# Farcaster Messages

*Contributors: Paul Fletcher-Hill, Shane da Silva, Varun Srinivasan*

- Why? Helps developers align on how Farcaster Messages should work.
- What? Specifies how farcaster messages should be constructed (the schema), how big they can become(sizes) and other restrictions (validation rules).
- Not: the rules of sets or x-message validation

## Message

- Represent any action taken by a user like making a post, etc etc
- Tamper-proof self authenticating objects signed by an fid
- contain a flexible data body that is defined by the sub type
- signature is usually an eddsa signature, with a few exceptions where messages are signed by ethereum addresses using eth typed signature and explain the signer.
- Messages are constructed using flatbuffers because of performance reasons

table Message {
  data: [ubyte] (nested_flatbuffer: "Farcaster.MessageData", required);
  signature: [ubyte] (required);
  signature_scheme: SignatureScheme = 1;
  signer: [ubyte] (required);
}

enum SignatureScheme: uint8 {
  Ed25519 = 1,
  EthSignTypedData = 2  // should this be called EIP712 instead?
}

- Contains a body and type which is metadata about the body
- Contains 3 other parameters that are common in every message
- Timestamp is the 32-bit epoch timestamp starting on Feb 1, 2021
- Fid is the farcaster id of the username on the appropriate netwokr
- Network defines which network we are operating on

The data object carries the payload of the message. All messages must contain a few common parameters:

- `fid` — fid of the signer of the message
- `network` — id that prevents replaying of messages between testnet and mainnet
- `timestamp` — epoch timestamp in seconds starting from Jan 1, 2021
- `type` — type of farcaster message

The `body` must also be a table that matches the type declared in the `type` enumeration.

table MessageData 
  type: MessageType = 1;
  body: MessageBody (required);
  fid: [ubyte] (required);
  network: FarcasterNetwork = 1;
  timestamp: uint64;
}

union MessageBody {
  CastAddBody,
  CastRemoveBody,
  ReactionBody,
  FollowBody
  // TODO: Signers, Verifications, ... 
}

enum MessageType: uint16 {
  CastAdd = 1,
  CastRemove = 2,
  ReactionAdd = 3,
  ReactionRemove = 4,
  FollowAdd = 5,
  FollowRemove = 6,
  VerificationAddEthAddress = 7,
  VerificationRemove = 8, // 
  SignerAdd = 9,
  SignerRemove = 10,
  UserDataAdd = 11
}

enum FarcasterNetwork: uint8 {
  Mainnet = 1,
  Testnet = 2,
  Devnet = 3
}

### Casts

- Cast is a public broadcast
- Two types of messages, adding and removing

table CastAddBody {
  embeds: [string];
  mentions: [UserID];
  parent: CastID;
  text: string (required);
}

table CastRemoveBody {
  hash: [ubyte] (required);
}

### Reactions

table ReactionBody {
  cast: CastID (required);
  type: ReactionType = 1;
}

enum ReactionType: uint16 {
  Like = 1,
  Recast = 2
}

table FollowBody {
  user: UserID (required);
}

### Helpers

// TODO: should this be fid + timestash + hash ? 
table CastID {
  fid: [ubyte] (required)
  timestampHash: [ubyte] (required);
}

table UserID {
  fid: [ubyte] (required);
}

## Casts

* `embeds` - allows upto two URI strings, each of which can be 256 chars
* `mentions` - upto 5 fids
// 320 character limit with tokens (i.e. $0$) for each mention

table CastAddBody {
  embeds?: URI[]; // Up to 2 URIs (max 256 chars each)
  mentions?: [ubyte][32]; // Up to 5 fids
  parent?: CastID; // <fid>:<hash>
  text: [ubyte][320]; 
}

## Todo

- [ ] Add Recasts back into MessageType and other parts of the spec