mirror of https://github.com/vacp2p/rfc.git
100 lines
3.8 KiB
Markdown
100 lines
3.8 KiB
Markdown
---
|
|
title: MVDS Metadata Field
|
|
version: 0.1.0
|
|
status: Draft
|
|
authors: Oskar Thorén <oskar@status.im>, Dean Eigenmann <dean@status.im>
|
|
---
|
|
|
|
## Table of Contents
|
|
|
|
1. [Abstract](#abstract)
|
|
2. [Motivation](#motivation)
|
|
3. [Format](#format)
|
|
1. [Fields](#fields)
|
|
4. [Usage](#usage)
|
|
1. [`parents`](#parents)
|
|
2. [`ephemeral`](#ephemeral)
|
|
5. [Footnotes](#footnotes)
|
|
6. [Changelog](#changelog)
|
|
7. [Acknowledgements](#acknowledgements)
|
|
8. [Copyright](#copyright)
|
|
|
|
## Abstract
|
|
|
|
In this specification, we describe a method to construct message history that will aid the consistency guarantees of [MVDS](mvds.md). Additionally we explain how data sync can be used for more lightweight messages that do not require full synchronization.
|
|
|
|
## Motivation
|
|
|
|
In order for more efficient synchronization of conversational messages, information should be provided allowing a node to more effectively synchronize the dependencies for any given message.
|
|
|
|
## Format
|
|
|
|
We introduce the metadata message which is used to convey information about a message and how it SHOULD be handled.
|
|
|
|
```protobuf
|
|
package vac.mvds;
|
|
|
|
message Metadata {
|
|
repeated bytes parents = 1;
|
|
bool ephemeral = 2;
|
|
}
|
|
```
|
|
|
|
Nodes MAY transmit a `Metadata` message by extending the MVDS [message](mvds.md#payloads) with a `metadata` field.
|
|
|
|
```diff
|
|
message Message {
|
|
bytes group_id = 1;
|
|
int64 timestamp = 2;
|
|
bytes body = 3;
|
|
+ Metadata metadata = 4;
|
|
}
|
|
```
|
|
|
|
### Fields
|
|
|
|
| Name | Description |
|
|
| ---------------------- | -------------------------------------------------------------------------------------------------------------------------------- |
|
|
| `parents` | list of parent [`message identifier`s](mvds.md#payloads) for the specific message. |
|
|
| `ephemeral` | indicates whether a message is ephemeral or not. |
|
|
|
|
## Usage
|
|
|
|
### `parents`
|
|
|
|
This field contains a list of parent [`message identifier`s](mvds.md#payloads) for the specific message. It MUST NOT contain any messages as parent whose `ack` flag was set to `false`. This establishes a directed acyclic graph (DAG)<sup>1</sup> of persistent messages.
|
|
|
|
Nodes MAY buffer messages until dependencies are satisfied for causal consistency<sup>2</sup>, they MAY also pass the messages straight away for eventual consistency<sup>3</sup>.
|
|
|
|
A parent is any message before a new message that a node is aware of that has no children.
|
|
|
|
The number of parents for a given message is bound by [0, N], where N is the number of nodes participating in the conversation, therefore the space requirements for the `parents` field is O(N).
|
|
|
|
If a message has no parents it is considered a root. There can be multiple roots, which might be disconnected, giving rise to multiple DAGs.
|
|
|
|
### `ephemeral`
|
|
|
|
When the `ephemeral` flag is set to `false`, a node MUST send an acknowledgement when they have received and processed a message. If it is set to `true`, it SHOULD NOT send any acknowledgement. The flag is `false` by default.
|
|
|
|
Nodes MAY decide to not persist ephemeral messages, however they MUST NOT be shared as part of the message history.
|
|
|
|
Nodes SHOULD send ephemeral messages in batch mode. As their delivery is not needed to be guaranteed.
|
|
|
|
## Footnotes
|
|
1. <https://en.wikipedia.org/wiki/Directed_acyclic_graph>
|
|
2. <https://jepsen.io/consistency/models/causal>
|
|
3. <https://en.wikipedia.org/wiki/Eventual_consistency>
|
|
|
|
## Changelog
|
|
|
|
| Version | Comment |
|
|
| :-----: | ------- |
|
|
| [0.1.0](https://github.com/vacp2p/specs/blob/53bc8585add58695c28cfaf4382818f4daf8de84/mdf.md) | Initial Release |
|
|
|
|
## Acknowledgements
|
|
- Andrea Maria Piana
|
|
|
|
## Copyright
|
|
|
|
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
|