Author: Alistair Keiller

InfluxDB

CAN-to-InfluxDB Telemetry (Line Protocol)

Transforms strongly-typed telemetry readings into InfluxDB Line Protocol after MQTT verification. The key helper is to_line_protocol, which turns any Reading into a write-ready line.

Function: to_line_protocol<T: Reading>(message: &T) -> String

• Measurement: Uses T::topic() as the measurement name.
• Fields: Serializes number, string, and boolean fields; unsupported types are skipped.
• Timestamp: Appends current UTC time in nanoseconds.

Field Formatting

• Integers (i64, u64): Suffixed with i, e.g., rpm=1200i.
• Floats: Written as-is, e.g., voltage=12.34.
• Strings: Quoted, e.g., state="OK".
• Booleans: Lowercase true/false.

Example Output

• Input: TelemetryData { rpm: 1200, voltage: 12.34, state: "OK", fault: false }
• Topic: telemetry
• Output: telemetry rpm=1200i,voltage=12.34,state="OK",fault=false 1734043200000000000

Workflow Inside to_line_protocol

1. Start with T::topic() as the measurement.
2. Serialize message to JSON (serde_json::to_value).
3. Iterate object fields, formatting supported values and comma-separating them.
4. Append the UTC nanosecond timestamp from chrono::Utc::now().timestamp_nanos_opt().
5. Return the completed line protocol string.

End-to-End Flow

1. Collect CAN telemetry (speed, torque, voltage, current, temps, fault states) into a TelemetryData that implements Reading.
2. Publish the struct as JSON to the telemetry MQTT topic with QoS AtLeastOnce.
3. MQTT listener verifies the payload matches the expected TelemetryData.
4. On verification success, convert to line protocol via to_line_protocol and write to InfluxDB.

Writing to InfluxDB

• Endpoint: HTTP POST /api/v2/write?org=<org>&bucket=<bucket>&precision=ns or the official Influx client.
• Body: The string returned by to_line_protocol.
• Auth: Authorization: Token <token> header.
• Precision: ns to match the timestamp source.
• Reliability: Add retries/backoff for transient failures and log write errors.

Minimal sketch:

1. let lp = to_line_protocol(&telemetry);
2. POST lp to the write endpoint with precision=ns.

Testing Guidance

• Unit tests: verify integer i suffixing, string quoting, boolean casing, and timestamp inclusion.
• Integration: pair with the MQTT listener test to cover publish → verify → convert → write.

Troubleshooting

• Missing fields: Ensure fields are serde-serializable scalars (no nested objects/arrays).
• Wrong measurement: Confirm T::topic() returns the intended measurement.
• Write failures: Check token, bucket, org, precision, and server availability.
• Timestamp None: Verify system clock and timestamp_nanos_opt() support on the target platform.