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CMU CS 15213 - Recitation

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15-213 Recitation 9 Greg ReshkoOutlineUnix File I/OUnix File I/O: Read/WriteUnix File I/O: More RobustStandard I/O vs. Unix I/ONetworkingClient Code PathServer Code PathServer: InitServer: LoopServer: The RestLogging and Network I/OReading to/from Network & FileSlide 15Slide 16Slide 17Lab 7 – Logging Web Proxy15-213 Recitation 9Greg ReshkoOffice Hours: Wed 2:00-3:00PMApril 21st, 2003OutlineFile I/ONetworkingLab 7Unix 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 fileUnix 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 RobustRobust 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-fileNetworkingTwo sides to networkingClient / ServerDistinction is fadingPeer-to-peer systems mean a node is bothClient 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 importantServer: Initvoid 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: Loopwhile(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 appropriateLogging 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 nowReading to/from Network & Filevoid main (){ FILE* log; /* open file */ log = fopen ( "log.txt“, "a“ ); while ( true ) { /* * Main Loop (inside thread) */ } fclose ( log );}Reading to/from Network & Filevoid *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 ); temp = read ( serverfd, buf, BUFSIZE ); }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


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CMU CS 15213 - Recitation

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