beacon block, flatbuffers style

datatypes.fbs

struct Bytes8 {
  v0: ubyte;
  v1: ubyte;
  v2: ubyte;
  v3: ubyte;
  v4: ubyte;
  v5: ubyte;
  v6: ubyte;
  v7: ubyte;
  v8: ubyte;
}

struct Bytes32 {
  v0: Bytes8;
  v1: Bytes8;
  v2: Bytes8;
  v3: Bytes8;
}

struct ValidatorSig {
  a: Bytes32;
  b: Bytes32;
}

struct ValidatorPubKey {
  a: Bytes32;
}

table Eth1Data {
  deposit_root: Bytes32;
  block_hash: Bytes32;
}

table ProposalSignedData {
  slot: uint64;
  shard: uint64;
  block_root: Bytes32;
}

table ProposerSlashing {
  proposer_index: uint64;
  proposal_data_1: ProposalSignedData;
  proposal_signature_1: ValidatorSig;
  proposal_data_2: ProposalSignedData;
  proposal_signature_2: ValidatorSig;
}

struct Crosslink {
  epoch: uint64;
  shard_block_root: Bytes32;
}

struct AttestationData {
  slot: uint64;
  shard: uint64;
  beacon_block_root: Bytes32;
  epoch_boundary_root: Bytes32;
  shard_block_root: Bytes32;
  latest_crosslink: Crosslink;
  justified_epoch: uint64;
  justified_block_root: Bytes32;
}

table SlashableAttestation {
  validator_indices: [uint64];
  data: AttestationData;
  custody_bitfield: [byte];
  aggregate_signature: ValidatorSig;
}

table AttesterSlashing {
  slashable_attestation_1: SlashableAttestation;
  slashable_attestation_2: SlashableAttestation;
}

table Attestation {
  aggregation_bitfield: [byte];
  data: AttestationData;
  custody_bitfield: [byte];
  aggregate_signature: ValidatorSig;
}

struct AttestationDataAndCustodyBit {
  data: AttestationData;
  custody_bit: bool;
}

table Deposit {
  branch: [Bytes32];
  index: uint64;
  deposit_data: DepositData;
}

struct DepositInput {
  pubkey: ValidatorPubKey;
  withdrawal_credentials: Bytes32;
  proof_of_possession: ValidatorSig;
}

struct DepositData {
  amount: uint64;
  timestamp: uint64;
  deposit_input: DepositInput;
}


struct VoluntaryExit {
  epoch: uint64;
  validator_index: uint64;
  signature: ValidatorSig;
}

struct Transfer {
  from_field: uint64;
  to: uint64;
  amount: uint64;
  fee: uint64;
  slot: uint64;
  pubkey: ValidatorPubKey;
  signature: ValidatorSig;
}

table BeaconBlockBody {
  proposer_slashings: [ProposerSlashing];
  attester_slashings: [AttesterSlashing];
  attestations: [Attestation];
  deposits: [Deposit];
  voluntary_exits: [VoluntaryExit];
  transfers: [Transfer];
}

table BeaconBlock {
  slot: uint64;
  parent_root: Bytes32;
  state_root: Bytes32;
  randao_reveal: ValidatorSig;
  eth1_data: Eth1Data;
  signature: ValidatorSig;
  body: BeaconBlockBody;
}

struct Bytes32 {
  v0: ubyte;
  v1: ubyte;
  v2: ubyte;
  v3: ubyte;
}

I guess you meant to say Bytes8 instead of ubyte here.

fixed