Fabric-Batch-Chaincode

Fabric-Batch-Chaincode (FBC) is a library that enables batch transactions in chaincode without additional trusted systems.

Overview

In FBC, one unit of processing is called Msg, and it provides SubmitMsg function to submit it to the ledger, and Commit function to execute the submitted Msgs.

Each function performs the following operations:

• SubmitMsg(msg: Msg, current_time: int64)

  • SubmitMsg is a function that takes a Msg and timestamp current_time arguments
  • The validity of current_time is explained in Validation for Current Time.
  • Validate that there is no commit after current_time.
  • Msg is stored in association with a key that contains current_time as prefix.

• Commit(commit_time: int64)

  • Commit is a function that takes a timestamp commit_time argument.
  • The commit_time should be less than the "Current Time Window" described later.
  • Get Msgs between the last committed time and commit_time.
  • Execute these Msgs, and save a commit log with commit_time as key prefix.

It also keeps the following states:

• last committed time: "lct" => {timestamp}
• msg: "msg/{timestamp}{TxID}"
• commit log: "commit/{timestamp}"

Validation for Current Time

In fabric, no timestamp indicates the current time that is agreed between peers. Of course, it can get a current time in the chaincode, but this is based on the local clock and will be a different value for each peer.

FBC defines "Current Time" as a range defined by a parameter TimeGapAllowance based on the local clock of endorser peers.

Correctness

FBC satisfies the following three properties:

(1) All Msgs will eventually be submitted

• Insert Msg with current_time as key prefix in SubmitMsg
• Commit can only be performed at a time older than Current Time

The above points guarantee that a Msg will eventually be submitted if a submitter can get a valid current time.

(2) There is no commit log newer than the time of the uncommitted Msg

• Verify that there is no commit log newer than the current time with GetStateByRange(current_time, ∞)

This will recheck for the existence of the commit logs during the validation phase, and if there is a commit log with a time newer than current_time, the tx that contains the SubmitMsg will fail. Therefore, (2) is guaranteed.

(3) All submitted Msgs will eventually be committed

• commit_time is always newer than previous commit_time
• Timestamp of a Msg to be committed is within the range between the previous time and commit_time.

The above points and (2) guarantees (3) under the assumption that an actor performs Commit.

TODO

• Implement ChaincodeStubInterface for BatchState
• Design for Msg authentication
• Enhance integration with fabric-contract-api-go
  • It should be possible to integrate it into an existing chaincode implementation with a few modifications

Maintainers

• Jun Kimura