lbcd/blockchain/accept.go

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// Copyright (c) 2013-2017 The btcsuite developers
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// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package blockchain
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import (
"fmt"
"github.com/lbryio/lbcd/database"
btcutil "github.com/lbryio/lbcutil"
)
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// maybeAcceptBlock potentially accepts a block into the block chain and, if
// accepted, returns whether or not it is on the main chain. It performs
// several validation checks which depend on its position within the block chain
// before adding it. The block is expected to have already gone through
// ProcessBlock before calling this function with it.
//
// The flags are also passed to checkBlockContext and connectBestChain. See
// their documentation for how the flags modify their behavior.
blockchain: Rework to use new db interface. This commit is the first stage of several that are planned to convert the blockchain package into a concurrent safe package that will ultimately allow support for multi-peer download and concurrent chain processing. The goal is to update btcd proper after each step so it can take advantage of the enhancements as they are developed. In addition to the aforementioned benefit, this staged approach has been chosen since it is absolutely critical to maintain consensus. Separating the changes into several stages makes it easier for reviewers to logically follow what is happening and therefore helps prevent consensus bugs. Naturally there are significant automated tests to help prevent consensus issues as well. The main focus of this stage is to convert the blockchain package to use the new database interface and implement the chain-related functionality which it no longer handles. It also aims to improve efficiency in various areas by making use of the new database and chain capabilities. The following is an overview of the chain changes: - Update to use the new database interface - Add chain-related functionality that the old database used to handle - Main chain structure and state - Transaction spend tracking - Implement a new pruned unspent transaction output (utxo) set - Provides efficient direct access to the unspent transaction outputs - Uses a domain specific compression algorithm that understands the standard transaction scripts in order to significantly compress them - Removes reliance on the transaction index and paves the way toward eventually enabling block pruning - Modify the New function to accept a Config struct instead of inidividual parameters - Replace the old TxStore type with a new UtxoViewpoint type that makes use of the new pruned utxo set - Convert code to treat the new UtxoViewpoint as a rolling view that is used between connects and disconnects to improve efficiency - Make best chain state always set when the chain instance is created - Remove now unnecessary logic for dealing with unset best state - Make all exported functions concurrent safe - Currently using a single chain state lock as it provides a straight forward and easy to review path forward however this can be improved with more fine grained locking - Optimize various cases where full blocks were being loaded when only the header is needed to help reduce the I/O load - Add the ability for callers to get a snapshot of the current best chain stats in a concurrent safe fashion - Does not block callers while new blocks are being processed - Make error messages that reference transaction outputs consistently use <transaction hash>:<output index> - Introduce a new AssertError type an convert internal consistency checks to use it - Update tests and examples to reflect the changes - Add a full suite of tests to ensure correct functionality of the new code The following is an overview of the btcd changes: - Update to use the new database and chain interfaces - Temporarily remove all code related to the transaction index - Temporarily remove all code related to the address index - Convert all code that uses transaction stores to use the new utxo view - Rework several calls that required the block manager for safe concurrency to use the chain package directly now that it is concurrent safe - Change all calls to obtain the best hash to use the new best state snapshot capability from the chain package - Remove workaround for limits on fetching height ranges since the new database interface no longer imposes them - Correct the gettxout RPC handler to return the best chain hash as opposed the hash the txout was found in - Optimize various RPC handlers: - Change several of the RPC handlers to use the new chain snapshot capability to avoid needlessly loading data - Update several handlers to use new functionality to avoid accessing the block manager so they are able to return the data without blocking when the server is busy processing blocks - Update non-verbose getblock to avoid deserialization and serialization overhead - Update getblockheader to request the block height directly from chain and only load the header - Update getdifficulty to use the new cached data from chain - Update getmininginfo to use the new cached data from chain - Update non-verbose getrawtransaction to avoid deserialization and serialization overhead - Update gettxout to use the new utxo store versus loading full transactions using the transaction index The following is an overview of the utility changes: - Update addblock to use the new database and chain interfaces - Update findcheckpoint to use the new database and chain interfaces - Remove the dropafter utility which is no longer supported NOTE: The transaction index and address index will be reimplemented in another commit.
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//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) maybeAcceptBlock(block *btcutil.Block, flags BehaviorFlags) (bool, error) {
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// The height of this block is one more than the referenced previous
// block.
prevHash := &block.MsgBlock().Header.PrevBlock
prevNode := b.index.LookupNode(prevHash)
if prevNode == nil {
str := fmt.Sprintf("previous block %s is unknown", prevHash)
return false, ruleError(ErrPreviousBlockUnknown, str)
} else if b.index.NodeStatus(prevNode).KnownInvalid() {
str := fmt.Sprintf("previous block %s is known to be invalid", prevHash)
return false, ruleError(ErrInvalidAncestorBlock, str)
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}
blockHeight := prevNode.height + 1
block.SetHeight(blockHeight)
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// The block must pass all of the validation rules which depend on the
// position of the block within the block chain.
blockchain: Convert to full block index in mem. This reworks the block index code such that it loads all of the headers in the main chain at startup and constructs the full block index accordingly. Since the full index from the current best tip all the way back to the genesis block is now guaranteed to be in memory, this also removes all code related to dynamically loading the nodes and updates some of the logic to take advantage of the fact traversing the block index can longer potentially fail. There are also more optimizations and simplifications that can be made in the future as a result of this. Due to removing all of the extra overhead of tracking the dynamic state, and ensuring the block node structs are aligned to eliminate extra padding, the end result of a fully populated block index now takes quite a bit less memory than the previous dynamically loaded version. The main downside is that it now takes a while to start whereas it was nearly instant before, however, it is much better to provide more efficient runtime operation since that is its ultimate purpose and the benefits far outweigh this downside. Some benefits are: - Since every block node is in memory, the recent code which reconstructs headers from block nodes means that all headers can always be served from memory which is important since the majority of the network has moved to header-based semantics - Several of the error paths can be removed since they are no longer necessary - It is no longer expensive to calculate CSV sequence locks or median times of blocks way in the past - It will be possible to create much more efficient iteration and simplified views of the overall index - The entire threshold state database cache can be removed since it is cheap to construct it from the full block index as needed An overview of the logic changes are as follows: - Move AncestorNode from blockIndex to blockNode and greatly simplify since it no longer has to deal with the possibility of dynamically loading nodes and related failures - Rename RelativeNode to RelativeAncestor, move to blockNode, and redefine in terms of AncestorNode - Move CalcPastMedianTime from blockIndex to blockNode and remove no longer necessary test for nil - Change calcSequenceLock to use Ancestor instead of RelativeAncestor since it reads more clearly
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err := b.checkBlockContext(block, prevNode, flags)
if err != nil {
return false, err
}
// Insert the block into the database if it's not already there. Even
// though it is possible the block will ultimately fail to connect, it
// has already passed all proof-of-work and validity tests which means
// it would be prohibitively expensive for an attacker to fill up the
// disk with a bunch of blocks that fail to connect. This is necessary
// since it allows block download to be decoupled from the much more
// expensive connection logic. It also has some other nice properties
// such as making blocks that never become part of the main chain or
// blocks that fail to connect available for further analysis.
err = b.db.Update(func(dbTx database.Tx) error {
return dbStoreBlock(dbTx, block)
})
if err != nil {
return false, err
}
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// Create a new block node for the block and add it to the node index. Even
// if the block ultimately gets connected to the main chain, it starts out
// on a side chain.
blockHeader := &block.MsgBlock().Header
newNode := newBlockNode(blockHeader, prevNode)
newNode.status = statusDataStored
b.index.AddNode(newNode)
err = b.index.flushToDB()
if err != nil {
return false, err
}
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// Connect the passed block to the chain while respecting proper chain
// selection according to the chain with the most proof of work. This
// also handles validation of the transaction scripts.
isMainChain, err := b.connectBestChain(newNode, block, flags)
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if err != nil {
return false, err
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}
// Notify the caller that the new block was accepted into the block
// chain. The caller would typically want to react by relaying the
// inventory to other peers.
b.chainLock.Unlock()
b.sendNotification(NTBlockAccepted, block)
b.chainLock.Lock()
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return isMainChain, nil
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}