Slide 1AnnouncementsSimple Client OverviewSockets and TCP/IPSocket API for ClientSockets API for ServerTypical Request-Response Client-Server PairTypical Request-Response Client-Server PairExample Daytime ServerMain StructuresUseful FunctionsMore NotesGradingResourcesSockets ProgrammingCS144 Review Session 1April 4, 2008Ben NhamAnnouncements•New classroom for lecture–200-034, MW 4:15-5:30•Simple client assignment due Wednesday, 4/9•Use newsgroup for general questions–su.class.cs144–Refresh your newsgroup list from the server if you can’t find itSimple Client Overview•Opens TCP socket to other host–Does DNS lookup if necessary•Reads request from command line, appending "\r\n", and sends it through the socket•Echoes response to stdout•Demo: Sending HTTP request to SCS homepage–./sc www.scs.stanford.edu 80 "GET /"Sockets and TCP/IP•In TCP/IP:–Endpoint has unique (TCP port, IP address) pair–Connection between two endpoints is identified by the pair [(IP, port)src, (IP, port)dst]•All Unix I/O streams are referenced by descriptors –Socket maps a descriptor to an endpoint–Connecting sockets allows us to connect endpoints and do I/OProcessProcessProcessProcessApplicationTCP/UDPTCP/UDPTransportIPIPNetworkHardware InterfaceHardware InterfaceLinkSockets APIIP AddressPort PortPortsd sdsdSocket API for Clientint socket(int domain, int type, int protocol)•Returns a descriptor associated with a new endpointint bind(int sd, struct sockaddr *addr, u_int addr_len)•Set addr/port of endpoint for socket descriptor sd•Optional for client (lets the kernel choose some available port with the default IP address)int connect(int sd, struct sockaddr *addr, u_int addr_len)•Connect to destination address + port endpointint send(int sd, void *buf, int len, int flags)int recv(int sd, void *buf, int len, int flags)•Two-way communicationint shutdown(int sd, int how)•Partial or complete connection teardownsocketbindconnectsend/recvshutdownSockets API for Serverint socket(int, int, int)int bind(int, struct sockaddr *, u_int)int listen(int sd, int backlog)•Wait for a client to connect to this portint accept(int sd, struct sockaddr *addr, u_int *addr_len)•Accept connection, returning a new descriptor for this (IP, port)src – (IP, port)dst pairint send(int, void *, int)int recv(int, void *, int)int shutdown(int, int)socketbindsend/recvshutdownlistenacceptTypical Request-ResponseClient-Server Pairsocketbindconnectsend/recvsocketbindsend/recvshutdown shutdownlistenacceptClientServer"Can I connect?""Yes. Can I connect?"Request: "GET /"Response: "<html>…"One side starts shutdown"Yes."Typical Request-ResponseClient-Server Pairsocketbindconnectsend/recvsocketbindsend/recvshutdown shutdownlistenacceptClientServerSYNSYN/ACKRequest: "GET /"Response: "<html>…"One side starts shutdownACKExample Daytime Server•See the posted daytime.c•Problems–Doesn’t check return values of system calls•You should check the return value and use perror() or fprintf(stderr, strerror(errno)) to print out an informative error message–Doesn’t handle multiple clients simultaneously–Problems with re-using the same port (use setsockopt—covered in next review session)Main Structures•Generic socket addressstruct sockaddr { u_short sa_family; char sa_data[14];};•TCP/UDP + IPv4 specific address – convenience parallel struct for sockaddrstruct sockaddr_in { u_short sa_family; // usually AF_INET u_short sin_port; struct in_addr sin_addr; // see below char sin_zero[8]; // zero out};•IP Address struct in_addr { u_long s_addr; // Network byte order}; Next two slides by Clay CollierUseful Functionsstruct hostent *gethostbyname(const char *name)•Converts domain names and dotted-quad IP addresses into numerical IP addresses via DNSstruct servent *getservbyname(const char *name,const char *proto)•Query /etc/services to find expected protocol and port for a service•Example: getservbyname("http", NULL) to find it resides on tcp port 80getsockname(...), getpeername(...) •Gets IP address and port for source/destinationMore Notes•Partial sends and receives–Receive might not return with all the bytes requested•Endian issues–All shorts/ints going over the wire must be encoded using htons/htonl–All shorts/ints being read from the wire must be decoded using ntohs/ntohl–Why don’t we have to worry about endianness for text? For arbitrary binary data?Grading•No set rubric yet•Mostly functionality–Test yourself by sending (for example) http requests•Some style points–Don’t write everything in main–Handle partial receives and other edge cases–Check return values of system callsResources•IPC tutorial•Man pages•Outside references–Beej’s Sockets Tutorial: http://beej.us/guide/bgnet/–Unix Network Programming by Stevens•Newsgroup•Office
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