Fun Fun Project One
Building Your Very Own Web
Server
Fun Fun Project One
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What is a Web Server?
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Program that understands the HTTP
protocol and generates appropriate
responses
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Clients “connect” to the machine
Clients send a “request”
Server reads request, generates “response”
Client interprets response appropriately
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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
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What Does “Connect” Mean?
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For all practical purposes, it looks like
there’s data available via a file
descriptor
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Stream of bytes
Can be treated like any other file descriptor
Not a FILE * (like stdio, stderr)
Must use read() and write() system calls
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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
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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
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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\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
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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\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
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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
\r\n
HTTP/1.0 404 Not Found\r\n
\r\n
But also
Connection: close\r\n
Content-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
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For each list entry, add “/” if needed
Failure(Not Found)?
 Bad Request?
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Fun Fun Project One
Send 404
Send 400
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How to Test Your Server?
Use a browser(Netscape/IE)
 Use “wget”
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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
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What if Request Message is not send/received
in one packet…
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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/html
image/gif
image/jpeg
(Other types not needed for project 1.)
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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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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?
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Sort of like a FILE *
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It’s an integer provided by OS
Used to represent a stream of bytes
Can represent file or network connection
Behavior is slightly different
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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?
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Setup function
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Accept function
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Gets a connection from a client
File type function
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Makes server available for connections
Tells you what kind of file, if it exists
Tells you how many bytes if a regular file
Directory listing functions
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Gives you the file names one at a time
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Help! I’m Lost!
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Don’t know HTML?
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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
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