Add base64 decoder processor

[glinton]

Feature Request

Add a base64 (or configurable) decoder processor

Proposal:

Add to strings (not likely the correct place) a decoder, to decode a field.

Example config:

[agent]
  interval="1s"
  flush_interval="1s"

[[inputs.exec]]
  timeout = "1s"
  data_format = "json"
  commands = [
    "echo -en '{\"message\":{\"attributes\":{\"deviceId\":\"myPi\",\"deviceNumId\":\"2808946627307959\",\"deviceRegistryId\":\"my-registry\",\"deviceRegistryLocation\":\"us-central1\",\"projectId\":\"conference-demos\",\"subFolder\":\"\"},\"data\":\"dGVzdGluZ0dvb2dsZSxzZW5zb3I9Ym1lXzI4MCB0ZW1wX2M9MjMuOTUsaHVtaWRpdHk9NjIuODMgMTUzNjk1Mjk3NDU1MzUxMDIzMQ==\",\"messageId\":\"204004313210337\",\"message_id\":\"204004313210337\",\"publishTime\":\"2018-09-14T19:22:54.587Z\",\"publish_time\":\"2018-09-14T19:22:54.587Z\"},\"subscription\":\"projects/conference-demos/subscriptions/my-subscription\"}'"
  ]
  tag_keys = ["message_attributes_deviceId"]
  json_string_fields = ["message_data"]

[[processors.strings]]
  [[processors.strings.decode]]
    field = "message_data"
    dest  = "message_data"

[[processors.parser]]
  parse_fields = ["message_data"]
  # change to "json" if the encoded data contains json
  data_format="influx"
  merge="override"

[[outputs.file]]
  files = ["stdout"]

## Sample output
# testingGoogle,host=test,message_attributes_deviceId=myPi,sensor=bme_280 message_data="testingGoogle,sensor=bme_280 temp_c=23.95,humidity=62.83 1536952974553510231",temp_c=23.95,humidity=62.83 1536972180000000000

Desired behavior:

Decode a field so further processing can be done on it.

Use case:

Google IOT sends a data field base64 encoded, it would be nice to be able to pull this data out and store it.

[cliffordvandyk]

It seems to be common practice (I have other examples than the original Google Core IOT) to send multiple IOT numeric payload fields combined into a single base64-encoded string (presumably for OTA efficiency). It would be useful to have methods to decode a base64 string, and then split the resulting (HEX) into multiple (InfluxDB-friendly) fields.

Specific example: "{"applicationID":"1","applicationName":"AppSensors","devEUI":"393032357a377e05","deviceName":"dev-393032357a377e05","timestamp":1574109564,"fCnt":45,"fPort":2,"data":"VQP0DQwCiv7Qf28M5kkAqg==","data_encode":"base64"}"

Here the "data" key is a base64-encoded string, containg a number of fields.
However, after decoding, the resultant HEX string needs to then be split into a number of fields (on byte boundaries), that must then be converted to InfluxDB-friendly format. I'm not sure that there is a plug-in to accomplish this either.

[cliffordvandyk]

Also (someone else with same requirement):
https://community.influxdata.com/t/telegraf-influxdb-parse-base-64-data-payload/2610