lua-resty-dns - Lua DNS resolver for the ngx_lua based on the cosocket API
- Name
- Status
- Description
- Synopsis
- Methods
- Constants
- Automatic Error Logging
- Limitations
- TODO
- Author
- Copyright and License
- See Also
This library is considered production ready.
This Lua library provies a DNS resolver for the ngx_lua nginx module:
http://wiki.nginx.org/HttpLuaModule
This Lua library takes advantage of ngx_lua's cosocket API, which ensures 100% nonblocking behavior.
Note that at least ngx_lua 0.5.12 or OpenResty 1.2.1.11 is required.
Also, the bit library is also required. If you're using LuaJIT 2.0 with ngx_lua, then the bit
library is already available by default.
Note that, this library is bundled and enabled by default in the OpenResty bundle.
lua_package_path "/path/to/lua-resty-dns/lib/?.lua;;";
server {
location = /dns {
content_by_lua '
local resolver = require "resty.dns.resolver"
local r, err = resolver:new{
nameservers = {"8.8.8.8", {"8.8.4.4", 53} },
retrans = 5, -- 5 retransmissions on receive timeout
timeout = 2000, -- 2 sec
}
if not r then
ngx.say("failed to instantiate the resolver: ", err)
return
end
local answers, err = r:query("www.google.com")
if not answers then
ngx.say("failed to query the DNS server: ", err)
return
end
if answers.errcode then
ngx.say("server returned error code: ", answers.errcode,
": ", answers.errstr)
end
for i, ans in ipairs(answers) do
ngx.say(ans.name, " ", ans.address or ans.cname,
" type:", ans.type, " class:", ans.class,
" ttl:", ans.ttl)
end
';
}
}
syntax: r, err = class:new(opts)
Creates a dns.resolver object. Returns nil
and an message string on error.
It accepts a opts
table argument. The following options are supported:
-
nameservers
a list of nameservers to be used. Each nameserver entry can be either a single hostname string or a table holding both the hostname string and the port number. The nameserver is picked up by a simple round-robin algorithm for each
query
method call. This option is required. -
retrans
the total number of times of retransmitting the DNS request when receiving a DNS response times out according to the
timeout
setting. Default to5
times. When trying to retransmit the query, the next nameserver according to the round-robin algorithm will be picked up. -
timeout
the time in milliseconds for waiting for the respond for a single attempt of request transmition. note that this is ''not'' the maximal total waiting time before giving up, the maximal total waiting time can be calculated by the expression
timeout x retrans
. Thetimeout
setting can also be changed by calling theset_timeout
method. The defaulttimeout
setting is 2000 milliseconds, or 2 seconds. -
no_recurse
a boolean flag controls whether to disable the "recursion desired" (RD) flag in the UDP request. Default to
false
.
syntax: answers, err = r:query(name, options?)
Performs a DNS standard query to the nameservers specified by the new
method,
and returns all the answer records in an array-like Lua table. In case of errors, it will
return nil
and a string describing the error instead.
If the server returns a non-zero error code, the fields errcode
and errstr
will be set accordingly in the Lua table returned.
Each entry in the answers
returned table value is also a hash-like Lua table
which usually takes some of the following fields:
-
name
The resource record name.
-
type
The current resource record type, possible values are
1
(TYPE_A
),5
(TYPE_CNAME
),28
(TYPE_AAAA
), and any other values allowed by RFC 1035. -
address
The IPv4 or IPv6 address in their textual representations when the resource record type is either
1
(TYPE_A
) or28
(TYPE_AAAA
), respectively. Secussesive 16-bit zero groups in IPv6 addresses will not be compressed by default, if you want that, you need to call thecompress_ipv6_addr
static method instead. -
section
The section in the dns response. Tells you which section is the answer comes from. Possible values are
1
(SECTION_AN
) or2
(SECTION_NS
) or3
(SECTION_AR
). -
cname
The (decoded) record data value for
CNAME
resource records. Only present forCNAME
records. -
ttl
The time-to-live (TTL) value in seconds for the current resource record.
-
class
The current resource record class, possible values are
1
(CLASS_IN
) or any other values allowed by RFC 1035. -
preference
The preference integer number for
MX
resource records. Only present forMX
type records. -
exchange
The exchange domain name for
MX
resource records. Only present forMX
type records. -
nsdname
A domain-name which specifies a host which should be authoritative for the specified class and domain. Usually present for
NS
type records. -
rdata
The raw resource data (RDATA) for resource records that are not recognized.
-
txt
The record value for
TXT
records. When there is only one character string in this record, then this field takes a single Lua string. Otherwise this field takes a Lua table holding all the strings. -
ptrdname
The record value for
PTR
records.
This method also takes an optional options
argument table, which takes the following fields:
-
qtype
The type of the question. Possible values are
1
(TYPE_A
),5
(TYPE_CNAME
),28
(TYPE_AAAA
), or any other QTYPE value specified by RFC 1035 and RFC 3596. Default to1
(TYPE_A
). -
authority_section
The
answers
includes authority section of the dns response or not. Possible values aretrue
,false
. Default tofalse
. -
additional_section
The
answers
includes additional section of the dns response or not. Possible values aretrue
,false
. Default tofalse
.
When data truncation happens, the resolver will automatically retry using the TCP transport mode to query the current nameserver. All TCP connections are short lived.
syntax: answers, err = r:tcp_query(name, options?)
Just like the query
method, but enforce the TCP transport mode instead of UDP.
All TCP connections are short lived.
Here is an example:
local resolver = require "resty.dns.resolver"
local r, err = resolver:new{
nameservers = { "8.8.8.8" }
}
if not r then
ngx.say("failed to instantiate resolver: ", err)
return
end
local ans, err = r:tcp_query("www.google.com", { qtype = r.TYPE_A })
if not ans then
ngx.say("failed to query: ", err)
return
end
local cjson = require "cjson"
ngx.say("records: ", cjson.encode(ans))
syntax: r:set_timeout(time)
Overrides the current timeout
setting by the time
argument in milliseconds for all the nameserver peers.
syntax: compressed = resty.dns.resolver.compress_ipv6_addr(address)
Compresses the successive 16-bit zero groups in the textual format of the IPv6 address.
For example,
local resolver = require "resty.dns.resolver"
local compress = resolver.compress_ipv6_addr
local new_addr = compress("FF01:0:0:0:0:0:0:101")
will yield FF01::101
in the new_addr
return value.
syntax: expanded = resty.dns.resolver.expand_ipv6_addr(address)
Expands the successive 16-bit zero groups in the textual format of the IPv6 address.
For example,
local resolver = require "resty.dns.resolver"
local expand = resolver.expand_ipv6_addr
local new_addr = expand("FF01::101")
will yield FF01:0:0:0:0:0:0:101
in the new_addr
return value.
syntax: arpa_record = resty.dns.resolver.arpa_str(address)
Generates the reverse domain name for PTR lookups for both IPv4 and IPv6 addresses. Compressed IPv6 addresses will be automatically expanded.
For example,
local resolver = require "resty.dns.resolver"
local ptr4 = resolver.arpa_str("1.2.3.4")
local ptr6 = resolver.arpa_str("FF01::101")
will yield 4.3.2.1.in-addr.arpa
for ptr4
and 1.0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.F.F.ip6.arpa
for ptr6
.
syntax: answers, err = r:reverse_query(address)
Performs a PTR lookup for both IPv4 and IPv6 addresses. This function is basically a wrapper for the query
command
which uses the arpa_str
command to convert the IP address on the fly.
The A
resource record type, equal to the decimal number 1
.
The NS
resource record type, equal to the decimal number 2
.
The CNAME
resource record type, equal to the decimal number 5
.
The PTR
resource record type, equal to the decimal number 12
.
The MX
resource record type, equal to the decimal number 15
.
The TXT
resource record type, equal to the decimal number 16
.
syntax: typ = r.TYPE_AAAA
The AAAA
resource record type, equal to the decimal number 28
.
syntax: typ = r.TYPE_SRV
The SRV
resource record type, equal to the decimal number 33
.
See RFC 2782 for details.
syntax: typ = r.TYPE_SPF
The SPF
resource record type, equal to the decimal number 99
.
See RFC 4408 for details.
syntax: class = r.CLASS_IN
The Internet
resource record type, equal to the decimal number 1
.
syntax: stype = r.SECTION_AN
The Answer
section in the DNS response, equal to the decimal number 1
syntax: stype = r.SECTION_NS
The Authority
section in the DNS response, equal to the decimal number 2
syntax: stype = r.SECTION_AR
The Additional
section in the DNS response, equal to the decimal number 3
By default the underlying ngx_lua module does error logging when socket errors happen. If you are already doing proper error handling in your own Lua code, then you are recommended to disable this automatic error logging by turning off ngx_lua's lua_socket_log_errors directive, that is,
lua_socket_log_errors off;
- This library cannot be used in code contexts like set_by_lua*, log_by_lua*, and header_filter_by_lua* where the ngx_lua cosocket API is not available.
- The
resty.dns.resolver
object instance cannot be stored in a Lua variable at the Lua module level, because it will then be shared by all the concurrent requests handled by the same nginx worker process (see http://wiki.nginx.org/HttpLuaModule#Data_Sharing_within_an_Nginx_Worker ) and result in bad race conditions when concurrent requests are trying to use the sameresty.dns.resolver
instance. You should always initiateresty.dns.resolver
objects in function local variables or in thengx.ctx
table. These places all have their own data copies for each request.
- Concurrent (or parallel) query mode
- Better support for other resource record types like
TLSA
.
Yichun "agentzh" Zhang (章亦春) agentzh@gmail.com, CloudFlare Inc.
This module is licensed under the BSD license.
Copyright (C) 2012-2016, by Yichun "agentzh" Zhang (章亦春) agentzh@gmail.com, CloudFlare 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.
- the ngx_lua module: http://wiki.nginx.org/HttpLuaModule
- the lua-resty-memcached library.
- the lua-resty-redis library.
- the lua-resty-mysql library.