Output format¶

By default, datalink emits newline-delimited JSON on stdout.
Every decoded row uses a common DecodedEvent envelope.

JSONL format¶

datalink normalizes all supported input paths into a common event shape.

The output includes:

bearer: vhf, vdl2, hfdl, decoded, or unknown;
source: file, SDR, websocket, or standalone decode metadata;
receiver: channel information for I/Q receivers;
aircraft: best-effort ICAO24, aircraft id, or registration;
kinematics: best-effort position, speed, altitude, or meteorological values;
raw_frame_hex: raw frame bytes when available;
message: the protocol-specific decoded body.

An ADS-C event captured from the airframes.io websocket feed looks like this:

{
  "event": "message",
  "timestamp": 1781378212.80346,
  "bearer": "unknown",
  "source": {
    "id": "airframes",
    "name": "airframes.io",
    "class": "events",
    "format": "airframes.io"
  },
  "aircraft": {
    "icao24": "3c4582",
    "aircraft_id": 2727,
    "registration": "D-AALB"
  },
  "kinematics": {
    "position": {
      "latitude": 45.166098,
      "longitude": 24.740809
    },
    "altitude_ft": 37000,
    "track": 116.67,
    "derived_from": "airframes_flight"
  },
  "message": {
    "kind": "airframes",
    "data": {
      "payload": {
        "label": "A6",
        "text": "/PIKCPYA.ADS.D-AALB08060A1812B113227921E314E5DD",
        "from_hex": "90",
        "to_hex": "3C4582",
        "latitude": 0.0,
        "longitude": 0.0,
        "altitude": 0.0,
        "track": null,
        "source_type": "unknown",
        "timestamp": 1781378212.80346,
        "created_at": 1781378212.802201,
        "frequency": 0.0,
        "id": "6885605082",
        "airframe_id": 2727,
        "flight_id": 5544633336,
        "tail": "D-AALB",
        "link_direction": "uplink",
        "airframe": {
          "icao": "3C4582",
          "tail": "D-AALB"
        },
        "flight": {
          "latitude": 45.166098,
          "longitude": 24.740809,
          "altitude": 37000.0,
          "track": 116.67
        }
      },
      "dst": {
        "icao24": "3c4582",
        "addr_type": "aircraft"
      },
      "app": {
        "kind": "arinc622",
        "data": {
          "atsu_address": "PIKCPYA",
          "imi": "ADS",
          "registration": "D-AALB",
          "payload": {
            "kind": "adsc",
            "data": {
              "atsu_address": "PIKCPYA",
              "registration": "D-AALB",
              "tags": [
                {
                  "kind": "event_contract_request",
                  "data": {
                    "contract_number": 6,
                    "groups": [
                      {
                        "kind": "lateral_deviation_change",
                        "data": {
                          "threshold_nm": 3.0
                        }
                      },
                      {
                        "kind": "vertical_speed_change",
                        "data": {
                          "threshold_ft_per_min": -5056
                        }
                      },
                      {
                        "kind": "altitude_range",
                        "data": {
                          "ceiling_ft": 220425,
                          "floor_ft": 216675
                        }
                      },
                      {
                        "kind": "report_waypoint_changes"
                      }
                    ]
                  }
                }
              ]
            }
          }
        }
      }
    }
  }
}

For an ACARS frame decoded directly by the VHF path, the top-level envelope is the same, but message.kind is "acars" and message.data contains the ACARS fields such as label, text, and app.

CPDLC elements also include fragments, a phrase AST compiled from the bundled CPDLC catalog templates. Each fragment is either literal text or a typed value slot. Consumers resolve a value slot from the element body: if body.kind equals the slot, use body.data; otherwise use body.data[slot]:

{
  "id": 20,
  "catalog_name": "uM20Altitude",
  "fragments": [
    {
      "kind": "text",
      "data": "CLIMB TO AND MAINTAIN "
    },
    {
      "kind": "value",
      "data": "altitude"
    }
  ],
  "body": {
    "kind": "altitude",
    "data": {
      "kind": "flight_level",
      "data": 320
    }
  },
  "is_additional": false
}

{
  "id": 163,
  "catalog_name": "uM163ICAOfacilitydesignationTp4table",
  "fragments": [
    {
      "kind": "value",
      "data": "icao_facility_designation"
    },
    {
      "kind": "text",
      "data": " "
    },
    {
      "kind": "value",
      "data": "tp4_table"
    }
  ],
  "body": {
    "kind": "icao_facility_designation_tp4_table",
    "data": {
      "icao_facility_designation": {
        "kind": "icao",
        "data": "FNAN"
      },
      "tp4_table": "label_a"
    }
  },
  "is_additional": false
}

The exact nested body depends on the decoded protocol, but the top-level envelope is designed to make mixed sources easier to consume.

Sinks¶

By default, decoded events are written to stdout as JSONL.

[output]
jsonl = "-"

Write to a file and optionally publish to Redis:

[output]
jsonl = "datalink.jsonl"
redis_url = "redis://localhost:6379"

Redis topics are selected from decoded application type where possible, including:

datalink-acars
datalink-adsc
datalink-cpdlc
datalink-hfdl
datalink-sq
datalink-vdl2
datalink-x25
datalink-xid
datalink-unknown