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NAME
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socket - create an endpoint for communication
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SYNOPSIS
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#include <network.h>
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int socket(int domain, int type, int protocol);
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DESCRIPTION
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Socket creates an endpoint for communication and returns a
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descriptor.
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The domain parameter specifies a communications domain
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within which communication will take place; this selects
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the protocol family which should be used. These families
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are defined in <sys/socket.h>. The currently understood
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formats include:
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PF_INET
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IPv4 Internet protocols; see ip(4)
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The socket has the indicated type, which specifies the
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semantics of communication. Currently defined types are:
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SOCK_STREAM
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Provides sequenced, reliable, two-way connection-
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based byte streams. An out-of-band data transmis-
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sion mechanism may be supported.
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SOCK_DGRAM
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Supports datagrams (connectionless, unreliable mes-
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sages of a fixed maximum length).
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SOCK_SEQPACKET
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Provides a sequenced, reliable, two-way connection-
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based data transmission path for datagrams of fixed
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maximum length; a consumer is required to read an
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entire packet with each read system call.
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SOCK_RAW
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Provides raw network protocol access.
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The protocol specifies a particular protocol to be used
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with the socket. Normally only a single protocol exists
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to support a particular socket type within a given proto-
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col family. However, it is possible that many protocols
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may exist, in which case a particular protocol must be
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specified in this manner. The protocol number to use is
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particular to the "communication domain" in which communi-
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cation is to take place; see protocols(5). See getpro-
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toent(3) on how to map protocol name strings to protocol
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numbers.
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Sockets of type SOCK_STREAM are full-duplex byte streams,
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similar to pipes. A stream socket must be in a connected
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state before any data may be sent or received on it. A
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connection to another socket is created with a connect(2)
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call. Once connected, data may be transferred using
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read(2) and write(2) calls or some variant of the send(2)
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and recv(2) calls. When a session has been completed a
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close(2) may be performed. Out-of-band data may also be
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transmitted as described in send(2) and received as
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described in recv(2).
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The communications protocols which implement a SOCK_STREAM
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ensure that data is not lost or duplicated. If a piece of
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data for which the peer protocol has buffer space cannot
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be successfully transmitted within a reasonable length of
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time, then the connection is considered When SO_KEEPALIVE
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is enabled on the socket the protocol checks in a proto-
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col-specific manner if the other end is still alive.
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SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams
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to correspondents named in send(2) calls. Datagrams are
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generally received with recvfrom(2), which returns the
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next datagram with its return address.
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When the network signals an error condition to the proto-
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col module (e.g. using a ICMP message for IP) the pending
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error flag is set for the socket. The next operation on
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this socket will return the error code of the pending
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error. For some protocols it is possible to enable a per-
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socket error queue to retrieve detailed information about
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the error; see IP_RECVERR in ip(4).
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The operation of sockets is controlled by socket level
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options. These options are defined in <sys/socket.h>.
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Setsockopt(2) and getsockopt(2) are used to set and get
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options, respectively.
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RETURN VALUES
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-1 is returned if an error occurs; otherwise the return
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value is a descriptor referencing the socket.
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ERRORS
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EPROTONOSUPPORT
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The protocol type or the specified protocol is not
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supported within this domain.
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EMFILE There are too many open files.
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EACCES Permission to create a socket of the specified
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type and/or protocol is denied.
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ENOBUFS or ENOMEM
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Insufficient memory is available. The socket can-
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not be created until sufficient resources are
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freed.
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EINVAL Unknown protocol, or protocol family not avail-
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able.
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