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Conditions

Conditions are boolean queries that can be executed based on the contents of a message, some processors such as switch use conditions for expressing their logic. There are many options but the most powerful type is the bloblang condition.

Conditions themselves can modify (not) and combine (and, or) other conditions, and can therefore be used to create complex boolean expressions.

The format of a condition is similar to other Benthos types:

condition:
  bloblang: meta("kafka_topic") == "foo"

And is usually found as the child of a processor:

pipeline:
  processors:
    - switch:
      - condition:
          bloblang: meta("kafka_topic") == "foo"
        processors:
          - resource: foo
      - processors:
          - resource: bar

Batching and Multipart Messages​

All conditions can be applied to a multipart message, which is synonymous with a batch. Some conditions target a specific part of a message batch, and require you specify the target index with the field part.

Part indexes can be negative, and if so the part will be selected from the end counting backwards starting from -1. E.g. if part = -1 then the selected part will be the last part of the message, if part = -2 then the part before the last element with be selected, and so on.

Reusing Conditions​

Sometimes large chunks of logic are reused across processors, or nested multiple times as branches of a larger condition. It is possible to avoid writing duplicate condition configs by using the resource condition.