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What is user agent data
A
user agent (
ua) is the client application used with a particular network protocol;
the phrase is most commonly used in reference to those which access the World Wide Web.
Web user agents range from web browsers and e-mail clients to search engine crawlers ("spiders"), as well as mobile phones,
screen readers and braille browsers used by people with disabilities, and scripts that sending some manual ua data. When Internet users visit a web site,
a text string is generally sent to identify the user agent to the server. Don't forget that sent user agent data can be not real, because client application
can send that it want, and nobody control it.
This forms part of the HTTP request, prefixed with User-Agent: (case does not matter) and typically includes information such as the application name,
version, host operating system, and language. Bots, such as web crawlers, often also include a URL and/or e-mail address so that the webmaster can contact the operator of the bot.
Lots of Web Browsers support replacing of ua string, for example Konqueror can send ua string of Google Bot.
User agent string
User agent string - it's string that sending browser/application during request.
The user-agent string is one of the criteria by which crawlers can be excluded from certain pages or parts of a website using the "Robots Exclusion Standard" (robots.txt).
This allows webmasters who feel that certain parts of their website should not be included in the data gathered by a particular crawler,
or that a particular crawler is using up too much bandwidth, to request that crawler not to visit those pages.
User agent header
User agent header - it's part of request, see example. Header can containg any string data, but as usualy it's looking like * (*) *.
| HTTP_USER_AGENT | Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.19)
Gecko/20081216 Ubuntu/8.04 (hardy) Firefox/2.0.0.19 |
| HTTP_ACCEPT | text/xml,application/xml,application/xhtml+xml,text/html;
q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 |
| HTTP_ACCEPT_LANGUAGE | en-us,en;q=0.5 |
| HTTP_ACCEPT_ENCODING | gzip,deflate |
| HTTP_ACCEPT_CHARSET | ISO-8859-1,utf-8;q=0.7,*;q=0.7 |
| HTTP_KEEP_ALIVE | 300 |
