The JSON Format for CloudEvents defines how events are expressed in JavaScript Object Notation (JSON) Data Interchange Format (RFC8259).
This document is a working draft.
CloudEvents is a standardized and protocol-agnostic definition of the structure and metadata description of events. This specification defines how the elements defined in the CloudEvents specification are to be represented in the JavaScript Object Notation (JSON) Data Interchange Format (RFC8259).
The Attributes section describes the naming conventions and data type mappings for CloudEvents attributes.
The Envelope section defines a JSON container for CloudEvents attributes and an associated media type.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119.
This section defines how CloudEvents attributes are mapped to JSON. This specification does not explicitly map each attribute, but provides a generic mapping model that applies to all current and future CloudEvents attributes, including extensions.
For clarity, extension attributes are serialized using the same rules as specification defined attributes. This includes their syntax and placement within the JSON object. In particular, extensions are placed as top-level JSON properties. Extensions MUST be serialized as a top-level JSON property. There were many reasons for this design decision and they are covered in more detail in the Primer.
The core CloudEvents specification defines a minimal abstract type system, which this mapping leans on.
The CloudEvents type system MUST be mapped to JSON types as follows, with exceptions noted below.
| CloudEvents | JSON |
|---|---|
| Boolean | boolean |
| Integer | number, only the integer component optionally prefixed with a minus sign is permitted |
| String | string |
| Binary | string, Base64-encoded binary |
| URI | string following RFC 3986 |
| URI-reference | string following RFC 3986 |
| Timestamp | string following RFC 3339 (ISO 8601) |
Unset attributes MAY be encoded to the JSON value of null. When decoding
attributes and a null value is encountered, it MUST be treated as the
equivalent of unset or omitted.
Extension specifications MAY define secondary mapping rules for the values of attributes they define, but MUST also include the previously defined primary mapping.
For instance, the attribute value might be a data structure defined in a standard outside of CloudEvents, with a formal JSON mapping, and there might be risk of translation errors or information loss when the original format is not preserved.
An extension specification that defines a secondary mapping rule for JSON, and any revision of such a specification, MUST also define explicit mapping rules for all other event formats that are part of the CloudEvents core at the time of the submission or revision.
If required, like when decoding Maps, the CloudEvents type can be determined by
inference using the rules from the mapping table, whereby the only potentially
ambiguous JSON data type is string. The value is compatible with the
respective CloudEvents type when the mapping rules are fulfilled.
The following table shows exemplary attribute mappings:
| CloudEvents | Type | Exemplary JSON Value |
|---|---|---|
| type | String | "com.example.someevent" |
| specversion | String | "1.0" |
| source | URI-reference | "/mycontext" |
| subject | String | "larger-context" |
| subject | String (null) | null |
| id | String | "1234-1234-1234" |
| time | Timestamp | "2018-04-05T17:31:00Z" |
| time | Timestamp (null) | null |
| datacontenttype | String | "application/json" |
The CloudEvents JSONSchema for the spec is located here and contains the definitions for validating events in JSON.
Each CloudEvents event can be wholly represented as a JSON object.
Such a representation MUST use the media type application/cloudevents+json.
All REQUIRED and all not omitted OPTIONAL attributes in the given event MUST become members of the JSON object, with the respective JSON object member name matching the attribute name, and the member's type and value being mapped using the type system mapping.
OPTIONAL not omitted attributes MAY be represeted as a null JSON value.
Before taking action, a JSON serializer MUST first determine the runtime data
type of the data content.
If the implementation determines that the type of data is Binary, the value
MUST be represented as a JSON string expression containing the
Base64 encoded binary value, and use the member name data_base64 to
store it inside the JSON object.
For any other type, the implementation MUST translate the data value into a
JSON value, and use the member name data to store it inside the
JSON object.
Out of this follows that use of the data and data_base64 members is mutually
exclusive in a JSON serialized CloudEvent.
When a CloudEvents is deserialized from JSON, the presence of the data_base64
member clearly indicates that the value is a Base64 encoded binary data, which
the serializer MUST decode into a binary runtime data type. When a data member
is present, it is decoded using the default JSON type mapping for the used
runtime.
Unlike attributes, for which value types are restricted to strings per the
type-system mapping, the resulting data member
JSON value is unrestricted, and MAY contain any valid JSON.
Example event with String-valued data:
{
"specversion" : "1.0",
"type" : "com.example.someevent",
"source" : "/mycontext",
"id" : "A234-1234-1234",
"time" : "2018-04-05T17:31:00Z",
"comexampleextension1" : "value",
"comexampleothervalue" : 5,
"unsetextension": null,
"datacontenttype" : "text/xml",
"data" : "<much wow=\"xml\"/>"
}Example event with Binary-valued data
{
"specversion" : "1.0",
"type" : "com.example.someevent",
"source" : "/mycontext",
"id" : "B234-1234-1234",
"time" : "2018-04-05T17:31:00Z",
"comexampleextension1" : "value",
"comexampleothervalue" : 5,
"datacontenttype" : "application/vnd.apache.thrift.binary",
"data_base64" : "... base64 encoded string ..."
}Example event with JSON data for the "data" member, either derived from a Map
or JSON data data:
{
"specversion" : "1.0",
"type" : "com.example.someevent",
"source" : "/mycontext",
"subject": null,
"id" : "C234-1234-1234",
"time" : "2018-04-05T17:31:00Z",
"comexampleextension1" : "value",
"comexampleothervalue" : 5,
"datacontenttype" : "application/json",
"data" : {
"appinfoA" : "abc",
"appinfoB" : 123,
"appinfoC" : true
}
}In the JSON Batch Format several CloudEvents are batched into a single JSON document. The document is a JSON array filled with CloudEvents in the JSON Event format.
Although the JSON Batch Format builds ontop of the JSON Format, it is considered as a separate format: a valid implementation of the JSON Format doesn't need to support it. The JSON Batch Format MUST NOT be used when only support for the JSON Format is indicated.
This section defines how a batch of CloudEvents is mapped to JSON.
The outermost JSON element is a JSON Array, which contains as elements CloudEvents rendered in accordance with the JSON event format specification.
A JSON Batch of CloudEvents MUST use the media type
application/cloudevents-batch+json.
An example containing two CloudEvents: The first with Binary-valued data, the
second with JSON data.
[
{
"specversion" : "1.0",
"type" : "com.example.someevent",
"source" : "/mycontext/4",
"id" : "B234-1234-1234",
"time" : "2018-04-05T17:31:00Z",
"comexampleextension1" : "value",
"comexampleothervalue" : 5,
"datacontenttype" : "application/vnd.apache.thrift.binary",
"data_base64" : "... base64 encoded string ..."
},
{
"specversion" : "1.0",
"type" : "com.example.someotherevent",
"source" : "/mycontext/9",
"id" : "C234-1234-1234",
"time" : "2018-04-05T17:31:05Z",
"comexampleextension1" : "value",
"comexampleothervalue" : 5,
"datacontenttype" : "application/json",
"data" : {
"appinfoA" : "abc",
"appinfoB" : 123,
"appinfoC" : true
}
}
]An example of an empty batch of CloudEvents (typically used in a response, but also valid in a request):
[]- RFC2046 Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
- RFC2119 Key words for use in RFCs to Indicate Requirement Levels
- RFC4627 The application/json Media Type for JavaScript Object Notation (JSON)
- RFC4648 The Base16, Base32, and Base64 Data Encodings
- RFC6839 Additional Media Type Structured Syntax Suffixes
- RFC8259 The JavaScript Object Notation (JSON) Data Interchange Format