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Freechains: Post / Message / Block

The terms post, message, and block are used interchangeably and they all represent the unit of content in Freechains. An author has a message to disseminate (e.g., a text or file) and creates a post in a chain, which stores it in a block that contains only that message.

A block is a data structure that persists a single message in a chain, linking back to past messages and being linked from future messages:

data Block :
    msg   : String              ; (1)
    sign? :                     ; (2)
        pub : HKey
        sig : String
    core  :                     ; (3)
        time  : Long
        msg   :
            crypt : Boolean
            hash  : Hash
        like? :
            hash : Hash
            n    : Int
        backs : Array<Hash>
    hash  : Hash                ; (4)

The block data structure is composed of four parts:

  1. The actual message to be held in the block.
  2. An optional signature including the public key of the signer (pub) and the actual signature (sig).
  3. The core of the block with all sensitive information about the message (its creation time, if it's encrypted, if it's a like or dislike), and links to previous blocks.
  4. The digest (hash) of the core which univocally identifies the block. The hash of the block takes into account the hash of actual message. The digest is prefixed with the height of the block in the chain, e.g., 5_F700CC98A6BA6A562CF6272AFC1044CB0F049E2E71D1076DA3391E85EE2CE2B8 (block is height 5 with digest F700CC...).

A post has three possible states: BLOCKED, ACCEPTED, or HIDDEN.

If the author has reputation, a new post is immediately ACCEPTED in the chain. Otherwise, it is BLOCKED and requires a like from another user. Blocked posts are not considered part of the chain DAG in the sense that new posts do not link back to it. Peers are not required to hold blocked posts and neither retransmit them to other peers. However, if blocked posts are not disseminated, new users will never have the chance to be welcomed with a like. Currently, Freechains holds at most 15 blocked posts in a temporary bag and retransmit them for some visibility in the network. Once accepted, a post becomes part of the chain and can never be removed again, since Merkle DAGs are immutable by design. However, if the number of dislikes exceeds the number of likes, the block becomes HIDDEN and its payload is not retransmitted to other peers. Note that a block hash depends only on its payload hash, so it is safe to remove the actual payload as long as one can prove its hidden state. Later, if the post receives new likes and changes its state again, it means that the payload is still known somewhere and peers can request it when synchronizing again.