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