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Update AVRO mappings to match current event schema and type system. #497

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Sep 14, 2019
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Update AVRO mappings to match current event schema and type system. #497

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8cf856a
Update AVRO mappings to match current event schema and type system.
evankanderson Aug 30, 2019
597453d
Address @duglin feedback.
evankanderson Sep 3, 2019
5d8285d
Make AVRO spec support nested JSON object data translated to structur…
evankanderson Sep 11, 2019
98862b9
Update Avro format definition to match avsc file.
evankanderson Sep 11, 2019
cef0a85
s/may/can/
evankanderson Sep 14, 2019
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164 changes: 90 additions & 74 deletions avro-format.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,8 @@

## Abstract

The Avro Format for CloudEvents defines how events attributes are expressed
in the [Avro 1.9.0 Specification][avro-spec].
The Avro Format for CloudEvents defines how events attributes are expressed in
the [Avro 1.9.0 Specification][avro-spec].

## Status of this document

Expand All @@ -13,7 +13,8 @@ This document is a working draft.

1. [Introduction](#1-introduction)
2. [Attributes](#2-attributes)
3. [Examples](#3-examples)
3. [Data](#3-data)
4. [Examples](#4-examples)

## 1. Introduction

Expand Down Expand Up @@ -47,108 +48,125 @@ The CloudEvents type system MUST be mapped to Avro types as follows.

| CloudEvents | Avro |
| ------------- | ---------------------------------------------------------------------- |
| Boolean | [boolean][avro-primitives] |
| Integer | [int][avro-primitives] |
| String | [string][avro-primitives] |
| Binary | [bytes][avro-primitives] |
| URI | [string][avro-primitives] following [RFC 3986 §4.3][rfc3986-section43] |
| URI-reference | [string][avro-primitives] following [RFC 3986 §4.1][rfc3986-section41] |
| Timestamp | [string][avro-primitives] following [RFC 3339][rfc3339] (ISO 8601) |
| Any | See [2.2](#22-mapping-any-typed-attributes) |

Extension specifications MAY define diverging mapping rules for the values of
attributes they define.

### 2.2 Mapping Any-typed Attributes

`Any`-typed CloudEvents values can either hold a `String`, or a `Binary` value,
or a `Map`, or any of all other types. Avro type system satisfies this requirement by employing a recursive reference,
where a `record` type is referenced as a value inside of its own `map`.

Example:

```json
{
"type":"record",
"name":"MyRecord",
"fields":[
{
"name":"wow",
"type":{
"type":"map",
"values":[
"null",
"string",
"MyRecord"
]
}
}
]
}
```

### 2.3 OPTIONAL Attributes

CloudEvents Spec defines OPTIONAL attributes. The Avro format defines that
these fields MUST use the `null` type and the actual type through
the [union][avro-unions].
CloudEvents Spec defines OPTIONAL attributes. The Avro format defines that these
fields MUST use the `null` type and the actual type through the
[union][avro-unions].

Example:

```json
[
"null",
"string"
]
["null", "string"]
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I can undo this JSON auto-fomatting if preferred.

```

### 2.4 Definition

Users of Avro MUST use a message whose binary encoding is identical
to the one described by the [CloudEvent Avro Schema](./spec.avsc):
Users of Avro MUST use a message whose binary encoding is identical to the one
described by the [CloudEvent Avro Schema](./spec.avsc):

```json
{
"namespace":"io.cloudevents",
"type":"record",
"name":"CloudEvent",
"version":"0.4-wip",
"doc":"Avro Event Format for CloudEvents",
"fields":[
"namespace": "io.cloudevents",
"type": "record",
"name": "CloudEvent",
"version": "0.4-wip",
"doc": "Avro Event Format for CloudEvents",
"fields": [
{
"name":"attribute",
"type":{
"type":"map",
"values":[
"null",
"int",
"string",
"bytes",
"CloudEvent"
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Not familiar with Avro... is the "CloudEvent" above replaced by the stuff on line 95? (the data/bytes thingy)

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The "CloudEvent" was a recursive allowed value of the same object, to support Map values.

Without Map, these structures don't need to be recursive in their definition, which makes me much more comfortable.

The actual diff here is +boolean -CloudEvent

]
"name": "attribute",
"type": {
"type": "map",
"values": ["null", "boolean", "int", "string", "bytes"]
}
},
{
"name": "data",
"type": [
"bytes",
"null",
"boolean",
{
"type": "map",
"values": [
"null",
"boolean",
{
"type": "record",
"name": "CloudEventData",
"doc": "Representation of a JSON Value",
"fields": [
{
"name": "value",
"type": {
"type": "map",
"values": [
"null",
"boolean",
{ "type": "map", "values": "CloudEventData" },
{ "type": "array", "items": "CloudEventData" },
"double",
"string"
]
}
}
]
},
"double",
"string"
]
},
{ "type": "array", "items": "CloudEventData" },
"double",
"string"
]
}
]
}
```

## 3 Examples
## 3 Data

Before encoding, the AVRO serializer MUST first determine the runtime data type
of the content. This can be determined by examining the data for invalid UTF-8
sequences or by consulting the `datacontenttype` attribute.

If the implementation determines that the type of the data is binary, the value
MUST be stored in the `data` field using the `bytes` type.

For other types (non-binary data without a `datacontenttype` attribute), the
implementation MUST translate the data value into a representation of the JSON
value using the union types described for the `data` record.

## 4 Examples

The following table shows exemplary mappings:

| CloudEvents | Type | Exemplary Avro Value |
| ------------ | --------- | ---------------------------------------------- |
| type | string | `"com.example.someevent"` |
| specversion | string | `"0.4-wip` |
| source | string | `"/mycontext"` |
| id | string | `"7a0dc520-c870-4193c8"` |
| time | string | `"2019-06-05T23:45:00Z"` |
| dataschema | string | `"http://registry.com/schema/v1/much.json"` |
| contenttype | string | `"application/json"` |
| data | string | `"{"much":{"wow":"json"}}"` |
||||
| dataschema | string | `"http://registry.com/subjects/ce/versions/1"` |
| contenttype | string | `"application/avro"` |
| data | string | `"Q2xvdWRFdmVudHM="` |
| CloudEvents | Type | Exemplary Avro Value |
| ----------- | ------ | ---------------------------------------------- |
| type | string | `"com.example.someevent"` |
| specversion | string | `"0.4-wip` |
| source | string | `"/mycontext"` |
| id | string | `"7a0dc520-c870-4193c8"` |
| time | string | `"2019-06-05T23:45:00Z"` |
| dataschema | string | `"http://registry.com/schema/v1/much.json"` |
| contenttype | string | `"application/json"` |
| data | bytes | `"{"much":{"wow":"json"}}"` |
| | | |
| dataschema | string | `"http://registry.com/subjects/ce/versions/1"` |
| contenttype | string | `"application/avro"` |
| data | string | `"Q2xvdWRFdmVudHM="` |

## References

Expand All @@ -158,9 +176,7 @@ The following table shows exemplary mappings:
[avro-primitives]: http://avro.apache.org/docs/1.9.0/spec.html#schema_primitive
[avro-logical-types]: http://avro.apache.org/docs/1.9.0/spec.html#Logical+Types
[avro-unions]: http://avro.apache.org/docs/1.9.0/spec.html#Unions

[ce]: ./spec.md

[rfc2119]: https://tools.ietf.org/html/rfc2119
[rfc3986-section41]: https://tools.ietf.org/html/rfc3986#section-4.1
[rfc3986-section43]: https://tools.ietf.org/html/rfc3986#section-4.3
Expand Down
46 changes: 44 additions & 2 deletions spec.avsc
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Expand Up @@ -11,12 +11,54 @@
"type":"map",
"values":[
"null",
"boolean",
"int",
"string",
"bytes",
"CloudEvent"
"bytes"
]
}
},
{
"name": "data",
"type": [
"bytes",
"null",
"boolean",
{
"type": "map",
"values": [
"null",
"boolean",
{
"type": "record",
"name": "CloudEventData",
"doc": "Representation of a JSON Value",
"fields": [
{
"name": "value",
"type": {
"type": "map",
"values": [
"null",
"boolean",
{ "type": "map", "values": "CloudEventData" },
{ "type": "array", "items": "CloudEventData" },
"double",
"string"
]
}
}
]
},
"double",
"string"
]
},
{ "type": "array", "items": "CloudEventData" },
"double",
"string"
]
}
]
}