SOCKET

C Interface

     #include <sys/types.h>

     #include <sys/socket.h>



     int socket(af, type, protocol)

     int af, type, protocol;

Description

The socket call creates an endpoint for communication and returns a descriptor. The socket descriptor returned is used in all subsequent socket-related system calls.he af parameter specifies an address family to be used to interpret addresses in later operations that specify the socket. These address families are defined in the include file <sys/socket.h>. The only currently supported address families are as follows:

   AF_INET  (DARPA Internet addresses)

   AF_UNIX  (directory path names on a local node)




	NOTE: If you do not have a supported networking link product installed on your system and you attempt to use the address family `AF_INET`, then the `EAFNOSUPPORT` error is returned. The `AF_UNIX` address family can be used to create socket connections without requiring a networking link product to be installed.

The type parameter specifies the communication semantics for the socket. Currently defined types are as follows:

   SOCK_STREAM

   SOCK_DGRAM

A SOCK_STREAM type provides sequenced, reliable, two-way, connection-based byte streams. A SOCK_DGRAM socket supports datagrams, which are connection-less, unreliable messages of a fixed, typically small, maximum length.

The protocol parameter specifies a particular protocol to be used with the socket. The protocol number to use depends on the communication domain in which communication is to take place. (Refer to the chapter on name services routines.) Protocol can be supplied as zero, in which case the system chooses a protocol type to use, based on the socket type.

Sockets of type SOCK_STREAM are byte streams similar to UNIX pipes, except that they are full-duplex instead of half-duplex. A stream socket must be in a connected state before any data can be sent or received on it. A connection to another socket is created with a connect or accept call. Once connected, data can be transferred using send and recv calls or read and write calls. When a session has been completed, a close can be performed.

The communications protocol (TCP) used to implement SOCK_STREAM for AF_INET sockets, ensures that data is not lost or duplicated. If a peer has buffer space for data and the data cannot be successfully transmitted within a reasonable length of time, the connection is considered broken and the next recv call indicates an error with errno set to ETIMEDOUT. An end-of-file condition (zero bytes read) is returned if a process tries to read on a broken stream. To use the errno global variable, include the file <sys/errno.h>.

SOCK_DGRAM sockets allow sending of messages to correspondents named in sendto calls. It is also possible to receive messages at a SOCK_DGRAM socket with recvfrom. The sockets operation is controlled by socket level options set by the setsockopt system call. (Refer to getsockopt or setsockopt.) These options are defined in the file <sys/socket.h>.

Return Value

If the call is successful, a valid file descriptor referencing the socket is returned. If it fails, a -1 is returned, and an error code is stored in errno.

Errors

The following errors are returned by socket:

[EHOSTDOWN]: The networking subsystem has not been started.
[EAFNOSUPPORT]: The specified address family is not supported on this version of the system.
[ESOCKTNOSUPPORT]: The specified socket type is not supported in this address family.
[EPROTONOSUPPORT]: The specified protocol is not supported.
[EMFILE]: The per-process descriptor table is full.
[ENOBUFS]: No buffer space is available. The socket cannot be created.
[ENFILE]: The system's table of open files is temporarily full, and no more socket calls can be accepted.
[EPROTOTYPE]: The type of socket and protocol do not match.
[ETIMEDOUT]: The connection timed out.

MPE/iX Specific

Break mode is supported on MPE/iX. This is true of all Berkeley Sockets/iX system calls described in this section.

Author

UCB (University of California at Berkeley)