ACS4 - Consensus Standard

ACS4 is used to customize consensus mechanisms.


If you want to customize the consensus mechanism, you need to implement the following five interfaces:

  • GetConsensusCommand, whose parameter is a binary array, returns ConsensusCommand defined in acs4.proto. This type is used to indicate the start time of the next block, the block time limit, and the final cut-off time for the account calling GetConsensus Command;
  • GetConsensusExtraData, the parameters and return values are binary arrays, which are used to generate consensus block header information through consensus contracts when a new block is produced;
  • GenerateConsensusTransactions, the parameter is a binary array, and the return value is of type TransactionList. It is used to generate a consensus system transaction when a block is generated. Each block will contain only one consensus transaction, which is used to write the latest consensus information to the State database;
  • ValidateConsensusBeforeExecution, the parameter is a binary array, and the return value is of type ValidationResult, is used to verify whether the consensus information in the block header is correct before the block executes;
  • ValidateConsensusAfterExecution, with the same parameter and return value, is used to verify that the consensus information written to the State is correct after the block executes.

ConsensusCommand, ValidationResult and TransactionList are defined as:

message ConsensusCommand {
    int32 limit_milliseconds_of_mining_block = 1;// Time limit of mining next block.
    bytes hint = 2;// Context of Hint is diverse according to the consensus protocol we choose, so we use bytes.
    google.protobuf.Timestamp arranged_mining_time = 3;
    google.protobuf.Timestamp mining_due_time = 4;
message ValidationResult {
    bool success = 1;
    string message = 2;
    bool is_re_trigger = 3;
message TransactionList {
    repeated aelf.Transaction transactions = 1;


The five interfaces defined in ACS4 basically correspond to the five methods of the IConsensusService interface in the AElf.Kernel.Consensus project:

ACS4 IConsensusService Methodology The Timing To Call

Task TriggerConsensusAsync

(ChainContext chainContext);

When TriggerConsensusAsync is called,

it will use the account configured by

the node to call the GetConsensusCommand

method of the consensus contract

to obtain block information

ConsensusCommand), and use it to

(see IConsensusScheduler implementation)


  1. When the node is started;
  2. When the BestChainFound-

EventData event is thrown;

  1. When the validation of consensus

data fails and the consensus needs

to be triggered again (The

IsReTrigger field of the

ValidationResult type is true);



Task<byte[]> GetConsensus



When a node produces a block, it will

generate block header information for

the new block by IBlockExtraDataService.

This service is implemented to traverse

all IBlockExtraDataProvider

implementations, and they generate

binary array information into the

ExtraData field of BlockHeader. The

consensus block header information is

provided by ConsensusExtraDataProvider,

in which the GetConsensusExtraDataAsync

of the IConsensusService in the

consensus contract is called, and the

GetConsensusExtraDataAsync method is

implemented by calling the

GetConsensusExtraData in the consensus


At the time that the node produces

a new block.






ChainContext chainContext);

In the process of generating new blocks,

a consensus transaction needs to be

generated as one of the system

transactions. The basic principle is the

same as GetConsensusExtraData.

At the time that the node produces

a new block.



Task<bool> ValidateConsensus


chainContext, byte[]


As long as the IBlockValidationProvider

interface is implemented, a new block

validator can be added. The consensus

validator is ConsensusValidationProvider

, where ValidateBlockBeforeExecuteAsync

is implemented by calling the

ValidateConsensusBeforeExecution method

of the consensus contract.

At the time that the node produces

a new block.



Task<bool> ValidateConsensus


( ChainContext chainContext,

byte[] consensusExtraData);

The implementation of

ValidateBlockAfterExecuteAsync in

ConsensusValidationProvider is to call

the ValidateConsensusAfterExecution

in the consensus contract.

At the time that the node produces

a new block.


You can refer to the implementation of the AEDPoS contract.