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Develop for Poly Chain

1. Requirements

Before developing for Poly chain, you have to be prepared with the listed three prerequisites.

1.1 Light client verification

The block header must contain the following information：

  • Hash of the previous block header
  • Merkle state root hash
  • Necessary information to prove the legitimacy of the block header varies from different consensus mechanisms.

[!Note|style:flat|label:Notice] If your chain doesn't support techniques like Simple Payment Verification (SPV) protocol in Bitcoin or Light Ethereum Subprotocol (LES) in Ethereum, get in touch with Poly team via for more support.

1.2 Block header structure and verification methods

The following information is necessary：

  • Block header structure
  • Serialization and Deserialization methods
  • Block header verification methods

1.3 Verifiable state root

The following information is necessary：

  • Merkle tree structure
  • State root verification methods

2. Development Specifications

With the prerequisites mentioned earlier, you can start developing methods for Poly chain following the guideline below from the perspective you need.

2.1 Synchronize block headers

Block Header Synchronization Methods

Method Description
SyncGenesisHeader It stores and handles the initial block header so that the subsequent block headers of blocks that contain cross-chain events can be verified and synchronized. This method will only be called for once in initializing the new chain. Please refer to the code for more details.
SyncBlockHeader It consistently synchronizes block cycle change and cross-chain transaction block headers from the new chain to the Poly chain. Please refer to the code for more details.

Block Header Synchronization Entrance Method

Method Description
SyncSideChainGenesisHeader It is the entrance method for synchronizing the genesis block header of the new chain to Poly chain and synchronizing the genesis header of Poly chain to CCM contract of the new chain. Please refer to the code for more details.

The key information for this method (submitted by .config):

  • Service provider (endpoint) Url of the new chain.
  • Genesis block height (Normally the latest.
  • Essential information for verifying genesis headers may exist in header information already or need to be fetched from block headers from other block heights.
  • Information required for the new chain block header verification.

2.2 Verify cross-chain transactions

Cross Chain Management

Method Description
MakeDepositProposal It acts as the entrance of verifyFromTx, verifying, storing, and returning MakeTxParam for processing cross-chain steps, verifies cross-chain transactions, and stores legitimate transactions to the Poly chain. Please refer to the code for more details. 
MakeDepositProposal:
Requires:
service *native.NativeService   //Native Service that carries values of information of cross-chain events
Returns:
type verifyFromTx struct {
	TxHash              []byte    
	CrossChainId        []byte    //ChainId of source chain
	FromContractAddress uint64    //Cross Chain Management Contarct address of source chain
	ToChainId           string    //ChainId of target chain
	ToContractAddress   uint64    //Cross Chain Management Contarct address of target chain
	Method              []byte    //Unlock or lock
	Args                []byte
}
Method Description
verifyFromTx It prepares block header and deserialized proof for verifyMerkleProof, decodes the extra data from tx, and constructs MakeTxParam. Please refer to the code for more details. 
verifyFromTx:
Requires:
service               *native.NativeService  
proof                 []byte    //the proof to be serialized and verified
extra                 []byte    //the transaction information that will be used for constructing verifyFromTx
fromChainID           uint64,   //ChainId of source chain
height                uint32,   //the block height corresponding to current transaction event
sideChain             *side_chain_manager.SideChain //source chain information that contains ccm contract address
Returns:
txParam               *scom.MakeTxParam
Method Description
verifyMerkleProof It verifies the Merkle proof obtained by the relayer generated from the source chain to ensure that all transactions included in this block header have been created and can be seen on the Poly chain. Please refer to the code for details. 
verifyMerkleProof:
Requires:
blockData             *types.Header //the blockheader corresponding to current transaction event  
proof                 []byte    //the serialized proof
Returns:
Val                   []byte    //the proof result for checking extra before constructing verifyFromTx