bmc.md

BTP Message Center(BMC)

Introduction

BTP Message Center is a smart contract which builds BTP Message and sends it to BTP Message Relay and handles Relay Message from the other.

Setup

1. Register BSHs for the services. BTP Token Service (BTS) is a BSH connected to BMC. (BSH should be deployed before the registration)
2. Add links, BMCs of directly connected blockchains
3. Add routes to other BMCs of in-directly connected blockchains

BMC Interfaces

The BMC contract has to implement the following methods.

• sendMessage
• handleRelayMessage

The BMC contract has to implement the following events.

• Message event

sendMessage

• Method

  • sendMessage

• Params

  Name	Type	Description
  _to	String	Network Address of the destination blockchain
  _svc	String	Name of the service.
  _sn	Integer	Serial number of the message.
  _msg	Bytes	Service message to be delivered.

• Description

  A service handler sends a message through BMC.sendMessage. It accepts the requests from the registered BTP Service Handler(BSH). If service name of those requests is different from registration, then they will be rejected.

  Then it builds a BTP Message from the request.

  1. Decide destination BMC from given Network Address
  2. Fill in other information from parameters.
  3. Serialize them for sending.

  Then it tries to send the BTP Message.

  1. Decide next BMC from the destination referring routing information.
  2. Get sequence number corresponding to the next.
  3. Emit the event, Message including the information.

  The event will be monitored by the Relay, it will build Relay Message for next BMC of destination chain.

• Implementation

  1. Java
  2. Solidity

handleRelayMessage

• Method

  • handleRelayMessage

• Params

  Name	Type	Description
  _prev	String	BTP Address of the previous BMC
  _msg	Bytes	serialized Relay Message including BTP Messages

• Description

  This method receives the Relay Message from the relay, then it tries to decode it. It may contain multiple BTP Messages. It dispatches received BTP Messages one-by-one in the sequence.

  If it is the destination, then it tries to find the BSH for the service, and then calls BSH.handleBTPMessage. It calls BSH.handleBTPError if it's an error.

  If it's not the destination, then it tries to send the message to the next route.

  If it fails, then it replies an error.

• Implementation

  1. Java
  2. Solidity

Message

• Event

  • Message

• Params

  Name	Type	Description
  _next	String	BTP Address of the next BMC
  _seq	Integer	Sequence number of the msg to the next BMC
  _msg	Bytes	Serialized BTP Message

• Description

  The sendMessage method in BMC Contract generates a Message eventlog for the relay to pick up and perform transaction based on this event on the destination chain.

• Implementation

  1. Java
  2. Solidity