Sensor data

The case CBOR was designed for: a measurement, an instant, and as few bytes as possible on the wire.

use CBOR\MapObject;
use CBOR\Tag\DecimalFractionTag;
use CBOR\Tag\TimestampTag;
use CBOR\TextStringObject;
use CBOR\UnsignedIntegerObject;

$sensorData = MapObject::create()
    ->add(
        TextStringObject::create('temperature'),
        DecimalFractionTag::createFromFloat(23.5)
    )
    ->add(
        TextStringObject::create('humidity'),
        UnsignedIntegerObject::create(65)
    )
    ->add(
        TextStringObject::create('timestamp'),
        TimestampTag::create(UnsignedIntegerObject::create(time()))
    );

$encoded = (string) $sensorData;

Two choices are worth noticing.

The temperature goes in as a decimal fraction rather than a float: 23.5 stays 23.5, where a binary float would carry a value that only prints as 23.5. It needs ext-bcmath at both ends.

The instant is tagged, so the reader gets a DateTimeImmutable without being told which of the numbers in the map was a date.

Shorter still: integer keys instead of text ones. 1, 2, 3 cost one byte each where "temperature" costs twelve, which is how CoAP and SenML payloads are written — at the price of needing the table of meanings on both sides.

$sensorData = MapObject::create()
    ->add(UnsignedIntegerObject::create(1), DecimalFractionTag::createFromFloat(23.5))
    ->add(UnsignedIntegerObject::create(2), UnsignedIntegerObject::create(65))
    ->add(UnsignedIntegerObject::create(3), TimestampTag::create(UnsignedIntegerObject::create(time())));