UNIX Network Programming Volume 1, Third Edition [Electronic resources] : The Sockets Networking API نسخه متنی

15.3 socketpair Function

The socketpair function creates two sockets that are then connected together. This function applies only to Unix domain sockets.

The

family must be AF_LOCAL and the

protocol must be 0. The

type , however, can be either SOCK_STREAM or SOCK_DGRAM. The two socket descriptors that are created are returned as

sockfd[0] and

sockfd[1] .

This function is similar to the Unix pipe function: Two descriptors are returned, and each descriptor is connected to the other. Indeed, Berkeley-derived implementations employ pipe by performing the same internal operations as socketpair (pp. 253254 of TCPv3).

The two created sockets are unnamed; that is, there is no implicit bind involved.

The result of socketpair with a

type of SOCK_STREAM is called a

stream pipe . It is similar to a regular Unix pipe (created by the pipe function), but a stream pipe is

full-duplex ; that is, both descriptors can be read and written. We show a picture of a stream pipe created by socketpair in Figure 15.7.

POSIX does not require full-duplex pipes. On SVR4, pipe returns two full-duplex descriptors, while Berkeley-derived kernels traditionally return two half-duplex descriptors (Figure 17.31 of TCPv3).