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                                 Apache License
                           Version 2.0, January 2004


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# The SO6-3 protocol

This repository contains the specification of a S2S protocol which can be used
to keep in sync several IRC servers.

The specification lies in `spec.md`.

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# The SO6-3 S2S protocol

This document describes and specify the *SO6-3*.  This protocol is meant to keep
in sync IRC servers that are part of the same IRC network.

Although SO6-3 is primarily used by ellidri, and is developed side-by-side with
this server, it is meant to be implemented by any IRC server that has
message-tag support.

To understand this document, it is necessary for the reader to have basic
knowledge on what a IRC network is, how it operates and what are its components.
For a good introduction on this points, see [modern.ircdocs.horse][], section
"IRC Concepts".  Although not all information in the linked section correlates
with what is described in this document, it provides enough knowledge to
understand SO6-3.

"SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document are to be
interpreted as described in [RFC 2119][].

Table of contents:

1. Protocol format
1. Topology
1. List of commands
1. Connection life cycle
1. Bootstrap process
99. Acknowledgments
99. Appendix and references

## N. Protocol format

A [character][] is a Unicode code point other than `U+0000`.   Although some
code points (for example, combining accents) do not correspond to characters in
an intuitive sense, all code points except `U+0000` count as characters for
purposes of this spec.

A [space][] (` `) is `U+0020`.

An [at][] (`@`) is `U+0040`.

A [colon][] (`:`) is `U+003A`.

A [newline][] (`\n`) is `U+000A`.

A [carriage return][] (`\r`) is `U+000D`.

A [digit][] (`0`..`9`) is one of `U+0030` to `U+0039` included.

An [ASCII letter][] (`A`..`Z` and `a`..`z`) is one of `U+0041` to `U+005A`
included, or one of `U+0061` to `U+007A` included.

A [word][] is a sequence of [characters][] other than [space][].

A [line ending][] is a [newline][], a [carriage return][] not followed by a
[newline][], or a [carriage return][] and a following [newline][].

A [line][] is a sequence of zero or more [characters][] other than [newline][]
or [carriage return][], followed by a [line ending][].

A [tag string][] is a [word][] that starts with an [at][].

A [source][] is a [word][] that starts with a [colon][].

A [command][] is a [word][] made of either 3 [digits][], or 1 or more [ASCII

A [parameter][] is either a [word][] that doesn't start with a [colon][], or a
sequence of [characters][] that starts with a [colon][] up to a [newline][] or
[carriage return][].

A [message][] is a [line][] that contains, and only contains the following:

- Optionally, a [tag string][] followed by a [space][], then,
- Optionally, a [source][] followed by a [space][], then,
- A [command][], then,
- Optionally, a [space][] followed by 1 to 15 [parameters][], each separated by
  a [space][].

Here are some examples of messages and how the parameters would be represented
as [JSON][] lists:

    :irc.example.com CAP * LIST :\r\n     ->  ["*", "LIST", ""]
    CAP * LS :multi-prefix sasl\n         ->  ["*", "LS", "multi-prefix sasl"]
    CAP REQ :sasl message-tags foo\r\n    ->  ["REQ", "sasl message-tags foo"]
    @msgid=2 :dan!d@localhost PRIVMSG #chan :Hey!\r\n  ->
                                              ["#chan", "Hey!"]
    :dan!d@localhost PRIVMSG #chan Hey!\n ->  ["#chan", "Hey!"]

An [S2S stream][] is a [TLS-encrypted][TLS] [TCP stream][TCP] that is entirely
made of [messages][].  While the [TLS][] link points to TLS version 1.3, other
versions of the protocol MAY be supported, and supporting version 1.3 is
OPTIONAL.  Because of how security standards evolve, it is up to the
implementation to choose which [TLS][] versions they support.  However,
[S2S streams][] MUST be encrypted.

## N. Topology

A [server][], also called a [node][], is a [TCP host][TCP] that is able to
initiate and accept [S2S streams][].

A [network ID][], abbreviated [NID][], is a [word][].

Each [node][] is assigned a [network ID][].

Two [nodes][] are part of the same [network][], or the same [graph][], if both
share the same [network ID][].

A [client][] is an [IRC client][IRC] that is connected to a [server][].

A [leaf node][] is a [server][] that accepts connections from [clients][].

A [core node][] is a [server][] that does not accept any connection from

TODO: define network/graph, server/node, IRC client, core node, leaf node
TODO: define how servers/nodes are connected to each other

## N. List of commands

TODO: say commands == IRC commands
TODO what information MUST and MAY be attached to a command (e.g. `time` tag)
TODO how rollback of conflicting commands (e.g. two NICK with the same nickname,
or a MODE after a KICK)

## N. Connection life cycle

TODO: define the order messages are issued by servers when they start/stop a
connection with another server.

## N. Bootstrap process

TODO: define how a server/node must join a network

## N. Acknowledgments

Inspiration for this document came from the CommonMark specification, and

## N. Appendix and references

[IRC]: https://modern.ircdocs.horse/
[JSON]: https://tools.ietf.org/html/rfc8259
[modern.ircdocs.horse]: https://modern.ircdocs.horse/
[RFC 2119]: https://tools.ietf.org/html/rfc2119
[TCP]: https://tools.ietf.org/html/rfc793
[TLS]: https://tools.ietf.org/html/rfc8446