Overview n Introduction to UNIX q UNIX commands

Overview n Introduction to UNIX q UNIX commands q Text editors q C/C++ compiling n Sockets

UNIX –Getting Started n Where/How? q Install linux on your home machine (dedicated machine or dual boot) n q Work on the sun machines in the pod n q q n Getting familiar with linux is really useful even beyond this class Log in and use the X-windows interface; each window will give you a unix shell Log in to bingsuns from home (preferrably using a secure shell client like puttyssh) Run VNC from your windows machine to get a unix work area (from a server running on bingsuns); help on class webpage This is a brief tutorial; many more detailed ones on class page

UNIX Commands change directory: cd dirname change to home dir: cd copy a file: cp old new move (rename) a file: mv old new remove a file: rm fname print working directory: pwd a new directory: mkdir new get the manual for command: man command type contents of a file: cat filename show by screens: less filename somecommand option argument|less count lines, words, chars: wc filename find a file in current dir: find. –name foo. bar -print search for something in files: grep “some thing” filename grep something /some/path/*. c grep –r something /some/folder

Text Editors in UNIX n VI (Visually Improved). q Example: vi filename. c q Enter : q to quit. n Pico q Pico is similar to Pine mail user agent. Good for first time UNIX users. Emacs q GNU Emacs Manual: http: //www. delorie. com/gnu/docs/emacs_toc. html XEmacs q A version for X-Windows. n n n Some exotic editors for linux out there now (anjuta, kwrite …)

Compilng C/C++ and Java n Compiling with gcc –o tcp. Client. c other. File. c –lnsl -lsocket n Use g++ in the same way for C++ files You should not ignore warnings. n n n Don’t forget –lnsl –lsocket on unix machines; they link in the name services library and the sockets library. On Linux, you don’t need –lsocket

Sockets Programming Socket to me!

Outline n What is a socket? q n Preliminaries q q n n n Ports Data structures and conversion DNS resolution TCP server with example UDP server with example Select() for concurrent servers

Network Application Programming Interface (API) n The services provided (often by the operating system) that provide the interface between application and protocol software. Application Sockets Do this Network API TCP UDP Etc…

Socket Basics n An end-point for a IP network connection q q n End point determined by two things: q q n what the application layer “plugs into” programmer cares about Application Programming Interface (API) Host address: IP address is Network Layer Port number: is Transport Layer Two end-points determine a connection: socket pair q q ex: 128. 226. 123. 101, p 21 + 198. 69. 10. 2, p 1500 ex: 128. 226. 123. 101, p 21 + 198. 69. 10. 2, p 1499

Aside -- Ports n Numbers (vary by OS): q q q 0 -1023 “reserved”, must be root to use 1024 - 5000 “ephemeral” however, many systems allow > 3977 ports n n (50, 000+ common) Well-known, reserved services (see /etc/services in Unix): q q q ftp 21/tcp ssh 22/tcp telnet 23/tcp finger 79/tcp snmp 161/udp

Transport Layer n UDP: User Datagram Protocol q q n no acknowledgements no retransmissions out of order, duplicates possible connectionless TCP: Transmission Control Protocol q q q reliable (in order, all arrive, no duplicates) flow control connection

Socket Descriptor Data Structure Descriptor Table 0 1 2 3 4 Family: PF_INET Service: SOCK_STREAM Local IP: 111. 22. 3. 4 Remote IP: 123. 45. 6. 78 Local Port: 2249 Remote Port: 3726

Preliminaries

Socket Address Structure struct in_addr { in_addr_t s_addr; }; struct sockaddr_in { unit 8_t sin_len; sa_family_t sin_family; in_port_t sin_port; struct in_addr sin_addr; char sin_zero[8]; } n /* 32 -bit IPv 4 addresses */ /* length of structure */ /* AF_INET */ /* TCP/UDP Port num */ /* IPv 4 address (above) */ /* unused */ Are also “generic” and “IPv 6” socket structures

Convert the natives! Byte order ‘h’ : host byte order ‘n’ : network byte order ‘s’ : short (16 bit) ‘l’ : long (32 bit) uint 16_t htons(uint 16_t); uint 16_t ntohs(uint_16_t); uint 32_t htonl(uint 32_t); uint 32_t ntohl(uint 32_t); In_addr values should be stored in network byte order (common mistake)

Aside – Using DNS server n Sockets use IP addresses to name hosts q q q Use DNS to resolve host names to IP addresses DNS is the “phone book” that maps machine names to IP addresses Done before Initiating a connection

Using DNS n To find out the IP address of a machine #include <unistd. h> int gethostname(char *name, int namelen); q name : is character array way to store the name Of the machine with null terminated q character. namelen : size of the chracter array This function puts the name of the host in name. It returns 0 if ok, -1 if error.

gethostbyname (cont) #include <netdb. h> struct hostent *gethostbyname(const char *name); This returns hostent structure with all necessary information related to host with name. struct hostent { char *h_name; /* canonical name of host*/ char **h_aliases; /* alias list */ int h_addrtype; /* host address type */ int h_length; /* length of address */ char **h_addr_list; /* list of addresses */ }; #define h_addr_list[0]

hostent n n Address stored in h_addr is in struct in_addr form. To obtain “. ” separated id address we could use #include <sys/types. h> #include <sys/socket. h> #include <netinet/in. h> #include <arpa/inet. h> char *inet_ntoa(const struct in_addr in); n The routine inet_ntoa() returns a pointer to a string in the base 256 notation d. d.

IP Addresses and how to deal with them n n ASCII to 32 -bit IP: q ina. sin_addr. s_addr = inet_addr("10. 12. 110. 57"); q Also can use inet_aton (ascii to network) 32 -bit IP to ASCII q a 1 = inet_ntoa(ina 2. sin_addr); // this is 10. 12. 110. 57 printf("address 1: %sn", a 1);

socket() bind() TCP Client-Server “well-known” port listen() Client accept() (Block until connection) socket() “Handshake” Data (request) recv() send() recv() close() connect() send() Data (reply) recv() End-of-File close()

creating a socket() int socket(int family, int type, int protocol); Create a socket/file descriptor, giving access to transport layer service. n n family is one of q AF_INET (IPv 4), AF_INET 6 (IPv 6), AF_LOCAL (local Unix), q AF_ROUTE (access to routing tables), AF_KEY (new, for encryption) type is one of q SOCK_STREAM (TCP), SOCK_DGRAM (UDP) q SOCK_RAW (for special IP packets, PING, etc. Must be root) n setuid bit (-rws--x--x root 1997 /sbin/ping*) protocol is 0 (used for some raw socket options) upon success returns socket descriptor q Integer, like file descriptor q Return -1 if failure

bind()-- What is my port? ? int bind(int sockfd, const struct sockaddr *myaddr, socklen_t addrlen); Assign a local protocol address (“name”) to a socket. n sockfd is socket descriptor from socket() n myaddr is a pointer to address struct with: q q q n n port number and IP address if port is 0, then host will pick ephemeral port IP address = INADDR_ANY (unless multiple nics) addrlen is length of structure returns 0 if ok, -1 on error q EADDRINUSE (“Address already in use”)

bind() example int sd; struct sockaddr_in ma; sd = socket(AF_INET, SOCK_STREAM, 0); ma. sin_family = AF_INET; ma. sin_port=htons(5100); ma. sin_addr. s_addr=htonl(INADDR_ANY); if(bind(sd, (struct sockaddr *) &ma, sizeof(ma))!= -1) { …}

listen() – will someone please talk to me? int listen(int sockfd, int backlog); Change socket state for TCP server. n sockfd is socket descriptor from socket() n backlog is maximum number of incomplete connections q q n historically 5 rarely above 15 on a even moderate Web server! Sockets default to active (for a client) q change to passive so OS will accept connection

accept()– thank you for calling my port int accept(int sockfd, struct sockaddr cliaddr, socklen_t *addrlen); Return next completed connection. n sockfd is socket descriptor from socket() n cliaddr and addrlen return protocol address from client returns brand new descriptor, created by OS note, if create new process or thread, can create concurrent server n n

listen/connect() example struct sockaddr_in ca; //After bind. . listen(sd, 5); calen = sizeof(ca); cd = accept(sd, (struct sockaddr *) ca, &calen); //read and write using cd

connect() int connect(int sockfd, const struct sockaddr *servaddr, socklen_t addrlen); Connect to server. n sockfd is socket descriptor from socket() n servaddr is a pointer to a structure with: q q n n addrlen is length of structure client doesn’t need bind() q n port number and IP address must be specified (unlike bind()) – how? OS will pick ephemeral port returns socket descriptor if ok, -1 on error

close()/shutdown – go away! int close(int sockfd); Close socket for use. n sockfd is socket descriptor from socket() n closes socket for reading/writing q q q returns (doesn’t block) attempts to send any unsent data socket option SO_LINGER n n q n . block until data sent or discard any remaining data returns -1 if error

connect() example int sd; struct sockaddr_in sa; sd = socket(AF_INET, SOCK_STREAM, 0); sa. sin_family = AF_INET; sa. sin_port=htons(5100); sa. sin_addr. s_addr= htonl(inet_addr(“ 128. 226. 123. 101”)); if(connect(sd, (struct sockaddr *) &sa, sizeof(sa))!= -1) { …}

Sending and Receiving – talk to me! int recv(int sockfd, void *buff, size_t mbytes, int flags); int send(int sockfd, void *buff, size_t mbytes, int flags);

UDP Client-Server socket() bind() “well-known” port Client recvfrom() socket() (Block until receive datagram) Data (request) sendto() recvfrom() Data (reply) - No “handshake” - No simultaneous close - No fork() for concurrent servers! close()

Sending and Receiving int recvfrom(int sockfd, void *buff, size_t mbytes, int flags, struct sockaddr *from, socklen_t *addrlen); int sendto(int sockfd, void *buff, size_t mbytes, int flags, const struct sockaddr *to, socklen_t addrlen); n Same as recv() and send() but for addr q q recvfrom fills in address of where packet came from sendto requires address of where sending packet to

getpeername()--Who are you? It will tell you who is at the other end of a connected stream socket. The synopsis: #include <sys/socket. h> int getpeername(int sockfd, struct sockaddr *addr, int *addrlen);

Gethostname() --Who am I? Returns the name of the computer that your program is running on. You can then use gethostbyname() to determine the IP address of your local machine. n Here's the breakdown: #include <unistd. h> int gethostname(char *hostname, size_t size); n

Example of Stream Server: echo /* stream server: echo what is received from client */ #include <sys/types. h> #include <sys/socket. h> #include <netinet/in. h> #include <arpa/inet. h> #include <string. h> #include <unistd. h> #include <stdlib. h> #include <stdio. h> int main (int argc, char *argv[]) { int s, t, sinlen; struct sockaddr_in sin; char msg[80];

Example of Stream Server: echo (cont’d) if (argc < 2) { printf (”%s portn”, argv[0] ); /* input error: need port no! */ return -1; } if ( (s = socket(AF_INET, SOCK_STREAM, 0 ) ) < 0) { /* create socket*/ perror(”socket”); /* socket error */ return -1; } sin_family = AF_INET; /*set protocol family to Internet */ sin_port = htons(atoi(argv[1])); /* set port no. */ sin_addr. s_addr = INADDR_ANY; /* set IP addr to any interface */ if (bind(s, (struct sockaddr *)&sin, sizeof(sin) ) < 0 ){ perror(”bind”); return -1; /* bind error */ }

Example of Stream Server: echo (cont’d) /* server indicates it’s ready, max. listen queue is 5 */ if (listen(s, 5)) { perror (”listen”); /* listen error*/ return -1; } sinlen = sizeof(sin); while (1) { /* accepting new connection request from client, socket id for the new connection is returned in t */ if ( (t = accept(s, (struct sockaddr *) &sin, &sinlen) ) < 0 ){ perror(”accept ”); /* accpet error */ return -1; }

Example of Stream Server: echo (cont’d) printf( ”From %s: %d. n”, inet_ntoa(sin. sin_addr), ntohs(sin. sin_port) ); if ( read(t, msg, sizeof(msg) ) <0) { /* read message from client */ perror(”read”); /* read error */ return -1; } if ( write(t, msg, strlen(msg) ) < 0 ) { /* echo message back */ perror(”write”); return -1; /* write error */ } /* close connection, clean up sockets */ if (close(t) < 0) { perror(”close”); return -1; } } // not reach below if (close(s) < 0) { perror(”close”); return -1; } return 0; }

Example of Stream Client: echo /* stream client: send a message to server */ #include <sys/types. h> #include <sys/socket. h> #include <netinet/in. h> #include <arpa/inet. h> #include <string. h> #include <unistd. h> #include <stdlib. h> #inlcude <stdio. h> #include <netdb. h> int main (int argc, char *argv[] ) { int s, n; struct sockaddr_in sin; struct hostent *hptr; char msg[80] = ”Hello World!”;

Example of Stream Client: echo (cont’d) if ( argc < 3 ) { printf ( ”%s host portn”, argv[0] ); /* input error: need host & port */ return -1; } if ( (s = socket(AF_INET, SOCK_STREAM, 0 ) ) < 0) { /* create socket*/ perror(”socket”); /* socket error */ return -1; } sin_family = AF_INET; /*set protocol family to Internet */ sin_port = htons(atoi(argv[2])); /* set port no. */ if ( (hptr = gethostbyname(argv[1]) ) == NULL){ fprintf(stderr, ”gethostname error: %s”, argv[1]); return = -1; } memcpy( &sin. sin_addr, hptr->h_length);

Example of Stream Client: echo (cont’d) if (connect (s, (struct sockaddr *)&sin, sizeof(sin) ) < 0 ){ perror(”connect”); return -1; /* connect error */ } if ( write(s, msg, strlen(msg) +1) < 0 ) { /* send message to server */ perror(”write”); return -1; /* write error */ } if ( ( n = read(s, msg, sizeof(msg) ) ) <0) { /* read message from server */ perror(”read”); return -1; /* read error */ } printf (” %d bytes: %sn”, n, msg); /* print message to screen */ /* close connection, clean up socket */ if (close(s) < 0) { perror(”close”); /* close error */ return -1; } return 0; }

Compiling and Executing garnet% g++ -o echo-server. c -lsocket -lnsl garnet% g++ -o echo-client. c -lsocket -lnsl garnet% echo-server 5700 & garnet% echo-client opal 5700 From 128. 226. 123. 110: 32938. 12 bytes: Hello World!

Concurrent Servers n n n Receive blocks; how do servers that support multiple clients work? Threaded servers; only a thread blocks Asynchronous receive; receive that doesn’t block Select() system call lets you test which sockets have something ready to receive so that you are guaranteed not to block Examples next time/on class webpage

select n n n #include <sys/select. h> #include <sys/time. h> int select ( int numfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout); Struct timeval { long tv_sec; /* seconds */ long tv_usec; /* microseconds */ }

select n Void FD_ZERO(fd_set *set) ; q n Void FD_SET(int fd, fd_set *set) ; q n Turn on the bit for fd in fdset Void FD_CLR(int fd, fd_set *set) ; q n Clear all bits in fdset. Turn off the bit for fd in fdset Int FD_ISSET(int fd, fd_set *set) ; q Is the bit for fd on in fdset?

Select example #include <sys/time. h> #include <sys/types. h> #include <unistd. h> #define STDIN 0 /* file descriptor for standard input */ main() { struct timeval tv; fd_set readfds; tv. tv_sec = 2; tv. tv_usec = 500000; FD_ZERO(&readfds); FD_SET(STDIN, &readfds); /* don't care about writefds and exceptfds: */ select(STDIN+1, &readfds, NULL, &tv); if (FD_ISSET(STDIN, &readfds)) printf("A key was pressed!n"); else printf("Timed out. n"); }

Extra stuff – probably not interesting

Socket Options n n setsockopt(), getsockopt() SO_LINGER q n SO_RCVBUF, SO_SNDBUF q q n upon close, discard data or block until sent change buffer sizes for TCP is “pipeline”, for UDP is “discard” SO_RCVTIMEO, SO_SNDTIMEO q timeouts

Socket Options (TCP) n TCP_KEEPALIVE q n TCP_MAXRT q n idle time before close (2 hours, default) set timeout value TCP_NODELAY q disable Nagle Algorithm

fcntl() n n n ‘File control’ but used for sockets, too Signal driven sockets Set socket owner Get socket owner Set socket non-blocking flags = fcntl(sockfd, F_GETFL, 0); flags |= O_NONBLOCK; fcntl(sockfd, F_SETFL, flags); Beware not getting flags before setting!