Blocks

type Block interface {
	choices.Decidable
 
	// Parent returns the ID of this block's parent.
	Parent() ids.ID
 
	// Verify that the state transition this block would make if accepted is
	// valid. If the state transition is invalid, a non-nil error should be
	// returned.
	//
	// It is guaranteed that the Parent has been successfully verified.
	//
	// If nil is returned, it is guaranteed that either Accept or Reject will be
	// called on this block, unless the VM is shut down.
	Verify(context.Context) error
 
	// Bytes returns the binary representation of this block.
	//
	// This is used for sending blocks to peers. The bytes should be able to be
	// parsed into the same block on another node.
	Bytes() []byte
 
	// Height returns the height of this block in the chain.
	Height() uint64
 
	// Time this block was proposed at. This value should be consistent across
	// all nodes. If this block hasn't been successfully verified, any value can
	// be returned. If this block is the last accepted block, the timestamp must
	// be returned correctly. Otherwise, accepted blocks can return any value.
	Timestamp() time.Time
}

/// Represents a block, specific to [`Vm`](crate::vm::Vm).
#[serde_as]
#[derive(Serialize, Deserialize, Clone, Derivative, Default)]
#[derivative(Debug, PartialEq, Eq)]
pub struct Block {
    /// The block Id of the parent block.
    parent_id: ids::Id,
    /// This block's height.
    /// The height of the genesis block is 0.
    height: u64,
    /// Unix second when this block was proposed.
    timestamp: u64,
    /// Arbitrary data.
    #[serde_as(as = "Hex0xBytes")]
    data: Vec<u8>,
 
    /// Current block status.
    #[serde(skip)]
    status: choices::status::Status,
    /// This block's encoded bytes.
    #[serde(skip)]
    bytes: Vec<u8>,
    /// Generated block Id.
    #[serde(skip)]
    id: ids::Id,
 
    /// Reference to the Vm state manager for blocks.
    #[derivative(Debug = "ignore", PartialEq = "ignore")]
    #[serde(skip)]
    state: state::State,
}

/// Verifies [`Block`](Block) properties (e.g., heights),
/// and once verified, records it to the [`State`](crate::state::State).
/// # Errors
/// Can fail if the parent block can't be retrieved.
pub async fn verify(&mut self) -> io::Result<()> {
    if self.height == 0 && self.parent_id == ids::Id::empty() {
        log::debug!(
            "block {} has an empty parent Id since it's a genesis block -- skipping verify",
            self.id
        );
        self.state.add_verified(&self.clone()).await;
        return Ok(());
    }
 
    // if already exists in database, it means it's already accepted
    // thus no need to verify once more
    if self.state.get_block(&self.id).await.is_ok() {
        log::debug!("block {} already verified", self.id);
        return Ok(());
    }
 
    let prnt_blk = self.state.get_block(&self.parent_id).await?;
 
    // ensure the height of the block is immediately following its parent
    if prnt_blk.height != self.height - 1 {
        return Err(Error::new(
            ErrorKind::InvalidData,
            format!(
                "parent block height {} != current block height {} - 1",
                prnt_blk.height, self.height
            ),
        ));
    }
 
    // ensure block timestamp is after its parent
    if prnt_blk.timestamp > self.timestamp {
        return Err(Error::new(
            ErrorKind::InvalidData,
            format!(
                "parent block timestamp {} > current block timestamp {}",
                prnt_blk.timestamp, self.timestamp
            ),
        ));
    }
 
    let one_hour_from_now = Utc::now() + Duration::hours(1);
    let one_hour_from_now = one_hour_from_now
        .timestamp()
        .try_into()
        .expect("failed to convert timestamp from i64 to u64");
 
    // ensure block timestamp is no more than an hour ahead of this nodes time
    if self.timestamp >= one_hour_from_now {
        return Err(Error::new(
            ErrorKind::InvalidData,
            format!(
                "block timestamp {} is more than 1 hour ahead of local time",
                self.timestamp
            ),
        ));
    }
 
    // add newly verified block to memory
    self.state.add_verified(&self.clone()).await;
    Ok(())
}

/// Mark this [`Block`](Block) rejected and updates [`State`](crate::state::State) accordingly.
/// # Errors
/// Returns an error if the state can't be updated.
pub async fn reject(&mut self) -> io::Result<()> {
    self.set_status(choices::status::Status::Rejected);
 
    // only decided blocks are persistent -- no reorg
    self.state.write_block(&self.clone()).await?;
 
    self.state.remove_verified(&self.id()).await;
    Ok(())
}

/// Mark this [`Block`](Block) accepted and updates [`State`](crate::state::State) accordingly.
/// # Errors
/// Returns an error if the state can't be updated.
pub async fn accept(&mut self) -> io::Result<()> {
    self.set_status(choices::status::Status::Accepted);
 
    // only decided blocks are persistent -- no reorg
    self.state.write_block(&self.clone()).await?;
    self.state.set_last_accepted_block(&self.id()).await?;
 
    self.state.remove_verified(&self.id()).await;
    Ok(())
}