sdget

README

sdget

A tool for using DNS TXT records as a key/value table.

sdget is designed for use in scripts, and is mostly based on RFC1464 ("Using the Domain Name System To Store Arbitrary String Attributes") and RFC6763 ("DNS-Based Service Discovery").

Quick Start

If foo.example.com has these TXT records:

foo.example.com. IN	TXT	"foo=bar"
foo.example.com. IN	TXT	"key=value"
foo.example.com. IN	TXT	"things=item1"
foo.example.com. IN	TXT	"things=item2"

they can be queried like this:

$ sdget foo.example.com key
value

Default values can be supplied, too:

$ sdget foo.example.com theanswer 42
42

Because sdget is designed for use in scripts and other automation, it's strict by default. If the domain has no TXT records, that's an error. sdget also expects exactly one key to match, unless the list type is set:

$ sdget --type list foo.example.com things
item1
item2

The output format can be changed as well:

$ sdget --type list --format json foo.example.com things
["item1","item2"]

Usage

usage: sdget [<flags>] <domain> <key> [<default>...]

Flags:
  -h, --help                   Show context-sensitive help (also try --help-long and --help-man).
  -f, --format=plain           Output format (plain, json)
  -@, --nameserver=NAMESERVER  Nameserver address (ns.example.com:53, 127.0.0.1)
  -t, --type=single            Data value type (single, list)

Args:
  <domain>     Domain name to query for TXT records
  <key>        Key name to look up in domain
  [<default>]  Default value(s) to use if key is not found

TXT format details

Each TXT string is treated as a simple key/value pair separated by a single =. Everything after the first = is considered a value, which can contain any valid characters, including spaces or more = signs. The key can contain any valid non-= characters. Repeated keys are interpreted as lists. Strings that aren't key/value pairs are simply ignored.

Here are some examples of valid key/value pairs:

foo=bar
org=Australian Digital Transformation Agency
Some Key=c29tZSBkYXRhCg==
list-key=1
list-key=2
list-key=3
empty value=

Note that TXT records themselves have some size limitations.