chat/README.md

# chat

**IRC plus message metadata, a signing system using it, and server-based
backlog queues for multiple connected clients on one nick. All via HTTP.**

A chat server written in Go. Decouples session state from transport
connections, enabling mobile-friendly persistent sessions over HTTP.

The **HTTP API is the primary interface**. It's designed to be simple enough
that writing a terminal IRC-style client against it is straightforward — just
`curl` and `jq` get you surprisingly far. The server also ships an embedded
web client as a convenience/reference implementation, but the API comes first.

## Motivation

IRC is in decline because session state is tied to the TCP connection. In a
mobile-first world, that's a nonstarter. Not everyone wants to run a bouncer
or pay for IRCCloud.

This project builds a chat server that:

- Holds session state server-side (message queues, presence, channel membership)
- Exposes a minimal, clean HTTP+JSON API — easy to build clients against
- Supports multiple concurrent clients per user session
- Provides IRC-like semantics: channels, nicks, topics, modes
- Uses structured JSON messages with IRC command names and numeric reply codes

## Why Not Just Use IRC / XMPP / Matrix?

This isn't a new protocol that borrows IRC terminology for familiarity. This
**is** IRC — the same command model, the same semantics, the same numeric
reply codes from RFC 1459/2812 — carried over HTTP+JSON instead of raw TCP.

The question isn't "why build something new?" It's "what's the minimum set of
changes to make IRC work on modern devices?" The answer turned out to be four
things:

### 1. HTTP transport instead of persistent TCP

IRC requires a persistent TCP connection. That's fine on a desktop. On a phone,
the OS kills your background socket, you lose your session, you miss messages.
Bouncers exist but add complexity and a second point of failure.

HTTP solves this cleanly: clients poll when they're awake, messages queue when
they're not. Works through firewalls, proxies, CDNs. Every language has an HTTP
client. No custom protocol parsers, no connection state machines.

### 2. Server-held session state

In IRC, the TCP connection *is* the session. Disconnect and you're gone — your
nick is released, you leave all channels, messages sent while you're offline
are lost forever. This is IRC's fundamental mobile problem.

Here, sessions persist independently of connections. Your nick, channel
memberships, and message queue survive disconnects. Multiple devices can share
a session simultaneously, each with its own delivery queue.

### 3. Structured message bodies

IRC messages are single lines of text. That's a protocol constraint from 1988,
not a deliberate design choice. It forces multiline content through ugly
workarounds (multiple PRIVMSG commands, paste flood).

Message bodies here are JSON arrays (one string per line) or objects (for
structured data like key material). This also enables deterministic
canonicalization via RFC 8785 JCS — you can't reliably sign something if the
wire representation is ambiguous.

### 4. Key/value metadata on messages

The `meta` field on every message envelope carries extensible attributes —
cryptographic signatures, content hashes, whatever clients want to attach.
IRC has no equivalent; bolting signatures onto IRC requires out-of-band
mechanisms or stuffing data into CTCP.

### What didn't change

Everything else is IRC. `PRIVMSG`, `JOIN`, `PART`, `NICK`, `TOPIC`, `MODE`,
`KICK`, `353`, `433` — same commands, same semantics. Channels start with `#`.
Joining a nonexistent channel creates it. Channels disappear when empty. Nicks
are unique per server. There are no accounts — identity is a key, a nick is a
display name.

### On the resemblance to JSON-RPC

All C2S commands go through `POST /messages` with a `command` field that
dispatches the action. This looks like JSON-RPC, but the resemblance is
incidental. It's IRC's command model — `PRIVMSG #channel :hello` becomes
`{"command": "PRIVMSG", "to": "#channel", "body": ["hello"]}` — encoded as
JSON rather than space-delimited text. The command vocabulary is IRC's, not
an invention.

The message envelope is deliberately identical for C2S and S2C. A `PRIVMSG` is
a `PRIVMSG` regardless of direction. A `JOIN` from a client is the same shape
as the `JOIN` relayed to channel members. This keeps the protocol simple and
makes signing consistent — you sign the same structure you send.

### Why not XMPP or Matrix?

XMPP is XML-based, overengineered for chat, and the ecosystem is fragmented
across incompatible extensions (XEPs). Matrix is a federated append-only event
graph with a spec that runs to hundreds of pages. Both are fine protocols, but
they're solving different problems at different scales.

This project wants IRC's simplicity with four specific fixes. That's it.

## Design Decisions

### Identity & Sessions — No Accounts

There are no accounts, no registration, no passwords. Identity is a signing
key; a nick is just a display name. The two are decoupled.

- **Session creation**: client connects → server assigns a **session UUID**
  (user identity for this server), a **client UUID** (this specific device),
  and an **opaque auth token** (random bytes, not JWT).
- The auth token implicitly identifies the client. Clients present it via
  `Authorization: Bearer <token>`.
- Nicks are changeable; the session UUID is the stable identity.
- Server-assigned UUIDs — clients do not choose their own IDs.

### Multi-Client Model

A single user session can have multiple clients (phone, laptop, terminal).

- Each client gets a **separate server-to-client (S2C) message queue**.
- The server fans out all S2C messages to every active client queue for that
  user session.
- `GET /api/v1/messages` delivers from the calling client's specific queue,
  identified by the auth token.
- Client queues have **independent expiry/pruning** — one client going offline
  doesn't affect others.

```
User (session UUID)
├── Client A (client UUID, token, queue)
├── Client B (client UUID, token, queue)
└── Client C (client UUID, token, queue)
```

### Message Immutability

Messages are **immutable** — no editing, no deletion by clients. This is a
deliberate design choice that enables cryptographic signing: if a message could
be modified after signing, signatures would be meaningless.

### Message Delivery

- **Long-poll timeout**: 15 seconds
- **Queue depth**: server-configurable, default at least 48 hours worth of
  messages
- **No delivery/read receipts** except in DMs
- **Bodies are structured** objects or arrays (never raw strings) — enables
  deterministic canonicalization via RFC 8785 JCS for signing

### Crypto & Signing

- Servers **relay signatures verbatim** — signatures are key/value metadata on
  message objects (`meta.sig`, `meta.alg`). Servers do not verify them.
- Clients handle key authentication via **TOFU** (trust on first use).
- **No key revocation mechanism** — keep your keys safe.
- **PUBKEY** message type for distributing signing keys to channel members.
- **E2E encryption for DMs** is planned for 1.0.

### Channels

- **Any user can create channels** — joining a nonexistent channel creates it,
  like IRC.
- **Ephemeral** — channels disappear when the last member leaves.
- No channel size limits.
- No channel-level encryption.

### Federation

- **Manual server linking only** — no autodiscovery, no mesh. Operators
  explicitly configure server links.
- Servers relay messages (including signatures) verbatim.

### Web Client

The SPA web client is a **convenience UI**. The primary interface is IRC-style
client apps talking directly to the HTTP API.

## Architecture

### Transport: HTTP only

All client↔server and server↔server communication uses HTTP/1.1+ with JSON
request/response bodies. No WebSockets, no raw TCP, no gRPC — just plain HTTP.

- **Client polling**: Clients long-poll `GET /api/v1/messages` — server holds
  the connection for up to 15 seconds until messages arrive or timeout.
  One endpoint for everything.
- **Client sending**: `POST /api/v1/messages` with a `to` field. That's it.
- **Server federation**: Servers exchange messages via HTTP to enable multi-server
  networks (like IRC server linking)

The entire read/write loop for a client is two endpoints. Everything else is
channel management and history.

### Session Model

```
┌─────────────────────────────────┐
│     User Session (UUID)         │
│     nick: "alice"               │
│     signing key: ed25519:...    │
│                                 │
│  ┌──────────┐ ┌──────────┐     │
│  │ Client A │ │ Client B │ ... │
│  │ UUID     │ │ UUID     │     │
│  │ token    │ │ token    │     │
│  │ queue    │ │ queue    │     │
│  └──────────┘ └──────────┘     │
└─────────────────────────────────┘
```

- **User session**: server-assigned UUID. Represents a user on this server.
  Has a nick (changeable, unique per server at any point in time).
- **Client**: each device/connection gets its own UUID and opaque auth token.
  The token is the credential — present it to authenticate.
- **Queue**: each client has an independent S2C message queue. The server fans
  out messages to all active client queues for the session.

Sessions persist across disconnects. Messages queue until retrieved. Client
queues expire independently after a configurable idle timeout.

### Message Protocol

All messages use **IRC command names and numeric reply codes** from RFC 1459/2812.
The `command` field identifies the message type.

#### Message Envelope

Every message is a JSON object with these fields:

| Field     | Type            | Required | Description |
|-----------|-----------------|----------|-------------|
| `command` | string          | ✓        | IRC command name or 3-digit numeric code |
| `from`    | string          |          | Sender nick or server name |
| `to`      | string          |          | Destination: `#channel` or nick |
| `params`  | array\<string\> |          | Additional IRC-style parameters |
| `body`    | array \| object |          | Structured body (never a raw string — see below) |
| `id`      | string (uuid)   |          | Server-assigned message UUID |
| `ts`      | string          |          | Server-assigned ISO 8601 timestamp |
| `meta`    | object          |          | Extensible metadata (signatures, hashes, etc.) |

**Important:** Message bodies are **structured objects or arrays**, never raw
strings. This is a deliberate departure from IRC wire format that enables:

- **Multiline messages** — body is a list of lines, no escape sequences
- **Deterministic canonicalization** — for hashing and signing (see below)
- **Structured data** — commands like PUBKEY carry key material as objects

For text messages, `body` is an array of strings (one per line):

```json
{"command": "PRIVMSG", "from": "nick", "to": "#channel", "body": ["hello world"]}
{"command": "PRIVMSG", "from": "nick", "to": "#channel", "body": ["line one", "line two"]}
```

For numeric replies with text trailing parameters:

```json
{"command": "001", "to": "nick", "body": ["Welcome to the network, nick"]}
{"command": "353", "to": "nick", "params": ["=", "#channel"], "body": ["@op1 alice bob"]}
```

For structured data (keys, etc.), `body` is an object:

```json
{"command": "PUBKEY", "from": "nick", "body": {"alg": "ed25519", "key": "base64..."}}
```

#### IRC Command Mapping

**Commands (C2S and S2C):**

| Command   | RFC          | Description                          |
|-----------|--------------|--------------------------------------|
| `PRIVMSG` | 1459 §4.4.1 | Message to channel or user           |
| `NOTICE`  | 1459 §4.4.2 | Notice (must not trigger auto-reply) |
| `JOIN`    | 1459 §4.2.1 | Join a channel                       |
| `PART`    | 1459 §4.2.2 | Leave a channel                      |
| `QUIT`    | 1459 §4.1.6 | Disconnect from server               |
| `NICK`    | 1459 §4.1.2 | Change nickname                      |
| `MODE`    | 1459 §4.2.3 | Set/query channel or user modes      |
| `TOPIC`   | 1459 §4.2.4 | Set/query channel topic              |
| `KICK`    | 1459 §4.2.8 | Kick user from channel               |
| `PING`    | 1459 §4.6.2 | Keepalive                            |
| `PONG`    | 1459 §4.6.3 | Keepalive response                   |
| `PUBKEY`  | (extension)  | Announce/relay signing public key    |

All C2S commands may be relayed S2C to other users (e.g. JOIN, PART, PRIVMSG).

**Numeric Reply Codes (S2C):**

| Code | Name                 | Description |
|------|----------------------|-------------|
| 001  | RPL_WELCOME          | Welcome after session creation |
| 002  | RPL_YOURHOST         | Server host information |
| 003  | RPL_CREATED          | Server creation date |
| 004  | RPL_MYINFO           | Server info and modes |
| 322  | RPL_LIST             | Channel list entry |
| 323  | RPL_LISTEND          | End of channel list |
| 332  | RPL_TOPIC            | Channel topic |
| 353  | RPL_NAMREPLY         | Channel member list |
| 366  | RPL_ENDOFNAMES       | End of NAMES list |
| 372  | RPL_MOTD             | MOTD line |
| 375  | RPL_MOTDSTART        | Start of MOTD |
| 376  | RPL_ENDOFMOTD        | End of MOTD |
| 401  | ERR_NOSUCHNICK       | No such nick/channel |
| 403  | ERR_NOSUCHCHANNEL    | No such channel |
| 433  | ERR_NICKNAMEINUSE    | Nickname already in use |
| 442  | ERR_NOTONCHANNEL     | Not on that channel |
| 482  | ERR_CHANOPRIVSNEEDED | Not channel operator |

**Server-to-Server (Federation):**

Federated servers use the same IRC commands. After link establishment, servers
exchange a burst of JOIN, NICK, TOPIC, and MODE commands to sync state.
PING/PONG serve as inter-server keepalives.

#### Message Examples

```json
{"command": "PRIVMSG", "from": "alice", "to": "#general", "body": ["hello world"]}

{"command": "PRIVMSG", "from": "alice", "to": "#general", "body": ["line one", "line two"], "meta": {"sig": "base64...", "alg": "ed25519"}}

{"command": "PRIVMSG", "from": "alice", "to": "bob", "body": ["hey, DM"]}

{"command": "JOIN", "from": "bob", "to": "#general"}

{"command": "PART", "from": "bob", "to": "#general", "body": ["later"]}

{"command": "NICK", "from": "oldnick", "body": ["newnick"]}

{"command": "001", "to": "alice", "body": ["Welcome to the network, alice"]}

{"command": "353", "to": "alice", "params": ["=", "#general"], "body": ["@op1 alice bob +voiced1"]}

{"command": "433", "to": "*", "params": ["alice"], "body": ["Nickname is already in use"]}

{"command": "PUBKEY", "from": "alice", "body": {"alg": "ed25519", "key": "base64..."}}
```

#### JSON Schemas

Full JSON Schema (draft 2020-12) definitions for all message types are in
[`schema/`](schema/). See [`schema/README.md`](schema/README.md) for the
complete index.

### Canonicalization and Signing

Messages support optional cryptographic signatures for integrity verification.
Servers relay signatures verbatim without verifying them — verification is
purely a client-side concern.

#### Canonicalization (RFC 8785 JCS)

To produce a deterministic byte representation of a message for signing:

1. Remove `meta.sig` from the message (the signature itself is not signed)
2. Serialize using [RFC 8785 JSON Canonicalization Scheme (JCS)](https://www.rfc-editor.org/rfc/rfc8785):
   - Object keys sorted lexicographically
   - No whitespace
   - Numbers in shortest form
   - UTF-8 encoding
3. The resulting byte string is the signing input

This is why `body` must be an object or array — raw strings would be ambiguous
under canonicalization.

#### Signing Flow

1. Client generates an Ed25519 keypair
2. Client announces public key: `{"command": "PUBKEY", "body": {"alg": "ed25519", "key": "base64..."}}`
3. Server relays PUBKEY to channel members / stores for the session
4. When sending a message, client:
   a. Constructs the message without `meta.sig`
   b. Canonicalizes per JCS
   c. Signs with private key
   d. Adds `meta.sig` (base64) and `meta.alg`
5. Recipients verify by repeating steps a–c and checking the signature
   against the sender's announced public key

#### PUBKEY Message

```json
{"command": "PUBKEY", "from": "alice", "body": {"alg": "ed25519", "key": "base64-encoded-pubkey"}}
```

Servers relay PUBKEY messages to all channel members. Clients cache public keys
and use them to verify `meta.sig` on incoming messages. Key distribution is
trust-on-first-use (TOFU). There is no key revocation mechanism.

### API Endpoints

All endpoints accept and return `application/json`. Authenticated endpoints
require `Authorization: Bearer <token>` header.

The API is the primary interface — designed for IRC-style clients. The entire
client loop is:

1. `POST /api/v1/session` — create a session, get a token
2. `GET /api/v1/state` — see who you are and what channels you're in
3. `GET /api/v1/messages?timeout=15` — long-poll for all messages (channel, DM, system)
4. `POST /api/v1/messages` — send to `"#channel"` or `"nick"`

That's the core. Everything else (join, part, history, members) is ancillary.

#### Quick example (curl)

```bash
# Create a session (get session UUID, client UUID, and auth token)
TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/session \
  -d '{"nick":"alice"}' | jq -r .token)

# Join a channel (creates it if it doesn't exist)
curl -s -X POST http://localhost:8080/api/v1/messages \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"command":"JOIN","to":"#general"}'

# Send a message
curl -s -X POST http://localhost:8080/api/v1/messages \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"command":"PRIVMSG","to":"#general","body":["hello world"]}'

# Poll for messages (long-poll, 15s timeout)
curl -s "http://localhost:8080/api/v1/messages?timeout=15" \
  -H "Authorization: Bearer $TOKEN"
```

#### Session

```
POST /api/v1/session         — Create session { "nick": "..." }
                                → { id, nick, token }
                                Token is opaque (random), not JWT.
                                Token implicitly identifies the client.
```

#### State

```
GET  /api/v1/state           — User state: nick, session_id, client_id,
                                and list of joined channels
```

#### Messages (unified stream)

```
GET  /api/v1/messages        — Single message stream (long-poll, 15s timeout)
                                All message types: channel, DM, notices, events
                                Delivers from the calling client's queue
                                (identified by auth token)
                                Query params: ?after=<message-id>&timeout=15
POST /api/v1/messages        — Send any C2S command (dispatched by "command" field)
```

All client-to-server commands use `POST /api/v1/messages` with a `command`
field. There are no separate endpoints for join, part, nick, topic, etc.

| Command   | Required Fields     | Optional Fields | Description |
|-----------|---------------------|-----------------|-------------|
| `PRIVMSG` | `to`, `body`        | `meta`          | Message to channel (`#name`) or user (nick) |
| `NOTICE`  | `to`, `body`        | `meta`          | Notice (must not trigger auto-reply) |
| `JOIN`    | `to`                |                 | Join a channel (creates if nonexistent) |
| `PART`    | `to`                | `body`          | Leave a channel |
| `NICK`    | `body`              |                 | Change nickname — `body: ["newnick"]` |
| `TOPIC`   | `to`, `body`        |                 | Set channel topic |
| `MODE`    | `to`, `params`      |                 | Set channel/user modes |
| `KICK`    | `to`, `params`      | `body`          | Kick user — `params: ["nick"]`, `body: ["reason"]` |
| `PING`    |                     |                 | Keepalive (server responds with PONG) |
| `PUBKEY`  | `body`              |                 | Announce signing key — `body: {"alg":..., "key":...}` |

Examples:

```json
{"command": "PRIVMSG", "to": "#channel", "body": ["hello world"]}
{"command": "JOIN", "to": "#channel"}
{"command": "PART", "to": "#channel"}
{"command": "NICK", "body": ["newnick"]}
{"command": "TOPIC", "to": "#channel", "body": ["new topic text"]}
{"command": "PING"}
```

Messages are immutable — no edit or delete endpoints.

#### History

```
GET  /api/v1/history         — Fetch history for a target (channel or DM)
                                Query params: ?target=#channel&before=<id>&limit=50
                                For DMs: ?target=nick&before=<id>&limit=50
```

#### Channels

```
GET  /api/v1/channels              — List all server channels
GET  /api/v1/channels/{name}/members   — Channel member list
```

Join and part are handled via `POST /api/v1/messages` with `JOIN` and `PART`
commands (see Messages above).

#### Server Info

```
GET  /api/v1/server          — Server info (name, MOTD)
GET  /.well-known/healthcheck.json  — Health check
```

### Federation (Server-to-Server)

Servers can link to form a network, similar to IRC server linking. Links are
**manually configured** — there is no autodiscovery.

```
POST /api/v1/federation/link     — Establish server link (mutual auth via shared key)
POST /api/v1/federation/relay    — Relay messages between linked servers
GET  /api/v1/federation/status   — Link status
```

Federation uses the same HTTP+JSON transport. S2S messages use the RELAY, LINK,
UNLINK, SYNC, PING, and PONG commands. Messages (including signatures) are
relayed verbatim between servers so users on different servers can share channels.

### Channel Modes

Inspired by IRC but simplified:

| Mode | Meaning |
|------|---------|
| `+i` | Invite-only |
| `+m` | Moderated (only voiced users can send) |
| `+s` | Secret (hidden from channel list) |
| `+t` | Topic locked (only ops can change) |
| `+n` | No external messages |

User channel modes: `+o` (operator), `+v` (voice)

### Configuration

Via environment variables (Viper), following gohttpserver conventions:

| Variable | Default | Description |
|----------|---------|-------------|
| `PORT` | `8080` | Listen port |
| `DBURL` | `""` | SQLite/Postgres connection string |
| `DEBUG` | `false` | Debug mode |
| `MAX_HISTORY` | `10000` | Max messages per channel history |
| `SESSION_TIMEOUT` | `86400` | Session idle timeout (seconds) |
| `QUEUE_MAX_AGE` | `172800` | Max client queue age in seconds (default 48h) |
| `MAX_MESSAGE_SIZE` | `4096` | Max message body size (bytes) |
| `LONG_POLL_TIMEOUT` | `15` | Long-poll timeout in seconds |
| `MOTD` | `""` | Message of the day |
| `SERVER_NAME` | hostname | Server display name |
| `FEDERATION_KEY` | `""` | Shared key for server linking |

### Storage

SQLite by default (single-file, zero-config), with Postgres support for
larger deployments. Tables:

- `sessions` — user sessions (UUID, nick, created_at)
- `clients` — client records (UUID, session_id, token_hash, last_seen)
- `channels` — channel metadata and modes
- `channel_members` — membership and user modes
- `messages` — message history (rotated per `MAX_HISTORY`)
- `client_queues` — per-client pending delivery queues
- `server_links` — federation peer configuration

### Project Structure

Following [gohttpserver CONVENTIONS.md](https://git.eeqj.de/sneak/gohttpserver/src/branch/main/CONVENTIONS.md):

```
chat/
├── cmd/
│   └── chatd/
│       └── main.go
├── internal/
│   ├── config/
│   ├── database/
│   ├── globals/
│   ├── handlers/
│   ├── healthcheck/
│   ├── logger/
│   ├── middleware/
│   ├── models/
│   ├── queue/
│   └── server/
├── schema/
│   ├── message.schema.json
│   ├── c2s/
│   ├── s2c/
│   ├── s2s/
│   └── README.md
├── web/
├── go.mod
├── go.sum
├── Makefile
├── Dockerfile
├── CONVENTIONS.md
└── README.md
```

### Required Libraries

Per gohttpserver conventions:

| Purpose | Library |
|---------|---------|
| DI | `go.uber.org/fx` |
| Router | `github.com/go-chi/chi` |
| Logging | `log/slog` (stdlib) |
| Config | `github.com/spf13/viper` |
| Env | `github.com/joho/godotenv/autoload` |
| CORS | `github.com/go-chi/cors` |
| Metrics | `github.com/prometheus/client_golang` |
| DB | `modernc.org/sqlite` + `database/sql` |

### Design Principles

1. **API-first** — the HTTP API is the product. Clients are thin. If you can't
   build a working IRC-style TUI client in an afternoon, the API is too complex.
2. **No accounts** — identity is a signing key, nick is a display name. No
   registration, no passwords. Session creation is instant.
3. **IRC semantics over HTTP** — command names and numeric codes from RFC 1459/2812.
   Familiar to anyone who's built IRC clients or bots.
4. **HTTP is the only transport** — no WebSockets, no raw TCP, no protocol
   negotiation. HTTP is universal, proxy-friendly, and works everywhere.
5. **Server holds state** — clients are stateless. Reconnect, switch devices,
   lose connectivity — your messages are waiting in your client queue.
6. **Structured messages** — JSON with extensible metadata. Bodies are always
   objects or arrays for deterministic canonicalization (JCS) and signing.
7. **Immutable messages** — no editing, no deletion. Fits naturally with
   cryptographic signatures.
8. **Simple deployment** — single binary, SQLite default, zero mandatory
   external dependencies.
9. **No eternal logs** — history rotates. Chat should be ephemeral by default.
   Channels disappear when empty.
10. **Federation optional** — single server works standalone. Linking is manual
    and opt-in.
11. **Signable messages** — optional Ed25519 signatures with TOFU key
    distribution. Servers relay signatures without verification.

## Status

**Implementation in progress.** Core API is functional with SQLite storage and
embedded web client.

## License

MIT