1. Building Your Very Own Web Server
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
implies a machine named and a default port of 80
Refers to local box ( is me)
Port # is 8080 (used for this project)
File is named index.html
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
Fun Fun Project One

7. 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: :31415\r\n
Accept: image/gif, image/jpeg, */*\r\n
Accept-Encoding: gzip\r\n
Accept-Language: en\r\n
Accept-Charset: iso ,*,utf-8\r\n
\r\n
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8. What Do You Care About? GET /index.html HTTP/1.0
In particular, just index.html
Assume “/” means “/index.html”
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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
Fun Fun Project One

10. What’s In A Response Message?
HTTP/ 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

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

13. How to Test Your Server? Use a browser(Netscape/IE) Use “wget”
Support HTTP protocol
create directory hierarchy for retrieving
Include some big images
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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
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15. What is Content-Type? text/html image/gif image/jpeg
(Other types not needed for project 1.)
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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( )
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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
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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
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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)
Fun Fun Project One

20. 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

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 80” and issue the GET manually (need to add “Host: header)
Ask
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22. Why Are We Doing This? Infrastructure for future projects
Some OS/Networking interaction
It’s fun, and not too bad
Fun Fun Project One

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