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Consensus Protocol

Consensus Message Format

P2P message format

SizeFieldTypeDescription
4MagicuintProtocol ID, defined in the configuration file protocol.json , mainnet is 7630401 , testnet is 1953787457
12CommandstringCommand, all consensus messages' command is consensus
4Lengthuint32Length of payload
4ChecksumuintChecksum
LengthPayloadbyte[]Content of message, all consensus messages' payload is ConsensusPayload

ConsensusPayload

SizeFieldTypeDescription
4VersionuintVersion of protocol, 0 for now
32PrevHashUInt256Previous block's hash
4BlockIndexuintHeight of the block
2ValidatorIndexushortThe index of the current consensus node in validators array
4TimestampuintTimestamp
?Databyte[]Includes ChangeView , PrepareRequest and PrepareResponse
1-uint8It's fixed to 1
?WitnessWitnessWitness contains invocation script and verificatioin script

ChangeView

SizeFieldTypeDescription
1TypeConsensusMessageType 0x00
1ViewNumberbyteCurrent view number
1NewViewNumberbyteNew view number

PrepareRequest

SizeFieldTypeDescription
1TypeConsensusMessageType 0x20
1ViewNumberbyteCurrent view number
8Nonceulongblock nonce
20NextConsensusUInt160The script hash of the next round consensus nodes' multi-signature contract
4 + 32 * lengthTransactionHashesUInt256[]The proposal block's transaction hashes
78MinerTransactionMinerTransactionIt is used to sum all the transaction fees of the current block as a reward for the speaker.
64Signaturebyte[]Block signature

PrepareResponse

SizeFieldTypeDescription
1TypeConsensusMessageType 0x21
1ViewNumberbyteCurrent view number
64Signaturebyte[]Block signature

Transport Protocol

When a consensus message enters the P2P network, it's broadcasted and transmitted like other messages. That is because consensus nodes do not have IP address of other consensus nodes. Consensus nodes are not directly connected. That is to say, ordinary nodes can also receive consensus message. The broadcast flow of consensus messages is as follows.

consensus_msg_seq

  1. Consensus node A will directly broadcast 'consensus' message to connected nodes(e.g. node B).

  2. After receiving the consensus message, node B firstly process the received consensus message and then forwards it. Before forwarding the consensus message, it sends an inv message which carries the hash data of the payload of the consensus message (to node C).

  3. If the node C has already known the data corresponding to the hash, it does not process the inv message. Otherwise, it proceeds to step 4.

  4. Node C sends a getdata message to node B, with the hash data in the inv message.

  5. After receiving the getdata message, node B sends a consensus message to node C.

  6. After receiving the consensus message, the node C triggers the consensus module to process the message, and forwards the consensus message, and then returns to step 2.

inv message format

SizeFieldTypeDescription
4MagicuintProtocol ID
12Commandstring inv
4Lengthuint32Length of payload
4ChecksumuintChecksum
LengthPayloadbyte[]Format: 0xe0 + 0x00000001 + ConsensusPayload.Hash

Payload's format: inv.type + inv.payloads.length + inv.payload inv message's payload has three types listed as follow:

  • 0x01 : Transaction. inv.payload is assigned to transaction's hash.

  • 0x02 : Block. inv.payload is assigned to ConsensusPayload message's hash.

  • 0xe0 : Consensus. inv.payload is assigned to block's hash.

getdata message format

SizeFieldTypeDescription
4MagicuintProtocol ID
12Commandstring getdata
4Lengthuint32Length of payload
4ChecksumuintChecksum
LengthPayloadbyte[]Format: 0xe0 + 0x00000001 + ConsensusPayload.Hash

The getdata message is mainly used to get the specific content in inv message.

Consensus Message Process

Verification

  1. Ignore the message if the ConsensusPayload.BlockIndex is lower than current block height.

  2. Ignore the message if the verification script failed or the script hash does not equal to ConsensusPayload.ValidatorIndex address's script hash.

  3. Ignore the message if the ConsensusPayload.ValidatorIndex equals to current node index.

  4. Ignore the message if the ConsensusPayload.Version does not equal to current consensus version.

  5. Ignore the message if the ConsensusPayload.PrevHash and ConsensusPayload.BlockIndex do not equal to the values in current node's context.

  6. Ignore the message if the ConsensusPayload.ValidatorIndex is out of index of the current consensus nodes array.

  7. Ignore the message if the ConsensusMessage.ViewNumber does not equal to the value in current node's context except that the consensus message is a ChangeView .

Process

  1. On receiving aPrepareRequestsent by speaker, attached with proposal block data.

    1. Ignore if the PrepareRequest has already been received.

    2. Ignore if the ConsensusPayload.ValidatorIndex is not the index of the current round speaker.

    3. Ignore if the ConsensusPayload.Timestamp is not more than the timestamp of the previous block, or is more than 10 minutes above current time.

    4. Ignore if the signature of the message is incorrect.

    5. Clear signatures saved in the context that does not match the received proposal message.

    6. Save the signature of the speaker into current context.

    7. Collect and verify transactions in the proposal block from memory pool.

    8. If the transaction failed to pass verification or policy check provided by plugin, it will stop the process and request ChangeView.

    9. Otherwise the transaction will be saved into current context.

    10. If all the transactions in the proposal block are collected, broadcast PrepareResponse message.

    11. Collect and verify transactions in the proposal block from unverified memory pool.

    12. Verify the MinerTransaction and add it into current context.

    13. If all transactions are collected verified, it will request PrepareResponse. Otherwise it will broadcast a getdata message to retrieve transactions from other nodes.

  2. On receiving aPrepareResponsesent by consensus nodes with their signture.

    1. Ignore it if current node has already saved the sender's signature.

    2. Save it temporarily if current node does not have information of corresponding PrepareRequest of the received PrepareResponse yet.

    3. Otherwise verify the signature. Save the signature if it pass the verification. Ignore it if not.

    4. If there are at least N-f signatures, accept the new block and broadcast it.

  3. On receiving aChangeviewsent by consensus nodes.

    1. Ignore it if the view number in the message is less than the view number in current context.

    2. If current node received at least N-f ChangeView messages with the same new view number, then ViewChange will happen. The current node reset the consensus process with the new view number.

  4. OnTimeouthappens

    1. If the process above timeout, the consensus node will broadcast ChangeView message directly.

    2. Timeout time starts from 30 seconds. Timeout interval doubles when each timeout happens.

  5. On receiving aNew Block

    1. resetting consensus process

  6. On receiving aNew Transactionfor consensus

    1. Ignore if the transaction is a MinerTransaction . (A MinerTransaction should not be broadcasted).

    2. Ignore if current node is speaker, or the node has sent PrepareRequest or PrepareResponse message, or in process of change view.

    3. Ignore if the transaction has been received before.

    4. Ignore if the received transacion isn't in the propoal block.

    5. Save the transaction into current context.