1. Servlets: HTTP Request Header Contents and Responses
HTTP Requests & Responses

2. HTTP Requests & Responses
Road Map
Recap and Overview
Reading HTTP Request Headers
Generating the Server Response
Case Study 1: Search Engines
Case Study 2: Basic Web Security
Restricting by User Name/Password
HTTP Requests & Responses

3. HTTP Requests & Responses
Recap and Overview
HTTP Requests & Responses

4. HTTP Requests & Responses
Overview
Interaction between browser and web server.
Web
Browser
Request
Web
Server
Response
HTTP Requests & Responses

5. HTTP Requests & Responses
Client Request Data
When a user submits a browser request to a web server, it sends two categories of data:
Form Data: Data that the user explicitly typed into an HTML form.
For example: registration information.
HTTP Request Header Data: Data that is automatically appended to the HTTP Request from the client.
For example: cookies, browser type, etc,
HTTP Requests & Responses

6. Reading HTTP Request Headers
HTTP Requests & Responses

7. HTTP Requests & Responses
Sample HTTP Request
A sample HTTP Request to Yahoo.com
GET / HTTP/1.1
Accept: */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)
Host:
Connection: Keep-Alive
Cookie: B=2td79o0sjlf5r&b=2
Tip: Check out:
HTTP Requests & Responses

8. Accessing HTTP Headers
As in the SnoopServlet Example:
To access any of these Headers, use the HTTPServletRequest getHeader() method.
For example:
String connection = req.getHeader(“Connection”);
To retrieve a list of all the Header Names, use the getHeaderNames() method.
getHeaderNames() returns an Enumeration object.
Enumeration enum = req.getHeaderNames();
HTTP Requests & Responses

9. Additional HTTP Information
getMethod()
Indicates the request method, e.g. GET or POST.
getRequestURI()
Returns the part of the URL that comes after the host and port. For example, for the URL: the request URI would be /servlet/search.
getProtocol()
Returns the protocol version, e.g. HTTP/1.0 or HTTP/1.1
HTTP Requests & Responses

10. HTTP Requests & Responses
Reading Browser Types
The User-Agent HTTP header indicates the browser and operating system.
For example:
user-agent Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
You can use this header to differentiate browser types or simply log browser requests.
HTTP Requests & Responses

11. HTTP Requests & Responses
Example User-Agents
Internet Explorer:
user-agent Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
Mozilla
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/
For strange historical reasons, IE identifies itself as “Mozilla”
HTTP Requests & Responses

12. Generating the Server Response
HTTP Requests & Responses

13. HTTP Requests & Responses
Sample HTTP Response
As a refresher, here’s a sample HTTP response:
HTTP/ OK
Date: Mon, 06 Dec :54:26 GMT
Server: Apache/1.3.6 (Unix)
Last-Modified: Fri, 04 Oct :06:11 GMT
Content-length: 327
Connection: close
Content-type: text/html
<title>Sample Homepage</title>
<img src="/images/oreilly_mast.gif">
<h1>Welcome</h2>Hi there, this is a simple web page. Granted, it may…
HTTP Requests & Responses

14. HTTP Requests & Responses
Generating Responses
Servlets can return any HTTP response they want.
Useful for lots of scenarios:
Redirecting to another web site.
Restricting access to approved users.
Specifying content-type other than text/html.
Return images instead of HTML.
HTTP Requests & Responses

15. Setting the HTTP Status Code
Normally, your Servlet will return an HTTP Status code of: OK to indicate that everything went fine.
To return a different status code, use the setStatus() method of the HttpServletResponse object.
Be sure to set the status code before sending any document content to the client.
HTTP Requests & Responses

16. HTTP Requests & Responses
Using setStatus()
setStatus takes an integer value. But, it’s best to use the predefined integers in the HttpServletResponse. Here are a few:
SC_BAD_REQUEST
Status code (400) indicating the request sent by the client was syntactically incorrect.
SC_FORBIDDEN
Status code (403) indicating the server understood the request but refused to fulfill it.
SC_INTERNAL_SERVER_ERROR
Status code (500) indicating an error inside the HTTP server which prevented it from fulfilling the request.
SC_NOT_FOUND
Status code (404) indicating that the requested resource is not available.
HTTP Requests & Responses

17. HTTP Requests & Responses
Sending Redirects
You can redirect the browser to a different URL by issuing a Moved Temporarily Status Code:
SC_MOVED_TEMPORARILY: Status code (302) indicating that the resource has temporarily moved to another location.
Because this is so common, the HttpServletResponse interface also has a sendRedirect() method.
Example:
res.sendRedirect( “
HTTP Requests & Responses

18. Example: Search Engines
HTTP Requests & Responses

19. Multiple Search Engines
SearchEngines Servlet
Enables users to submit a search query to one of four search engines.
Google
AllTheWeb
Yahoo
AltaVista, etc.
The code exploits the HTTP Response Header to redirect the user to the correct search engine.
HTTP Requests & Responses

20. HTTP Requests & Responses
Architecture
SearchEngines
Servlet
“I want to search for
Bill Gates on Google”
Web
Browser
“Go to Google”
“I want to search for
Bill Gates on Google”
Google
“Your results…”
HTTP Requests & Responses

21. HTTP Requests & Responses
SearchSpec.java
The SearchSpec object contains information about connecting to a specific search engine
public String makeURL (String searchString, String numResults)
You provide this method with a search string and the number of results, and it returns the URL and search query specific to Google, Yahoo, HotBot, etc.
Class is contained in SearchEngines.java on acad
HTTP Requests & Responses

22. HTTP Requests & Responses
SearchUtilities.java
The SearchUtilities.java code has an array of SearchSpec objects: one for Google, one for Yahoo, etc.
It also provides a makeUrl method…
HTTP Requests & Responses

23. HTTP Requests & Responses
SearchEngines.java
The main servlet code.
This code:
Extracts the searchEngine parameter.
If no such parameter exists, it sends an HTTP Error.
Otherwise, it calls SearchUtilities to construct the correct URL.
Finally, it redirects the user to this new URL.
HTTP Requests & Responses

24. Example: Basic Web Security
HTTP Requests & Responses

25. HTTP Requests & Responses
HTTP Authentication
The HTTP Protocol Includes a built-in authentication mechanism.
Useful for protecting web pages or servlets that require user name / password access.
First, let’s examine the basic mechanism and the HTTP Headers involved.
Then, let’s figure out how to build a servlet that exploits this mechanism.
HTTP Requests & Responses

26. HTTP Requests & Responses
Basic Authentication
If a web page is protected, the Web Server will issue an authentication “challenge”:
HTTP/ Authorization Required
Date: Sun, 27 Aug :51:25 GMT
Server: Apache/ (Unix) ApacheJServ/1.1 PHP/4.0.0 mod_ssl/ OpenSSL/0.9.5a
WWW-Authenticate: BASIC realm="privileged-few"
Keep-Alive: timeout=90, max=150
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html
HTTP Requests & Responses

27. HTTP Requests & Responses
WWW-Authenticate
WWW-Authenticate: BASIC realm=“realm"
When you issue a return status code of 401, “Authorization Required”, you need to tell the browser what type of authentication is required.
You do this via the WWW-Authenticate Header. This header has two parameters:
BASIC: Basic authorization requiring user name and password.
Realm: you can create multiple “realms” of authentication for different users, e.g. “Admin”, “User”, “Super_User”, etc.
HTTP Requests & Responses

28. Basic Authentication Cont.
Upon receiving an authentication challenge, the browser will prompt the user with a pop-up box requesting the user name and password.
Browser takes the “username:password” from the user and encrypts it using the Base 64 Encoding Algorithm.
For example: if the string is “marty:martypd”, the Base 64 string is “bWFydHk6bWFydHlwdw==”
We will not cover the details of Base 64, but remember that Base 64 is easy to decode. Therefore, even if your page is protected, someone can easily intercept your Base 64 string and decode it.
HTTP Requests & Responses

29. Basic Authentication Cont.
The browser reissues the request for the page. In the HTTP request, the browser indicates the Authorization string:
GET /servlet/coreservlets.ProtectedPage HTTP/1.1
Accept: image/gif, */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)
Host:
Connection: Keep-Alive
Authorization: Basic bWFydHk6bWFydHlwdw==
HTTP Requests & Responses

30. Basic Authentication Cont.
Web Server checks the user name and password.
If User Name/Password is correct, web server displays the protected page.
If the User Name/Password is incorrect, web server issues a second authentication challenge.
HTTP Requests & Responses

31. HTTP Requests & Responses
Almost there…
Before we examine the actual servlet code, there are two pieces of Java coding we need to examine:
sun.misc.BASE64Decoder.
java.util.Properties
HTTP Requests & Responses

32. HTTP Requests & Responses
Base 64 Encoding
Sun provides a class called: sun.misc.BASE64Decoder.
You can use the decodeBuffer() method to decode the Base 64 String sent from the user:
String userInfo = “bWFydHk6bWFydHlwdw==”
BASE64Decoder decoder = new BASE64Decoder();
String nameAndPassword =
new String(decoder.decodeBuffer(userInfo));
After this code, nameAndPassword will be set to “marty:martypd”
HTTP Requests & Responses

33. HTTP Requests & Responses
java.util.Properties
A utility class for reading in property files.
For example, suppose you have the following password.properties file:
#Passwords
#Sat Aug 26 11:15:42 EDT 2000
nathan=nathanpw
marty=martypw
lindsay=lindsaypw
bj=bjpw
HTTP Requests & Responses

34. HTTP Requests & Responses
java.util.Properties
You can easily and automatically load the password file and parse its contents:
passwordFile = "passwords.properties";
passwords = new Properties();
passwords.load(new FileInputStream(passwordFile));
Then, you can extract the password for a specific user name:
String password = properties.getProperty ("marty“);
HTTP Requests & Responses

35. HTTP Requests & Responses
ProtectedPage.java
Here’s how the Servlet Works:
Initialization: Read in a Password file of valid user names and passwords.
Check for the HTTP Authorization Header.
Decode the Authorization Header using Base 64 to obtain user name and password.
Check the User Name and Password against the valid names list.
If valid, show protected page.
Else, issue another authentication challenge.
HTTP Requests & Responses

36. Form Authentication System
BASE64 not secure
Need secure solution!
Use HTML form
Example: FormAuthenticate
Access of servlet attempts to access protected data
User redirected to login form web page
Example takes any combination
Once authenticated, redirected to desired page
Session object used to store desired destination during login diversion
HTTP Requests & Responses

37. HTTP Requests & Responses
Summary
Lots of hidden HTTP data, including headers and cookies are sent from browser to the server.
HTTP Header data can also be sent from server to the browser, e.g. error codes, redirection codes, etc.
HTTP Requests & Responses