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28 .\" From: @(#)send.2 8.2 (Berkeley) 2/21/94
31 .Dd September 13, 2006
38 .Nd send a message from a socket
45 .Fn send "int s" "const void *msg" "size_t len" "int flags"
47 .Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen"
49 .Fn sendmsg "int s" "const struct msghdr *msg" "int flags"
59 are used to transmit a message to another socket.
63 may be used only when the socket is in a
69 may be used at any time.
71 The address of the target is given by
76 The length of the message is given by
78 If the message is too long to pass atomically through the
79 underlying protocol, the error
82 the message is not transmitted.
84 No indication of failure to deliver is implicit in a
86 Locally detected errors are indicated by a return value of -1.
88 If no messages space is available at the socket to hold
89 the message to be transmitted, then
91 normally blocks, unless the socket has been placed in
92 non-blocking I/O mode.
95 system call may be used to determine when it is possible to
100 argument may include one or more of the following:
102 #define MSG_OOB 0x00001 /* process out-of-band data */
103 #define MSG_DONTROUTE 0x00004 /* bypass routing, use direct interface */
104 #define MSG_EOR 0x00008 /* data completes record */
105 #define MSG_EOF 0x00100 /* data completes transaction */
106 #define MSG_NOSIGNAL 0x20000 /* do not generate SIGPIPE on EOF */
113 data on sockets that support this notion (e.g.\&
115 the underlying protocol must also support
119 is used to indicate a record mark for protocols which support the
122 requests that the sender side of a socket be shut down, and that an
123 appropriate indication be sent at the end of the specified data;
124 this flag is only implemented for
130 is usually used only by diagnostic or routing programs.
134 generation when writing a socket that
139 for a description of the
143 The call returns the number of characters sent, or -1
144 if an error occurred.
156 An invalid descriptor was specified.
158 The destination address is a broadcast address, and
160 has not been set on the socket.
166 An invalid user space address was specified for an argument.
168 The socket requires that message be sent atomically,
169 and the size of the message to be sent made this impossible.
171 The socket is marked non-blocking and the requested operation
174 The system was unable to allocate an internal buffer.
175 The operation may succeed when buffers become available.
177 The output queue for a network interface was full.
178 This generally indicates that the interface has stopped sending,
179 but may be caused by transient congestion.
180 .It Bq Er EHOSTUNREACH
181 The remote host was unreachable.
183 A destination address was specified and the socket is already connected.
184 .It Bq Er ECONNREFUSED
185 The socket received an ICMP destination unreachable message
186 from the last message sent.
187 This typically means that the
188 receiver is not listening on the remote port.
190 The remote host was down.
192 The remote network was down.
196 socket was jailed and the source
197 address specified in the IP header did not match the IP
198 address bound to the prison.
200 The socket is unable to send anymore data
201 .Dv ( SBS_CANTSENDMORE
202 has been set on the socket).
203 This typically means that the socket
221 does not necessarily block until the data has been transferred, it
222 is possible to transfer an open file descriptor across an
229 it before it has actually been sent, the result being that the receiver
230 gets a closed file descriptor.
231 It is left to the application to
232 implement an acknowledgment mechanism to prevent this from happening.