User agent. User agent браузеров

User agent - Wikipedia

In computing, a user agent is software (a software agent) that is acting on behalf of a user. One common use of the term refers to a web browser telling a website information about the browser and operating system. This allows the website to customize content for the capabilities of a particular device, but also raises privacy issues.

There are other uses of the term "user agent". For example, an email reader is a mail user agent. In many cases, a user agent acts as a client in a network protocol used in communications within a client–server distributed computing system. In particular, the Hypertext Transfer Protocol (HTTP) identifies the client software originating the request, using a user-agent header, even when the client is not operated by a user. The Session Initiation Protocol (SIP) protocol (based on HTTP) followed this usage. In the SIP, the term user agent refers to both end points of a communications session.[1]

User agent identification[edit]

When a software agent operates in a network protocol, it often identifies itself, its application type, operating system, software vendor, or software revision, by submitting a characteristic identification string to its operating peer. In HTTP,[2] SIP,[1] and NNTP[3] protocols, this identification is transmitted in a header field User-Agent. 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.

Use in HTTP[edit]

In HTTP, the User-Agent string is often used for content negotiation, where the origin server selects suitable content or operating parameters for the response. For example, the User-Agent string might be used by a web server to choose variants based on the known capabilities of a particular version of client software. The concept of content tailoring is built into the HTTP standard in RFC 1945 "for the sake of tailoring responses to avoid particular user agent limitations.”

The User-Agent string is one of the criteria by which Web crawlers may be excluded from accessing certain parts of a website using the Robots Exclusion Standard (robots.txt file).

As with many other HTTP request headers, the information in the "User-Agent" string contributes to the information that the client sends to the server, since the string can vary considerably from user to user.[4]

Format for human-operated web browsers[edit]

The User-Agent string format is currently specified by section 5.5.3 of HTTP/1.1 Semantics and Content. The format of the User-Agent string in HTTP is a list of product tokens (keywords) with optional comments. For example, if a user's product were called WikiBrowser, their user agent string might be WikiBrowser/1.0 Gecko/1.0. The "most important" product component is listed first.

The parts of this string are as follows:

• product name and version (WikiBrowser/1.0)
• layout engine and version (Gecko/1.0)

During the first browser war, many web servers were configured to only send web pages that required advanced features, including frames, to clients that were identified as some version of Mozilla.[5] Other browsers were considered to be older products such as Mosaic, Cello, or Samba, and would be sent a bare bones HTML document.

For this reason, most Web browsers use a User-Agent string value as follows:

Mozilla/[version] ([system and browser information]) [platform] ([platform details]) [extensions]. For example, Safari on the iPad has used the following:

The components of this string are as follows:

• Mozilla/5.0: Previously used to indicate compatibility with the Mozilla rendering engine.
• (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us): Details of the system in which the browser is running.
• AppleWebKit/531.21.10: The platform the browser uses.
• (KHTML, like Gecko): Browser platform details.
• Mobile/7B405: This is used by the browser to indicate specific enhancements that are available directly in the browser or through third parties. An example of this is Microsoft Live Meeting which registers an extension so that the Live Meeting service knows if the software is already installed, which means it can provide a streamlined experience to joining meetings.

Before migrating to the Chromium code base, Opera was the most widely used web browser that did not have the User-Agent string with "Mozilla" (instead beginning it with "Opera"). Since July 15, 2013,[6] Opera's User-Agent string begins with "Mozilla/5.0" and, to avoid encountering legacy server rules, no longer includes the word "Opera" (instead using the string "OPR" to denote the Opera version).

Format for automated agents (bots)[edit]

Automated web crawling tools can use a simplified form, where an important field is contact information in case of problems. By convention the word "bot" is included in the name of the agent[citation needed]. For example:

Automated agents are expected to follow rules in a special file called "robots.txt".

User agent spoofing[edit]

The popularity of various Web browser products has varied throughout the Web's history, and this has influenced the design of websites in such a way that websites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the World Wide Web Consortium (W3C) or the Internet Engineering Task Force (IETF). Websites often include code to detect browser version to adjust the page design sent according to the user agent string received. This may mean that less-popular browsers are not sent complex content (even though they might be able to deal with it correctly) or, in extreme cases, refused all content.[7] Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content. For example, the Android browser identifies itself as Safari (among other things) in order to aid compatibility.[8][9]

Other HTTP client programs, like download managers and offline browsers, often have the ability to change the user agent string.

Spam bots and Web scrapers often use fake user agents.

At times it has been popular among Web developers to initiate Viewable With Any Browser campaigns,[10] encouraging developers to design Web pages that work equally well with any browser.

A result of user agent spoofing may be that collected statistics of Web browser usage are inaccurate.

User agent sniffing[edit]

The term user agent sniffing refers to the practice of websites showing different content when viewed with a certain user agent. On the Internet, this will result in a different site being shown when browsing the page with a specific browser. One example of this is Microsoft Exchange Server 2003's Outlook Web Access feature. When viewed with Internet Explorer 6 or newer, more functionality is displayed compared to the same page in any other browsers. User agent sniffing is now considered poor practice, since it encourages browser-specific design and penalizes new browsers with unrecognized user agent identifications. Instead, the W3C recommends creating HTML markup that is standard,[11] allowing correct rendering in as many browsers as possible, and to test for specific browser features rather than particular browser versions or brands.[12]

Websites specifically targeted towards mobile phones, like NTT DoCoMo's I-Mode or Vodafone's Vodafone Live! portals, often rely heavily on user agent sniffing, since mobile browsers often differ greatly from each other. Many developments in mobile browsing have been made in the last few years,[when?] while many older phones that do not possess these new technologies are still heavily used. Therefore, mobile Web portals will often generate completely different markup code depending on the mobile phone used to browse them. These differences can be small, e.g., resizing of certain images to fit smaller screens, or quite extensive, e.g., rendering of the page in WML instead of XHTML.

Encryption strength notations[edit]

Web browsers created in the United States, such as Netscape Navigator and Internet Explorer, previously used the letters U, I, and N to specify the encryption strength in the user agent string. Until 1996, when the United States government disallowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths. "U" stands for "USA" (for the version with 128-bit encryption), "I" stands for "International" – the browser has 40-bit encryption and can be used anywhere in the world – and "N" stands (de facto) for "None" (no encryption).[13] Following the lifting of export restrictions, most vendors supported 256-bit encryption.

See also[edit]

References[edit]

1. ^ a b RFC 3261, SIP: Session Initiation Protocol, IETF, The Internet Society (2002)
2. ^ RFC 7231, Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content, IETF, The Internet Society (June 2014)
3. ^ Netnews Article Format. IETF. November 2009. sec. 3.2.13. doi:10.17487/RFC5536. RFC 5536. https://tools.ietf.org/html/rfc5536#section-3.2.13. 
4. ^ Peter Eckersley. "Browser Versions Carry 10.5 Bits of Identifying Information on Average", Electronic Frontier Foundation, 27 January 2010. Retrieved 25 August 2011.
5. ^ History of the browser user-agent string. WebAIM.
6. ^ "Opera User Agent Strings: Opera 15 and Beyond". dev.opera.com. 15 July 2013. Retrieved 2014-05-05. 
7. ^ Burstein complaining "... I've been rejected until I come back with Netscape"
8. ^ "Android Browser Reports Itself as Apple Safari". Archived from the original on August 6, 2011. Retrieved August 9, 2011. 
9. ^ "User Agent String explained: Android Webkit Browser". UserAgentString.com. Retrieved 29 July 2012. Mozilla/5.0 (Linux; U; Android 2.2; en-sa; HTC_DesireHD_A9191 Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1 
10. ^ "Viewable with Any Browser" campaign
11. ^ Pemberton, Stephen. "W3C Markup Validation Service". W3C. Retrieved 2011-10-18. 
12. ^ Clary, Bob (10 February 2003). "Browser Detection and Cross Browser Support". Mozilla Developer Center. Mozilla. Retrieved 2009-05-30. 
13. ^ Zawinski, Jamie (28 March 1998). "user-agent strings (obsolete)". mozilla.org. Retrieved 2010-01-08. 

en.wikipedia.org

How to Change User-Agent in Browser

User-Agent is a line that sends information to the site about the software used. Originally, websites used such data to identify the OS and browser version in order to correctly display embedded content. However, due to various reasons, early Web developers used different user agents for different browsers, and many users started faking their User-Agent value to view sites the way they wanted. Eventually developers started offering the option to change the User-Agent right in the settings.

The User-Agent allows to determine the operating system, device you use to access the site (smartphone, laptop, tablet etc.), and features supported by your browser like ActiveX.

If you need to change your User-Agent in Opera, Chrome, or Firefox, here is how you do it.

Warning!

Please take note that the User-Agent is required to correctly display sites that lack responsive design, since different browsers use different styles and scripts to display the same content. Actual data about various values of these parameters are easily found on browscap.org and in the end of this post.

How to change User-Agent in Opera

In Opera, click on the address field and type the following address: opera:config#UserPrefs|CustomUser-Agent. In the field that appears with the title «Custom User-Agent», set the needed value of user-agent. Scroll the window down and save the changes made.

In more recent versions of Opera, for example 43.0, this feature is disabled. We recommend to install the extension User-Agent Switcher that allows to change the value in a handy menu.

How to change user agent in Google Chrome

Not all Chrome versions allow you to change your User-Agent easily. That said, the following guide works in all versions starting from 26. To change the User-Agent, click on the browser icon with the right mouse button, choose “Properties”, and in the new window, line “Start in”, type the key – -user-agent=””, and then in quotes the User-Agent you need.

Now click OK and launch Chrome. Alternatively, you can do the same by other methods, for example, by holding buttons Win and R, opening the “Run” window, and typing chrome – -user-agent=”needed value”.

To get to know the current value of this parameter, open the about local address:

How to change user agent in Mozilla Firefox

Like Chrome, not all versions of Firefox allow for easy changing of this parameter. The following guide works for versions starting from 34. In the address bar, type about:config, and in a page that opens, create the parameter general.useragent.override.

Choose the type of the parameter “String”, and in a new window type the user-agent value you need:

List of various user agents

— Mozilla/0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36

— Mozilla/5.0 (Windows NT 6.1; Win64; x86) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

— Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E; Media Center PC 6.0; CMNTDFJS; F9J; InfoPath.3; rv:11.0) like Gecko

— Opera 12.17 (Win 8 x64): Opera/9.80 (Windows NT 6.2; WOW64) Presto/2.12.388 Version/12.17

— Internet Explorer 11 (Win 8.1 x64): Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; ASU2JS; rv:11.0) like Gecko

whoer.net

Как изменить User Agent в Firefox, Opera и Chrome

Замечу сразу, что способы изменения User Agent-ов для описанных браузеров одинаковы, как в Linux так и в Windows.

Начнём, пожалуй, с Mozilla Firefox (текущая версия 3.5.5).В адресной строке набираем about:config и после предупреждения попадаем в настроеки фаерфокса. Набираем в фильтре (сверху) слово general.useragent и видим, что мозиллистые (или мозолистые? товарищи особо не балуют трудящихся широтой выбора, и полностью изменить UserAgent с помощью появившихся полей не получится. К счастью, для этого предусмотрена одна хитрая настройка, которая по дефолту в Firefox отсутствует, называется она general.useragent.override, и если создать настройку с таким названием (правой кнопкой мыши > создать > строка) и запихнуть в неё, например, строку «Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5», то проверив мозилку на сервисе, чекающем user agent-ы (она, так же есть, наверху страницы), увидим наш новый фейковый юзерагент.

На будущее, если понадобится настоящий UserAgent, то для этого достаточно очистить строку в general.useragent.override

То же самое можно сделать и плагинами, например, User Agent Switcher-ом, который добавляет пункт в меню «Инструменты», для переключения юзерагентов на ходу. Большой список юзерагентов можно скачать по адресу http://techpatterns.com/forums/about304.html и добавить через импорт, в настройках дополнения.

Теперь, на очереди Opera (текущая версия 10.10).

Опера еще беднее, в плане настроек User Agent-а, чем FireFox, в чём легко можно убедиться, набрав в панели адреса opera:config и открыв пункт «User Agent», поле «Spoof UserAgent ID», где цифрами обозначаются разные варианты UserAgent-ов:

1) представляться как Opera (по умолчанию)2) представляться как Mozilla3) представляться как Internet Explorer4) маскироваться под Mozilla (Opera не упоминается)5) маскироваться под Internet Explorer (кроме отсутствия упоминания Оперы, в качестве операционной системы показывается Windows)

Однако, в порядке облома, сразу скажу, что пункт «Spoof UserAgent ID» не ра-бо-та-ет и глобального действия не имеет, по крайней мере, в текущей версии. Opera позволяет менять юзерагент, лишь для конкретных сайтов, через меню «Инструменты» > «Быстрые настройки» > «Настройки для сайтов» > закладка «Сеть» > пункт «Идентификация браузера» либо щелкнув правой кнопкой по странице нужного сайта > «Настройки для сайтов» и далее, так же, как и в первом случае.

На всякий пожарный, приведу мои юзерагенты для всех пяти вариантов:

1) Представляться как Opera = Opera/9.80 (X11; Linux x86_64; U; ru) Presto/2.2.15 Version/10.10

2) Представляться как Mozilla = Mozilla/5.0 (X11; Linux x86_64; U; ru; rv:1.8.1) Gecko/20061208 Firefox/2.0.0 Opera 10.10

3) Представляться как Internet Explorer = Mozilla/4.0 (compatible; MSIE 6.0; X11; Linux x86_64; ru) Opera 10.10

4) Маскироваться под Mozilla = Mozilla/5.0 (X11; Linux x86_64; U; ru; rv:1.8.1) Gecko/20061208 Firefox/2.0.0

5) маскироваться под Internet Explorer (единственный виндовый user agent) = Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; ru)

Пожалуй, кроме четвертого и пятого, рабочих вариантов нет, зато третий получился самый весёлый

Для добавления нужных данных к существующим UserAgent-ам Оперы, в opera:config можно использовать поле «Id» пункта «ISP» и поле «Allow Components In UA String Comment» пункта «User Agent». Они понадобятся, если нужно зайти на сайт, требующий наличия в User Agent-е определенной строки, например, операционной системы мобильника, при заходе на сайт для мобильных телефонов.

И напоследок, проедемся по Google Chrome, благо недавно, наконец, вышли версии и для Linux.

Для Хрома, мне известен только один нормальный способ (без ковыряния в потрохах Chrome) изменить User Agent — это запуск с опцией ‘-user-agent’.

Для Windows, для этого можно модифицировать ярлык Google Chrome, чтобы в поле «Объект», где указывается полный путь до программы, было следующее:

Аналогично и в Linux, в консоль либо в ярлык запуска Google Chrome на используемой рабочей среде, вставляем следующее:

В обоих примерах, опция -user-agent с параметром, обрамлена обычными одинарными или двойными кавычками, а не фигурными, вордпресс, мать его, всё время калечит кавычки…

Теперь проверить User Agent в Chrome можно, если набрать в адресной строке браузера команду about:version

Вот и всё, что можно сказать по этой теме

www.cetlot.com

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