{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "description": "The Ditto Protocol envelope of a Ditto Protocol message. This wraps the actual payload in the `value` field.",
  "title": "Ditto Protocol envelope",
  "properties": {
    "topic": {
      "type": "string",
      "description": "Contains information about the contents of the payload:\n * the affected Thing (namespace and Thing ID)\n * the type of operation (command/event, create/retrieve/modify/delete) \n\nExample: `com.acme/xdk_53/things/twin/commands/modify`"
    },
    "headers": {
      "type": "object",
      "description": "Additional headers.",
      "properties": {
        "content-type": {
          "type": "string",
          "description": "The content-type of the message, for Ditto Protocol messages: `application/vnd.eclipse.ditto+json`."
        },
        "correlation-id": {
          "type": "string",
          "description": "The correlation-id header is used for linking one message with another. It typically links a reply message with its requesting message."
        },
        "ditto-originator": {
          "type": "string",
          "description": "Contains the first authorization subject of the command that caused the sending of this message. Set by Ditto."
        },
        "If-Match": {
          "type": "string",
          "description": "The `If-Match` header which has to conform to RFC-7232 (Conditional Requests). Common usages are:\n * optimistic locking by specifying the `ETag` from a previous response, e.g. `If-Match: \"hash:a75ece4e\"`\n * retrieving or modifying a resource only if it already exists, e.g. `If-Match: *`"
        },
        "If-None-Match": {
          "type": "string",
          "description": "The `If-None-Match` header which has to conform to RFC-7232 (Conditional Requests)."
        },
        "response-required": {
          "type": "boolean",
          "description": "Whether a response to a command is required or if it may be omitted (fire and forget semantics)."
        },
        "requested-acks": {
          "description": "Defining which acknowledgements (\"ack\") are requested for a command processed by Ditto.",
          "type": "array",
          "uniqueItems": true,
          "items": {
            "type": "string",
            "description": "A single acknowledgement label containing at least 3 characters.",
            "pattern": "[a-zA-Z0-9-_]{3,64}"
          }
        },
        "timeout": {
          "type": "string",
          "description": "The timeout value to apply on the Ditto server side, e.g. applied when waiting for requested acknowledgements. Examples:\n * `42s`\n * `250ms`\n * `1m`\n * `60` (interpreted as seconds)",
          "examples": [
            "42s",
            "250ms",
            "1m",
            "60"
          ]
        },
        "version": {
          "type": "integer",
          "description": "Determines the schema version of the payload.",
          "minimum": 1,
          "maximum": 2
        }
      },
      "required": [ "correlation-id" ]
    },
    "path": {
      "type": "string",
      "description": "A Path that references a part of a Thing which is affected by this message.\nExamples:\n * `/features/location/properties/longitude` (a single sensor value)\n * `/` (the whole Thing)"
    },
    "fields": {
      "type": "string",
      "description": "The fields that should be included in the response.\nExample: `thingId,attributes(location)`"
    },
    "value": {
      "type": ["object","string","number","array","boolean"],
      "description": "The `value` field contains the actual payload e.g. a sensor value."
    },
    "extra": {
      "type": "object",
      "description": "The `extra` object contains the `extraFields` which have optionally been selected to additionally be included."
    }
  },
  "required": [ "topic", "headers", "path", "value" ]
}