docs: refactor ABCI docs
* move spec/software/abci.md to spec/abci/apps.md and improve it * move some of app-dev/app-development.md to spec/abci/client-server.md
This commit is contained in:
Ethan Buchman
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# Application Development Guide
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## XXX
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This page is undergoing deprecation. All content is being moved to the new [home
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of the ABCI specification](../spec/abci/README.md).
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## ABCI Design
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The purpose of ABCI is to provide a clean interface between state
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@ -0,0 +1,19 @@
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# ABCI
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ABCI is the interface between Tendermint (a state-machine replication engine)
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and an application (the actual state machine). It consists of a set of
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*methods*, where each method has a corresponding `Request` and `Response`
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message type. Tendermint calls the ABCI methods on the ABCI application by sending the `Request*`
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messages and receiving the `Response*` messages in return.
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All message types are defined in a [protobuf file](https://github.com/tendermint/tendermint/blob/develop/abci/types/types.proto).
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This allows Tendermint to run applications written in any programming language.
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This specification is split as follows:
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- [Methods and Types](abci.md) - complete details on all ABCI methods and
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message types
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- [Applications](apps.md) - how to manage ABCI application state and other
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details about building ABCI applications
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- [Client and Server](client-server.md) - for those looking to implement their
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own ABCI application servers
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@ -1,13 +1,7 @@
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# Application Blockchain Interface (ABCI)
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# ABCI Methods and Types
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## Overview
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ABCI is the interface between Tendermint (a state-machine replication engine)
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and an application (the actual state machine). It consists of a set of
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*methods*, where each method has a corresponding `Request` and `Response` type.
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Tendermint calls the methods on the ABCI application by sending the `Request*`
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messages and receiving the `Response*` messages in return.
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The ABCI message types are defined in a [protobuf
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file](https://github.com/tendermint/tendermint/blob/develop/abci/types/types.proto).
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@ -26,7 +20,6 @@ The `Info Connection` is for initialization and for queries from the user.
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Additionally, there is a `Flush` method that is called on every connection,
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and an `Echo` method that is just for debugging.
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## Errors
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Some methods (`Echo, Info, InitChain, BeginBlock, EndBlock, Commit`),
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@ -0,0 +1,207 @@
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# ABCI Applications
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Please ensure you've first read the spec for [ABCI Methods and Types](abci.md)
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Here we cover the following components of ABCI applications:
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- [State](#State) - the interplay between ABCI connections and application state
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and the differences between `CheckTx` and `DeliverTx`.
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- [Validator Set Updates](#Validator-Set-Updates) - how validator sets are
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changed during `InitChain` and `EndBlock`
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- [Query](#Query) - standards for using the `Query` method
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- [Crash Recovery](#Crash-Recovery) - handshake protocol to synchronize
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Tendermint and the application on startup.
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## State
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Since Tendermint maintains multiple concurrent ABCI connections, it is typical
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for an application to maintain a distinct state for each, and for the states to
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be sycnronized during `Commit`.
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### Commit
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Before `Commit` is called, Tendermint locks and flushes the mempool so that no new messages will
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be received on the mempool connection. This provides an opportunity to safely update all three
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states to the latest committed state at once.
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When `Commit` completes, it unlocks the mempool.
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Note that it is not possible to send transactions to Tendermint during `Commit` - if your app
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tries to send a `/broadcast_tx` to Tendermint during Commit, it will deadlock.
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### Consensus Connection
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The Consensus Connection should maintain a `DeliverTxState` -
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the working state for block execution. It should be updated by the calls to
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`BeginBlock`, `DeliverTx`, and `EndBlock` during block execution and committed to
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disk as the "latest committed state" during `Commit`.
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Updates made to the DeliverTxState by each method call must be readable by each subsequent method -
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ie. the updates are linearizeable.
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### Mempool Connection
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The Mempool Connection should maintain a `CheckTxState` -
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to process pending transactions in the mempool that have
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not yet been committed. It should be initialized to the latest committed state
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at the end of every `Commit`. Note it may be updated concurrently with the
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DeliverTxState.
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Before calling `Commit`, Tendermint will lock and flush the mempool,
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ensuring that all existing CheckTx are responded to and no new ones can
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begin.
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After `Commit`, CheckTx is run again on all transactions that remain in the
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node's local mempool after filtering those included in the block. To prevent the
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mempool from rechecking all transactions every time a block is committed, set
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the configuration option `mempool.recheck=false`.
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Finally, the mempool will unlock and new transactions can be processed through CheckTx again.
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Note that CheckTx doesn't have to check everything that affects transaction validity; the
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expensive things can be skipped. In fact, CheckTx doesn't have to check
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anything; it might say that any transaction is a valid transaction.
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Unlike DeliverTx, CheckTx is just there as
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a sort of weak filter to keep invalid transactions out of the blockchain. It's
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weak, because a Byzantine node doesn't care about CheckTx; it can propose a
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block full of invalid transactions if it wants.
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### Info Connection
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The Mempool Connection should maintain a `QueryState` for answering queries from the user,
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and for initialization when Tendermint first starts up.
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It should always contain the latest committed state associated with the
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latest commited block.
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QueryState should be set to the latest `DeliverTxState` at the end of every `Commit`,
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ie. after the full block has been processed and the state committed to disk.
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Otherwise it should never be modified.
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## Validator Updates
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### EndBlock
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Updates to the Tendermint validator set can be made by returning
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`ValidatorUpdate` objects in the `ResponseEndBlock`:
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```
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message ValidatorUpdate {
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PubKey pub_key
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int64 power
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}
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message PubKey {
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string type
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bytes data
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}
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```
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The `pub_key` currently supports only one type:
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- `type = "ed25519" and`data = <raw 32-byte public key>`
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The `power` is the new voting power for the validator, with the
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following rules:
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- power must be non-negative
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- if power is 0, the validator must already exist, and will be removed from the
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validator set
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- if power is non-0:
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- if the validator does not already exist, it will be added to the validator
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set with the given power
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- if the validator does already exist, its power will be adjusted to the given power
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### InitChain
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ResponseInitChain has the option to return a list of validators.
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If the list is not empty, Tendermint will adopt it for the validator set.
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This way the application can determine the initial validator set for the
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blockchain.
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ResponseInitChain also includes ConsensusParams, but these are presently
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ignored.
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## Query
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Query is a generic message type with lots of flexibility to enable diverse sets
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of queries from applications. Tendermint has no requirements from the Query
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message for normal operation - that is, the ABCI app developer need not implement Query functionality if they do not wish too.
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That said, Tendermint makes a number of queries to support some optional
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features. These are:
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### Peer Filtering
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When Tendermint connects to a peer, it sends two queries to the ABCI application
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using the following paths, with no additional data:
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- `/p2p/filter/addr/<IP:PORT>`, where `<IP:PORT>` denote the IP address and
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the port of the connection
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- `p2p/filter/id/<ID>`, where `<ID>` is the peer node ID (ie. the
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pubkey.Address() for the peer's PubKey)
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If either of these queries return a non-zero ABCI code, Tendermint will refuse
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to connect to the peer.
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## Crash Recovery
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On startup, Tendermint calls the `Info` method on the Info Connection to get the latest
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committed state of the app. The app MUST return information consistent with the
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last block it succesfully completed Commit for.
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If the app succesfully committed block H but not H+1, then `last_block_height = H` and `last_block_app_hash = <hash returned by Commit for block H>`. If the app
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failed during the Commit of block H, then `last_block_height = H-1` and
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`last_block_app_hash = <hash returned by Commit for block H-1, which is the hash in the header of block H>`.
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We now distinguish three heights, and describe how Tendermint syncs itself with
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the app.
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```
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storeBlockHeight = height of the last block Tendermint saw a commit for
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stateBlockHeight = height of the last block for which Tendermint completed all
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block processing and saved all ABCI results to disk
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appBlockHeight = height of the last block for which ABCI app succesfully
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completely Commit
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```
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Note we always have `storeBlockHeight >= stateBlockHeight` and `storeBlockHeight >= appBlockHeight`
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Note also we never call Commit on an ABCI app twice for the same height.
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The procedure is as follows.
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First, some simeple start conditions:
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If `appBlockHeight == 0`, then call InitChain.
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If `storeBlockHeight == 0`, we're done.
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Now, some sanity checks:
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If `storeBlockHeight < appBlockHeight`, error
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If `storeBlockHeight < stateBlockHeight`, panic
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If `storeBlockHeight > stateBlockHeight+1`, panic
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Now, the meat:
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If `storeBlockHeight == stateBlockHeight && appBlockHeight < storeBlockHeight`,
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replay all blocks in full from `appBlockHeight` to `storeBlockHeight`.
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This happens if we completed processing the block, but the app forgot its height.
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If `storeBlockHeight == stateBlockHeight && appBlockHeight == storeBlockHeight`, we're done
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This happens if we crashed at an opportune spot.
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If `storeBlockHeight == stateBlockHeight+1`
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This happens if we started processing the block but didn't finish.
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If `appBlockHeight < stateBlockHeight`
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replay all blocks in full from `appBlockHeight` to `storeBlockHeight-1`,
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and replay the block at `storeBlockHeight` using the WAL.
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This happens if the app forgot the last block it committed.
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If `appBlockHeight == stateBlockHeight`,
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replay the last block (storeBlockHeight) in full.
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This happens if we crashed before the app finished Commit
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If appBlockHeight == storeBlockHeight {
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update the state using the saved ABCI responses but dont run the block against the real app.
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This happens if we crashed after the app finished Commit but before Tendermint saved the state.
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@ -0,0 +1,104 @@
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# ABCI Client and Server
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This section is for those looking to implement their own ABCI Server, perhaps in
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a new programming language.
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You are expected to have read [ABCI Methods and Types](abci.md) and [ABCI
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Applications](apps.md).
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See additional details in the [ABCI
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readme](https://github.com/tendermint/tendermint/blob/develop/abci/README.md)(TODO: deduplicate
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those details).
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## Message Protocol
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The message protocol consists of pairs of requests and responses defined in the
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[protobuf file](https://github.com/tendermint/tendermint/blob/develop/abci/types/types.proto).
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Some messages have no fields, while others may include byte-arrays, strings, integers,
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or custom protobuf types.
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For more details on protobuf, see the [documentation](https://developers.google.com/protocol-buffers/docs/overview).
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For each request, a server should respond with the corresponding
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response, where the order of requests is preserved in the order of
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responses.
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## Server
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To use ABCI in your programming language of choice, there must be a ABCI
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server in that language. Tendermint supports two kinds of implementation
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of the server:
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- Asynchronous, raw socket server (Tendermint Socket Protocol, also
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known as TSP or Teaspoon)
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- GRPC
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Both can be tested using the `abci-cli` by setting the `--abci` flag
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appropriately (ie. to `socket` or `grpc`).
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See examples, in various stages of maintenance, in
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[Go](https://github.com/tendermint/tendermint/tree/develop/abci/server),
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[JavaScript](https://github.com/tendermint/js-abci),
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[Python](https://github.com/tendermint/tendermint/tree/develop/abci/example/python3/abci),
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[C++](https://github.com/mdyring/cpp-tmsp), and
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[Java](https://github.com/jTendermint/jabci).
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### GRPC
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If GRPC is available in your language, this is the easiest approach,
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though it will have significant performance overhead.
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To get started with GRPC, copy in the [protobuf
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file](https://github.com/tendermint/tendermint/blob/develop/abci/types/types.proto)
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and compile it using the GRPC plugin for your language. For instance,
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for golang, the command is `protoc --go_out=plugins=grpc:. types.proto`.
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See the [grpc documentation for more details](http://www.grpc.io/docs/).
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`protoc` will autogenerate all the necessary code for ABCI client and
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server in your language, including whatever interface your application
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must satisfy to be used by the ABCI server for handling requests.
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### TSP
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If GRPC is not available in your language, or you require higher
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performance, or otherwise enjoy programming, you may implement your own
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ABCI server using the Tendermint Socket Protocol, known affectionately
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as Teaspoon. The first step is still to auto-generate the relevant data
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types and codec in your language using `protoc`. Messages coming over
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the socket are proto3 encoded, but additionally length-prefixed to
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facilitate use as a streaming protocol. proto3 doesn't have an
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official length-prefix standard, so we use our own. The first byte in
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the prefix represents the length of the Big Endian encoded length. The
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remaining bytes in the prefix are the Big Endian encoded length.
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For example, if the proto3 encoded ABCI message is 0xDEADBEEF (4
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bytes), the length-prefixed message is 0x0104DEADBEEF. If the proto3
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encoded ABCI message is 65535 bytes long, the length-prefixed message
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would be like 0x02FFFF....
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Note this prefixing does not apply for grpc.
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An ABCI server must also be able to support multiple connections, as
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Tendermint uses three connections.
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### Async vs Sync
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The main ABCI server (ie. non-GRPC) provides ordered asynchronous messages.
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This is useful for DeliverTx and CheckTx, since it allows Tendermint to forward
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transactions to the app before it's finished processing previous ones.
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Thus, DeliverTx and CheckTx messages are sent asycnhronously, while all other
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messages are sent synchronously.
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## Client
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There are currently two use-cases for an ABCI client. One is a testing
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tool, as in the `abci-cli`, which allows ABCI requests to be sent via
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command line. The other is a consensus engine, such as Tendermint Core,
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which makes requests to the application every time a new transaction is
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received or a block is committed.
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It is unlikely that you will need to implement a client. For details of
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our client, see
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[here](https://github.com/tendermint/tendermint/tree/develop/abci/client).
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@ -1,185 +1,3 @@
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# Application Blockchain Interface (ABCI)
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ABCI is the interface between Tendermint (a state-machine replication engine)
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and an application (the actual state machine).
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|
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The ABCI message types are defined in a [protobuf
|
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file](https://github.com/tendermint/tendermint/blob/develop/abci/types/types.proto).
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For full details on the ABCI message types and protocol, see the [ABCI
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specification](https://github.com/tendermint/tendermint/blob/develop/docs/app-dev/abci-spec.md).
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Be sure to read the specification if you're trying to build an ABCI app!
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For additional details on server implementation, see the [ABCI
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readme](https://github.com/tendermint/tendermint/blob/develop/abci/README.md).
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Here we provide some more details around the use of ABCI by Tendermint and
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clarify common "gotchas".
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## ABCI connections
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Tendermint opens 3 ABCI connections to the app: one for Consensus, one for
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Mempool, one for Queries.
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## Async vs Sync
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The main ABCI server (ie. non-GRPC) provides ordered asynchronous messages.
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This is useful for DeliverTx and CheckTx, since it allows Tendermint to forward
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transactions to the app before it's finished processing previous ones.
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Thus, DeliverTx and CheckTx messages are sent asycnhronously, while all other
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messages are sent synchronously.
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## CheckTx and Commit
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It is typical to hold three distinct states in an ABCI app: CheckTxState, DeliverTxState,
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QueryState. The QueryState contains the latest committed state for a block.
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The CheckTxState and DeliverTxState may be updated concurrently with one another.
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Before Commit is called, Tendermint locks and flushes the mempool so that no new changes will happen
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to CheckTxState. When Commit completes, it unlocks the mempool.
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Thus, during Commit, it is safe to reset the QueryState and the CheckTxState to the latest DeliverTxState
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(ie. the new state from executing all the txs in the block).
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Note, however, that it is not possible to send transactions to Tendermint during Commit - if your app
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tries to send a `/broadcast_tx` to Tendermint during Commit, it will deadlock.
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## EndBlock Validator Updates
|
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Updates to the Tendermint validator set can be made by returning `Validator`
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objects in the `ResponseBeginBlock`:
|
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|
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```
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message Validator {
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PubKey pub_key
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int64 power
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}
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|
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message PubKey {
|
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string type
|
||||
bytes data
|
||||
}
|
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```
|
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|
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The `pub_key` currently supports two types:
|
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|
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- `type = "ed25519" and`data = <raw 32-byte public key>`
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- `type = "secp256k1" and `data = <33-byte OpenSSL compressed public key>`
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If the address is provided, it must match the address of the pubkey, as
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specified [here](/docs/spec/blockchain/encoding.md#Addresses)
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(Note: In the v0.19 series, the `pub_key` is the [Amino encoded public
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key](/docs/spec/blockchain/encoding.md#public-key-cryptography).
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For Ed25519 pubkeys, the Amino prefix is always "1624DE6220". For example, the 32-byte Ed25519 pubkey
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`76852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85` would be
|
||||
Amino encoded as
|
||||
`1624DE622076852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85`)
|
||||
|
||||
(Note: In old versions of Tendermint (pre-v0.19.0), the pubkey is just prefixed with a
|
||||
single type byte, so for ED25519 we'd have `pub_key = 0x1 | pub`)
|
||||
|
||||
The `power` is the new voting power for the validator, with the
|
||||
following rules:
|
||||
|
||||
- power must be non-negative
|
||||
- if power is 0, the validator must already exist, and will be removed from the
|
||||
validator set
|
||||
- if power is non-0:
|
||||
- if the validator does not already exist, it will be added to the validator
|
||||
set with the given power
|
||||
- if the validator does already exist, its power will be adjusted to the given power
|
||||
|
||||
## InitChain Validator Updates
|
||||
|
||||
ResponseInitChain has the option to return a list of validators.
|
||||
If the list is not empty, Tendermint will adopt it for the validator set.
|
||||
This way the application can determine the initial validator set for the
|
||||
blockchain.
|
||||
|
||||
ResponseInitChain also includes ConsensusParams, but these are presently
|
||||
ignored.
|
||||
|
||||
## Query
|
||||
|
||||
Query is a generic message type with lots of flexibility to enable diverse sets
|
||||
of queries from applications. Tendermint has no requirements from the Query
|
||||
message for normal operation - that is, the ABCI app developer need not implement Query functionality if they do not wish too.
|
||||
That said, Tendermint makes a number of queries to support some optional
|
||||
features. These are:
|
||||
|
||||
### Peer Filtering
|
||||
|
||||
When Tendermint connects to a peer, it sends two queries to the ABCI application
|
||||
using the following paths, with no additional data:
|
||||
|
||||
- `/p2p/filter/addr/<IP:PORT>`, where `<IP:PORT>` denote the IP address and
|
||||
the port of the connection
|
||||
- `p2p/filter/id/<ID>`, where `<ID>` is the peer node ID (ie. the
|
||||
pubkey.Address() for the peer's PubKey)
|
||||
|
||||
If either of these queries return a non-zero ABCI code, Tendermint will refuse
|
||||
to connect to the peer.
|
||||
|
||||
## Info and the Handshake/Replay
|
||||
|
||||
On startup, Tendermint calls Info on the Query connection to get the latest
|
||||
committed state of the app. The app MUST return information consistent with the
|
||||
last block it succesfully completed Commit for.
|
||||
|
||||
If the app succesfully committed block H but not H+1, then `last_block_height = H` and `last_block_app_hash = <hash returned by Commit for block H>`. If the app
|
||||
failed during the Commit of block H, then `last_block_height = H-1` and
|
||||
`last_block_app_hash = <hash returned by Commit for block H-1, which is the hash in the header of block H>`.
|
||||
|
||||
We now distinguish three heights, and describe how Tendermint syncs itself with
|
||||
the app.
|
||||
|
||||
```
|
||||
storeBlockHeight = height of the last block Tendermint saw a commit for
|
||||
stateBlockHeight = height of the last block for which Tendermint completed all
|
||||
block processing and saved all ABCI results to disk
|
||||
appBlockHeight = height of the last block for which ABCI app succesfully
|
||||
completely Commit
|
||||
```
|
||||
|
||||
Note we always have `storeBlockHeight >= stateBlockHeight` and `storeBlockHeight >= appBlockHeight`
|
||||
Note also we never call Commit on an ABCI app twice for the same height.
|
||||
|
||||
The procedure is as follows.
|
||||
|
||||
First, some simeple start conditions:
|
||||
|
||||
If `appBlockHeight == 0`, then call InitChain.
|
||||
|
||||
If `storeBlockHeight == 0`, we're done.
|
||||
|
||||
Now, some sanity checks:
|
||||
|
||||
If `storeBlockHeight < appBlockHeight`, error
|
||||
If `storeBlockHeight < stateBlockHeight`, panic
|
||||
If `storeBlockHeight > stateBlockHeight+1`, panic
|
||||
|
||||
Now, the meat:
|
||||
|
||||
If `storeBlockHeight == stateBlockHeight && appBlockHeight < storeBlockHeight`,
|
||||
replay all blocks in full from `appBlockHeight` to `storeBlockHeight`.
|
||||
This happens if we completed processing the block, but the app forgot its height.
|
||||
|
||||
If `storeBlockHeight == stateBlockHeight && appBlockHeight == storeBlockHeight`, we're done
|
||||
This happens if we crashed at an opportune spot.
|
||||
|
||||
If `storeBlockHeight == stateBlockHeight+1`
|
||||
This happens if we started processing the block but didn't finish.
|
||||
|
||||
If `appBlockHeight < stateBlockHeight`
|
||||
replay all blocks in full from `appBlockHeight` to `storeBlockHeight-1`,
|
||||
and replay the block at `storeBlockHeight` using the WAL.
|
||||
This happens if the app forgot the last block it committed.
|
||||
|
||||
If `appBlockHeight == stateBlockHeight`,
|
||||
replay the last block (storeBlockHeight) in full.
|
||||
This happens if we crashed before the app finished Commit
|
||||
|
||||
If appBlockHeight == storeBlockHeight {
|
||||
update the state using the saved ABCI responses but dont run the block against the real app.
|
||||
This happens if we crashed after the app finished Commit but before Tendermint saved the state.
|
||||
This page has [moved](../spec/abci/apps.md).
|
||||
|
|
|
|||
Loading…
Reference in New Issue