Answer 1)
HTTP headers expose a great deal of
information about your client as well as the server.
In the Hypertext Transfer Protocol (HTTP), HTTP header fields contain the operating parameters of an
HTTP request or response. With the request or response line (first line of
message), they form the message header.
The header fields define various characteristics of the data
transfer that is requested or the data that is provided in the message body.
Header fields start with the field name, terminated with a colon character,
followed by the field value.
Request Headers (headers sent by browser
to server) Generally the request headers will be sent by browser to server. And
it contains information regarding type of browser, user language preferences (like English, German or Spanish), browser capabilities (like weather it can understand html
or only text and type of compressions supported by requesting browser) and cookies
(if any sent by server).
Here are sample headers how it looks like in a HTTP request. Request
Headers
|
Host
|
mr-ponna.com
|
|
User-Agent
|
Mozilla/5.0 (Windows; U; Windows
NT 6.1; en-US; rv:1.9.2.4) Gecko/20100611 Firefox/3.6.4
|
|
Accept
|
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8,text/vnd.wap.wml;q=0.6
|
|
Accept-Language
|
en-us,en;q=0.5
|
|
Accept-Encoding
|
gzip,deflate
|
|
Accept-Charset
|
ISO-8859-1,utf-8;q=0.7,*;q=0.7
|
|
Keep-Alive
|
115
|
|
Connection
|
keep-alive
|
|
Cookie
|
mr-ponna-state=c4t1tfw1c4k5ooerpld5105z;
|
Response Headers (headers sent by server
to browser) Response headers will be sent by server to browser. And it
contains information such as type of web server, response time, incoming
content-type (weather response is text, html or image), cache information (weather
browser can cache the response or not), cookies and status code (like File not
found and Internal server error).
Here are sample headers how it looks like in a HTTP response.
Response
Headers
|
Cache-Control
|
private
|
|
Content-Length
|
40209
|
|
Content-Type
|
text/html; charset=utf-8
|
|
Server
|
Microsoft-IIS/7.5
|
|
X-AspNet-Version
|
4.0.30319
|
|
X-Powered-By
|
ASP.NET
|
|
Date
|
Tue, 24 Aug 2010 12:27:37 GMT
|
Keep
in mind these HTTP headers not meant for ASP.NET, it’s for all web applications
irrespective of technology.
In ASP.NET,
you will deal with following 2 objects to read/send HTTP headers.
Request.Headers (to read all
incoming headers)
Response.Headers (to send/modify
response headers)
Here
is sample code snippet to read all request headers:
foreach (string key in
Request.Headers.AllKeys)
{
Response.Write(string.Format("Header field name: {0} -> Value:
{1}<br/>", key, Request.Headers[key]));
}
Here
is sample code snippet for controlling client caching using response headers:
Response.Headers.Add("Pragma",
"no-cache");
For
more information regarding HTTP headers see:
Quick reference to HTTP headers
HTTP
Header Field
| 
