slide on web servers

1. Fun Fun Project One 1
Fun Fun Project One
Building Your Very Own Web
Server

2. 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

3. 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

4. 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

5. 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

6. Fun Fun Project One 6
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

7. Fun Fun Project One 7
What’s In A Request Message?
GET /index.html HTTP/1.0rn
Connection: Keep-Alivern
User-Agent: Mozilla/4.72 [en] (X11..)rn
Host: 127.0.0.1:31415rn
Accept: image/gif, image/jpeg, */*rn
Accept-Encoding: gziprn
Accept-Language: enrn
Accept-Charset: iso-8859-1,*,utf-8rn
rn

8. Fun Fun Project One 8
What Do You Care About?
GET /index.html HTTP/1.0
In particular, just index.html
Assume “/” means “/index.html”

9. Fun Fun Project One 9
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

10. Fun Fun Project One 10
What’s In A Response
Message?
HTTP/1.0 200 OKrn
Date: blah-blah-blahrn
Server: blah-blah-blahrn
Content-Type: importantrn
Content-Length: 12345rn
Last-Modified: blah-blah-blahrn
rn
Raw data

11. Fun Fun Project One 11
What’s a Minimal Response?
HTTP/1.0 200 OKrn
Content-Type: stuffrn
rn
Data
HTTP/1.0 302 Movedrn
Location: newurlrn
rn
HTTP/1.0 404 Not Foundrn
rn
But also
Connection: closern
Content-Length: yyyrn

12. Fun Fun Project One 12
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

13. Fun Fun Project One 13
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

14. Fun Fun Project One 14
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

15. Fun Fun Project One 15
What is Content-Type?
text/html
image/gif
image/jpeg
(Other types not needed for project 1.)

16. Fun Fun Project One 16
Need more info?
HTTP 1.1 Specification – RFC2068
HTTP 1.0 – RFC 1945
man pages
man man
man –k blah
read( ), write( ), open( ), close( )

17. Fun Fun Project One 17
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

18. Fun Fun Project One 18
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

19. Fun Fun Project One 19
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)

20. Fun Fun Project One 20
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

21. Fun Fun Project One 21
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

22. Fun Fun Project One 22
Why Are We Doing This?
 Infrastructure for future projects
 Some OS/Networking interaction
 It’s fun, and not too bad

23. Fun Fun Project One 23
Wrap Up
 Thanks!
 Q&A session next week!
 Office Hour: Wed 4:30-5:30