16.2. Socket Descriptors
A socket is an abstraction of a communication endpoint. Just as they would use file descriptors to access a file, applications use socket descriptors to access sockets. Socket descriptors are implemented as file descriptors in the UNIX System. Indeed, many of the functions that deal with file descriptors, such as read and write, will work with a socket descriptor.To create a socket, we call the socket function. #include <sys/socket.h>
int socket(int domain , int type , int protocol );
| | Returns: file (socket) descriptor if OK, 1 on error | The domain argument determines the nature of the communication, including the address format (described in more detail in the next section). Section 17.3. Most systems define the AF_LOCAL domain also, which is an alias for AF_UNIX. The AF_UNSPEC domain is a wildcard that represents "any" domain. Historically, some platforms provide support for additional network protocols, such as AF_IPX for the NetWare protocol family, but domain constants for these protocols are not defined by the POSIX.1 standard.The type argument determines the type of the socket, which further determines the communication characteristics. The socket types defined by POSIX.1 are summarized in Section 3.3) | deallocates the socket |
| dup, dup2 (Section 3.12) | duplicates the file descriptor as normal |
| fchdir (Section 4.22) | fails with errno set to ENOTDIR
|
| fchmod (Section 4.9) | unspecified |
| fchown (Section 4.11) | implementation defined |
| fcntl (Section 3.14) | some commands supported, including F_DUPFD, F_GETFD, F_GETFL, F_GETOWN, F_SETFD, F_SETFL, and F_SETOWN
|
| fdatasync, fsync (Section 3.13) | implementation defined |
| fstat (Section 4.2) | some stat structure members supported, but how left up to the implementation |
| ftruncate (Section 4.13) | unspecified |
| getmsg, getpmsg (Section 14.4) | works if sockets are implemented with STREAMS (i.e., on Solaris) |
| ioctl (Section 3.15) | some commands work, depending on underlying device driver |
| lseek (Section 3.6) | implementation defined (usually fails with errno set to ESPIPE) |
| mmap (Section 14.9) | unspecified |
| poll (Section 14.5.2) | works as expected |
| putmsg, putpmsg (Section 14.4) | works if sockets are implemented with STREAMS (i.e., on Solaris) |
| read (Section 3.7) and readv (Section 14.7) | equivalent to recv (Section 16.5) without any flags |
| select (Section 14.5.1) | works as expected |
| write (Section 3.8) and writev (Section 14.7) | equivalent to send (Section 16.5) without any flags |
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