javascript

Chapter 9: Client Detection
All of these user - agent strings indicate Gecko - based browsers (albeit using different versions).
Oftentimes, looking for a particular browser is not as important as understanding whether it ’ s Gecko -
based. The Mozilla version hasn ’ t changed from 5.0 since the first Gecko - based browser was released,
and it likely won ’ t change again.
WebKit
In 2003, Apple announced that it would release its own web browser, called Safari. The Safari rendering
engine, called WebKit, began as a fork of the KHTML rendering engine used in the Linux - based
Konqueror web browser. A couple of years later, WebKit was split off into its own open - source project,
focusing on development of the rendering engine.
Developers of this new browser and rendering engine faced a problem similar to that faced by Internet
Explorer 3.0: how do you ensure that the browser isn ’ t locked out of popular sites? The answer is, put
enough information into the user - agent string to convince web sites that the browser is compatible with
another popular browser. This led to a user - agent string with the following format:
Mozilla/5.0 ( Platform ; Encryption ; OS-or-CPU ; Language ) AppleWebKit /
AppleWebKitVersion (KHTML, like Gecko) Safari/ SafariVersion
Here ’ s an example:
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/124 (KHTML, like Gecko)
Safari/125.1
As you can see, this is another long user - agent string. It takes into account not only the version of the
Apple WebKit but also the Safari version. A point of contention over whether to identify the browser as
Mozilla was resolved rather quickly for compatibility reasons. Now, all WebKit - based browsers identify
themselves as Mozilla 5.0, the same as all Gecko - based browsers. The Safari version has typically been
the build number of the browser, not necessarily a representation of the release version number. So
although Safari 1.25 has the number 125.1 in the user - agent string, there may not always be a one - to - one
match.
The most interesting and controversial part of this user - agent string is the addition of the string
" (KHTML, like Gecko) ” in a pre - 1.0 version of Safari. Apple got a lot of pushback from developers
who saw this as a blatant attempt to trick clients and servers into thinking Safari was actually Gecko (as
if adding Mozilla/5.0 wasn ’ t enough). Apple ’ s response was similar to Microsoft ’ s when the IE user -
agent string came under fire: Safari is compatible with Mozilla, and web sites shouldn ’ t block out Safari
users because they appear to be using an unsupported browser.
Safari ’ s user - agent string was augmented slightly when version 3 was released. The following version
token is now used to identify the actual version of Safari being used:
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/522.15.5 (KHTML, like
Gecko) Version/3.0.3 Safari/522.15.5
Note that this change was made only to Safari, not to WebKit, so other WebKit - based browsers may not
have this change. Generally speaking, as with Gecko, it ’ s typical to determine that a browser is WebKit -
based rather than trying to identify Safari specifically.
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