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Document TXT AUTOSPLIT (#957)

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* Document TXT AUTOSPLIT

* Update docs/_functions/domain/TXT.md

Co-authored-by: Jakob Ackermann <das7pad@outlook.com>

Co-authored-by: Jakob Ackermann <das7pad@outlook.com>
This commit is contained in:
Tom Limoncelli
2020-11-22 09:16:56 -05:00
committed by GitHub
parent f30610065c
commit 6fe4ca6996
1 changed files with 47 additions and 9 deletions
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docs/_functions/domain/TXT.md
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@@ -24,14 +24,52 @@ Modifiers can be any number of [record modifiers](#record-modifiers) or json obj
{% include startExample.html %} {% include startExample.html %}
{% highlight js %} {% highlight js %}
D("example.com", REGISTRAR, ....,
D("example.com", REGISTRAR, ...., TXT('@', '598611146-3338560'),
TXT('@', '598611146-3338560'), TXT('listserve', 'google-site-verification=12345'),
TXT('listserve', 'google-site-verification=12345'), TXT('multiple', ['one', 'two', 'three']), // Multiple strings
TXT('multiple', ['one', 'two', 'three']), // Multiple strings TXT('quoted', 'any "quotes" and escapes? ugh; no worries!'),
TXT('quoted', 'any "quotes" and escapes? ugh; no worries!'), TXT('_domainkey', 't=y; o=-;'), // Escapes are done for you automatically.
TXT('_domainkey', 't=y; o=-;') // Escapes are done for you automatically. TXT('long', '#'.repeat(10), AUTOSPLIT) // Escapes are done for you automatically.
); );
{%endhighlight%} {%endhighlight%}
{% include endExample.html %} {% include endExample.html %}
# Long and multiple strings
DNS RFCs limit TXT strings to 255 bytes, but you can have multiple
such strings. Most applications blindly concatenate the strings but
some services that use TXT records join them with a space between each
substring (citation needed!).
Not all providers support multiple strings and those that do often put
limits on them.
Therefore, DNSControl requires you to explicitly mark TXT records that
should be split.
Here are some examples:
VERY_LONG_STRING = 'Z'.repeat(300)
// This will produce a validation-time error:
TXT('long1', VERY_LONG_STRING),
// String will be split on 255-byte boundaries:
TXT('long', VERY_LONG_STRING, AUTOSPLIT),
// String split manually:
TXT('long', ['part1', 'part2', 'part3']),
NOTE: Old releases of DNSControl blindly sent long strings to
providers. Some gave an error at that time, others quietly truncated
the strings, and some silently split them into multiple short
strings. If you see an error that mentions
`ERROR: txt target >255 bytes and AUTOSPLIT not set` this means you
need to add AUTOSPLIT to explicitly split the string manually.
An example error might look like this:
2020/11/21 00:03:21 printIR.go:94: ERROR: txt target >255 bytes and AUTOSPLIT not set: label="20201._domainkey" index=0 len=424 string[:50]="v=DKIM1; k=rsa; t=s; s=email; p=MIIBIjANBgkqhkiG9w..."