Tendermint Socket Protocol (ABCI)

Blockchains are a system for creating shared multi-master application state. ABCI is a socket protocol enabling a blockchain consensus engine, running in one process,

For more information on ABCI, motivations, and tutorials, please visit our blog post.

Other implementations:

• cpp-abci by Martin Dyring-Andersen
• js-abci
• jABCI for Java

Contents

This repository holds a number of important pieces:

• types/types.proto

  • the protobuf file defining ABCI message types, and the optional grpc interface.
    • to build, run make protoc
  • see protoc --help and the grpc docs for examples and details of other languages

• golang implementation of ABCI client and server

  • two implementations:
    • asynchronous, ordered message passing over unix or tcp;
      • messages are serialized using protobuf and length prefixed
    • grpc
  • TendermintCore runs a client, and the application runs a server

• cmd/abci-cli

  • command line tool wrapping the client for probing/testing a ABCI application
  • use abci-cli --version to get the ABCI version

• examples:

  • the cmd/counter application, which illustrates nonce checking in txs
  • the cmd/dummy application, which illustrates a simple key-value merkle tree

Message format

Since this is a streaming protocol, all messages are encoded with a length-prefix followed by the message encoded in Protobuf3. Protobuf3 doesn't have an official length-prefix standard, so we use our own. The first byte represents the length of the big-endian encoded length.

For example, if the Protobuf3 encoded ABCI message is 0xDEADBEEF (4 bytes), the length-prefixed message is 0x0104DEADBEEF. If the Protobuf3 encoded ABCI message is 65535 bytes long, the length-prefixed message would be like 0x02FFFF....

Note this prefixing does not apply for grpc.

Message types

ABCI requests/responses are simple Protobuf messages. Check out the schema file.

DeliverTx

• Arguments:
  • Data ([]byte): The request transaction bytes
• Returns:
  • Code (uint32): Response code
  • Data ([]byte): Result bytes, if any
  • Log (string): Debug or error message
• Usage:
  Append and run a transaction. If the transaction is valid, returns CodeType.OK

CheckTx

• Arguments:

  • Data ([]byte): The request transaction bytes

• Returns:

  • Code (uint32): Response code
  • Data ([]byte): Result bytes, if any
  • Log (string): Debug or error message

• Usage:
  Validate a mempool transaction, prior to broadcasting or proposing. This message should not mutate the main state, but application developers may want to keep a separate CheckTx state that gets reset upon Commit.

  CheckTx can happen interspersed with DeliverTx, but they happen on different connections - CheckTx from the mempool connection, and DeliverTx from the consensus connection. During Commit, the mempool is locked, so you can reset the mempool state to the latest state after running all those delivertxs, and then the mempool will re run whatever txs it has against that latest mempool stte

  Transactions are first run through CheckTx before broadcast to peers in the mempool layer. You can make CheckTx semi-stateful and clear the state upon Commit or BeginBlock, to allow for dependent sequences of transactions in the same block.

Commit

• Returns:
  • Data ([]byte): The Merkle root hash
  • Log (string): Debug or error message
• Usage:
  Return a Merkle root hash of the application state.

Query

• Arguments:
  • Data ([]byte): The query request bytes
• Returns:
  • Code (uint32): Response code
  • Data ([]byte): The query response bytes
  • Log (string): Debug or error message

Proof

• Arguments:
  • Key ([]byte): The key whose data you want to verifiably query
  • Height (int64): The block height for which you want the proof (default=0 returns the proof for last committed block)
• Returns:
  • Code (uint32): Response code
  • Data ([]byte): The query response bytes
  • Log (string): Debug or error message
• Usage:
  Return a Merkle proof from the key/value pair back to the application hash.
  Please note The current implementation of go-merkle doesn't support querying proofs from past blocks, so for the present moment, any height other than 0 will return an error. Hopefully this will be improved soon(ish)

Flush

• Usage:
  Flush the response queue. Applications that implement types.Application need not implement this message -- it's handled by the project.

Info

• Returns:
  • Data ([]byte): The info bytes
• Usage:
  Return information about the application state. Application specific.

SetOption

• Arguments:
  • Key (string): Key to set
  • Value (string): Value to set for key
• Returns:
  • Log (string): Debug or error message
• Usage:
  Set application options. E.g. Key="mode", Value="mempool" for a mempool connection, or Key="mode", Value="consensus" for a consensus connection. Other options are application specific.

InitChain

• Arguments:
  • Validators ([]Validator): Initial genesis validators
• Usage:
  Called once upon genesis

BeginBlock

• Arguments:
  • Height (uint64): The block height that is starting
• Usage:
  Signals the beginning of a new block. Called prior to any DeliverTxs.

EndBlock

• Arguments:
  • Height (uint64): The block height that ended
• Returns:
  • Validators ([]Validator): Changed validators with new voting powers (0 to remove)
• Usage:
  Signals the end of a block. Called prior to each Commit after all transactions

Changelog

Mar 26h, 2016

• Introduce BeginBlock

Mar 6th, 2016

• Added InitChain, EndBlock

Feb 14th, 2016

• s/GetHash/Commit/g
• Document Protobuf request/response fields

Jan 23th, 2016

• Added CheckTx/Query ABCI message types
• Added Result/Log fields to DeliverTx/CheckTx/SetOption
• Removed Listener messages
• Removed Code from ResponseSetOption and ResponseGetHash
• Made examples BigEndian

Jan 12th, 2016

• Added "RetCodeBadNonce = 0x06" return code

Jan 8th, 2016

• Tendermint/ABCI now comes to consensus on the order first before DeliverTx.