chore: extend Schema Object to allow defining custom formats

[magicmatatjahu]

---

title: "extend Schema Object to allow defining custom formats"

---

Related issue(s): https://github.com/asyncapi/spec/issues/622

---

This PR suggests how we could use custom schemas (in custom formats):

• a new keyword customSchema has been added, which belongs to the AsyncAPI Schema Object vocabulary (described by Custom Schema Object)
• is possible to refer custom schemas in the same way as normal JSON Schema
• the schemaFormat in the Message Object is deprecated
• is possible to use JSON Schema keywords, but only for documentation like title, description, externalDocs alongside customSchema keyword

Examples

Model defined by Custom Schema

{
  "customSchema": {
    "format": "application/vnd.apache.avro+json;version=1.9.0",
    "definition": {
      "type": "record",
      "namespace": "com.example.common",
      "name": "Student",
      "fields": [
        {
          "name": "Name",
          "type": "string"
        },
        {
          "name": "Age",
          "type": "int"
        }
      ]
    }
  }
}

customSchema:
  format: application/vnd.apache.avro+yaml;version=1.9.0
  definition:
    type: record
    namespace: com.example.common
    name: Student
    fields:
    - name: Name
      type: string
    - name: Age
      type: int

Model defined by Custom Schema with documentation fields

{
  "title": "Student Model",
  "description": "A model describing a Student object, defined using the AVRO format.",
  "customSchema": {
    "format": "application/vnd.apache.avro+json;version=1.9.0",
    "definition": {
      "type": "record",
      "namespace": "com.example.common",
      "name": "Student",
      "fields": [
        {
          "name": "Name",
          "type": "string"
        },
        {
          "name": "Age",
          "type": "int"
        }
      ]
    }
  },
  "externalDocs": {
    "description": "Find more info here",
    "url": "https://example.com"
  }
}

title: Student Model
description: A model describing a Student object, defined using the AVRO format.
customSchema:
  format: application/vnd.apache.avro+yaml;version=1.9.0
  definition:
    type: record
    namespace: com.example.common
    name: Student
    fields:
    - name: Name
      type: string
    - name: Age
      type: int
externalDocs:
  description: Find more info here
  url: https://example.com

Model using nested Custom Schema Format

{
  "type": "object",
  "properties": {
    "grades": {
      "type": "array",
      "items": {
        "type": "integer"
      }
    },
    "student": {
      "customSchema": {
        "format": "application/vnd.apache.avro+json;version=1.9.0",
        "definition": {
          "type": "record",
          "namespace": "com.example",
          "name": "Student",
          "fields": [
            {
              "name": "Name",
              "type": "string"
            },
            {
              "name": "Age",
              "type": "int"
            }
          ]
        }
      }
    }
  }
}

type: object
properties:
  grades:
    type: array
    items:
      type: integer
  student:
    customSchema:
      format: application/vnd.apache.avro+yaml;version=1.9.0
      definition:
        type: record
        namespace: com.example
        name: Student
        fields:
        - name: Name
          type: string
        - name: Age
          type: int

Message with custom format (show usage of $ref)

{
  "name": "UserSignup",
  "title": "User signup",
  "summary": "Action to sign a user up.",
  "description": "A longer description",
  "tags": [
    { "name": "user" },
    { "name": "signup" },
    { "name": "register" }
  ],
  "payload": {
    "customSchema": {
      "format": "application/vnd.apache.avro+json;version=1.9.0",
      "definition": {
        "$ref": "path/to/user-create.avsc"
      }
    }
  }
}

name: UserSignup
title: User signup
summary: Action to sign a user up.
description: A longer description
tags:
  - name: user
  - name: signup
  - name: register
payload:
  customSchema:
    format: 'application/vnd.apache.avro+yaml;version=1.9.0'
    definition:
      $ref: 'path/to/user-create.avsc'

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[fmvilas]

type: object
properties:
  grades:
    type: array
    items:
      type: integer
  student:
    customSchema:
      format: application/vnd.apache.avro+yaml;version=1.9.0
      definition:
        type: record
        namespace: com.example
        name: Student
        fields:
        - name: Name
          type: string
        - name: Age
          type: int

I'd not allow this. This requires changing JSON Schema. IMHO we should go in a direction where we get rid of the differences with JSON Schema instead of adding more "extra" keys. This also adds an incredible complexity for flexibility I doubt anyone would need.

This is Avro inside a JSON Schema object but what about the opposite? Should we also alter Avro to accept JSON Schema inside? Aren't we mixing different things in the same place? I mean, JSON Schema is a constraint system and Avro is a data-serialization system. I know the same applies without this feature but at least we don't mix and match 🤔

[magicmatatjahu]

More info why I'm closing -> https://github.com/asyncapi/spec/issues/622#issuecomment-1346847902 We can always reopen it, when we will have conclusion.