Building Your Very Own Web Server Fun Fun Project One Building Your Very Own Web Server Fun Fun Project One

What is a Web Server? Program that understands the HTTP protocol and generates appropriate responses Clients “connect” to the machine Clients send a “request” Server reads request, generates “response” Client interprets response appropriately Fun Fun Project One

A Simplified Web Server Client asks for file Server finds appropriate file Server sends back a response header followed by the requested file’s data Server closes connection Fun Fun Project One

What Does “Connect” Mean? For all practical purposes, it looks like there’s data available via a file descriptor Stream of bytes Can be treated like any other file descriptor Not a FILE * (like stdio, stderr) Must use read() and write() system calls Fun Fun Project One

How Do You Identify Machines Domain names/IP address and ports http://www.cs.princeton.edu implies a machine named www.cs.princeton.edu and a default port of 80 http://127.0.0.1:8080/index.html Refers to local box (127.0.0.1 is me) Port # is 8080 (used for this project) File is named index.html Fun Fun Project One

How Do You Identify Files? File name is specified in Request Message Server maps that name to a real file Mapping can be done in whichever way server wants For example, /~vivek/index.html is actually /n/fs/fac/vivek/public_html/index.html In your web server, you can choose your own Fun Fun Project One

What’s In A Request Message? GET /index.html HTTP/1.0\r\n Connection: Keep-Alive\r\n User-Agent: Mozilla/4.72 [en] (X11..)\r\n Host: 127.0.0.1:31415\r\n Accept: image/gif, image/jpeg, */*\r\n Accept-Encoding: gzip\r\n Accept-Language: en\r\n Accept-Charset: iso-8859-1,*,utf-8\r\n \r\n Fun Fun Project One

What Do You Care About? GET /index.html HTTP/1.0 In particular, just index.html Assume “/” means “/index.html” Fun Fun Project One

What Could They Want? An honest-to-goodness file (me.jpg) An indirect request for such a file (such as “/” meaning index.html) An implied directory with index (/home/vivek instead of /home/vivek/) Just a directory listing A query (we don’t care about these) An invalid/nonexistent file Fun Fun Project One

What’s In A Response Message? HTTP/1.0 200 OK\r\n Date: blah-blah-blah\r\n Server: blah-blah-blah\r\n Content-Type: important\r\n Content-Length: 12345\r\n Last-Modified: blah-blah-blah\r\n \r\n Raw data Fun Fun Project One

What’s a Minimal Response? HTTP/1.0 200 OK\r\n Content-Type: stuff\r\n \r\n Data HTTP/1.0 302 Moved\r\n Location: newurl\r\n HTTP/1.0 404 Not Found\r\n \r\n But also Connection: close\r\n Content-Length: yyy\r\n Fun Fun Project One

Response when… File exists? Send it Directory without “/” suffix? Redirect Directory with index.html? Send it Directory with no index.html? List it For each list entry, add “/” if needed Failure(Not Found)? Send 404 Bad Request? Send 400 Fun Fun Project One

How to Test Your Server? Use a browser(Netscape/IE) Use “wget” Support HTTP protocol http://www.gnu.org/manual/wget create directory hierarchy for retrieving Include some big images Fun Fun Project One

More Test Cases What if Request Message is not send/received in one packet… The server must read all the Request Messages before it gives any response message Remember the double carriage return and line feed? Your web server must consider this! I’ll distribute more test programs later on, check http://www.cs.princeton.edu/~yongwang/cos318 Fun Fun Project One

What is Content-Type? text/html image/gif image/jpeg (Other types not needed for project 1.) Fun Fun Project One

Need more info? HTTP 1.1 Specification – RFC2068 HTTP 1.0 – RFC 1945 man pages man man man –k blah read( ), write( ), open( ), close( ) Fun Fun Project One

Why open instead of fopen? Compare fopen, fread, etc., with open, read, etc We’re dealing with functions closer to the OS – easier to use in some cases Fun Fun Project One

What’s a File Descriptor? Sort of like a FILE * It’s an integer provided by OS Used to represent a stream of bytes Can represent file or network connection Behavior is slightly different Especially when reading/writing network Fun Fun Project One

General Steps Setup, and then Get next connection If file, read from disk If directory, generate listing Send all to client Close connection, wait for next one(nonpersistent connection) Fun Fun Project One

What Am I Given? Setup function Accept function File type function Makes server available for connections Accept function Gets a connection from a client File type function Tells you what kind of file, if it exists Tells you how many bytes if a regular file Directory listing functions Gives you the file names one at a time Fun Fun Project One

Help! I’m Lost! Don’t know HTML? Use Netscape composer to see what to do View page source for various pages Do “telnet www.domain.com 80” and issue the GET manually (need to add “Host: www.domain.com” header) Ask Fun Fun Project One

Why Are We Doing This? Infrastructure for future projects Some OS/Networking interaction It’s fun, and not too bad Fun Fun Project One

Wrap Up Thanks! Q&A session next week! Office Hour: Wed 4:30-5:30 Fun Fun Project One