Fun Fun Project One 1

Fun Fun Project One

Building Your Very Own Web Server

Fun Fun Project One 2

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 3

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 4

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 5

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

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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

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What’s In A Request Message?

GET /index.html HTTP/1.0\r\nConnection: Keep-Alive\r\nUser-Agent: Mozilla/4.72 [en] (X11..)\r\nHost: 127.0.0.1:31415\r\nAccept: image/gif, image/jpeg, */*\r\nAccept-Encoding: gzip\r\nAccept-Language: en\r\nAccept-Charset: iso-8859-1,*,utf-8\r\n\r\n

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What Do You Care About?

GET /index.html HTTP/1.0

In particular, just index.html

Assume “/” means “/index.html”

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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

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What’s In A Response Message?

HTTP/1.0 200 OK\r\nDate: blah-blah-blah\r\nServer: blah-blah-blah\r\nContent-Type: important\r\nContent-Length: 12345\r\nLast-Modified: blah-blah-blah\r\n\r\nRaw data

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What’s a Minimal Response?

HTTP/1.0 200 OK\r\nContent-Type: stuff\r\n\r\nData

HTTP/1.0 302 Moved\r\nLocation: newurl\r\n\r\n

HTTP/1.0 404 Not Found\r\n

\r\n

But alsoConnection: close\r\nContent-Length: yyy\r\n

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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

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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

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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

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What is Content-Type?

text/htmlimage/gifimage/jpeg

(Other types not needed for project 1.)

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Need more info?

HTTP 1.1 Specification – RFC2068HTTP 1.0 – RFC 1945man pagesman manman –k blahread( ), write( ), open( ), close( )

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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

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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

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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)

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What Am I Given?

Setup 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

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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

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Why Are We Doing This?

Infrastructure for future projects Some OS/Networking interaction It’s fun, and not too bad

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Wrap Up

Thanks! Q&A session next week! Office Hour: Wed 4:30-5:30