1 SEND(3C) Standard C Library Functions SEND(3C)
2
3 NAME
4 send, sendto, sendmsg - send a message from a socket
5
6 LIBRARY
7 Standard C Library (libc, -lc)
8
9 SYNOPSIS
10 #include <sys/types.h>
11 #include <sys/socket.h>
12
13 ssize_t
14 send(int s, const void *msg, size_t len, int flags);
15
16 ssize_t
17 sendto(int s, const void *msg, size_t len, int flags,
18 const struct sockaddr *to, socklen_t tolen);
19
20 ssize_t
21 sendmsg(int s, const struct msghdr *msg, int flags);
22
23 DESCRIPTION
24 The send(), sendto(), and sendmsg() functions are used to transmit a
25 message to another transport end-point. The send() function can be used
26 only when the socket is in a connected state. See connect(3C). The
27 sendto() and sendmsg() functions can be used at any time. The s socket
28 is created with socket(3C).
29
30 The address of the target is supplied by to with a tolen parameter used
31 to specify the size. The length of the message is supplied by the len
32 parameter. For socket types such as SOCK_DGRAM and SOCK_RAW that require
33 atomic messages, the error EMSGSIZE is returned and the message is not
34 transmitted when it is too long to pass atomically through the underlying
35 protocol. The same restrictions do not apply to SOCK_STREAM sockets.
36
37 A return value -1 indicates locally detected errors. It does not imply a
38 delivery failure.
39
40 If the socket does not have enough buffer space available to hold a
41 message, the send() function blocks the message, unless the socket has
42 been placed in non-blocking I/O mode (see fcntl(2)). The select(3C) or
43 poll(2) call can be used to determine when it is possible to send more
44 data.
45
46 The flags parameter is formed from the bitwise OR of zero or more of the
47 following:
48
49 MSG_OOB Send out-of-band data on sockets that support this notion.
50 The underlying protocol must also support out-of-band
51 data. Only SOCK_STREAM sockets created in the AF_INET or
52 the AF_INET6 address family support out-of-band data.
53
54 MSG_DONTROUTE The SO_DONTROUTE option is turned on for the duration of
55 the operation. It is used only by diagnostic or routing
56 programs.
57
58 MSG_NOSIGNAL Don't generate the SIGPIPE signal when a stream-oriented
59 socket is no longer connected.
60
61 See recv(3C) for a description of the msghdr structure.
62
63 RETURN VALUES
64 Upon successful completion, these functions return the number of bytes
65 sent. Otherwise, they return -1 and set errno to indicate the error.
66
67 ERRORS
68 The send(), sendto(), and sendmsg() functions return errors under the
69 following conditions:
70
71 [EBADF] s is not a valid file descriptor.
72
73 [ECONNRESET] The s argument refers to a connection oriented socket
74 and the connection was forcibly closed by the peer and
75 is no longer valid. I/O can no longer be performed to
76 filedes.
77
78 [EINTR] The operation was interrupted by delivery of a signal
79 before any data could be buffered to be sent.
80
81 [EMSGSIZE] The message is too large to be sent all at once (as
82 the socket requires), or the msg_iovlen member of the
83 msghdr structure pointed to by message is less than or
84 equal to 0 or is greater than {IOV_MAX}.
85
86 [ENOMEM] Insufficient memory is available to complete the
87 operation.
88
89 [ENOSR] Insufficient STREAMS resources are available for the
90 operation to complete.
91
92 [ENOTSOCK] s is not a socket.
93
94 [EWOULDBLOCK] The socket is marked non-blocking and the requested
95 operation would block. EWOULDBLOCK is also returned
96 when sufficient memory is not immediately available to
97 allocate a suitable buffer. In such a case, the
98 operation can be retried later.
99
100 [ECONNREFUSED] The requested connection was refused by the peer. For
101 connected IPv4 and IPv6 datagram sockets, this
102 indicates that the system received an ICMP
103 "Destination Port Unreachable" message from the peer
104 in response to some prior transmission.
105
106 The send() and sendto() functions return errors under the following
107 conditions:
108
109 [EINVAL] The len argument overflows a ssize_t.
110
111 Inconsistent port attributes for system call.
112
113 The sendto() function returns errors under the following conditions:
114
115 [EINVAL] The value specified for the tolen parameter is not the
116 size of a valid address for the specified address
117 family.
118
119 [EISCON] A destination address was specified and the socket is
120 already connected.
121
122 The sendmsg() function returns errors under the following conditions:
123
124 [EINVAL] The msg_iovlen member of the msghdr structure pointed
125 to by msg is less than or equal to 0, or the sum of
126 the iov_len values in the msg_iov array overflows a
127 ssize_t.
128
129 One of the iov_len values in the msg_iov array member
130 of the msghdr structure pointed to by msg is negative,
131 or the sum of the iov_len values in the msg_iov array
132 overflows a ssize_t.
133
134 msg_iov contents are inconsistent with port
135 attributes.
136
137 The send() function returns errors under the following conditions:
138
139 [EPIPE] The socket is shut down for writing, or the socket is
140 connection-mode and is no longer connected. In the
141 latter case, if the socket is of type SOCK_STREAM, the
142 SIGPIPE signal is generated to the calling thread
143 unless the MSG_NOSIGNAL flag is set.
144
145 MT-LEVEL
146 Safe
147
148 SEE ALSO
149 fcntl(2), poll(2), write(2), connect(3C), getsockopt(3C), recv(3C),
150 select(3C), sockaddr(3C), socket(3C), socket.h(3HEAD), attributes(5)
151
152 illumos August 2, 2018 illumos