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The accept VMOD sanitizes
content negotiations headers,
most notably, Accept-Language. As backends can deliver different
objects for the same URL based on these headers, it can be necessary to normalize
them to avoid object duplication.
The VMOD follows RFC 7231; it evaluates a list of possible candidates and
returns a match to the user’s header, if any, according to the quality
(the q parameter) specified by the client for each choice.
Note: Varnish already handles the Accept-Encoding header, so you shouldn’t
do it in VCL.
import accept;
sub vcl_init {
# our server can only return html, json, and its default, plain text
new format = accept.rule("text/plain");
format.add("text/html");
format.add("application/json");
# also, the content is available in english (the default)
# as well as french
new lang = accept.rule("en");
lang.add("fr");
}
sub vcl_recv {
# only leave one choice for each header
set req.http.accept = format.filter(req.http.accept);
set req.http.accept-language = lang.filter(req.http.accept-language);
}
OBJECT rule(STRING string)
This creates a new rule object using string as a fallback in case no match is
found.
Arguments:
string accepts type STRINGType: Object
Returns: Object.
VOID .add(STRING string)
This is a method of the rule object and adds string to the list of
acceptable candidates.
Arguments:
string accepts type STRINGType: Method
Returns: None
VOID .remove(STRING string)
This method removes string from the list of candidates.
Arguments:
string accepts type STRINGType: Method
Returns: None
STRING .filter(STRING string)
This processes string and compares it with the list of candidates. The one with the
highest quality is returned or, failing that, the fallback string specified at
the rule object creation is used.
Arguments:
string accepts type STRINGType: Method
Returns: String
The accept VMOD is available in Varnish Enterprise version 6.0.1r1 and later.