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The rewrite vmod aims to reduce the amount of VCL code dedicated to url and
headers manipulation. The usual way of handling things in VCL is a long list of
if-else clauses:
sub vcl_recv {
if (req.url ~ "pattern1") {
set req.url = regsub(req.url, "regex1", "substitute1");
} else if (req.url ~ "pattern2") {
set req.url = regsub(req.url, "regex2", "substitute2");
...
}
Using vmod_rewrite, the VCL boils down to:
import rewrite;
sub vcl_init {
new rs = rewrite.ruleset("/path/to/file.rules");
}
sub vcl_recv {
set req.url = rs.match_rewrite(req.url);
}
with file.rules containing:
"regex1" "substitute1"
"regex2" "substitute2"
...
This is specially useful to clean URL normalization code as well as redirection generation. Thanks to the object-oriented approach, you can create multiple rulesets, eg. one for each task, and keep your VCL code clean and isolated.
OBJECT ruleset(STRING path = 0, STRING string = 0, INT min_fields = 2, ENUM {any, regex, prefix, suffix, exact, glob, glob_path, glob_dot} type = "regex", ENUM {quoted, blank, auto, braces} field_separator = quoted)
Parse the file indicated by path or contained in string and
create a new rules object. This loads all the rewrite rules described in
the file.
The file lists all the rules, one per line, with following format (except if type=any):
PATTERN [SUBSTITUTION]
If type=any, a first field is inserted to give the type for that line:
TYPE PATTERN [SUBSTITUTION]
Patterns and their respective substitutions are both quoted strings. TYPE is not quoted. Each parameter is separated by white-space. Pattern is the regular expression (regex) to match and substitution is the string to rewrite (or replace) any matches with. Empty lines and those starting with “#” are ignored.
Substitutions are optional, and the reason for that is that patterns can be used alone with the match() function.
TYPE (in the rule file) and type (as function argument) can be:
regex: Pattern is matched as a regular expression.prefix: Pattern is a string that tries to match the beginning of the target.suffix: Pattern is a string that tries to match the end of the target.exact: Pattern is a string and tries to match the full string.glob: Pattern is matched as a wildcard (* matches any group of characters)glob_path: Same as glob, but * doesn’t match slashes (useful to
match paths).glob_dots: Same as glob, but * doesn’t match dots (useful to match
IP addresses).any: use the first field in the rule file to decide (can’t be used
in the rule file).min_fields dictate how many strings each line should contain (not including
TYPE), if that minimum isn’t reached, the call will fail and the VCL won’t load.
field_separator specifies how the strings are quoted:
quoted: double-quotes delimit a string and are not included in said string.blank: string starts with its first non-whitespace character, and end with
its last.braces: Braces ({ and }) delimit a string, and the outermost
braces are not included in said string. The string itself can include braces,
as long as the number of opening and closing braces is balanced. Braces
escaped with \ are not counted towards the braces balance.auto: each word in the ruleset can use either quoted (starts with
double-quotes), braces (starts with an opening brace), or blank (starts
with anything else).This method is called in sub vcl_init and you can create as many objects as you
need:
sub vcl_init {
new redirect = rewrite.ruleset("/path/to/redirect.rules");
new normalize = rewrite.ruleset(string = {"
# this is a comment
pattern1 substitute1
(?i)PaTtERn2 substitute2
pattern([0-9]*) substitute\1
json {{"key1":"value1", "key2":"value2"}}
"}, field_separator = auto);
}
Arguments:
path accepts type STRING with a default value of 0 optional
string accepts type STRING with a default value of 0 optional
min_fields accepts type INT with a default value of 2 optional
type is an ENUM that accepts values of any, regex, prefix, suffix, exact, glob, glob_path, and glob_dot with a default value of regex optional
field_separator is an ENUM that accepts values of quoted, blank, auto, and braces with a default value of quoted optional
Type: Object
Returns: Object.
VOID .add_rules(STRING path = 0, STRING string = 0, ENUM {any, regex, prefix, suffix, exact, glob, glob_path, glob_dot} type = "regex", ENUM {quoted, blank, auto, braces} field_separator = quoted)
Add rules to an existing ruleset. This is a convenience for split-VCL setups where rules need to be centralized in a single ruleset, but initialized in multiple places to be co-located with related logic.
This function can only be called from sub vcl_init. Just like ruleset
constructors, path and string arguments are mutual-exclusive. When
rules are added in multiple places, they are then treated in the same order
they were added. It is possible to both specify rules in a ruleset constructor
and then add more rules.
Arguments:
path accepts type STRING with a default value of 0 optional
string accepts type STRING with a default value of 0 optional
type is an ENUM that accepts values of any, regex, prefix, suffix, exact, glob, glob_path, and glob_dot with a default value of regex optional
field_separator is an ENUM that accepts values of quoted, blank, auto, and braces with a default value of quoted optional
Type: Method
Returns: None
STRING .match_rewrite(STRING term, INT field = 2, ENUM {regsub, regsuball, only_matching} mode = regsuball)
This is a convenience function combining the .match() and .rewrite()
methods:
redirect.match_rewrite(req.url, field = 3, mode = regsuball);
is functionally equivalent to:
redirect.match(req.url);
redirect.rewrite(field = 3, mode = regsuball);
You can use it to apply the first matching rewrite rule to a string:
import rewrite;
sub vcl_init {
new rs = rewrite.ruleset(string = {"
"^(api|www).example.com$" "example.com"
"^img(|1|2|3).example.com$" "img.example.com"
"temp.example.com" "test.example.com"
"});
}
sub vcl_recv {
# normalize the host
set req.url = rs.match_rewrite(req.url);
}
Arguments:
term accepts type STRING
field accepts type INT with a default value of 2 optional
mode is an ENUM that accepts values of regsub, regsuball, and only_matching with a default value of regsuball optional
Type: Method
Returns: String
BOOL .match(STRING term)
Returns true if a rule in the ruleset matched the string argument, false
otherwise.
Example:
import rewrite;
sub vcl_init {
new rs = rewrite.ruleset(string = {"
"^/admin/"
"^/purge/"
"^/private"
"}, min_fields = 1);
}
sub vcl_recv {
if (rs.match(req.url)) {
return (synth(405, "Restricted");
}
}
Arguments:
term accepts type STRINGType: Method
Returns: Bool
STRING .rewrite(INT field = 2, ENUM {regsub, regsuball, only_matching} mode = regsuball)
.rewrite() is called after .match(), and applies the previously matched
rule, skipping the lookup operation.
By default, the first substitute string (index 2 of the rule definition) is
used, but you can specify a different field if needed. If the field doesn’t
exist, the string is not rewritten.
mode dictates how the string should be rewritten:
--only-matching
option of GNU grep.For example, considering this rule:
"bar" "qux"
and the string “/foo/bar/bar”:
You can use this function to retrieve multiple values associated to one rule:
import std;
import rewrite;
sub vcl_init {
new rs = rewrite.ruleset(string = {"
# pattern ttl grace keep
"\.(js|css)" "1m" "10m" "1d"
"\.(jpg|png)" "1w" "1w" "10w"
"});
}
sub vcl_backend_response {
# if there's a match, convert text to duration
if (rs.match(bereq.url)) {
set beresp.ttl = std.duration(rs.rewrite(0, mode = only_matching), 0s);
set beresp.grace = std.duration(rs.rewrite(1, mode = only_matching), 0s);
set beresp.keep = std.duration(rs.rewrite(2, mode = only_matching), 0s);
}
}
Arguments:
field accepts type INT with a default value of 2 optional
mode is an ENUM that accepts values of regsub, regsuball, and only_matching with a default value of regsuball optional
Type: Method
Returns: String
STRING .field(INT field)
.field() must be called after a successful .match(), it returns the
corresponding field by number from the matched rule.
For example, considering this VCL:
import rewrite;
sub vcl_init {
new rs = rewrite.ruleset(string = """
"foo" "bar" "baz"
"qux" "quxx"
""");
}
sub vcl_recv {
if (rs.match(req.url)) {
set req.http.field = rs.field(2);
}
}
A request with a URL containing “foo” would add a header “Field: bar” to the request.
Arguments:
field accepts type INTType: Method
Returns: String
STRING .replace(STRING, INT field = 2, ENUM {regsub, regsuball, only_matching} mode = regsuball)
.replace() is deprecated. Please use .match_rewrite() instead.
Arguments:
field accepts type INT with a default value of 2 optional
mode is an ENUM that accepts values of regsub, regsuball, and only_matching with a default value of regsuball optional
Type: Method
Returns: String
The rewrite VMOD is available in Varnish Enterprise version 6.0.0r0 and later.