1. Web Server Architecture

2. Complex –Helpful to consider best design practices Items to consider –Response Time Use concurrency –Features HTTP/1.1 CGI

3. Web Server Architecture Client Web Server CGI program stdin stdout http use dup2 to redirect stdin and stdout back to the web server use dup2 to redirect stdin and stdout back to the web server

4. Web Server Architecture Client Main Thread for(j=0;j<nthread; pthread_create() while(1) newsock = accept() enQ(newsock) Connect() Thread Pool while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() recv() process send() close(sock) while(1) sock = deQ() read() process write() close(sock) Connection Queue

5. Web Server Architecture Minimize Overhead –Launch threads that stay around –Use semaphores to eliminate busy wait Be Careful with shared data structures –Connection Queue Producer - main thread Consumers - connection handling threads

6. Web Server Architecture #include … Queue connectionQ; main() { // Use signal handlers to shut down nicely SetUpSignalHandlers() SetUpSocket() for(j = 0; j < nthreads; j++) pthread_create(thread[j], HandleConn,args) pthread_create(logthread, LogWriter, args) for(;;) { sock = accept(…) connectionQ.enQ(sock) } void *HandleConn(void *args) { while(we are still running) { // This call should block until I have a connection // You will need producer-consumer code sock = connectionQ.deQ(); recv(sock, message…) processURL() if (cgi) DoCGI() else { read file send(sock, response…) close(sock) }

7. Shared Data Structures Queue of socket connections Strategy –Write a template queue that inherits from the STL queue class –Override the enqueue and dequeue methods init(EmptySem, QSIZE); init(PresentSem, 0); init(mutex, 1); template void MyQueue ::enqueue(const Elem &Item) { wait(EmptySem) wait(mutex) super.enqueue(Item) post(mutex) post(PresentSem) } template Elem MyQueue ::dequeue(void) { wait(PresentSem) wait(mutex) super.dequeue(Item) signal(mutex) signal(EmptySem) }

8. Sample Exchange HTTP/1.0 200 OK Date: Fri, 31 Dec 1999 23:59:59 GMT Content-Type: text/html Content-Length: 1354 Happy New Year! (more fiile contents)... GET /path/file.html HTTP/1.1 Host: www.host1.com:80 [blank line here]

9. Web Request Processing Receive the request Process the URL –Append URL to DocumentRoot –Use stat to determine if file exists or if it is a directory Send Response GET /CS360 HTTP/1.1 Host: star.cs.byu.edu HTTP/1.1 200 OK Content-type: text/html, image/jpg or other mime type Content-length: #bytes as reported by stat Binary Data (Write a loop that reads a buffer full of data and writes it to the socket until EOF)