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6.2. Content Negotiation
There may be different ways to handle the data that Apache returns, and there are two equivalent ways of implementing this functionality. The multiviews method is simpler (and more limited) than the *.var method, so we shall start with it. The Config file (from ... /site.multiview) looks like this:
User webuser Group webgroup ServerName www.butterthlies.com DocumentRoot /usr/www/APACHE3/site.multiview/htdocs ScriptAlias /cgi-bin /usr/www/APACHE3/cgi-bin AddLanguage it .it AddLanguage en .en AddLanguage ko .ko LanguagePriority it en ko <Directory /usr/www/APACHE3/site.multiview/htdocs> Options + MultiViews </Directory>
For historical reasons, you have to say:
Options +MultiViews
even though you might reasonably think that Options All would cover the case. The general idea is that whenever you want to offer variations of a file (e.g., JPG, GIF, or bitmap for images, or different languages for text), multiviews will handle it. Apache v2 offers a relevant directive.
6.2.1. MultiviewsMatch
MultiviewsMatch permits three different behaviors for mod_negotiation's Multiviews feature.
MultiviewsMatch [NegotiatedOnly] [Handlers] [Filters] [Any] server config, virtual host, directory, .htaccess Compatibility: only available in Apache 2.0.26 and later.
Multiviews allows a request for a file, e.g., index.html, to match any negotiated extensions following the base request, e.g., index.html.en, index.html.fr, or index.html.gz.
The NegotiatedOnly option provides that every extension following the base name must correlate to a recognized mod_mime extension for content negotiation, e.g., Charset, Content-Type, Language, or Encoding. This is the strictest implementation with the fewest unexpected side effects, and it's the default behavior.
To include extensions associated with Handlers and/or Filters, set the MultiviewsMatch directive to either Handlers, Filters, or both option keywords. If all other factors are equal, the smallest file will be served, e.g., in deciding between index.html.cgi of 500 characters and index.html.pl of 1,000 bytes, the .cgi file would win in this example. Users of .asis files might prefer to use the Handler option, if .asis files are associated with the asis-handler.
You may finally allow Any extensions to match, even if mod_mime doesn't recognize the extension. This was the behavior in Apache 1.3 and can cause unpredictable results, such as serving .old or .bak files that the webmaster never expected to be served.
6.2.2. Image Negotiation
Image negotiation is a special corner of general content negotiation because the Web has a variety of image files with different levels of support: for instance, some browsers can cope with PNG files and some can't, and the latter have to be sent the simpler, more old-fashioned, and bulkier GIF files. The client's browser sends a message to the server telling it which image files it accepts:
HTTP_ACCEPT=image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*
Browsers almost always lie about the content types they accept or prefer, so this may not be all that reliable. In theory, however, the server uses this information to guide its search for an appropriate file, and then it returns it. We can demonstrate the effect by editing our ... /htdocs/catalog_summer.html file to remove the .jpg extensions on the image files. The appropriate lines now look like this:
... <img src="bench" alt="Picture of a Bench"> ... <img src="hen" alt="Picture of a hencoop like a pagoda"> ...
When Apache has the Multiviews option turned on and is asked for an image called bench, it looks for the smaller of bench.jpg and bench.gif — assuming the client's browser accepts both — and returns it.
Apache v2 introduces a new directive, which is related to the Filter mechanism (see later in this chapter, Section 6.6).
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| 6. Content Description and Modification |  | 6.3. Language Negotiation |
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