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Version: v4.24

read_grok

read_grok pattern:string, [pattern_definitions=string, indexed_captures=bool,
          include_unnamed=bool, schema=string, selector=string,
          schema_only=bool, merge=bool, raw=bool, unflatten=string]

Description​

read_grok uses a regular expression based parser similar to the Logstash grok plugin in Elasticsearch. Tenzir ships with the same built-in patterns as Elasticsearch, found here.

In short, pattern consists of replacement fields, that look like %{SYNTAX[:SEMANTIC[:CONVERSION]]}, where:

  • SYNTAX is a reference to a pattern, either built-in or user-defined through the pattern_defintions option.
  • SEMANTIC is an identifier that names the field in the parsed record.
  • CONVERSION is either infer (default), string (default with raw=true), int, or float.

The supported regular expression syntax is the one supported by Boost.Regex, which is effectively Perl-compatible.

pattern: string​

The grok pattern used for matching. Must match the input in its entirety.

pattern_definitions = string (optional)​

A user-defined newline-delimited list of patterns, where a line starts with the pattern name, followed by a space, and the grok-pattern for that pattern. For example, the built-in pattern INT is defined as follows:

INT (?:[+-]?(?:[0-9]+))

indexed_captures = bool (optional)​

All subexpression captures are included in the output, with the SEMANTIC used as the field name if possible, and the capture index otherwise.

include_unnamed = bool (optional)​

By default, only fields that were given a name with SEMANTIC, or with the regular expression named capture syntax (?<name>...) are included in the resulting record.

With include_unnamed=true, replacement fields without a SEMANTIC are included in the output, using their SYNTAX value as the record field name.

merge = bool (optional)​

Merges all incoming events into a single schema* that converges over time. This option is usually the fastest for reading highly heterogeneous data, but can lead to huge schemas filled with nulls and imprecise results. Use with caution.

*: In selector mode, only events with the same selector are merged.

raw = bool (optional)​

Use only the raw types that are native to the parsed format. Fields that have a type specified in the chosen schema will still be parsed according to the schema.

Since grok is just textual parsing, this means that no parsing of data takes place at all and every value remains a string, unless the field is in the schema.

schema = string (optional)​

Provide the name of a schema to be used by the parser.

If a schema with a matching name is installed, the result will always have all fields from that schema.

  • Fields that are specified in the schema, but did not appear in the input will be null.
  • Fields that appear in the input, but not in the schema will also be kept. schema_only=true can be used to reject fields that are not in the schema.

If the given schema does not exist, this option instead assigns the output schema name only.

The schema option is incompatible with the selector option.

selector = string (optional)​

Designates a field value as schema name with an optional dot-separated prefix.

The string is parsed as <fieldname>[:<prefix>]. The prefix is optional and will be prepended to the field value to generate the schema name.

For example, the Suricata EVE JSON format includes a field event_type that contains the event type. Setting the selector to event_type:suricata causes an event with the value flow for the field event_type to map onto the schema suricata.flow.

The selector option is incompatible with the schema option.

schema_only = bool (optional)​

When working with an existing schema, this option will ensure that the output schema has only the fields from that schema. If the schema name is obtained via a selector and it does not exist, this has no effect.

This option requires either schema or selector to be set.

unflatten = string (optional)​

A delimiter that, if present in keys, causes values to be treated as values of nested records.

A popular example of this is the Zeek JSON format. It includes the fields id.orig_h, id.orig_p, id.resp_h, and id.resp_p at the top-level. The data is best modeled as an id record with four nested fields orig_h, orig_p, resp_h, and resp_p.

Without an unflatten separator, the data looks like this:

Without unflattening
{
  "id.orig_h": "1.1.1.1",
  "id.orig_p": 10,
  "id.resp_h": "1.1.1.2",
  "id.resp_p": 5
}

With the unflatten separator set to ., Tenzir reads the events like this:

With 'unflatten'
{
  "id": {
    "orig_h": "1.1.1.1",
    "orig_p": 10,
    "resp_h": "1.1.1.2",
    "resp_p": 5
  }
}

Examples​

Parse a fictional HTTP request log​

// Input: 55.3.244.1 GET /index.html 15824 0.043
read_grok "%{IP:client} %{WORD} %{URIPATHPARAM:req} %{NUMBER:bytes} %{NUMBER:dur}"
{
  client: 55.3.244.1,
  req: "/index.html",
  bytes: 15824,
  dur: 0.043
}