Define schema for simple propagator

[marcalff]

Currently, propagator.json reads as:

{
    "$id": "https://opentelemetry.io/otelconfig/propagator.json",
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "title": "Propagator",
    "type": "object",
    "minProperties": 1,
    "maxProperties": 1,
    "additionalProperties": true,
    "properties": {
        "composite": {
            "type": "array",
            "items": {
                "type": "string"
            }
        }
    }
}

This defines how a composite proparator is represented, but leaves the definition for the simple propagator open to any interpretation, with additional properties.

All the following can be considered valid [1] per the schema:

propagator:
  tracecontext

propagator:
  this_also:
    is_valid: yes
    is_intented: probably_not
    use: tracecontext

Please add another property for simple, with a type string, and do not allow additionalProperties.

The intended representation should be:

propagator:
  simple: tracecontext

Not well versed in json-schema, but I would expect something like:

{
    "$id": "https://opentelemetry.io/otelconfig/propagator.json",
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "title": "Propagator",
    "type": "object",
    "minProperties": 1,
    "maxProperties": 1,
    "properties": {
        "composite": {
            "type": "array",
            "items": {
                "type": "string"
            }
        },
        "simple": {
            "type": "string"
        }
    }
}

[1] From casually reading the schema and writing yaml, I did not try a validator.

[jack-berg]

@marcalff what is the advantage of specifying simple propagator? Isn't it the same as composite propagator with a single entry?

[marcalff]

@marcalff what is the advantage of specifying simple propagator? Isn't it the same as composite propagator with a single entry?

A "composite" propagator with only one entry will work too.

If we want to model it this way:

• "additionalProperties": true, is misleading, there will never be additional properties
• consider renaming composite

The spec defines a composite as "multiple propagators", I would assume multiple means N > 1, not N >= 1.

Basically, when reading:

    "minProperties": 1,
    "maxProperties": 1,
    "additionalProperties": true,

it means there is either one property named composite, or another unspecified property, hence the issue report.

[marcalff]

Resolved by #141

The following was removed:

"minProperties": 1,
"maxProperties": 1,
"additionalProperties": true,

so that there can no longer by arbitrary nodes used as an extension for a simple propagator.

For a simple propagator, the modeling should use a composite propagator, with an array of one element.

Closing as resolved.