socket - create an endpoint for communication

creates an endpoint for communication and returns a descriptor. The 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 the include file The currently understood formats are AF_UNIX (UNIX internal protocols) AF_INET (ARPA Internet protocols) AF_ISO (ISO protocols) AF_NS (Xerox Network Systems protocols) AF_IMPLINK (IMP “host at IMP” link layer) The socket has the indicated which specifies the semantics of communication. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
A type provides sequenced, reliable, two-way connection based byte streams. An out-of-band data transmission mechanism may be supported. A socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length). A socket may provide a sequenced, reliable, two-way connection-based data transmission path for datagrams of fixed maximum length; a consumer may be required to read an entire packet with each read system call. This facility is protocol specific, and presently implemented only for sockets provide access to internal network protocols and interfaces. The types which is available only to the super-user, and which is planned, but not yet implemented, are not described here. The 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 protocol 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 communication is to take place; see Sockets of type are full-duplex byte streams, similar to pipes. A stream socket must be in a state before any data may be sent or received on it. A connection to another socket is created with a call. Once connected, data may be transferred using and calls or some variant of the and calls. When a session has been completed a may be performed. Out-of-band data may also be transmitted as described in and received as described in The communications protocols used to implement a insure 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 broken and calls will indicate an error with -1 returns and with as the specific code in the global variable The protocols optionally keep sockets by forcing transmissions roughly every minute in the absence of other activity. An error is then indicated if no response can be elicited on an otherwise idle connection for a extended period (e.g. 5 minutes). A signal is raised if a process sends on a broken stream; this causes naive processes, which do not handle the signal, to exit. sockets employ the same system calls as sockets. The only difference is that calls will return only the amount of data requested, and any remaining in the arriving packet will be discarded. and sockets allow sending of datagrams to correspondents named in calls. Datagrams are generally received with which returns the next datagram with its return address. An call can be used to specify a process group to receive a signal when the out-of-band data arrives. It may also enable non-blocking I/O and asynchronous notification of I/O events via The operation of sockets is controlled by socket level These options are defined in the file and are used to set and get options, respectively. A -1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket. The protocol type or the specified protocol is not supported within this domain. The per-process descriptor table is full. The system file table is full. Permission to create a socket of the specified type and/or protocol is denied. Insufficient buffer space is available. The socket cannot be created until sufficient resources are freed.

HISTORY
The function call appeared in BSD 4.2.

"An Introductory 4.3 BSD Interprocess Communication Tutorial" is reprinted in

"BSD Interprocess Communication Tutorial" is reprinted in