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 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 lab
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