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Protocol Buffers Event Format for CloudEvents - Version 0.3

Abstract

The Protocol Buffers Format for CloudEvents (CE) defines the encoding of CloudEvents in the Protocol Buffers binary format.

Status of this document

This document is a working draft.

1. Introduction

This specification defines how the Context Attributes defined in the CloudEvents specification MUST be encoded in the protocol buffer binary format. Transcoding to and from other formats (e.g. JSON) is out of the scope of this document.

Protocol Buffers are a language-neutral, platform-neutral extensible mechanism for serializing structured data. The Google reference implementation of Protocol Buffers includes support for an interface descriptor language (IDL), and this document makes use of language level 3 IDL from Protocol Buffers v3.5.0. CloudEvents systems using Protocol Buffers are not mandated to use the IDL or any particular implementation of Protocol Buffers as long as they produce messages which match the binary encoding defined by the IDL.

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.

2. Protocol Buffers format

Protocol Buffers provide a binary data serialization format which is substantially more compact and efficient to parse when compared to XML or JSON, along with a variety of language-specific libraries to perform automatic serialization and deserialization. The Protocol Buffers specification defines a well-known encoding format which is the basis of this specification. This specification is described using the Protocol Buffers project IDL for readability, but the ultimate basis of this specification is the Protocol Buffers binary encoding.

2.1 Definition

Users of Protocol Buffers MUST use a message whose binary encoding is identical to the one described by the CloudEventMap message:

syntax = "proto3";

package io.cloudevents;

// allows a map to appear inside `oneof`
message CloudEventMap {
  map<string, CloudEventAny> value = 1;
}

message CloudEventAny {
  oneof value {
    string string_value = 1;
    bytes binary_value = 2;
    uint32 int_value = 3;
    CloudEventMap map_value = 4;
  }
}

The CloudEvents type system MUST be mapped into the fields of CloudEventAny as follows:

CloudEvents CloudEventAny field
String string_value
Binary binary_value
URI-reference string_value (string expression conforming to URI-reference as defined in RFC 3986 §4.1)
Timestamp string_value (string expression as defined in RFC 3339)
Map map_value
Integer int_value
Any Not applicable. Any is the enclosing CloudEventAny message itself

Protocol Buffer representations of CloudEvents MUST use the media type application/cloudevents+proto.

3. Examples

Below is an example of how to create a CloudEvent Protocol Buffer message using the Java Google Protocol Buffers library:

import com.google.common.base.Charsets;
import com.google.protobuf.ByteString;


CloudEventMap event = CloudEventMap.newBuilder()
  .putValue(
    "type",
    CloudEventAny.newBuilder()
      .setStringValue("com.example.emitter.event")
      .build())
  .putValue(
    "specversion",
    CloudEventAny.newBuilder()
      .setStringValue("0.3")
      .build())
  .putValue(
    "time",
    CloudEventAny.newBuilder()
      .setStringValue("2018-10-25T00:00:00+00:00")
      .build())
  .putValue(
    "source",
    CloudEventAny.newBuilder()
      .setStringValue("com.example.source.host1")
      .build())
  .putValue(
    "comExampleCustomextension",
    CloudEventAny.newBuilder()
      .setStringValue("some value for the extension")
      .build())
  .putValue(
    "data",
    CloudEventAny.newBuilder()
      .setBinaryValue(ByteString.copyFrom("a binary string", Charsets.UTF_8))
      .build())
  .build();