15-213 Recitation 9 Greg Reshko Office Hours: Wed 2:00-3:00PM April 21st, 2003

Outline File I/O Networking Lab 7

Unix File I/O All I/O devices are modeled as files Networks, disks, terminals, etc All input and output is performed by reading and writing the appropriate files Kernel maintains all information about files and just returns a file descriptor to an application that wants access to a given file

Unix File I/O: Read/Write #include <unistd.h> ssize_t read(int fd, void *buf, size_t count); ssize_t write(int fd, const void *buf, size_t count);

Unix File I/O: More Robust Robust I/O (RIO) Package: Unbuffered: ssize_t readn(int fd, void *buf, size_t count); ssize_t writen(int fd, const void *buf, size_t count); ssize_t readline(int fd, void *buf, size_t maxlen); Buffered (thread-safe): ssize_t readnb(int fd, void *buf, size_t count); ssize_t writenb(int fd, const void *buf, size_t count); ssize_t readlineb(int fd, void *buf, size_t maxlen);

Standard I/O vs. Unix I/O Standard I/O almost always preferred fopen, fclose, fseek, fread, fwrite, fscanf, fprintf, etc. A higher-level abstraction than UNIX I/O Models files as streams, like file descriptors in being full-duplex Restrictions exist that interact badly with restrictions on sockets Input function cannot follow an output function (or vice versa) without a call to fflush, fseek, fsetpos, rewind, or and end-of-file

Networking Two sides to networking Client / Server Distinction is fading Peer-to-peer systems mean a node is both

Client Code Path Clients typically connect to servers, perform a task, then close the connection Create a socket() Connect() Write()/read() Close()

Server Code Path Servers wait for connections and handle them as they arrive Create a socket() Bind() to a port Listen() for connections Select() a ready connection Accept() a connection Read()/Write() Close() the connection We’ll focus on TCP, but UDP is just as important

Server: Init void CreateTCPServer() { struct sockaddr_in myAddr; int myAddrLen; int reuseAddrFlg=1; tcpSocketfd = socket(AF_INET,SOCK_STREAM,0); bzero((void *)(&myAddr),sizeof(myAddr)); myAddr.sin_family = AF_INET; myAddr.sin_port = htons((unsigned short)atoi(chatTCPServerPort)); myAddr.sin_addr.s_addr = htonl(INADDR_ANY); setsockopt(tcpSocketfd,SOL_SOCKET,SO_REUSEADDR,(void *) &reuseAddrFlg,sizeof(reuseAddrFlg)); bind(tcpSocketfd,(struct sockaddr *)&myAddr,sizeof(myAddr)); listen(tcpSocketfd,MAX_BACKLOG); }

Server: Loop while(1) { readSet=allSet; numReadyDescriptors=select(maxfd+1,&readSet,NULL,NULL,NULL); if(FD_ISSET(tcpSocketfd,&readSet)) /* Incoming request for new connection */ struct sockaddr_in clientAddr; int clientAddrLen; slavefd=accept(tcpSocketfd,(struct sockaddr *) &clientAddr, &clientAddrLen); /* Save slavefd so we know to check it later */ FD_SET(slavefd,&allSet); if(slavefd > maxfd) maxfd=slavefd; fflush(stdout); numReadyDescriptors--; if(numReadyDescriptors <= 0) continue; }

Server: The Rest Check whether interesting socket descriptors are in the read/write set Do appropriate action if they are (i.e., read() or write()) Close() the connection when appropriate

Logging and Network I/O Have a server set up to receive requests and respond to them Read in request, parse, and return response Need to read/write to a network stream, and log events to a file for record-keeping purposes Main loop opens file for logging and spawns children threads Each thread has own network streams, but shares logging file stream Use of mutex to lock resources glossed over for now

Reading to/from Network & File void main () { FILE* log; /* open file */ log = fopen ( "log.txt“, "a“ ); while ( true ) /* * Main Loop (inside thread) */ } fclose ( log );

Reading to/from Network & File void *thread ( void *vargp ) { FILE* stream; char method[BUFSIZE], uri[BUFSIZE], version[BUFSIZE]; /* create mutex */ /* given argument, set file descriptor for proper access to streams */ childfd = *((int *)vargp); free(vargp); /* open file descriptors for reading network socket, set buffer type */ if ((stream = fdopen(childfd, "r+")) == NULL) error("ERROR on fdopen"); setvbuf(stream, NULL, _IONBF, 0); /* get header off the stream and save */ fgets(buf, BUFSIZE, stream); sscanf(buf, "%s %s %s\n", method, uri, version);

Reading to/from Network & File /* * Parse, error check, ready for server communication. */ * determine size of information to be written back * in this case, copying from some other stream (buf) * to the network stream (stream) /* get size of remaining buffer from stream */ temp = read ( serverfd, buf, BUFSIZE ); while ( temp > 0 ) { data.byte += temp; * write current buffered amount to network socket * get size of remaining buffer from stream fwrite ( buf, sizeof ( char ), temp, stream ); }

Reading to/from Network & File /** init mutex **/ /** lock mutex **/ /* write to log file */ fprintf(log, "%s %s %s %d\n", data.date, data.ip, data.address, data.byte); /** unlock mutex **/ /* close network buffer */ fclose(stream); }

Lab 7 – Logging Web Proxy Start early (yeah, that’s a new one…) Read the book carefully Everything you need for this lab is in the book – make sure you understand it Concurrency issues Test it with your web browser i.e. Internet Explorer This is the coolest part of the lab