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Name

ngx.re - Lua API for convenience utilities for ngx.re.

Table of Contents

Status

This Lua module is currently considered experimental.

Synopsis

local ngx_re = require "ngx.re"

-- split
local res, err = ngx_re.split("a,b,c,d", ",")
--> res is now {"a", "b", "c", "d"}

-- opt
ngx_re.opt("jit_stack_size", 128 * 1024)
--> the PCRE jit stack can now handle more complex regular expressions

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Description

This Lua module provides a Lua API which implements convenience utilities for the ngx.re API.

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Methods

All the methods of this module are static (or module-level). That is, you do not need an object (or instance) to call these methods.

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split

syntax: res, err = ngx_re.split(subject, regex, options?, ctx?, max?, res?)

Splits the subject string using the Perl compatible regular expression regex with the optional options.

This function returns a Lua (array) table (with integer keys) containing the splitted values.

In case of error, nil will be returned as well as a string describing the error.

When regex contains a sub-match capturing group, and when such a match is found, the first submatch capture will be inserted in between each splitted value, like so:

local ngx_re = require "ngx.re"

local res, err = ngx_re.split("a,b,c,d", "(,)")
-- res is now {"a", ",", "b", ",", "c", ",", "d"}

When regex is empty string "", the subject will be split into chars, like so:

local ngx_re = require "ngx.re"

local res, err = ngx_re.split("abcd", "")
-- res is now {"a", "b", "c", "d"}

The optional ctx table argument can be a Lua table holding an optional pos field. When the pos field in the ctx table argument is specified, ngx_re.split will start splitting the subject from that index:

local ngx_re = require "ngx.re"

local res, err = ngx_re.split("a,b,c,d", ",", nil, {pos = 5})
-- res is now {"c", "d"}

The optional max argument is a number that when specified, will prevent ngx_re.split from adding more than max matches to the res array:

local ngx_re = require "ngx.re"

local res, err = ngx_re.split("a,b,c,d", ",", nil, nil, 3)
-- res is now {"a", "b", "c,d"}

Specifying max <= 0 disables this behavior, meaning that the number of results won't be limited.

The optional 6th argument res can be a table that ngx_re.split will re-use to hold the results instead of creating a new one, which can improve performance in hot code paths. It is used like so:

local ngx_re = require "ngx.re"

local my_table = {"hello world"}

local res, err = ngx_re.split("a,b,c,d", ",", nil, nil, nil, my_table)
-- res/my_table is now {"a", "b", "c", "d"}

When provided with a res table, ngx_re.split won't clear the table for performance reasons, but will rather insert a trailing nil value when the split is completed:

local ngx_re = require "ngx.re"

local my_table = {"W", "X", "Y", "Z"}

local res, err = ngx_re.split("a,b", ",", nil, nil, nil, my_table)
-- res/my_table is now {"a", "b", nil, "Z"}

When the trailing nil is not enough for your purpose, you should clear the table yourself before feeding it into the split function.

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opt

syntax: ngx_re.opt(option, value)

Allows changing of regex settings. Currently, it can only change the jit_stack_size of the PCRE engine, like so:

 init_by_lua_block { require "ngx.re".opt("jit_stack_size", 200 * 1024) }

 server {
     location /re {
         content_by_lua_block {
             -- full regex and string are taken from https://github.com/JuliaLang/julia/issues/8278
             local very_long_string = [[71.163.72.113 - - [30/Jul/2014:16:40:55 -0700] ...]]
             local very_complicated_regex = [[([\d\.]+) ([\w.-]+) ([\w.-]+) (\[.+\]) ...]]
             local from, to, err = ngx.re.find(very_long_string, very_complicated_regex, "jo")

             -- with the regular jit_stack_size, we would get the error 'pcre_exec() failed: -27'
             -- instead, we get a match
             ngx.print(from .. "-" .. to) -- prints '1-1563'
         }
     }
 }

The jit_stack_size cannot be set to a value lower than PCRE's default of 32K.

This method requires the PCRE library enabled in Nginx.

This feature was first introduced in the v0.1.12 release.

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Community

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English Mailing List

The openresty-en mailing list is for English speakers.

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Chinese Mailing List

The openresty mailing list is for Chinese speakers.

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Bugs and Patches

Please report bugs or submit patches by

  1. creating a ticket on the GitHub Issue Tracker,
  2. or posting to the OpenResty community.

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Author

Thibault Charbonnier - (@thibaultcha)

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Copyright and License

This module is licensed under the BSD license.

Copyright (C) 2016-2017, by Yichun "agentzh" Zhang, OpenResty Inc.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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See Also

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