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docs & spec: deduplicate block-structure.md (#2331)

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Zach 2018-09-05 12:21:04 -04:00 committed by Ethan Buchman
parent eb5cf0f0dd
commit 7f6bd5c161
4 changed files with 43 additions and 220 deletions
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62
docs/spec/blockchain/blockchain.md
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@ -27,6 +27,13 @@ type Block struct {
}
```
The signatures returned along with block `X` are those validating block
`X-1`. This can be a little confusing, but consider that
the `Header` also contains the `LastCommitHash`. It would be impossible
for a Header to include the commits that sign it, as it would cause an
infinite loop here. But when we get block `X`, we find
`Header.LastCommitHash`, which must match the hash of `LastCommit`.
## Header
A block header contains metadata about the block and about the consensus, as well as commitments to
@ -34,32 +41,30 @@ the data in the current block, the previous block, and the results returned by t
```go
type Header struct {
// block metadata
Version string // Version string
ChainID string // ID of the chain
Height int64 // Current block height
Time int64 // UNIX time, in millisconds
// basic block info
ChainID string `json:"chain_id"`
Height int64 `json:"height"`
Time time.Time `json:"time"`
NumTxs int64 `json:"num_txs"`
TotalTxs int64 `json:"total_txs"`
// current block
NumTxs int64 // Number of txs in this block
TxHash []byte // SimpleMerkle of the block.Txs
LastCommitHash []byte // SimpleMerkle of the block.LastCommit
// prev block info
LastBlockID BlockID `json:"last_block_id"`
// previous block
TotalTxs int64 // prevBlock.TotalTxs + block.NumTxs
LastBlockID BlockID // BlockID of prevBlock
// hashes of block data
LastCommitHash cmn.HexBytes `json:"last_commit_hash"` // commit from validators from the last block
DataHash cmn.HexBytes `json:"data_hash"` // transactions
// application
ResultsHash []byte // SimpleMerkle of []abci.Result from prevBlock
AppHash []byte // Arbitrary state digest
ValidatorsHash []byte // SimpleMerkle of the current ValidatorSet
NextValidatorsHash []byte // SimpleMerkle of the next ValidatorSet
ConsensusParamsHash []byte // SimpleMerkle of the ConsensusParams
// hashes from the app output from the prev block
ValidatorsHash cmn.HexBytes `json:"validators_hash"` // validators for the current block
NextValidatorsHash cmn.HexBytes `json:"next_validators_hash"` // validators for the next block
ConsensusHash cmn.HexBytes `json:"consensus_hash"` // consensus params for current block
AppHash cmn.HexBytes `json:"app_hash"` // state after txs from the previous block
LastResultsHash cmn.HexBytes `json:"last_results_hash"` // root hash of all results from the txs from the previous block
// consensus
EvidenceHash []byte // SimpleMerkle of []Evidence
ProposerAddress []byte // Address of the original proposer of the block
}
// consensus info
EvidenceHash cmn.HexBytes `json:"evidence_hash"` // evidence included in the block
ProposerAddress Address `json:"proposer_address"` // original proposer of the block
```
Further details on each of these fields is described below.
@ -224,6 +229,17 @@ These are the votes that committed the previous block.
The first block has `block.Header.LastCommitHash == []byte{}`
### DataHash
The `DataHash` can provide a nice check on the
[Data](https://godoc.org/github.com/tendermint/tendermint/types#Data)
returned in this same block. If you are subscribed to new blocks, via
tendermint RPC, in order to display or process the new transactions you
should at least validate that the `DataHash` is valid. If it is
important to verify autheniticity, you must wait for the `LastCommit`
from the next block to make sure the block header (including `DataHash`)
was properly signed.
### TotalTxs
```go
@ -270,7 +286,7 @@ The first block has `block.Header.ResultsHash == []byte{}`.
block.AppHash == state.AppHash
```
Arbitrary byte array returned by the application after executing and commiting the previous block.
Arbitrary byte array returned by the application after executing and commiting the previous block. It serves as the basis for validating any merkle proofs that comes from the ABCI application and represents the state of the actual application rather than the state of the blockchain itself.
The first block has `block.Header.AppHash == []byte{}`.

2
docs/spec/consensus/consensus.md
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@ -17,7 +17,7 @@
vote](https://godoc.org/github.com/tendermint/tendermint/types#FirstPrecommit)
for something.
- A vote _at_ `(H,R)` is a vote signed with the bytes for `H` and `R`
included in its [sign-bytes](block-structure.html#vote-sign-bytes).
included in its [sign-bytes](../blockchain/blockchain.md).
- _+2/3_ is short for "more than 2/3"
- _1/3+_ is short for "1/3 or more"
- A set of +2/3 of prevotes for a particular block or `<nil>` at

198
docs/tendermint-core/block-structure.md
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@ -7,200 +7,6 @@ nodes. This blockchain is accessible via various rpc endpoints, mainly
`/blockchain?minHeight=_&maxHeight=_` to get a list of headers. But what
exactly is stored in these blocks?
## Block
The [specification](../spec/blockchain/blockchain.md) contains a detailed description of each component - that's the best place to get started.
A
[Block](https://godoc.org/github.com/tendermint/tendermint/types#Block)
contains:
- a [Header](#header) contains merkle hashes for various chain states
- the
[Data](https://godoc.org/github.com/tendermint/tendermint/types#Data)
is all transactions which are to be processed
- the [LastCommit](#commit) &gt; 2/3 signatures for the last block
The signatures returned along with block `H` are those validating block
`H-1`. This can be a little confusing, but we must also consider that
the `Header` also contains the `LastCommitHash`. It would be impossible
for a Header to include the commits that sign it, as it would cause an
infinite loop here. But when we get block `H`, we find
`Header.LastCommitHash`, which must match the hash of `LastCommit`.
## Header
The
[Header](https://godoc.org/github.com/tendermint/tendermint/types#Header)
contains lots of information (follow link for up-to-date info). Notably,
it maintains the `Height`, the `LastBlockID` (to make it a chain), and
hashes of the data, the app state, and the validator set. This is
important as the only item that is signed by the validators is the
`Header`, and all other data must be validated against one of the merkle
hashes in the `Header`.
The `DataHash` can provide a nice check on the
[Data](https://godoc.org/github.com/tendermint/tendermint/types#Data)
returned in this same block. If you are subscribed to new blocks, via
tendermint RPC, in order to display or process the new transactions you
should at least validate that the `DataHash` is valid. If it is
important to verify autheniticity, you must wait for the `LastCommit`
from the next block to make sure the block header (including `DataHash`)
was properly signed.
The `ValidatorHash` contains a hash of the current
[Validators](https://godoc.org/github.com/tendermint/tendermint/types#Validator).
Tracking all changes in the validator set is complex, but a client can
quickly compare this hash with the [hash of the currently known
validators](https://godoc.org/github.com/tendermint/tendermint/types#ValidatorSet.Hash)
to see if there have been changes.
The `AppHash` serves as the basis for validating any merkle proofs that
come from the ABCI application. It represents the state of the actual
application, rather that the state of the blockchain itself. This means
it's necessary in order to perform any business logic, such as verifying
an account balance.
**Note** After the transactions are committed to a block, they still
need to be processed in a separate step, which happens between the
blocks. If you find a given transaction in the block at height `H`, the
effects of running that transaction will be first visible in the
`AppHash` from the block header at height `H+1`.
Like the `LastCommit` issue, this is a requirement of the immutability
of the block chain, as the application only applies transactions _after_
they are commited to the chain.
## Commit
The
[Commit](https://godoc.org/github.com/tendermint/tendermint/types#Commit)
contains a set of
[Votes](https://godoc.org/github.com/tendermint/tendermint/types#Vote)
that were made by the validator set to reach consensus on this block.
This is the key to the security in any PoS system, and actually no data
that cannot be traced back to a block header with a valid set of Votes
can be trusted. Thus, getting the Commit data and verifying the votes is
extremely important.
As mentioned above, in order to find the `precommit votes` for block
header `H`, we need to query block `H+1`. Then we need to check the
votes, make sure they really are for that block, and properly formatted.
Much of this code is implemented in Go in the
[light-client](https://github.com/tendermint/light-client) package. If
you look at the code, you will notice that we need to provide the
`chainID` of the blockchain in order to properly calculate the votes.
This is to protect anyone from swapping votes between chains to fake (or
frame) a validator. Also note that this `chainID` is in the
`genesis.json` from _Tendermint_, not the `genesis.json` from the
basecoin app ([that is a different
chainID...](https://github.com/cosmos/cosmos-sdk/issues/32)).
Once we have those votes, and we calculated the proper [sign
bytes](https://godoc.org/github.com/tendermint/tendermint/types#Vote.WriteSignBytes)
using the chainID and a [nice helper
function](https://godoc.org/github.com/tendermint/tendermint/types#SignBytes),
we can verify them. The light client is responsible for maintaining a
set of validators that we trust. Each vote only stores the validators
`Address`, as well as the `Signature`. Assuming we have a local copy of
the trusted validator set, we can look up the `Public Key` of the
validator given its `Address`, then verify that the `Signature` matches
the `SignBytes` and `Public Key`. Then we sum up the total voting power
of all validators, whose votes fulfilled all these stringent
requirements. If the total number of voting power for a single block is
greater than 2/3 of all voting power, then we can finally trust the
block header, the AppHash, and the proof we got from the ABCI
application.
### Vote Sign Bytes
The `sign-bytes` of a vote is produced by taking a
[stable-json](https://github.com/substack/json-stable-stringify)-like
deterministic JSON [wire](./wire-protocol.html) encoding of the vote
(excluding the `Signature` field), and wrapping it with
`{"chain_id":"my_chain","vote":...}`.
For example, a precommit vote might have the following `sign-bytes`:
```
{"chain_id":"my_chain","vote":{"block_hash":"611801F57B4CE378DF1A3FFF1216656E89209A99","block_parts_header":{"hash":"B46697379DBE0774CC2C3B656083F07CA7E0F9CE","total":123},"height":1234,"round":1,"type":2}}
```
## Block Hash
The [block
hash](https://godoc.org/github.com/tendermint/tendermint/types#Block.Hash)
is the [Simple Tree hash](./merkle.html#simple-tree-with-dictionaries)
of the fields of the block `Header` encoded as a list of `KVPair`s.
## Transaction
A transaction is any sequence of bytes. It is up to your ABCI
application to accept or reject transactions.
## BlockID
Many of these data structures refer to the
[BlockID](https://godoc.org/github.com/tendermint/tendermint/types#BlockID),
which is the `BlockHash` (hash of the block header, also referred to by
the next block) along with the `PartSetHeader`. The `PartSetHeader` is
explained below and is used internally to orchestrate the p2p
propogation. For clients, it is basically opaque bytes, but they must
match for all votes.
## PartSetHeader
The
[PartSetHeader](https://godoc.org/github.com/tendermint/tendermint/types#PartSetHeader)
contains the total number of pieces in a
[PartSet](https://godoc.org/github.com/tendermint/tendermint/types#PartSet),
and the Merkle root hash of those pieces.
## 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 securely
propagate a large chunk of data (like a block) 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
```
To dig deeper, check out the [types package documentation](https://godoc.org/github.com/tendermint/tendermint/types).

1
types/block.go
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@ -207,6 +207,7 @@ func (b *Block) StringShort() string {
// Header defines the structure of a Tendermint block header
// TODO: limit header size
// NOTE: changes to the Header should be duplicated in the abci Header
// and in /docs/spec/blockchain/blockchain.md
type Header struct {
// basic block info
ChainID string `json:"chain_id"`