Introduction to Project 1Project GoalsHTTP UsageRequest - ResponseHTTP requestFour partsWhy do we need sockets?SocketFunctionsTypes of SocketsAddressingClient – high level viewSlide 13Server – high level viewSlide 15accepting a client connection (TCP)Sending / Receiving DataSlide 18Dealing with blocking callsDealing with blocking (cont..)select function callQuestions?Introduction to Project 1Web Client and ServerJan 2006Project GoalsImplement a simple WWW client and serverImplement a tiny subset of HTTPTo give you experience with HTTP and sockets programmingTo be familiar with Unix, Minet and prepare for the subsequent part of the projectHTTP UsageHTTP is the protocol that supports communication between web browsers and web servers.Most clients/servers today use version 1.1, but 1.0 is also in use.HTTP protocol works on top of TCP.telnet www.cs.northwestern.edu 80 telnet www.ece.northwestern.edu 80Request - ResponseHTTP has a simple structure:client sends a requestserver returns a replyHTTP requestRequest lineMethod URL HTTP-Version\r\nHeader linesContentRequest-LineHeaders...Content...blank lineblank lineFour parts0: Get build, configure and run the Minet stack1: HTTP Client2: Connection-at-a-time HTTP Server3: Simple select-based Multiple-connection-at-a-time server4: Complex Select-based Multiple-connection-at-a-time Serve ( Extra Credit )Why do we need sockets?Provides an abstraction for interprocess communicationSocketThe services (often provided by the operating system) provide the interface between application and protocol software.ApplicationApplicationNetwork APINetwork APIProtocol AProtocol AProtocol BProtocol BProtocol CProtocol CFunctionsDefine an “end- point” for communicationInitiate and accept a connectionSend and receive dataTerminate a connection gracefullyExamples File transfer apps (FTP), Web browsers(HTTP), Email (SMTP/ POP3), etc…Types of SocketsTwo different types of sockets :stream vs. datagramStream socket :( a. k. a. connection- oriented socket)It provides reliable, connected networking serviceError free; no out- of- order packets (uses TCP)applications: telnet/ ssh, http, …Datagram socket :( a. k. a. connectionless socket)It provides unreliable, best- effort networking servicePackets may be lost; may arrive out of order (uses UDP)applications: streaming audio/ video (realplayer), …AddressingClientServerClient – high level viewCreate a socketSetup the server addressConnect to the serverRead/write dataShutdown connectionint connect_ socket( char *hostname, int port) {int sock;struct sockaddr_in sin;struct hostent *host;sock = socket( AF_ INET, SOCK_ STREAM, 0);if (sock == -1)return sock;host = gethostbyname( hostname);if (host == NULL) {close( sock);return -1;}memset (& sin, 0, sizeof( sin));sin. sin_ family = AF_ INET;sin. sin_ port = htons( port);sin. sin_ addr. s_ addr = *( unsigned long *) host-> h_ addr_ list[ 0];if (connect( sock, (struct sockaddr *) &sin, sizeof( sin)) != 0) {close (sock);return -1;}return sock;}Resolve the hoststruct hostent *gethostbyname( const char *hostname);/*Return nonnull pointer if OK, NULL on error */Setup up the structunit16_t htons(unit16_t host16bitvaule)/*Change the port number from host byte order to network byte order */Connectconnect(int socketfd, const struct sockaddr * servaddr, socket_t addrlen)/*Perform the TCP three way handshaking*/Hostent structurestruct hostent{ char * h_name /*official name of host*/ char ** h_aliases; /* pointer of array of\ pointers to alias name*/ int h_addrtype /* host address type*/ int h_length /* length of address */ char ** h_addr_list /*prt to array of ptrs with \ IPv4 or IPv6 address*/}Ipv4 socket address structurestruct socketaddr_in{ uint8_t sin_len; /*length of the structure (16)*/ sa_falimily_t sin_family /* AF_INT*/ in_port_t sin_port /* 16 bit TCP or UDP port number*/ struct in_addr sin_addr /* 32 bit Ipv4 address */ char sin_zero(8)/* unused*/}RMake the socketSocket(int family , int type, in t protocol); return nonnegative value for OK, -1 for errorServer – high level viewCreate a socketBind the socketListen for connectionsAccept new client connectionsRead/write to client connectionsShutdown connectionint make_ listen_ socket( int port) {struct sockaddr_ in sin;int sock;sock = socket( AF_ INET, SOCK_ STREAM, 0);if (sock < 0)return -1;memset(& sin, 0, sizeof( sin));sin. sin_ family = AF_ INET;sin. sin_ addr. s_ addr = htonl( INADDR_ ANY);sin. sin_ port = htons( port);if (bind( sock, (struct sockaddr *) &sin, sizeof( sin)) < 0)return -1;return sock;}Make the socketSetup up the structBindbind(int sockfd, const struct sockaddr * myaddr, socklen_t addrlen);/* return 0 if OK, -1 on errorassigns a local protocol adress to a socket*/Listening on a port (TCP)accepting a client connection (TCP)int get_ client_ socket( int listen_ socket) {struct sockaddr_ in sin;int sock;int sin_ len;memset(& sin, 0, sizeof( sin));sin_ len = sizeof( sin);sock = accept( listen_ socket, (struct sockaddr *) &sin, &sin_ len);return sock;}Setup up the structAccept the client connectionaccept(int sockefd, struct sockaddr * claddr, socklen_t * addrlen)/* return nonnegative descriptor if OK, -1 on error return the next completed connection from the front of the completed connection queue. if the queue is empty, the process is put to sleep(assuming blocking socket)*/Sending / Receiving DataWith a connection (SOCK_STREAM):int count = write(sock, &buf, len);count: # bytes transmitted (-1 if error)buf: char[], buffer to be transmittedlen: integer, length of buffer (in bytes) to transmitint count = read(sock, &buf, len);count: # bytes received (-1 if error)buf: void[], stores received byteslen: # bytes receivedCalls are blocking [returns only after data is sent (to socket buf) / received]socket()bind()listen()accept()read()write()read()close()Socket()connect()write()read()close()TCP ClientTCP ServerWell-known portblocks until connection from clientprocess requestConnection establishmentData(request)Data(reply)End-of-file notificationDealing with blocking callsMany functions block accept(), connect(), All read() and write()For simple programs this is fineWhat about complex connection routinesMultiple connectionsSimultaneous sends and