by to with tolen specifying its size.
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The length of the message is given by len. If the message is too long to
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pass atomically through the underlying protocol, the error EMSGSIZE is
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returned, and the message is not transmitted.
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No indication of failure to deliver is implicit in a send(). Locally
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detected errors are indicated by a return value of -1.
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If no messages space is available at the socket to hold the message to be
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transmitted, then send() normally blocks, unless the socket has been
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placed in non-blocking I/O mode. The select(2) or poll(2) system calls
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may be used to determine when it is possible to send more data.
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The flags parameter may include one or more of the following:
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#define MSG_OOB 0x1 /* process out-of-band data */
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#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */
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The flag MSG_OOB is used to send ``out-of-band'' data on sockets that
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support this notion (e.g., SOCK_STREAM); the underlying protocol must
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also support ``out-of-band'' data. MSG_DONTROUTE is usually used only by
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diagnostic or routing programs.
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See recv(2) for a description of the msghdr structure.
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RETURN VALUES
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The call returns the number of characters sent, or -1 if an error
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occurred.
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ERRORS
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send(), sendto(), and sendmsg() fail if:
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[EBADF] An invalid descriptor was specified.
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[ENOTSOCK] The argument s is not a socket.
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[EFAULT] An invalid user space address was specified for a
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parameter.
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[EMSGSIZE] The socket requires that message be sent atomically,
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and the size of the message to be sent made this
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impossible.
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[EAGAIN] The socket is marked non-blocking and the requested
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operation would block.
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[ENOBUFS] The system was unable to allocate an internal buffer.
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The operation may succeed when buffers become avail-
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able.
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[ENOBUFS] The output queue for a network interface was full.
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This generally indicates that the interface has
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stopped sending, but may be caused by transient con-
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gestion.
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[EACCES] The SO_BROADCAST option is not set on the socket, and
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a broadcast address was given as the destination.
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[EHOSTUNREACH] The destination address specified an unreachable host.
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[EINVAL] The flags parameter is invalid.
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[EHOSTDOWN] The destination address specified a host that is down.
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[ENETDOWN] The destination address specified a network that is
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down.
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[ECONNREFUSED] The destination host rejected the message (or a previ-
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ous one). This error can only be returned by con-
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nected sockets.
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[ENOPROTOOPT] There was a problem sending the message. This error
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can only be returned by connected sockets.
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[EDESTADDRREQ] The socket is not connected, and no destination
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address was specified.
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[EISCONN] The socket is already connected, and a destination
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address was specified.
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In addition, send() and sendto() may return the following error:
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[EINVAL] len was larger than SSIZE_MAX.
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Also, sendmsg() may return the following errors:
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[EINVAL] The sum of the iov_len values in the msg_iov array
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overflowed an ssize_t.
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[EMSGSIZE] The msg_iovlen member of msg was less than 0 or larger
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than IOV_MAX.
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[EAFNOSUPPORT] Addresses in the specified address family cannot be
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used with this socket.
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SEE ALSO
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fcntl(2), getsockopt(2), poll(2), recv(2), select(2), poll(2), socket(2),
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write(2)
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HISTORY
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The send() function call appeared in 4.2BSD.
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BSD July 28, 1998 BSD
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</PRE
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