The dissect library will be used for the ingest node as an alternative
to Grok to split a string based on a pattern. Dissect differs from
Grok such that regular expressions are not used to split the string.
Note - Regular expressions are used during construction of the
objects, but not in the hot path.
A dissect pattern takes the form of: '%{a} %{b},%{c}' which is
composed of 3 keys (a,b,c) and two delimiters (space and comma).
This dissect pattern will match a string of the form: 'foo bar,baz'
and will result a key/value pairing of 'a=foo, b=bar, and c=baz'.
See the comments in DissectParser for a full explanation.
This commit does not include the ingest node processor that will consume
it. However, the consumption should be a trivial mapping between the
key/value pairing returned by the parser and the key/value pairing
needed for the IngestDocument.
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