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c80314d Dec 5, 2018
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NATS Transport Binding for CloudEvents

Abstract

The NATS Transport Binding for CloudEvents defines how events are mapped to NATS messages.

Status of this document

This document is a working draft.

Table of Contents

  1. Introduction
  1. Use of CloudEvents Attributes
  1. NATS Message Mapping
  1. References

1. Introduction

CloudEvents is a standardized and transport-neutral definition of the structure and metadata description of events. This specification defines how the elements defined in the CloudEvents specification are to be used in the NATS protocol as client produced and consumed messages.

1.1. Conformance

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.

1.2. Relation to NATS

This specification does not prescribe rules constraining transfer or settlement of event messages with NATS; it solely defines how CloudEvents are expressed in the NATS protocol as client messages that are produced and consumed.

1.3. Content Modes

The specification defines two content modes for transferring events: structured and binary.

NATS will only support structured data mode at this time. Today, the NATS protocol does not support custom message headers, necessary for binary mode.

Event metadata attributes and event data are placed into the NATS message payload using an event format.

1.4. Event Formats

Event formats, used with the stuctured content mode, define how an event is expressed in a particular data format. All implementations of this specification MUST support the JSON event format.

1.5. Security

This specification does not introduce any new security features for NATS, or mandate specific existing features to be used.

2. Use of CloudEvents Attributes

This specification does not further define any of the CloudEvents event attributes.

2.1. contenttype Attribute

The contenttype attribute is assumed to contain a media-type expression compliant with RFC2046.

2.2. data Attribute

The data attribute is assumed to contain opaque application data that is encoded as declared by the contenttype attribute.

An application is free to hold the information in any in-memory representation of its choosing, but as the value is transposed into NATS as defined in this specification, core NATS provides data available as a sequence of bytes.

For instance, if the declared contenttype is application/json;charset=utf-8, the expectation is that the data attribute value is made available as UTF-8 encoded JSON text.

3. NATS Message Mapping

With NATS, the content mode is always structured and the NATS message payload MUST be the JSON event format serialized as specified by the UTF-8 encoded JSON text for use in NATS.

The structured content mode keeps event metadata and data together, allowing simple forwarding of the same event across multiple routing hops, and across multiple transports.

3.1 Event Data Encoding

The chosen event format defines how all attributes, including the payload, are represented.

The event metadata and data MUST then be rendered in accordance with the event format specification and the resulting data becomes the payload.

3.2 Example

This example shows a JSON event format encoded event in client messages that are produced and consumed.

------------------ Message -------------------

Subject: mySubject

------------------ payload -------------------

{
    "specversion" : "0.2",
    "type" : "com.example.someevent",

    ... further attributes omitted ...

    "data" : {
        ... application data ...
    }
}

-----------------------------------------------

4. References

  • NATS The NATS Messaging System
  • NATS-PUB-PROTO The NATS protocol for messages published by a client
  • NATS-MSG-PROTO The NATS protocol for messages received by a client
  • RFC2046 Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
  • RFC2119 Key words for use in RFCs to Indicate Requirement Levels
  • RFC3629 UTF-8, a transformation format of ISO 10646
  • RFC7159 The JavaScript Object Notation (JSON) Data Interchange Format