# Protocol Core

- [Protocol Core](#protocol-core)
  - [Transport](#transport)
  - [Entity ID](#entity-id)
  - [BaseMessage](#basemessage)
  - [Errors](#errors)
  - [User devices](#user-devices)
  - [Account registration/login](#account-registrationlogin)
    - [Login into account (by username)](#login-into-account-by-username)

## Transport
For starting we simply use JSON + Websockets.

## Entity ID
* Room alias: `#<roomAlias>@<serverpart>`
* Username: `@<username>@<serverpart>`
* User ID with any 3PID: `%<type>:<data>@<serverpart>`
  * Currently supported only following types: `email` and `msisdn`.
* Raw User ID: `@<UUID>@<serverpart>`
* Message ID: `&<uuid>@<serverpart (from which server the message was sent)>`
* Room ID: `!<roomID>@<serverpart>`
* Single server-part: `<serverpart>`

**Server-part**:
- hostname: `IPv4 / [IPv6] / dns-domain:<port (1-65535)>` (for end-users use)
- server ID: static SHA256 hash string from 4096 characters (for internal protocol use) 

**Username/Room alias/RoomID** - MUST NOT be empty, and MUST contain only the characters `a-z`, `0-9`, `.`, `_`, `=`, `-`, and `/`.

**Special business rules**: 
- RoomID SHOULD be UUID identifier.
- Servers MUST use server ID in internal purposes instead of normal server-part with hostname. Only end-users MUST use normal server-part with hostname. This is done for easy multi-domain serving.

## BaseMessage
BaseMessage is a basic message model, basis of the whole protocol. It is used for a very easy protocol extension process.

BaseMessage scheme:
```typescript
interface BaseMessage {
    /**
     * Message identifier (used to track the request-response chain)
     */
    id: string,

    /**
     * Type of message (used to determine which extension this message belongs to)
     */
    type: string,
    /**
     * From which entity this message is send
     */
    from: EntityID,

    /**
     * Message recipient
     */
    to: EntityID,

    /**
     * Operation success indicator (used to determine if the error happened while processing request)
     */
    ok: boolean,

    /**
     * Message payload (used to store extra information in message, list of permissible fields in the payload depends on "type" field)
     */
    payload: Map<K,V>
}
```

## Errors
Mechanism of error processing included into protocol.
Adds into type name `:error` postfix.

**Payload**:
```typescript
interface ErrorPayload {
    /**
     * Error code (defined in extensions, may be same per extensions)
     */
    errCode: number,

    /**
     * Explanation of error in human-readable view
     */
    errText: string,

    /**
     * Advanced error information (fields defined in extensions)
     */
    errPayload: Map<K,V>
}
```

**Usecase**:  

*Request*:
```json
{
    "id": "abcd",
    "type": "incorrectMessageType",
    "from": "@juliet@cadmium.im",
    "to": "cadmium.im",
    "payload": {
        "test": "test"
    }
}
```

*Response*:
```json
{
    "id": "abcd",
    "type": "incorrectMessageType:error",
    "from": "cadmium.im",
    "to": "@juliet@cadmium.im",
    "payload": {
        "errCode": 0,
        "errText": "Incorrect type of message (type isn't implemented in the server)",
        "errPayload": {}
    }
}
```

## User devices
`todo`

## Account registration/login

### Login into account (by username)
**Description**: Login into user account on a server by username
**Type**: `profile:login`  
**Payload**:
- Request:
```typescript
interface LoginRequestPayload {
    /**
     * The username of account which user wants to login
     */
    username: string,
    
    /**
     * Password of new account
     */
    password: string
}
```
- Response:
```typescript
interface LoginResponsePayload {
    /**
     * Authentication token which required for various user actions (UUID)
     */
    authToken: string,
    
    /**
     * Identifier of new user device (created by this login action)
     */
    deviceID: string
}
```

**Errors**:  
- 0: limit exceed
- 1: user ID/password isn't valid

**Usecase**:

*Request*:
```json
{
    "id": "abcd",
    "type": "profile:login",
    "to": "cadmium.org",
    "payload": {
        "username": "juliet",
        "password": "romeo1"
    }
}
```

*Response*:
```json
{
    "id": "abcd",
    "type": "profile:login",
    "from": "cadmium.org",
    "ok": true,
    "payload": {
        "authToken": "3b5135a5-aff5-4396-a629-a254f383e82f",
        "deviceID": "ABCDEFG"
    }
}
```

*<b>Error</b> response*:
```json
{
    "id": "abcd",
    "type": "profile:login",
    "from": "cadmium.org",
    "ok": false,
    "payload": {
        "errCode": 1,
        "errText": "Username/password isn't valid"
    }
}
```

**Special business rules**: none.