tendermint/docs/archived.wiki/Block-Structure.md

NOTE: this wiki is mostly deprecated and left for archival purposes. Please see the documentation website which is built from the docs directory. Additional information about the specification can also be found in that directory.

Block

A Block is composed of:

• Header: basic information about the chain and last state
• Data: transactions and other data
• LastCommit: +2/3 precommit signatures for the previous block

Header

The block Header is composed of:

• ChainId (string): name of the blockchain, e.g. "tendermint"
• Height (int): sequential block number starting with 1
• Time (time): local time of the proposer who proposed this block
• LastBlockHash ([]byte): block hash of the previous block at height Height-1
• LastBlockParts (PartSetHeader): partset header of the previous block
• StateHash ([]byte): state hash of the state after processing this block

Data

The block Data is composed of:

• Txs ([]Tx): a list of transactions

Commit

The block Commit is composed of:

• Precommits ([]Vote): a list of precommit votes

Vote

A Vote is composed of:

• Height (int): The block height being decided on
• Round (int): The consensus round number, starting with 0
• Type (byte): The type of vote, either a prevote or a precommit
• BlockHash ([]byte): The block hash of a valid block, or nil
• BlockParts (PartSetHeader): The corresponding partset header, or x0000 if the block hash is nil
• Signature (Signature): The signature of this Vote's sign-bytes

Vote Sign Bytes

The sign-bytes of a transaction is produced by taking a stable-json-like deterministic JSON wire encoding of the vote (excluding the Signature field), and wrapping it with {"chain_id":"tendermint","vote":...}.

For example, a precommit vote might have the following sign-bytes:

{"chain_id":"tendermint","vote":{"block_hash":"611801F57B4CE378DF1A3FFF1216656E89209A99","block_parts_header":{"hash":"B46697379DBE0774CC2C3B656083F07CA7E0F9CE","total":123},"height":1234,"round":1,"type":2}}

Block Hash

The block hash is the Simple Tree hash of the fields of the block Header encoded as a list of KVPairs.

State Hash

The state hash is the Simple Tree hash of the state's fields (e.g. BondedValidators, UnbondingValidators, Accounts, ValidatorInfos, and NameRegistry) encoded as a list of KVPairs. This state hash is recursively included in the block Header and thus the block hash indirectly.

Transaction

A transaction is any sequence of bytes. It is up to your TMSP application to accept or reject transactions.

PartSet

PartSet is used to split a byteslice of data into parts (pieces) for transmission. By splitting data into smaller parts and computing a Merkle root hash on the list, you can verify that a part is legitimately part of the complete data, and the part can be forwarded to other peers before all the parts are known. In short, it's a fast way to propagate a large file over a gossip network.

PartSet was inspired by the LibSwift project.

Usage:

data := RandBytes(2 << 20) // Something large

partSet := NewPartSetFromData(data)
partSet.Total()     // Total number of 4KB parts
partSet.Count()     // Equal to the Total, since we already have all the parts
partSet.Hash()      // The Merkle root hash
partSet.BitArray()  // A BitArray of partSet.Total() 1's

header := partSet.Header() // Send this to the peer
header.Total        // Total number of parts
header.Hash         // The merkle root hash

// Now we'll reconstruct the data from the parts
partSet2 := NewPartSetFromHeader(header)
partSet2.Total()    // Same total as partSet.Total()
partSet2.Count()    // Zero, since this PartSet doesn't have any parts yet.
partSet2.Hash()     // Same hash as in partSet.Hash()
partSet2.BitArray() // A BitArray of partSet.Total() 0's

// In a gossip network the parts would arrive in arbitrary order, perhaps
// in response to explicit requests for parts, or optimistically in response
// to the receiving peer's partSet.BitArray().
for !partSet2.IsComplete() {
    part := receivePartFromGossipNetwork()
    added, err := partSet2.AddPart(part)
    if err != nil {
		// A wrong part,
        // the merkle trail does not hash to partSet2.Hash()
    } else if !added {
        // A duplicate part already received
    }
}

data2, _ := ioutil.ReadAll(partSet2.GetReader())
bytes.Equal(data, data2) // true