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292 lines
10 KiB
292 lines
10 KiB
ABCI Specification
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==================
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Message Types
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~~~~~~~~~~~~~
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ABCI requests/responses are defined as simple Protobuf messages in `this
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schema
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file <https://github.com/tendermint/abci/blob/master/types/types.proto>`__.
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TendermintCore sends the requests, and the ABCI application sends the
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responses. Here, we provide an overview of the messages types and how they
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are used by Tendermint. Then we describe each request-response pair as a
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function with arguments and return values, and add some notes on usage.
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Some messages (``Echo, Info, InitChain, BeginBlock, EndBlock, Commit``), don't
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return errors because an error would indicate a critical failure in the
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application and there's nothing Tendermint can do. The problem should be
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addressed and both Tendermint and the application restarted. All other
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messages (``SetOption, Query, CheckTx, DeliverTx``) return an
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application-specific response ``Code uint32``, where only ``0`` is reserved for
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``OK``.
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Some messages (``SetOption, Query, CheckTx, DeliverTx``) return
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non-deterministic data in the form of ``Info`` and ``Log``. The ``Log`` is
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intended for the literal output from the application's logger, while the
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``Info`` is any additional info that should be returned.
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The first time a new blockchain is started, Tendermint calls ``InitChain``.
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From then on, the Block Execution Sequence that causes the committed state to
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be updated is as follows:
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``BeginBlock, [DeliverTx], EndBlock, Commit``
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where one ``DeliverTx`` is called for each transaction in the block.
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Cryptographic commitments to the results of DeliverTx, EndBlock, and
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Commit are included in the header of the next block.
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Tendermint opens three connections to the application to handle the different message
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types:
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- ``Consensus Connection - InitChain, BeginBlock, DeliverTx, EndBlock, Commit``
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- ``Mempool Connection - CheckTx``
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- ``Info Connection - Info, SetOption, Query``
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The ``Flush`` message is used on every connection, and the ``Echo`` message
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is only used for debugging.
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Note that messages may be sent concurrently across all connections -
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a typical application will thus maintain a distinct state for each
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connection. They may be referred to as the ``DeliverTx state``, the
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``CheckTx state``, and the ``Commit state`` respectively.
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See below for more details on the message types and how they are used.
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Echo
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^^^^
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- **Arguments**:
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- ``Message (string)``: A string to echo back
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- **Returns**:
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- ``Message (string)``: The input string
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- **Usage**:
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- Echo a string to test an abci client/server implementation
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Flush
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^^^^^
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- **Usage**:
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- Signals that messages queued on the client should be flushed to
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the server. It is called periodically by the client implementation
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to ensure asynchronous requests are actually sent, and is called
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immediately to make a synchronous request, which returns when the
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Flush response comes back.
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Info
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^^^^
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- **Arguments**:
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- ``Version (string)``: The Tendermint version
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- **Returns**:
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- ``Data (string)``: Some arbitrary information
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- ``Version (Version)``: Version information
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- ``LastBlockHeight (int64)``: Latest block for which the app has
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called Commit
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- ``LastBlockAppHash ([]byte)``: Latest result of Commit
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- **Usage**:
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- Return information about the application state.
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- Used to sync Tendermint with the application during a handshake that
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happens on startup.
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- Tendermint expects ``LastBlockAppHash`` and ``LastBlockHeight`` to be
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updated during ``Commit``, ensuring that ``Commit`` is never called twice
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for the same block height.
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SetOption
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^^^^^^^^^
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- **Arguments**:
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- ``Key (string)``: Key to set
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- ``Value (string)``: Value to set for key
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- **Returns**:
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- ``Code (uint32)``: Response code
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- ``Log (string)``: The output of the application's logger. May be non-deterministic.
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- ``Info (string)``: Additional information. May be non-deterministic.
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- **Usage**:
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- Set non-consensus critical application specific options.
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- e.g. Key="min-fee", Value="100fermion" could set the minimum fee required for CheckTx
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(but not DeliverTx - that would be consensus critical).
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InitChain
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^^^^^^^^^
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- **Arguments**:
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- ``Validators ([]Validator)``: Initial genesis validators
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- ``AppStateBytes ([]byte)``: Serialized initial application state
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- **Usage**:
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- Called once upon genesis.
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Query
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^^^^^
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- **Arguments**:
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- ``Data ([]byte)``: Raw query bytes. Can be used with or in lieu of
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Path.
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- ``Path (string)``: Path of request, like an HTTP GET path. Can be
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used with or in liue of Data.
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- Apps MUST interpret '/store' as a query by key on the underlying
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store. The key SHOULD be specified in the Data field.
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- Apps SHOULD allow queries over specific types like '/accounts/...'
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or '/votes/...'
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- ``Height (int64)``: The block height for which you want the query
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(default=0 returns data for the latest committed block). Note that
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this is the height of the block containing the application's
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Merkle root hash, which represents the state as it was after
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committing the block at Height-1
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- ``Prove (bool)``: Return Merkle proof with response if possible
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- **Returns**:
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- ``Code (uint32)``: Response code.
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- ``Log (string)``: The output of the application's logger. May be non-deterministic.
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- ``Info (string)``: Additional information. May be non-deterministic.
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- ``Index (int64)``: The index of the key in the tree.
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- ``Key ([]byte)``: The key of the matching data.
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- ``Value ([]byte)``: The value of the matching data.
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- ``Proof ([]byte)``: Proof for the data, if requested.
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- ``Height (int64)``: The block height from which data was derived.
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Note that this is the height of the block containing the
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application's Merkle root hash, which represents the state as it
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was after committing the block at Height-1
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- **Usage**:
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- Query for data from the application at current or past height.
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- Optionally return Merkle proof.
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BeginBlock
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^^^^^^^^^^
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- **Arguments**:
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- ``Hash ([]byte)``: The block's hash. This can be derived from the
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block header.
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- ``Header (struct{})``: The block header
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- ``AbsentValidators ([]int32)``: List of indices of validators not
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included in the LastCommit
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- ``ByzantineValidators ([]Evidence)``: List of evidence of
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validators that acted maliciously
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- **Usage**:
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- Signals the beginning of a new block. Called prior to any DeliverTxs.
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- The header is expected to at least contain the Height.
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- The ``AbsentValidators`` and ``ByzantineValidators`` can be used to
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determine rewards and punishments for the validators.
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CheckTx
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^^^^^^^
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- **Arguments**:
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- ``Tx ([]byte)``: The request transaction bytes
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- **Returns**:
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- ``Code (uint32)``: Response code
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- ``Data ([]byte)``: Result bytes, if any.
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- ``Log (string)``: The output of the application's logger. May be non-deterministic.
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- ``Info (string)``: Additional information. May be non-deterministic.
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- ``GasWanted (int64)``: Amount of gas request for transaction.
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- ``GasUsed (int64)``: Amount of gas consumed by transaction.
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- ``Tags ([]cmn.KVPair)``: Key-Value tags for filtering and indexing transactions (eg. by account).
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- ``Fee (cmn.KI64Pair)``: Fee paid for the transaction.
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- **Usage**: Validate a mempool transaction, prior to broadcasting or
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proposing. CheckTx should perform stateful but light-weight checks
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of the validity of the transaction (like checking signatures and account balances),
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but need not execute in full (like running a smart contract).
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Tendermint runs CheckTx and DeliverTx concurrently with eachother,
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though on distinct ABCI connections - the mempool connection and the consensus
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connection, respectively.
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The application should maintain a separate state to support CheckTx.
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This state can be reset to the latest committed state during ``Commit``,
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where Tendermint ensures the mempool is locked and not sending new ``CheckTx``.
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After ``Commit``, the mempool will rerun CheckTx on all remaining
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transactions, throwing out any that are no longer valid.
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Keys and values in Tags must be UTF-8 encoded strings (e.g. "account.owner": "Bob", "balance": "100.0", "date": "2018-01-02")
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DeliverTx
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^^^^^^^^^
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- **Arguments**:
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- ``Tx ([]byte)``: The request transaction bytes.
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- **Returns**:
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- ``Code (uint32)``: Response code.
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- ``Data ([]byte)``: Result bytes, if any.
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- ``Log (string)``: The output of the application's logger. May be non-deterministic.
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- ``Info (string)``: Additional information. May be non-deterministic.
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- ``GasWanted (int64)``: Amount of gas requested for transaction.
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- ``GasUsed (int64)``: Amount of gas consumed by transaction.
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- ``Tags ([]cmn.KVPair)``: Key-Value tags for filtering and indexing transactions (eg. by account).
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- ``Fee (cmn.KI64Pair)``: Fee paid for the transaction.
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- **Usage**:
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- Deliver a transaction to be executed in full by the application. If the transaction is valid,
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returns CodeType.OK.
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- Keys and values in Tags must be UTF-8 encoded strings (e.g. "account.owner": "Bob", "balance": "100.0", "time": "2018-01-02T12:30:00Z")
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EndBlock
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^^^^^^^^
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- **Arguments**:
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- ``Height (int64)``: Height of the block just executed.
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- **Returns**:
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- ``ValidatorUpdates ([]Validator)``: Changes to validator set (set
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voting power to 0 to remove).
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- ``ConsensusParamUpdates (ConsensusParams)``: Changes to
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consensus-critical time, size, and other parameters.
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- **Usage**:
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- Signals the end of a block.
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- Called prior to each Commit, after all transactions.
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- Validator set and consensus params are updated with the result.
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- Validator pubkeys are expected to be go-wire encoded.
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Commit
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^^^^^^
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- **Returns**:
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- ``Data ([]byte)``: The Merkle root hash
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- **Usage**:
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- Persist the application state.
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- Return a Merkle root hash of the application state.
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- It's critical that all application instances return the same hash. If not,
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they will not be able to agree on the next block, because the hash is
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included in the next block!
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