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add documentation

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README.rst
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......@@ -12,9 +12,9 @@
vmod_re2
========
-----------------------------------------------
access the Google RE2 regular expression engine
-----------------------------------------------
---------------------------------------------------------------------
Varnish Module for access to the Google RE2 regular expression engine
---------------------------------------------------------------------
:Manual section: 3
......@@ -24,6 +24,177 @@ SYNOPSIS
import re2 [from "path"] ;
::
# regex object interface
new OBJECT = re2.regex(STRING pattern [, <regex options>])
BOOL <obj>.match(STRING)
STRING <obj>.backref(INT ref)
STRING <obj>.namedref(STRING name)
STRING <obj>.sub(STRING text, STRING rewrite)
STRING <obj>.suball(STRING text, STRING rewrite)
STRING <obj>.extract(STRING text, STRING rewrite)
# regex function interface
BOOL re2.match(STRING pattern, STRING subject [, <regex options>])
STRING re2.backref(INT ref)
STRING re2.namedref(STRING name)
STRING re2.sub(STRING pattern, STRING text, STRING rewrite [, <regex options>])
STRING re2.suball(STRING pattern, STRING text, STRING rewrite [, <regex options>])
STRING re2.extract(STRING pattern, STRING text, STRING rewrite [, <regex options>])
# set object interface
new OBJECT = re2.set([ENUM anchor] [, <regex options>])
VOID <obj>.add(STRING)
VOID <obj>.compile()
BOOL <obj>.match(STRING)
DESCRIPTION
===========
Varnish Module (VMOD) for access to the Google RE2 regular expression engine.
Varnish VCL uses the PCRE library (Perl Compatible Regular Expressions) for
its native regular expressions, which runs very efficiently for many common
uses of pattern matching in VCL, as attested by years of successful use of
PCRE with Varnish.
But for certain kinds of patterns, the worst-case running time of the PCRE
matcher is exponential in the length of the string to be matched. The
matcher uses backtracking, implemented with recursive calls to the internal
``match()`` function. In principle there is no upper bound to the possible
depth of backtracking and recursion, except as imposed by the ``varnishd``
runtime parameters ``pcre_match_limit`` and ``pcre_match_limit_recursion``;
matches fail if either of these limits are met. Stack overflow caused by
deep backtracking has occasionally been the subject of ``varnishd`` issues.
RE2 differs from PCRE in that it limits the syntax of patterns so that they
always specify a regular language in the formally strict sense. Most notably,
backreferences within a pattern are not permitted, for example ``(foo|bar)\1``
to match ``foofoo`` and ``barbar``, but not ``foobar`` or ``barfoo``. See the
link in ``SEE ALSO`` for the specification of RE2 syntax.
This means that an RE2 matcher runs as a finite automaton, which guarantees
linear running time in the length of the matched string. There is no
backtracking, and hence no risk of deep recursion or stack overflow.
The relative advantages and disadvantages of RE2 and PCRE is a broad subject,
beyond the scope of this manual. See the references in ``SEE ALSO`` for more
in-depth discussion.
regex object and function interfaces
------------------------------------
The VMOD provides regular expression operations by way of the ``regex`` object
interface and a functional interface. For ``regex`` objects, the pattern is
compiled at VCL initialization time, and the compiled pattern is re-used for
each invocation of its methods. Compilation failures (due to errors in the
pattern) cause failure at initialization time, and the VCL fails to load. The
``.backref()`` and ``.namedref()`` methods refer back to the last invocation
of the ``.match()`` method for the same object.
The functional interface provides the same set of operations, but the pattern
is compiled at runtime on each invocation (and then discarded). Compilation
failures are reported as errors in the Varnish log. The ``backref()`` and
``namedref()`` functions refer back to the last invocation of the ``match()``
function, for any pattern.
Compiling a pattern at runtime on each invocation is considerably more costly
than re-using a compiled pattern. So for patterns that are fixed and known
at VCL initialization, the object interface should be used. The functional
interface should only be used for patterns whose contents are not known until
runtime.
set object interface
--------------------
``set`` objects provide a shorthand for constructing patterns that consist of
an alternation -- a group of patterns combined with ``|`` for "or". For
example::
import re2;
sub vcl_init {
new myset = re2.set();
myset.add("foo");
myset.add("bar");
myset.add("baz");
myset.compile();
}
``myset.match(<string>)`` can now be used to match a string against the
pattern ``foo|bar|baz``.
regex options
-------------
Where a pattern is compiled -- in the ``regex`` and ``set`` constructors, and
in functions that require compilation -- options may be specified that can
affect the interpretation of the pattern or the operation of the matcher. There
are default values for each option, and it is only necessary to specify options
in VCL that differ from the defaults. Options specified in a ``set``
constructor apply to all of the patterns in the resulting alternation.
``utf8``
If true, characters in a pattern match Unicode code points, and hence may
match more than one byte. If false, the pattern and strings to be matched
are interpreted as Latin-1 (ISO 8859-1), and a pattern character matches
exactly one byte. Default is **false**. Note that this differs from the
RE2 default.
``posix_syntax``
If true, patterns are restricted to POSIX (egrep) syntax. Otherwise,
the pattern syntax resembles that of PCRE, with some deviations. See the
link in ``SEE ALSO`` for the syntax specification. Default is **false**.
The options ``perl_classes``, ``word_boundary`` and ``one_line`` are
only consulted when this option is true.
``longest_match``
If true, the matcher searches for the longest possible match where
alternatives are possible. Otherwise, search for the first match. For
example with the pattern ``a(b|bb)`` and the string ``abb``, ``abb``
matches when ``longest_match`` is true, and backref 1 is ``bb``. Otherwise,
``ab`` matches, and backref 1 is ``b``. Default is **false**.
``max_mem``
An upper bound (in bytes) for the size of the compiled pattern. If ``max_mem``
is too small, the matcher may fall back to less efficient algorithms, or the
pattern may fail to compile. Default is the RE2 default (8MB), which should
suffice for typical patterns.
``literal``
If true, the pattern is interpreted as a literal string, and no regex
metacharacters (such as ``*``, ``+``, ``^`` and so forth) have their special
meaning. Default is **false**.
``never_nl``
If true, the newline character ``\n`` in a string is never matched, even if it
appears in the pattern. Default is **false**.
``dot_nl``
If true, then the dot character ``.`` in a pattern matches everything,
including newline. Otherwise, ``.`` never matches newline. Default is
**false**.
``never_capture``
If true, parentheses in a pattern are interpreted as non-capturing, and all
invocations of the ``backref`` and ``namedref`` methods or functions will
fail, including ``backref(0)`` after a successful match. Default is **false**,
except for set objects, for which ``never_capture`` is always true (and cannot
be changed), since back references are not possible with sets.
``case_sensitive``
If true, matches are case-sensitive. A pattern can override this option with
the ``(?i)`` flag, unless ``posix_syntax`` is true. Default is **true**.
The following options are only consulted when ``posix_syntax`` is true. If
``posix_syntax`` is false, then these features are always enabled and cannot be
turned off.
``perl_classes``
If true, then the perl character classes ``\d``, ``\s``, ``\w``, ``\D``,
``\S`` and ``\W`` are permitted in a pattern. Default is **false**.
``word_boundary``
If true, the perl assertions ``\b`` and ``\B`` (word boundary and not a word
boundary) are permitted. Default is **false**.
``one_line``
If true, then ``^`` and ``$`` only match at the beginning and end of the
string to be matched, regardless of newlines. Otherwise, ``^`` also matches
just after a newline, and ``$`` also matches just before a newline. Default is
**false**.
CONTENTS
========
......@@ -52,6 +223,25 @@ Object regex
============
Prototype
new OBJECT = re2.regex(STRING pattern [, <regex options>])
Description
Create a regex object from ``pattern`` and the given options (or option
defaults). If the pattern is invalid, then VCL will fail to load and the VCC
compiler will emit an error message.
Example::
sub vcl_init {
new domainmatcher = re2.regex("^www\.([^.]+)\.com$");
new maxagematcher = re2.regex("max-age\s*=\s*(\d+)");
# Group possible subdomains without capturing
new submatcher = re2.regex("^www\.(domain1|domain2)\.com$",
never_capture=true);
}
.. _func_regex.match:
BOOL regex.match(STRING)
......@@ -60,6 +250,16 @@ BOOL regex.match(STRING)
Prototype
BOOL regex.match(STRING)
Description
Returns ``true`` if and only if the compiled regex matches the given
string; corresponds to VCL's infix operator ``~``.
Example::
if (myregex.match(req.http.Host)) {
call do_on_match;
}
.. _func_regex.backref:
STRING regex.backref(INT, STRING)
......@@ -68,6 +268,59 @@ STRING regex.backref(INT, STRING)
Prototype
STRING regex.backref(INT ref, STRING fallback)
Description
Returns the `nth` captured subexpression from the most recent successful
call of the ``.match()`` method for this object in the same client or backend,
context, or a fallback string in case the capture fails. Backref 0 indicates
the entire matched string. Thus this function behaves like the ``\n`` in the
native VCL functions ``regsub`` and ``regsuball``, and the ``$1``, ``$2`` ...
variables in Perl.
Since Varnish client and backend operations run in different threads,
``.backref()`` can only refer back to a ``.match()`` call in the same
thread. Thus a ``.backref()`` call in any of the ``vcl_backend_*``
subroutines -- the backend context -- refers back to a previous ``.match()``
in any of those same subroutines; and a call in any of the other VCL
subroutines -- the client context -- refers back to a ``.match()`` in the
same client context.
After unsuccessful matches, the ``fallback`` string is returned for any call
to ``.backref()``. The default value of ``fallback`` is ``"**BACKREF METHOD
FAILED**"``. ``.backref()`` always fails after a failed match, even if
``.match()`` had been called successfully before the failure.
``.backref()`` may also return ``fallback`` after a successful match, if
no captured group in the matching string corresponds to the backref number.
For example, when the pattern ``(a|(b))c`` matches the string ``ac``, there
is no backref 2, since nothing matches ``b`` in the string.
The VCL infix operators ``~`` and ``!~`` do not affect this method, nor do
the functions ``regsub`` or ``regsuball``. Nor is it affected by the matches
performed by any other method or function in this VMOD (such as the ``sub()``,
``suball()`` or ``extract()`` methods or functions, or the ``set`` object's
``.match()`` method).
``.backref()`` fails, returning ``fallback`` and writing an error
message to the Varnish log with the ``VCL_Error`` tag, under the
following conditions (even if a previous match was successful and a
substring could have been captured):
* The ``fallback`` string is undefined, for example if set from an unset
header variable.
* The ``never_capture`` option was set to ``true`` for this object. In this
case, even ``.backref(0)`` fails after a successful match (otherwise, backref
0 always returns the full matched string).
* ``ref`` (the backref number) is out of range, i.e. it is larger than the
highest number for a capturing group in the pattern.
* ``.match()`` was never called for this object prior to calling ``.backref()``.
* There is insufficient workspace for the string to be returned.
Example::
if (domainmatcher.match(req.http.Host)) {
set req.http.X-Domain = domainmatcher.backref(1);
}
.. _func_regex.namedref:
STRING regex.namedref(STRING, STRING)
......@@ -76,6 +329,48 @@ STRING regex.namedref(STRING, STRING)
Prototype
STRING regex.namedref(STRING name, STRING fallback)
Description
Returns the captured subexpression designated by ``name`` from the most
recent successful call to ``.match()`` in the current context (client or
backend), or ``fallback`` in case of failure.
Named capturing groups are written in RE2 as: ``(?P<name>re)``. (Note that
this syntax with ``P``, inspired by Python, differs from the notation for
named capturing groups in PCRE.) Thus when ``(?P<foo>.+)bar$`` matches
``bazbar``, then ``.namedref("foo")`` returns ``baz``.
Note that a named capturing group can also be referenced as a numbered group.
So in the previous example, ``.backref(1)`` also returns ``baz``.
``fallback`` is returned when ``.namedref()`` is called after an
unsuccessful match. The default fallback is ``"**NAMEDREF METHOD FAILED**"``.
Like ``.backref()``, ``.namedref()`` is not affected by native VCL regex
operations, nor by any other matches performed by methods or functions of
the VMOD, except for a prior ``.match()`` for the same object.
``.namedref()`` fails, returning ``fallback`` and logging a ``VCL_Error``
message, if:
* The ``fallback`` string is undefined.
* ``name`` is undefined or the empty string.
* The ``never_capture`` option was set to ``true``.
* There is no such named group.
* ``.match()`` was not called for this object.
* There is insufficient workspace for the string to be returned.
Example::
sub vcl_init {
new domainmatcher = re2.regex("^www\.(?P<domain>[^.]+)\.com$");
}
sub vcl_recv {
if (domainmatcher.match(req.http.Host)) {
set req.http.X-Domain = domainmatcher.namedref("domain");
}
}
.. _func_regex.sub:
STRING regex.sub(STRING, STRING, STRING)
......@@ -84,6 +379,35 @@ STRING regex.sub(STRING, STRING, STRING)
Prototype
STRING regex.sub(STRING text, STRING rewrite, STRING fallback)
Description
If the compiled pattern for this regex object matches ``text``, then
return the result of replacing the first match in ``text`` with ``rewrite``.
Within ``rewrite``, ``\1`` through ``\9`` can be used to insert the
the numbered capturing group from the pattern, and ``\0`` to insert the
entire matching text. This method corresponds to the VCL native function
``regsub()``.
``fallback`` is returned if the pattern does not match ``text``. The default
fallback is ``"**SUB METHOD FAILED**"``.
``.sub()`` fails, returning ``fallback`` and logging a ``VCL_Error`` message,
if:
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
Example::
sub vcl_init {
new bmatcher = re2.regex("b+");
}
sub vcl_recv {
# If Host contains "www.yabba.dabba.doo.com", then this will
# set X-Yada to "www.yada.dabba.doo.com".
set req.http.X-Yada = bmatcher.sub(req.http.Host, "d");
}
.. _func_regex.suball:
STRING regex.suball(STRING, STRING, STRING)
......@@ -92,43 +416,61 @@ STRING regex.suball(STRING, STRING, STRING)
Prototype
STRING regex.suball(STRING text, STRING rewrite, STRING fallback)
.. _func_regex.extract:
Description
Like ``.sub()``, except that all successive non-overlapping matches in
``text`` are replaced with ``rewrite``. This method corresponds to VCL
native ``regsuball()``.
STRING regex.extract(STRING, STRING, STRING)
--------------------------------------------
The default fallback is ``"**SUBALL METHOD FAILED**"``. ``.suball()``
fails under the same conditions as ``.sub()``.
Prototype
STRING regex.extract(STRING text, STRING rewrite, STRING fallback)
Since only non-overlapping matches are substituted, replacing ``"ana"``
within ``"banana"`` only results in one substitution, not two.
.. _obj_set:
Example::
Object set
==========
sub vcl_init {
new bmatcher = re2.regex("b+");
}
sub vcl_recv {
# If Host contains "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dada.doo.com".
set req.http.X-Yada = bmatcher.suball(req.http.Host, "d");
}
.. _func_set.add:
.. _func_regex.extract:
VOID set.add(STRING)
--------------------
STRING regex.extract(STRING, STRING, STRING)
--------------------------------------------
Prototype
VOID set.add(STRING)
STRING regex.extract(STRING text, STRING rewrite, STRING fallback)
.. _func_set.compile:
Description
If the compiled pattern for this regex object matches ``text``, then
return ``rewrite`` with substitutions from the matching portions of
``text``. Non-matching substrings of ``text`` are ignored.
VOID set.compile()
------------------
The default fallback is ``"**EXTRACT METHOD FAILED**"``. Like ``.sub()``
and ``.suball()``, ``.extract()`` fails if:
Prototype
VOID set.compile()
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
.. _func_set.match:
Example::
BOOL set.match(STRING)
----------------------
sub vcl_init {
new email = re2.regex("(.*)@([^.]*)");
}
Prototype
BOOL set.match(STRING)
sub vcl_deliver {
# Sets X-UUCP to "kremvax!boris"
set resp.http.X-UUCP = email.extract("boris@kremvax.ru", "\2!\1");
}
regex functional interface
==========================
.. _func_match:
......@@ -138,6 +480,21 @@ BOOL match(PRIV_TASK, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL, BOOL, B
Prototype
BOOL match(PRIV_TASK, STRING pattern, STRING subject, BOOL utf8, BOOL posix_syntax, BOOL longest_match, INT max_mem, BOOL literal, BOOL never_nl, BOOL dot_nl, BOOL never_capture, BOOL case_sensitive, BOOL perl_classes, BOOL word_boundary, BOOL one_line)
Description
Like the ``regex.match()`` method, return ``true`` if ``pattern`` matches
``subject``, where ``pattern`` is compiled with the given options (or default
options) on each invocation.
If ``pattern`` fails to compile, then an error message is logged with
the ``VCL_Error`` tag, and ``false`` is returned.
Example::
# Match the bereq Host header against a backend response header
if (re2.match(pattern=bereq.http.Host, subject=beresp.http.X-Host)) {
call do_on_match;
}
.. _func_backref:
STRING backref(PRIV_TASK, INT, STRING)
......@@ -146,6 +503,37 @@ STRING backref(PRIV_TASK, INT, STRING)
Prototype
STRING backref(PRIV_TASK, INT ref, STRING fallback)
Description
Returns the `nth` captured subexpression from the most recent successful
call of the ``match()`` function in the current client or backend context,
or a fallback string if the capture fails. The default ``fallback`` is
``"**BACKREF FUNCTION FAILED**"``.
Similarly to the ``regex.backref()`` method, ``fallback`` is returned
after any failed invocation of the ``match()`` function, or if there
is no captured group corresponding to the backref number. The function
is not affected by native VCL regex operations, or any other method or
function of the VMOD except for the ``match()`` function.
The function fails, returning ``fallback`` and logging a ``VCL_Error``
message, under the same conditions as the corresponding method:
* ``fallback`` is undefined.
* ``never_capture`` was true in the previous invocation of the ``match()``
function.
* ``ref`` is out of range.
* The ``match()`` function was never called in this context.
* The pattern failed to compile for the previous ``match()`` call.
* There is insufficient workspace for the captured subexpression.
Example::
# Match against a pattern provided in a beresp header, and capture
# subexpression 1.
if (re2.match(pattern=beresp.http.X-Pattern, bereq.http.X-Foo)) {
set beresp.http.X-Capture = re2.backref(1);
}
.. _func_namedref:
STRING namedref(PRIV_TASK, STRING, STRING)
......@@ -154,6 +542,32 @@ STRING namedref(PRIV_TASK, STRING, STRING)
Prototype
STRING namedref(PRIV_TASK, STRING name, STRING fallback)
Description
Returns the captured subexpression designated by ``name`` from the most
recent successful call to the ``match()`` function in the current context, or
``fallback`` in case of failure. The default fallback is ``"**NAMEDREF
FUNCTION FAILED**"``.
The function returns ``fallback`` when the previous invocation of the
``match()`` function failed, and is only affected by use of the ``match()``
function. The function fails, returning ``fallback`` and logging a
``VCL_Error`` message, under the same conditions as the corresponding
method:
* ``fallback`` is undefined.
* ``name`` is undefined or the empty string.
* The ``never_capture`` option was set to ``true``.
* There is no such named group.
* ``match()`` was not called in this context.
* The pattern failed to compile for the previous ``match()`` call.
* There is insufficient workspace for the captured expression.
Example::
if (re2.match(beresp.http.X-Pattern-With-Names, bereq.http.X-Foo)) {
set beresp.http.X-Capture = re2.namedref("foo");
}
.. _func_sub:
STRING sub(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL)
......@@ -162,6 +576,31 @@ STRING sub(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL, BO
Prototype
STRING sub(STRING pattern, STRING text, STRING rewrite, STRING fallback, BOOL utf8, BOOL posix_syntax, BOOL longest_match, INT max_mem, BOOL literal, BOOL never_nl, BOOL dot_nl, BOOL never_capture, BOOL case_sensitive, BOOL perl_classes, BOOL word_boundary, BOOL one_line)
Description
Compiles ``pattern`` with the given options, and if it matches ``text``,
then return the result of replacing the first match in ``text`` with
``rewrite``. As with the ``regex.sub()`` method, ``\0`` through ``\9``
may be used in ``rewrite`` to substitute captured groups from the
pattern.
``fallback`` is returned if the pattern does not match ``text``. The default
fallback is ``"**SUB FUNCTION FAILED**"``.
``sub()`` fails, returning ``fallback`` and logging a ``VCL_Error`` message,
if:
* ``pattern`` cannot be compiled.
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
Example::
# If the beresp header X-Sub-Letters contains "b+", and Host contains
# "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dabba.doo.com".
set beresp.http.X-Yada = re2.sub(beresp.http.X-Sub-Letters,
bereq.http.Host, "d");
.. _func_suball:
STRING suball(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL)
......@@ -170,6 +609,21 @@ STRING suball(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL,
Prototype
STRING suball(STRING pattern, STRING text, STRING rewrite, STRING fallback, BOOL utf8, BOOL posix_syntax, BOOL longest_match, INT max_mem, BOOL literal, BOOL never_nl, BOOL dot_nl, BOOL never_capture, BOOL case_sensitive, BOOL perl_classes, BOOL word_boundary, BOOL one_line)
Description
Like the ``sub()`` function, except that all successive non-overlapping
matches in ``text`` are replace with ``rewrite``.
The default fallback is ``"**SUBALL FUNCTION FAILED**"``. The ``suball()``
function fails under the same conditions as ``sub()``.
Example::
# If the beresp header X-Sub-Letters contains "b+", and Host contains
# "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dada.doo.com".
set beresp.http.X-Yada = re2.suball(beresp.http.X-Sub-Letters,
bereq.http.Host, "d");
.. _func_extract:
STRING extract(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL)
......@@ -178,6 +632,150 @@ STRING extract(STRING, STRING, STRING, STRING, BOOL, BOOL, BOOL, INT, BOOL, BOOL
Prototype
STRING extract(STRING pattern, STRING text, STRING rewrite, STRING fallback, BOOL utf8, BOOL posix_syntax, BOOL longest_match, INT max_mem, BOOL literal, BOOL never_nl, BOOL dot_nl, BOOL never_capture, BOOL case_sensitive, BOOL perl_classes, BOOL word_boundary, BOOL one_line)
Description
Compiles ``pattern`` with the given options, and if it matches ``text``,
then return ``rewrite`` with substitutions from the matching portions of
``text``, ignoring the non-matching portions.
The default fallback is ``"**EXTRACT FUNCTION FAILED**"``. The ``extract()``
function fails under the same conditions as ``sub()`` and ``suball()``.
Example::
# If beresp header X-Params contains "(foo|bar)=(baz|quux)", and the
# URL contains "bar=quux", then set X-Query to "bar:quux".
set beresp.http.X-Query = re2.extract(beresp.http.X-Params, bereq.url,
"\1:\2");
.. _obj_set:
Object set
==========
Prototype
new OBJECT = re2.set([ENUM anchor] [, <regex options>])
Description
Initialize a set object that represents several patterns combined by
alternation -- ``|`` for "or".
Optional parameters control the interpretation of the resulting composed
pattern. The ``anchor`` parameter is an enum that can have the values
``none``, ``start`` or ``both``, where ``none`` is the default. ``start``
means that each pattern is matched as if it begins with ``^`` for
start-of-text, and ``both`` means that each pattern is anchored with both
``^`` at the beginning and ``$`` for end-of-text at the end. ``none`` means
that each pattern is interpreted as a partial match (although individual
patterns within the set may have either of ``^`` of ``$``).
For example, if a set is initialized with ``anchor=both``, and the patterns
``foo`` and ``bar`` are added, then matches against the set match a string
against ``^foo$|^bar$``, or equivalently ``^(foo|bar)$``.
The usual regex options can be set, which then control matching against
the resulting composed pattern. However, the ``never_capture`` option
cannot be set, and is always implicitly true, since backrefs and
namedrefs are not possible with sets.
Example::
sub vcl_init {
# Initialize a regex set for partial matches
# with default options
new foo = re2.set();
# Initialize a regex set for case insensitive matches
# with anchors on both ends (^ and $).
new bar = re2.set(anchor=both, case_sensitive=false);
# Initialize a regex set using POSIX syntax, but allowing
# Perl character classes, and anchoring at the left (^).
new baz = re2.set(anchor=start, posix_syntax=true,
perl_classes=true);
}
.. _func_set.add:
VOID set.add(STRING)
--------------------
Prototype
VOID set.add(STRING)
Description
Add the given pattern to the set. If the pattern is invalid, ``.add()``
fails, and the VCL will fail to load, with an error message describing
the problem.
``.add()`` MUST be called in ``vcl_init``, and MAY NOT be called after
``.compile()``. If ``.add()`` is called in any other subroutine, an
error message with ``VCL_Error`` is logged, and the call has no effect.
If it is called in ``vcl_init`` after ``.compile()``, then the VCL load
will fail with an error message.
In other words, add all patterns to the set in ``vcl_init``, and finally
call ``.compile()`` when you're done.
Example::
sub vcl_init {
# literal=true means that the dots are interpreted as literal
# dots, not "match any character".
new hostmatcher = re2.set(anchor=both, case_sensitive=false,
literal=true);
hostmatcher.add("www.domain1.com");
hostmatcher.add("www.domain2.com");
hostmatcher.add("www.domain3.com");
hostmatcher.compile();
}
.. _func_set.compile:
VOID set.compile()
------------------
Prototype
VOID set.compile()
Description
Compile the compound pattern represented by the set -- an alternation of
all patterns added by ``.add()``.
``.compile()`` may fail if the ``max_mem`` setting is not large enough
for the composed pattern. In that case, the VCL load will fail with an
error message (then consider a larger value for ``max_mem`` in the set
constructor).
``.compile()`` MUST be called in ``vcl_init``, and MAY NOT be called
more than once for a set object. If it is called in any other subroutine,
a ``VCL_Error`` message is logged, and the call has no effect. If it
is called a second time in ``vcl_init``, the VCL load will fail.
See above for examples.
.. _func_set.match:
BOOL set.match(STRING)
----------------------
Prototype
BOOL set.match(STRING)
Description
Returns ``true`` if the given string matches the compound pattern
represented by the set, i.e. if it matches any of the patterns that
were added to the set.
``.match()`` MUST be called after ``.compile()``; otherwise the
match always fails.
Example::
if (hostmatcher.match(req.http.Host)) {
call do_when_a_host_matched;
}
.. _func_version:
STRING version()
......@@ -185,3 +783,17 @@ STRING version()
Prototype
STRING version()
Description
Return the version string for this VMOD.
Example::
std.log("Using VMOD re2 version: " + re2.version());
REQUIREMENTS
============
The VMOD requires Varnish 4.1.2 and the RE2 library. It has been tested
against RE2 versions 2015-05-01 through 2016-04-01.
src/vmod_re2.vcc
View file @ f515f8c6
......@@ -7,9 +7,178 @@
# See LICENSE
#
$Module re2 3 access the Google RE2 regular expression engine
$Module re2 3 Varnish Module for access to the Google RE2 regular expression engine
$Event event
::
# regex object interface
new OBJECT = re2.regex(STRING pattern [, <regex options>])
BOOL <obj>.match(STRING)
STRING <obj>.backref(INT ref)
STRING <obj>.namedref(STRING name)
STRING <obj>.sub(STRING text, STRING rewrite)
STRING <obj>.suball(STRING text, STRING rewrite)
STRING <obj>.extract(STRING text, STRING rewrite)
# regex function interface
BOOL re2.match(STRING pattern, STRING subject [, <regex options>])
STRING re2.backref(INT ref)
STRING re2.namedref(STRING name)
STRING re2.sub(STRING pattern, STRING text, STRING rewrite [, <regex options>])
STRING re2.suball(STRING pattern, STRING text, STRING rewrite [, <regex options>])
STRING re2.extract(STRING pattern, STRING text, STRING rewrite [, <regex options>])
# set object interface
new OBJECT = re2.set([ENUM anchor] [, <regex options>])
VOID <obj>.add(STRING)
VOID <obj>.compile()
BOOL <obj>.match(STRING)
DESCRIPTION
===========
Varnish Module (VMOD) for access to the Google RE2 regular expression engine.
Varnish VCL uses the PCRE library (Perl Compatible Regular Expressions) for
its native regular expressions, which runs very efficiently for many common
uses of pattern matching in VCL, as attested by years of successful use of
PCRE with Varnish.
But for certain kinds of patterns, the worst-case running time of the PCRE
matcher is exponential in the length of the string to be matched. The
matcher uses backtracking, implemented with recursive calls to the internal
``match()`` function. In principle there is no upper bound to the possible
depth of backtracking and recursion, except as imposed by the ``varnishd``
runtime parameters ``pcre_match_limit`` and ``pcre_match_limit_recursion``;
matches fail if either of these limits are met. Stack overflow caused by
deep backtracking has occasionally been the subject of ``varnishd`` issues.
RE2 differs from PCRE in that it limits the syntax of patterns so that they
always specify a regular language in the formally strict sense. Most notably,
backreferences within a pattern are not permitted, for example ``(foo|bar)\1``
to match ``foofoo`` and ``barbar``, but not ``foobar`` or ``barfoo``. See the
link in ``SEE ALSO`` for the specification of RE2 syntax.
This means that an RE2 matcher runs as a finite automaton, which guarantees
linear running time in the length of the matched string. There is no
backtracking, and hence no risk of deep recursion or stack overflow.
The relative advantages and disadvantages of RE2 and PCRE is a broad subject,
beyond the scope of this manual. See the references in ``SEE ALSO`` for more
in-depth discussion.
regex object and function interfaces
------------------------------------
The VMOD provides regular expression operations by way of the ``regex`` object
interface and a functional interface. For ``regex`` objects, the pattern is
compiled at VCL initialization time, and the compiled pattern is re-used for
each invocation of its methods. Compilation failures (due to errors in the
pattern) cause failure at initialization time, and the VCL fails to load. The
``.backref()`` and ``.namedref()`` methods refer back to the last invocation
of the ``.match()`` method for the same object.
The functional interface provides the same set of operations, but the pattern
is compiled at runtime on each invocation (and then discarded). Compilation
failures are reported as errors in the Varnish log. The ``backref()`` and
``namedref()`` functions refer back to the last invocation of the ``match()``
function, for any pattern.
Compiling a pattern at runtime on each invocation is considerably more costly
than re-using a compiled pattern. So for patterns that are fixed and known
at VCL initialization, the object interface should be used. The functional
interface should only be used for patterns whose contents are not known until
runtime.
set object interface
--------------------
``set`` objects provide a shorthand for constructing patterns that consist of
an alternation -- a group of patterns combined with ``|`` for "or". For
example::
import re2;
sub vcl_init {
new myset = re2.set();
myset.add("foo");
myset.add("bar");
myset.add("baz");
myset.compile();
}
``myset.match(<string>)`` can now be used to match a string against the
pattern ``foo|bar|baz``.
regex options
-------------
Where a pattern is compiled -- in the ``regex`` and ``set`` constructors, and
in functions that require compilation -- options may be specified that can
affect the interpretation of the pattern or the operation of the matcher. There
are default values for each option, and it is only necessary to specify options
in VCL that differ from the defaults. Options specified in a ``set``
constructor apply to all of the patterns in the resulting alternation.
``utf8``
If true, characters in a pattern match Unicode code points, and hence may
match more than one byte. If false, the pattern and strings to be matched
are interpreted as Latin-1 (ISO 8859-1), and a pattern character matches
exactly one byte. Default is **false**. Note that this differs from the
RE2 default.
``posix_syntax``
If true, patterns are restricted to POSIX (egrep) syntax. Otherwise,
the pattern syntax resembles that of PCRE, with some deviations. See the
link in ``SEE ALSO`` for the syntax specification. Default is **false**.
The options ``perl_classes``, ``word_boundary`` and ``one_line`` are
only consulted when this option is true.
``longest_match``
If true, the matcher searches for the longest possible match where
alternatives are possible. Otherwise, search for the first match. For
example with the pattern ``a(b|bb)`` and the string ``abb``, ``abb``
matches when ``longest_match`` is true, and backref 1 is ``bb``. Otherwise,
``ab`` matches, and backref 1 is ``b``. Default is **false**.
``max_mem``
An upper bound (in bytes) for the size of the compiled pattern. If ``max_mem``
is too small, the matcher may fall back to less efficient algorithms, or the
pattern may fail to compile. Default is the RE2 default (8MB), which should
suffice for typical patterns.
``literal``
If true, the pattern is interpreted as a literal string, and no regex
metacharacters (such as ``*``, ``+``, ``^`` and so forth) have their special
meaning. Default is **false**.
``never_nl``
If true, the newline character ``\n`` in a string is never matched, even if it
appears in the pattern. Default is **false**.
``dot_nl``
If true, then the dot character ``.`` in a pattern matches everything,
including newline. Otherwise, ``.`` never matches newline. Default is
**false**.
``never_capture``
If true, parentheses in a pattern are interpreted as non-capturing, and all
invocations of the ``backref`` and ``namedref`` methods or functions will
fail, including ``backref(0)`` after a successful match. Default is **false**,
except for set objects, for which ``never_capture`` is always true (and cannot
be changed), since back references are not possible with sets.
``case_sensitive``
If true, matches are case-sensitive. A pattern can override this option with
the ``(?i)`` flag, unless ``posix_syntax`` is true. Default is **true**.
The following options are only consulted when ``posix_syntax`` is true. If
``posix_syntax`` is false, then these features are always enabled and cannot be
turned off.
``perl_classes``
If true, then the perl character classes ``\d``, ``\s``, ``\w``, ``\D``,
``\S`` and ``\W`` are permitted in a pattern. Default is **false**.
``word_boundary``
If true, the perl assertions ``\b`` and ``\B`` (word boundary and not a word
boundary) are permitted. Default is **false**.
``one_line``
If true, then ``^`` and ``$`` only match at the beginning and end of the
string to be matched, regardless of newlines. Otherwise, ``^`` also matches
just after a newline, and ``$`` also matches just before a newline. Default is
**false**.
$Object regex(STRING pattern, BOOL utf8=0, BOOL posix_syntax=0,
BOOL longest_match=0, INT max_mem=8388608, BOOL literal=0,
......@@ -17,33 +186,222 @@ $Object regex(STRING pattern, BOOL utf8=0, BOOL posix_syntax=0,
BOOL case_sensitive=1, BOOL perl_classes=0,
BOOL word_boundary=0, BOOL one_line=0)
Prototype
new OBJECT = re2.regex(STRING pattern [, <regex options>])
Description
Create a regex object from ``pattern`` and the given options (or option
defaults). If the pattern is invalid, then VCL will fail to load and the VCC
compiler will emit an error message.
Example::
sub vcl_init {
new domainmatcher = re2.regex("^www\.([^.]+)\.com$");
new maxagematcher = re2.regex("max-age\s*=\s*(\d+)");
# Group possible subdomains without capturing
new submatcher = re2.regex("^www\.(domain1|domain2)\.com$",
never_capture=true);
}
$Method BOOL .match(STRING)
Description
Returns ``true`` if and only if the compiled regex matches the given
string; corresponds to VCL's infix operator ``~``.
Example::
if (myregex.match(req.http.Host)) {
call do_on_match;
}
$Method STRING .backref(INT ref, STRING fallback = "**BACKREF METHOD FAILED**")
Description
Returns the `nth` captured subexpression from the most recent successful
call of the ``.match()`` method for this object in the same client or backend,
context, or a fallback string in case the capture fails. Backref 0 indicates
the entire matched string. Thus this function behaves like the ``\n`` in the
native VCL functions ``regsub`` and ``regsuball``, and the ``$1``, ``$2`` ...
variables in Perl.
Since Varnish client and backend operations run in different threads,
``.backref()`` can only refer back to a ``.match()`` call in the same
thread. Thus a ``.backref()`` call in any of the ``vcl_backend_*``
subroutines -- the backend context -- refers back to a previous ``.match()``
in any of those same subroutines; and a call in any of the other VCL
subroutines -- the client context -- refers back to a ``.match()`` in the
same client context.
After unsuccessful matches, the ``fallback`` string is returned for any call
to ``.backref()``. The default value of ``fallback`` is ``"**BACKREF METHOD
FAILED**"``. ``.backref()`` always fails after a failed match, even if
``.match()`` had been called successfully before the failure.
``.backref()`` may also return ``fallback`` after a successful match, if
no captured group in the matching string corresponds to the backref number.
For example, when the pattern ``(a|(b))c`` matches the string ``ac``, there
is no backref 2, since nothing matches ``b`` in the string.
The VCL infix operators ``~`` and ``!~`` do not affect this method, nor do
the functions ``regsub`` or ``regsuball``. Nor is it affected by the matches
performed by any other method or function in this VMOD (such as the ``sub()``,
``suball()`` or ``extract()`` methods or functions, or the ``set`` object's
``.match()`` method).
``.backref()`` fails, returning ``fallback`` and writing an error
message to the Varnish log with the ``VCL_Error`` tag, under the
following conditions (even if a previous match was successful and a
substring could have been captured):
* The ``fallback`` string is undefined, for example if set from an unset
header variable.
* The ``never_capture`` option was set to ``true`` for this object. In this
case, even ``.backref(0)`` fails after a successful match (otherwise, backref
0 always returns the full matched string).
* ``ref`` (the backref number) is out of range, i.e. it is larger than the
highest number for a capturing group in the pattern.
* ``.match()`` was never called for this object prior to calling ``.backref()``.
* There is insufficient workspace for the string to be returned.
Example::
if (domainmatcher.match(req.http.Host)) {
set req.http.X-Domain = domainmatcher.backref(1);
}
$Method STRING .namedref(STRING name,
STRING fallback = "**NAMEDREF METHOD FAILED**")
Description
Returns the captured subexpression designated by ``name`` from the most
recent successful call to ``.match()`` in the current context (client or
backend), or ``fallback`` in case of failure.
Named capturing groups are written in RE2 as: ``(?P<name>re)``. (Note that
this syntax with ``P``, inspired by Python, differs from the notation for
named capturing groups in PCRE.) Thus when ``(?P<foo>.+)bar$`` matches
``bazbar``, then ``.namedref("foo")`` returns ``baz``.
Note that a named capturing group can also be referenced as a numbered group.
So in the previous example, ``.backref(1)`` also returns ``baz``.
``fallback`` is returned when ``.namedref()`` is called after an
unsuccessful match. The default fallback is ``"**NAMEDREF METHOD FAILED**"``.
Like ``.backref()``, ``.namedref()`` is not affected by native VCL regex
operations, nor by any other matches performed by methods or functions of
the VMOD, except for a prior ``.match()`` for the same object.
``.namedref()`` fails, returning ``fallback`` and logging a ``VCL_Error``
message, if:
* The ``fallback`` string is undefined.
* ``name`` is undefined or the empty string.
* The ``never_capture`` option was set to ``true``.
* There is no such named group.
* ``.match()`` was not called for this object.
* There is insufficient workspace for the string to be returned.
Example::
sub vcl_init {
new domainmatcher = re2.regex("^www\.(?P<domain>[^.]+)\.com$");
}
sub vcl_recv {
if (domainmatcher.match(req.http.Host)) {
set req.http.X-Domain = domainmatcher.namedref("domain");
}
}
$Method STRING .sub(STRING text, STRING rewrite,
STRING fallback = "**SUB METHOD FAILED**")
Description
If the compiled pattern for this regex object matches ``text``, then
return the result of replacing the first match in ``text`` with ``rewrite``.
Within ``rewrite``, ``\1`` through ``\9`` can be used to insert the
the numbered capturing group from the pattern, and ``\0`` to insert the
entire matching text. This method corresponds to the VCL native function
``regsub()``.
``fallback`` is returned if the pattern does not match ``text``. The default
fallback is ``"**SUB METHOD FAILED**"``.
``.sub()`` fails, returning ``fallback`` and logging a ``VCL_Error`` message,
if:
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
Example::
sub vcl_init {
new bmatcher = re2.regex("b+");
}
sub vcl_recv {
# If Host contains "www.yabba.dabba.doo.com", then this will
# set X-Yada to "www.yada.dabba.doo.com".
set req.http.X-Yada = bmatcher.sub(req.http.Host, "d");
}
$Method STRING .suball(STRING text, STRING rewrite,
STRING fallback = "**SUBALL METHOD FAILED**")
Description
Like ``.sub()``, except that all successive non-overlapping matches in
``text`` are replaced with ``rewrite``. This method corresponds to VCL
native ``regsuball()``.
The default fallback is ``"**SUBALL METHOD FAILED**"``. ``.suball()``
fails under the same conditions as ``.sub()``.
Since only non-overlapping matches are substituted, replacing ``"ana"``
within ``"banana"`` only results in one substitution, not two.
Example::
sub vcl_init {
new bmatcher = re2.regex("b+");
}
sub vcl_recv {
# If Host contains "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dada.doo.com".
set req.http.X-Yada = bmatcher.suball(req.http.Host, "d");
}
$Method STRING .extract(STRING text, STRING rewrite,
STRING fallback = "**EXTRACT METHOD FAILED**")
$Object set(ENUM { none, start, both } anchor="none", BOOL utf8=0,
BOOL posix_syntax=0, BOOL longest_match=0, INT max_mem=8388608,
BOOL literal=0, BOOL never_nl=0, BOOL dot_nl=0,
BOOL case_sensitive=1, BOOL perl_classes=0, BOOL word_boundary=0,
BOOL one_line=0)
Description
If the compiled pattern for this regex object matches ``text``, then
return ``rewrite`` with substitutions from the matching portions of
``text``. Non-matching substrings of ``text`` are ignored.
$Method VOID .add(STRING)
The default fallback is ``"**EXTRACT METHOD FAILED**"``. Like ``.sub()``
and ``.suball()``, ``.extract()`` fails if:
$Method VOID .compile()
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
$Method BOOL .match(STRING)
Example::
sub vcl_init {
new email = re2.regex("(.*)@([^.]*)");
}
sub vcl_deliver {
# Sets X-UUCP to "kremvax!boris"
set resp.http.X-UUCP = email.extract("boris@kremvax.ru", "\2!\1");
}
regex functional interface
==========================
$Function BOOL match(PRIV_TASK, STRING pattern, STRING subject, BOOL utf8=0,
BOOL posix_syntax=0, BOOL longest_match=0,
......@@ -52,12 +410,84 @@ $Function BOOL match(PRIV_TASK, STRING pattern, STRING subject, BOOL utf8=0,
BOOL case_sensitive=1, BOOL perl_classes=0,
BOOL word_boundary=0, BOOL one_line=0)
Description
Like the ``regex.match()`` method, return ``true`` if ``pattern`` matches
``subject``, where ``pattern`` is compiled with the given options (or default
options) on each invocation.
If ``pattern`` fails to compile, then an error message is logged with
the ``VCL_Error`` tag, and ``false`` is returned.
Example::
# Match the bereq Host header against a backend response header
if (re2.match(pattern=bereq.http.Host, subject=beresp.http.X-Host)) {
call do_on_match;
}
$Function STRING backref(PRIV_TASK, INT ref,
STRING fallback = "**BACKREF FUNCTION FAILED**")
Description
Returns the `nth` captured subexpression from the most recent successful
call of the ``match()`` function in the current client or backend context,
or a fallback string if the capture fails. The default ``fallback`` is
``"**BACKREF FUNCTION FAILED**"``.
Similarly to the ``regex.backref()`` method, ``fallback`` is returned
after any failed invocation of the ``match()`` function, or if there
is no captured group corresponding to the backref number. The function
is not affected by native VCL regex operations, or any other method or
function of the VMOD except for the ``match()`` function.
The function fails, returning ``fallback`` and logging a ``VCL_Error``
message, under the same conditions as the corresponding method:
* ``fallback`` is undefined.
* ``never_capture`` was true in the previous invocation of the ``match()``
function.
* ``ref`` is out of range.
* The ``match()`` function was never called in this context.
* The pattern failed to compile for the previous ``match()`` call.
* There is insufficient workspace for the captured subexpression.
Example::
# Match against a pattern provided in a beresp header, and capture
# subexpression 1.
if (re2.match(pattern=beresp.http.X-Pattern, bereq.http.X-Foo)) {
set beresp.http.X-Capture = re2.backref(1);
}
$Function STRING namedref(PRIV_TASK, STRING name,
STRING fallback = "**NAMEDREF FUNCTION FAILED**")
Description
Returns the captured subexpression designated by ``name`` from the most
recent successful call to the ``match()`` function in the current context, or
``fallback`` in case of failure. The default fallback is ``"**NAMEDREF
FUNCTION FAILED**"``.
The function returns ``fallback`` when the previous invocation of the
``match()`` function failed, and is only affected by use of the ``match()``
function. The function fails, returning ``fallback`` and logging a
``VCL_Error`` message, under the same conditions as the corresponding
method:
* ``fallback`` is undefined.
* ``name`` is undefined or the empty string.
* The ``never_capture`` option was set to ``true``.
* There is no such named group.
* ``match()`` was not called in this context.
* The pattern failed to compile for the previous ``match()`` call.
* There is insufficient workspace for the captured expression.
Example::
if (re2.match(beresp.http.X-Pattern-With-Names, bereq.http.X-Foo)) {
set beresp.http.X-Capture = re2.namedref("foo");
}
$Function STRING sub(STRING pattern, STRING text, STRING rewrite,
STRING fallback = "**SUB FUNCTION FAILED**",
BOOL utf8=0, BOOL posix_syntax=0, BOOL longest_match=0,
......@@ -65,6 +495,31 @@ $Function STRING sub(STRING pattern, STRING text, STRING rewrite,
BOOL dot_nl=0, BOOL never_capture=0, BOOL case_sensitive=1,
BOOL perl_classes=0, BOOL word_boundary=0, BOOL one_line=0)
Description
Compiles ``pattern`` with the given options, and if it matches ``text``,
then return the result of replacing the first match in ``text`` with
``rewrite``. As with the ``regex.sub()`` method, ``\0`` through ``\9``
may be used in ``rewrite`` to substitute captured groups from the
pattern.
``fallback`` is returned if the pattern does not match ``text``. The default
fallback is ``"**SUB FUNCTION FAILED**"``.
``sub()`` fails, returning ``fallback`` and logging a ``VCL_Error`` message,
if:
* ``pattern`` cannot be compiled.
* Any of ``text``, ``rewrite`` or ``fallback`` are undefined.
* There is insufficient workspace for the rewritten string.
Example::
# If the beresp header X-Sub-Letters contains "b+", and Host contains
# "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dabba.doo.com".
set beresp.http.X-Yada = re2.sub(beresp.http.X-Sub-Letters,
bereq.http.Host, "d");
$Function STRING suball(STRING pattern, STRING text, STRING rewrite,
STRING fallback = "**SUBALL FUNCTION FAILED**",
BOOL utf8=0, BOOL posix_syntax=0, BOOL longest_match=0,
......@@ -73,6 +528,21 @@ $Function STRING suball(STRING pattern, STRING text, STRING rewrite,
BOOL case_sensitive=1, BOOL perl_classes=0,
BOOL word_boundary=0, BOOL one_line=0)
Description
Like the ``sub()`` function, except that all successive non-overlapping
matches in ``text`` are replace with ``rewrite``.
The default fallback is ``"**SUBALL FUNCTION FAILED**"``. The ``suball()``
function fails under the same conditions as ``sub()``.
Example::
# If the beresp header X-Sub-Letters contains "b+", and Host contains
# "www.yabba.dabba.doo.com", then set X-Yada to
# "www.yada.dada.doo.com".
set beresp.http.X-Yada = re2.suball(beresp.http.X-Sub-Letters,
bereq.http.Host, "d");
$Function STRING extract(STRING pattern, STRING text, STRING rewrite,
STRING fallback = "**EXTRACT FUNCTION FAILED**",
BOOL utf8=0, BOOL posix_syntax=0, BOOL longest_match=0,
......@@ -81,4 +551,257 @@ $Function STRING extract(STRING pattern, STRING text, STRING rewrite,
BOOL case_sensitive=1, BOOL perl_classes=0,
BOOL word_boundary=0, BOOL one_line=0)
Description
Compiles ``pattern`` with the given options, and if it matches ``text``,
then return ``rewrite`` with substitutions from the matching portions of
``text``, ignoring the non-matching portions.
The default fallback is ``"**EXTRACT FUNCTION FAILED**"``. The ``extract()``
function fails under the same conditions as ``sub()`` and ``suball()``.
Example::
# If beresp header X-Params contains "(foo|bar)=(baz|quux)", and the
# URL contains "bar=quux", then set X-Query to "bar:quux".
set beresp.http.X-Query = re2.extract(beresp.http.X-Params, bereq.url,
"\1:\2");
$Object set(ENUM { none, start, both } anchor="none", BOOL utf8=0,
BOOL posix_syntax=0, BOOL longest_match=0, INT max_mem=8388608,
BOOL literal=0, BOOL never_nl=0, BOOL dot_nl=0,
BOOL case_sensitive=1, BOOL perl_classes=0, BOOL word_boundary=0,
BOOL one_line=0)
Prototype
new OBJECT = re2.set([ENUM anchor] [, <regex options>])
Description
Initialize a set object that represents several patterns combined by
alternation -- ``|`` for "or".
Optional parameters control the interpretation of the resulting composed
pattern. The ``anchor`` parameter is an enum that can have the values
``none``, ``start`` or ``both``, where ``none`` is the default. ``start``
means that each pattern is matched as if it begins with ``^`` for
start-of-text, and ``both`` means that each pattern is anchored with both
``^`` at the beginning and ``$`` for end-of-text at the end. ``none`` means
that each pattern is interpreted as a partial match (although individual
patterns within the set may have either of ``^`` of ``$``).
For example, if a set is initialized with ``anchor=both``, and the patterns
``foo`` and ``bar`` are added, then matches against the set match a string
against ``^foo$|^bar$``, or equivalently ``^(foo|bar)$``.
The usual regex options can be set, which then control matching against
the resulting composed pattern. However, the ``never_capture`` option
cannot be set, and is always implicitly true, since backrefs and
namedrefs are not possible with sets.
Example::
sub vcl_init {
# Initialize a regex set for partial matches
# with default options
new foo = re2.set();
# Initialize a regex set for case insensitive matches
# with anchors on both ends (^ and $).
new bar = re2.set(anchor=both, case_sensitive=false);
# Initialize a regex set using POSIX syntax, but allowing
# Perl character classes, and anchoring at the left (^).
new baz = re2.set(anchor=start, posix_syntax=true,
perl_classes=true);
}
$Method VOID .add(STRING)
Description
Add the given pattern to the set. If the pattern is invalid, ``.add()``
fails, and the VCL will fail to load, with an error message describing
the problem.
``.add()`` MUST be called in ``vcl_init``, and MAY NOT be called after
``.compile()``. If ``.add()`` is called in any other subroutine, an
error message with ``VCL_Error`` is logged, and the call has no effect.
If it is called in ``vcl_init`` after ``.compile()``, then the VCL load
will fail with an error message.
In other words, add all patterns to the set in ``vcl_init``, and finally
call ``.compile()`` when you're done.
Example::
sub vcl_init {
# literal=true means that the dots are interpreted as literal
# dots, not "match any character".
new hostmatcher = re2.set(anchor=both, case_sensitive=false,
literal=true);
hostmatcher.add("www.domain1.com");
hostmatcher.add("www.domain2.com");
hostmatcher.add("www.domain3.com");
hostmatcher.compile();
}
$Method VOID .compile()
Description
Compile the compound pattern represented by the set -- an alternation of
all patterns added by ``.add()``.
``.compile()`` may fail if the ``max_mem`` setting is not large enough
for the composed pattern. In that case, the VCL load will fail with an
error message (then consider a larger value for ``max_mem`` in the set
constructor).
``.compile()`` MUST be called in ``vcl_init``, and MAY NOT be called
more than once for a set object. If it is called in any other subroutine,
a ``VCL_Error`` message is logged, and the call has no effect. If it
is called a second time in ``vcl_init``, the VCL load will fail.
See above for examples.
$Method BOOL .match(STRING)
Description
Returns ``true`` if the given string matches the compound pattern
represented by the set, i.e. if it matches any of the patterns that
were added to the set.
``.match()`` MUST be called after ``.compile()``; otherwise the
match always fails.
Example::
if (hostmatcher.match(req.http.Host)) {
call do_when_a_host_matched;
}
$Function STRING version()
Description
Return the version string for this VMOD.
Example::
std.log("Using VMOD re2 version: " + re2.version());
REQUIREMENTS
============
The VMOD requires Varnish 4.1.2 and the RE2 library. It has been
tested against RE2 versions 2015-05-01 through 2016-04-01.
INSTALLATION
============
The VMOD is built against a Varnish installation, and the autotools
use ``pkg-config(1)`` to locate the necessary header files and other
resources for both Varnish and RE2. This sequence will install the VMOD::
> ./autogen.sh # for builds from the git repo
> ./configure
> make
> make check # to run unit tests in src/tests/*.vtc
> make distcheck # run check and prepare a distribution tarball
> sudo make install
If you have installed Varnish and/or RE2 in non-standard directories,
call ``autogen.sh`` and ``configure`` with the ``PKG_CONFIG_PATH``
environment variable set to include the paths where the ``.pc`` files
can be located for ``varnishapi`` and ``re2``. For example, when
varnishd configure was called with ``--prefix=$PREFIX``, use::
> PKG_CONFIG_PATH=${PREFIX}/lib/pkgconfig
> export PKG_CONFIG_PATH
By default, the vmod ``configure`` script installs the vmod in
the same directory as Varnish, determined via ``pkg-config(1)``. The
vmod installation directory can be overridden by passing the
``VMOD_DIR`` variable to ``configure``.
Other files such as this man-page are installed in the locations
determined by ``configure``, which inherits its default ``--prefix``
setting from Varnish.
For developers
--------------
The VMOD source code is in C and C++, since the RE2 API is
C++. Compilation has been tested with gcc/g++ and clang.
The build specifies C99 conformance for C sources (``-std=c99``), and
C++11 for C++ (``-std=c++11``). For both, all compiler warnings are
turned on, and all warnings are considered errors (``-Werror -Wall``).
The code should always build without warnings or errors under these
constraints.
By default, ``CFLAGS`` and ``CXXFLAGS`` are set to ``-g -O2``, so that
symbols are included in the shared library, and optimization is at
level ``O2``. To change or disable these options, set ``CFLAGS``
and/or ``CXXFLAGS`` explicitly before calling ``configure`` (they may
be set to the empty string).
For development/debugging cycles, the ``configure`` option
``--enable-debugging`` is recommended (off by default). This will turn
off optimizations and function inlining, so that a debugger will step
through the code as expected.
By default, the VMOD is built with the stack protector enabled
(compile option ``-fstack-protector``), but it can be disabled with
the ``configure`` option ``--disable-stack-protector``.
LIMITATIONS
===========
The VMOD allocates Varnish workspace for captured groups and rewritten
strings. If operations fail with "insufficient workspace" error
messages in the Varnish log (with the ``VCL_Error`` tag), increase the
varnishd runtime parameters ``workspace_client`` and/or
``workspace_backend``.
The RE2 documentation states that successful matches are slowed quite
a bit when they also capture substrings. There is also additional
overhead from the VMOD, unless the ``never_capture`` flag is true, to
manage data about captured groups in the workspace. This overhead is
incurred even if there are no capturing expressions in a pattern,
since it is always possible to call ``backref(0)`` to obtain the
matched portion of a string.
So if you are using a pattern only to match against strings, and never
to capture subexpressions, consider setting the ``never_capture``
option to true, to eliminate the extra work for both RE2 and the VMOD.
AUTHOR
======
* Geoffrey Simmons <geoff@uplex.de>
UPLEX Nils Goroll Systemoptimierung
HISTORY
=======
* version 0.1: initial version
SEE ALSO
========
* varnishd(1)
* vcl(7)
* RE2 git repo: https://github.com/google/re2
* RE2 syntax: https://github.com/google/re2/wiki/Syntax
* "Implementing Regular Expressions": https://swtch.com/~rsc/regexp/
* Series of articles motivating the design of RE2, with discussion
of how RE2 compares with PCRE
COPYRIGHT
=========
This document is licensed under the same conditions as the libvmod-re2
project. See LICENSE for details.
* Copyright (c) 2016 UPLEX Nils Goroll Systemoptimierung
$Event event
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