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SEND !!!SEND NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS CONFORMING TO NOTE SEE ALSO ---- !!NAME send, sendto, sendmsg - send a message from a socket !!SYNOPSIS __#include __ #include __ __int send(int__ ''s''__, const void *__''msg''__, size_t__ ''len''__, int__ ''flags''__); int sendto(int__ ''s''__, const void *__''msg''__, size_t__ ''len''__, int__ ''flags''__, const struct sockaddr *__''to''__, socklen_t__ ''tolen''__); int sendmsg(int__ ''s''__, const struct msghdr *__''msg''__, int__ ''flags''__);__ !!DESCRIPTION __Send__, __sendto__, and __sendmsg__ are used to transmit a message to another socket. __Send__ may be used only when the socket is in a ''connected'' state, while __sendto__ and __sendmsg__ may be used at any time. The address of the target is given by ''to'' with ''tolen'' specifying its size. The length of the message is given by ''len''. If the message is too long to pass atomically through the underlying protocol, the error __EMSGSIZE__ is returned, and the message is not transmitted. No indication of failure to deliver is implicit in a __send__. Locally detected errors are indicated by a return value of -1. When the message does not fit into the send buffer of the socket, __send__ normally blocks, unless the socket has been placed in non-blocking I/O mode. In non-blocking mode it would return __EAGAIN__ in this case. The select(2) call may be used to determine when it is possible to send more data. The ''flags'' parameter is a flagword and can contain the following flags: __MSG_OOB__ Sends ''out-of-band'' data on sockets that support this notion (e.g. __SOCK_STREAM__); the underlying protocol must also support ''out-of-band'' data. __MSG_DONTROUTE__ Dont't use a gateway to send out the packet, only send to hosts on directly connected networks. This is usually used only by diagnostic or routing programs. This is only defined for protocol families that route; packet sockets don't. __MSG_DONTWAIT__ Enables non-blocking operation; if the operation would block, __EAGAIN__ is returned (this can also be enabled using the __O_NONBLOCK__ with the __F_SETFL fcntl(2)).__ __MSG_NOSIGNAL__ Requests not to send __SIGPIPE__ on errors on stream oriented sockets when the other end breaks the connection. The __EPIPE__ error is still returned. __MSG_CONFIRM__ (Linux 2.3+ only) Tell the link layer that forward process happened: you got a successful reply from the other side. If the link layer doesn't get this it'll regularly reprobe the neighbour (e.g. via a unicast ARP). Only valid on __SOCK_DGRAM__ and __SOCK_RAW__ sockets and currently only implemented for IPv4 and IPv6. See arp(7) for details. The definition of the ''msghdr'' structure follows. See recv(2) and below for an exact description of its fields. struct msghdr { void * msg_name; /* optional address */ socklen_t msg_namelen; /* size of address */ struct iovec * msg_iov; /* scatter/gather array */ size_t msg_iovlen; /* # elements in msg_iov */ void * msg_control; /* ancillary data, see below */ socklen_t msg_controllen; /* ancillary data buffer len */ int msg_flags; /* flags on received message */ }; You may send control information using the ''msg_control'' and ''msg_controllen'' members. The maximum control buffer length the kernel can process is limited per socket by the __net.core.optmem_max__ sysctl; see socket(7). !!RETURN VALUE The calls return the number of characters sent, or -1 if an error occurred. !!ERRORS These are some standard errors generated by the socket layer. Additional errors may be generated and returned from the underlying protocol modules; see their respective manual pages. __EBADF__ An invalid descriptor was specified. __ENOTSOCK__ The argument ''s'' is not a socket. __EFAULT__ An invalid user space address was specified for a parameter. __EMSGSIZE__ The socket requires that message be sent atomically, and the size of the message to be sent made this impossible. __EAGAIN__ or __EWOULDBLOCK__ The socket is marked non-blocking and the requested operation would block. __ENOBUFS__ The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion. (This cannot occur in Linux, packets are just silently dropped when a device queue overflows.) __EINTR__ A signal occurred. __ENOMEM__ No memory available. __EINVAL__ Invalid argument passed. __EPIPE__ The local end has been shut down on a connection oriented socket. In this case the process will also receive a __SIGPIPE__ unless __MSG_NOSIGNAL__ is set. !!CONFORMING TO 4.4BSD, SVr4, POSIX 1003.1g draft (these function calls appeared in 4.2BSD). __MSG_CONFIRM__ is a Linux extension. !!NOTE The prototypes given above follow the Single Unix Specification, as glibc2 also does; the ''flags'' argument was `int' in BSD 4.*, but `unsigned int' in libc4 and libc5; the ''len'' argument was `int' in BSD 4.* and libc4, but `size_t' in libc5; the ''tolen'' argument was `int' in BSD 4.* and libc4 and libc5. See also accept(2). !!SEE ALSO fcntl(2), recv(2), select(2), getsockopt(2), sendfile(2), socket(2), write(2), socket(7), ip(7), tcp(7), udp(7) ----
6 pages link to
sendto(2)
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udp(7)
socketcall(2)
Man2s
socket(7)
sendmsg(2)
NetworkProgrammingOld
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