CS 3411 Systems Programming

Transcription

1 CS 3411 Systems Programming Department of Computer Science Michigan Technological University Sockets

2 Today's Topics New Way of Communicating Between Processes Sockets

3 Standard" Unix Processes/IPC IPC stands for Inter-Process Communication in this context Until know, we did communication through: File system: File descriptors, read()/write() and pipes IPC construct is shared through normal process hierarchy inheritance rules, pipes created through pipe() are nameless Totally reliable byte stream between producer and consumer Ties in to conventional UNIX semantics of process creation and termination

4 New Ideas We want to create a generalization of the pipe construct for network-based I/O That means we still want le descriptors and read()/write() calls to work We need to take some extra features into consideration: Network Protocol Stacks Network Naming Conventions Requirements of Protocol-Specic Message Passing The BSD and UNIX solution is the socket() call. Most concisely, it can be described as a communication endpoint. The call returns a le descriptor. int socket(int domain, int type, int protocol);

5 Communication Domain This basically species a protocol stack. Some systems contain a richer set of communication domains than others AF_UNIX or AF_LOCAL: The UNIX IPC domain, local to a single machine AF_INET: The Internet domain, global in scope AF_INET6: The Internet domain, using IPv6 Once a domain is specied, we know how to associate a name with the socket As well as knowing the semantics of supported IPC mechanisms

6 Unix Domain Sockets (in brief) Let's start with the simpler (but less interesting) case of the AF_UNIX communication domain The header le <sys/un.h> denes addresses #d e f i n e UNIX_PATH_MAX 108 s t r u c t sockaddr_un { unsigned s h o r t sun_ family ; / AF_UNIX / char sun_path [UNIX_PATH_MAX ] ; / Pathname / } ; Some examples of Unix domain sockets can be found under the /dev directory

7 Types of Sockets in Unix Domain We'll be looking at two types of sockets available in Unix SOCK_DGRAM provides datagram communication semantics Only promises best-eort delivery Unix may discard datagrams in times of buer congestion Connectionless!

8 Types of Sockets in Unix Domain We'll be looking at two types of sockets available in Unix SOCK_STREAM implements virtual circuit communication semantics Reliable FIFO point-to-point communications Appears as a byte stream to applications This is actually how some later UNIX systems implement pipes! Socket type should be chosen according to the needs of the application, and should be programmed in accordance with well-specied delivery semantics of chosen type.

9 Operations on Sockets Binding a name to a socket: i n t b i n d ( i n t s o c k f d, s t r u c t s o c k a d d r my_addr, i n t a d d r l e n ) ; Sending datagram on a socket (asynchronous): i n t s e n d t o ( i n t s, const v o i d msg, i n t l e n, unsigned i n t f l a g s const s t r u c t s o c k a d d r to, i n t t o l e n ) ; Receiving datagram from a socket (synchronous, blocking): i n t r e c v f r o m ( i n t s, v o i d buf, i n t l e n, unsigned i n t f l a g s, s t r u c t s o c k a d d r from, i n t f r o m l e n ) ;

10 Server I #i n c l u d e <e r r n o. h> #i n c l u d e < s t r i n g s. h> #i n c l u d e <s t d i o. h> #i n c l u d e <u n i s t d. h> #i n c l u d e <s y s / s o c k e t. h> #i n c l u d e <s y s /un. h> main ( ) { s h o r t p_len ; i n t socket_fd, cc, h_len, f s i z e, namelen ; v o i d p r i n t s u n ( ) ; s t r u c t sockaddr_un s_un, from ; s i z e _ t a d d r l e n g t h ; s t r u c t { char head ; u_long body ; char t a i l ; } msg ; s o c k e t _ f d = s o c k e t (AF_UNIX, SOCK_DGRAM, 0 ) ; s_un. sun_ family = AF_UNIX ;

11 Server II } s t r c p y ( s_un. sun_path, " udgram " ) ; a d d r l e n g t h = s i z e o f ( s_un. s u n _ f a m i l y ) + s i z e o f ( s_un. sun_path ) ; u n l i n k ( " udgram " ) ; b i n d ( socket_fd, ( s t r u c t s o c k a d d r )&s_un, a d d r l e n g t h ) ; f o r ( ; ; ) { f s i z e = s i z e o f ( from ) ; cc = r e c v f r o m ( socket_fd, &msg, s i z e o f ( msg ), 0, ( s t r u c t s o c k a d d r )& from, & f s i z e ) ; p r i n t s u n (&from, " unix_rdgram : ", " Packet from " ) ; p r i n t f ( " Got d a t a ::% c%l d%c \n", msg. head, msg. body, msg. t a i l ) ; f f l u s h ( s t d o u t ) ; } v o i d p r i n t s u n ( Sun, s1, s2 ) s t r u c t sockaddr_un Sun ; char s1, s2 ; { p r i n t f ( "%s %s \n", s1, s2 ) ; p r i n t f ( " f a m i l y <%d> a d d r <%s >\n", Sun >sun_ family, Sun >sun_path ) ; }

12 Client I #i n c l u d e <e r r n o. h> #i n c l u d e < s t r i n g s. h> #i n c l u d e <s t d i o. h> #i n c l u d e <u n i s t d. h> #i n c l u d e <s y s / s o c k e t. h> #i n c l u d e <s y s /un. h> main ( ) { i n t socket_fd, cc ; // l o n g g e t p i d ( ) ; s t r u c t sockaddr_un d e s t ; s t r u c t { char head ; u_long body ; char t a i l ; } msgbuf ; s o c k e t _ f d = s o c k e t (AF_UNIX, SOCK_DGRAM, 0 ) ; d e s t. s u n _ f a m i l y = AF_UNIX ; s t r c p y ( d e s t. sun_path, " udgram " ) ; msgbuf. head = '< ' ;

13 Client II msgbuf. body = ( u_long ) g e t p i d ( ) ; msgbuf. t a i l = '> ' ; } cc = s e n d t o ( socket_fd, &msgbuf, s i z e o f ( msgbuf ), 0, ( s t r u c t s o c k a d d r )& d e s t, s i z e o f ( d e s t ) ) ;

14 Sockets and the Internet (IPv4) AF_INET communication domain SOCK_DGRAM - Same as before! UDP/IP SOCK_STREAM - Same as before! TCP/IP We need a way to associate names with sockets to be able to do network I/O through a socket le descriptor

15 Sockets and the Internet (IPv4) The header le <netinet/in.h> denes a 32-bit for an Internet host. This actually identies a specic network interface on a specic system on the Internet. It's represented by a 32 bit unsigned number s t r u c t in_addr { u32 s_addr ; }