424 lines
14 KiB
Go
424 lines
14 KiB
Go
|
// Copyright (c) 2017 The btcsuite developers
|
||
|
|
// Use of this source code is governed by an ISC
|
||
|
|
// license that can be found in the LICENSE file.
|
||
|
|
|
||
|
|
package blockchain
|
||
|
|
|
||
|
|
import (
|
||
|
|
"sync"
|
||
|
|
)
|
||
|
|
|
||
|
|
// approxNodesPerWeek is an approximation of the number of new blocks there are
|
||
|
|
// in a week on average.
|
||
|
|
const approxNodesPerWeek = 6 * 24 * 7
|
||
|
|
|
||
|
|
// log2FloorMasks defines the masks to use when quickly calculating
|
||
|
|
// floor(log2(x)) in a constant log2(32) = 5 steps, where x is a uint32, using
|
||
|
|
// shifts. They are derived from (2^(2^x) - 1) * (2^(2^x)), for x in 4..0.
|
||
|
|
var log2FloorMasks = []uint32{0xffff0000, 0xff00, 0xf0, 0xc, 0x2}
|
||
|
|
|
||
|
|
// fastLog2Floor calculates and returns floor(log2(x)) in a constant 5 steps.
|
||
|
|
func fastLog2Floor(n uint32) uint8 {
|
||
|
|
rv := uint8(0)
|
||
|
|
exponent := uint8(16)
|
||
|
|
for i := 0; i < 5; i++ {
|
||
|
|
if n&log2FloorMasks[i] != 0 {
|
||
|
|
rv += exponent
|
||
|
|
n >>= exponent
|
||
|
|
}
|
||
|
|
exponent >>= 1
|
||
|
|
}
|
||
|
|
return rv
|
||
|
|
}
|
||
|
|
|
||
|
|
// chainView provides a flat view of a specific branch of the block chain from
|
||
|
|
// its tip back to the genesis block and provides various convenience functions
|
||
|
|
// for comparing chains.
|
||
|
|
//
|
||
|
|
// For example, assume a block chain with a side chain as depicted below:
|
||
|
|
// genesis -> 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8
|
||
|
|
// \-> 4a -> 5a -> 6a
|
||
|
|
//
|
||
|
|
// The chain view for the branch ending in 6a consists of:
|
||
|
|
// genesis -> 1 -> 2 -> 3 -> 4a -> 5a -> 6a
|
||
|
|
type chainView struct {
|
||
|
|
mtx sync.Mutex
|
||
|
|
nodes []*blockNode
|
||
|
|
}
|
||
|
|
|
||
|
|
// newChainView returns a new chain view for the given tip block node. Passing
|
||
|
|
// nil as the tip will result in a chain view that is not initialized. The tip
|
||
|
|
// can be updated at any time via the setTip function.
|
||
|
|
func newChainView(tip *blockNode) *chainView {
|
||
|
|
// The mutex is intentionally not held since this is a constructor.
|
||
|
|
var c chainView
|
||
|
|
c.setTip(tip)
|
||
|
|
return &c
|
||
|
|
}
|
||
|
|
|
||
|
|
// genesis returns the genesis block for the chain view. This only differs from
|
||
|
|
// the exported version in that it is up to the caller to ensure the lock is
|
||
|
|
// held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) genesis() *blockNode {
|
||
|
|
if len(c.nodes) == 0 {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
return c.nodes[0]
|
||
|
|
}
|
||
|
|
|
||
|
|
// Genesis returns the genesis block for the chain view.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Genesis() *blockNode {
|
||
|
|
c.mtx.Lock()
|
||
|
|
genesis := c.genesis()
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return genesis
|
||
|
|
}
|
||
|
|
|
||
|
|
// tip returns the current tip block node for the chain view. It will return
|
||
|
|
// nil if there is no tip. This only differs from the exported version in that
|
||
|
|
// it is up to the caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) tip() *blockNode {
|
||
|
|
if len(c.nodes) == 0 {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
return c.nodes[len(c.nodes)-1]
|
||
|
|
}
|
||
|
|
|
||
|
|
// Tip returns the current tip block node for the chain view. It will return
|
||
|
|
// nil if there is no tip.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Tip() *blockNode {
|
||
|
|
c.mtx.Lock()
|
||
|
|
tip := c.tip()
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return tip
|
||
|
|
}
|
||
|
|
|
||
|
|
// setTip sets the chain view to use the provided block node as the current tip
|
||
|
|
// and ensures the view is consistent by populating it with the nodes obtained
|
||
|
|
// by walking backwards all the way to genesis block as necessary. Further
|
||
|
|
// calls will only perform the minimum work needed, so switching between chain
|
||
|
|
// tips is efficient. This only differs from the exported version in that it is
|
||
|
|
// up to the caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for writes).
|
||
|
|
func (c *chainView) setTip(node *blockNode) {
|
||
|
|
if node == nil {
|
||
|
|
// Keep the backing array around for potential future use.
|
||
|
|
c.nodes = c.nodes[:0]
|
||
|
|
return
|
||
|
|
}
|
||
|
|
|
||
|
|
// Create or resize the slice that will hold the block nodes to the
|
||
|
|
// provided tip height. When creating the slice, it is created with
|
||
|
|
// some additional capacity for the underlying array as append would do
|
||
|
|
// in order to reduce overhead when extending the chain later. As long
|
||
|
|
// as the underlying array already has enough capacity, simply expand or
|
||
|
|
// contract the slice accordingly. The additional capacity is chosen
|
||
|
|
// such that the array should only have to be extended about once a
|
||
|
|
// week.
|
||
|
|
needed := node.height + 1
|
||
|
|
if int32(cap(c.nodes)) < needed {
|
||
|
|
nodes := make([]*blockNode, needed, needed+approxNodesPerWeek)
|
||
|
|
copy(nodes, c.nodes)
|
||
|
|
c.nodes = nodes
|
||
|
|
} else {
|
||
|
|
prevLen := int32(len(c.nodes))
|
||
|
|
c.nodes = c.nodes[0:needed]
|
||
|
|
for i := prevLen; i < needed; i++ {
|
||
|
|
c.nodes[i] = nil
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
for node != nil && c.nodes[node.height] != node {
|
||
|
|
c.nodes[node.height] = node
|
||
|
|
node = node.parent
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// SetTip sets the chain view to use the provided block node as the current tip
|
||
|
|
// and ensures the view is consistent by populating it with the nodes obtained
|
||
|
|
// by walking backwards all the way to genesis block as necessary. Further
|
||
|
|
// calls will only perform the minimum work needed, so switching between chain
|
||
|
|
// tips is efficient.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) SetTip(node *blockNode) {
|
||
|
|
c.mtx.Lock()
|
||
|
|
c.setTip(node)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
}
|
||
|
|
|
||
|
|
// height returns the height of the tip of the chain view. It will return -1 if
|
||
|
|
// there is no tip (which only happens if the chain view has not been
|
||
|
|
// initialized). This only differs from the exported version in that it is up
|
||
|
|
// to the caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) height() int32 {
|
||
|
|
return int32(len(c.nodes) - 1)
|
||
|
|
}
|
||
|
|
|
||
|
|
// Height returns the height of the tip of the chain view. It will return -1 if
|
||
|
|
// there is no tip (which only happens if the chain view has not been
|
||
|
|
// initialized).
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Height() int32 {
|
||
|
|
c.mtx.Lock()
|
||
|
|
height := c.height()
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return height
|
||
|
|
}
|
||
|
|
|
||
|
|
// nodeByHeight returns the block node at the specified height. Nil will be
|
||
|
|
// returned if the height does not exist. This only differs from the exported
|
||
|
|
// version in that it is up to the caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) nodeByHeight(height int32) *blockNode {
|
||
|
|
if height < 0 || height >= int32(len(c.nodes)) {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
return c.nodes[height]
|
||
|
|
}
|
||
|
|
|
||
|
|
// NodeByHeight returns the block node at the specified height. Nil will be
|
||
|
|
// returned if the height does not exist.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) NodeByHeight(height int32) *blockNode {
|
||
|
|
c.mtx.Lock()
|
||
|
|
node := c.nodeByHeight(height)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return node
|
||
|
|
}
|
||
|
|
|
||
|
|
// Equals returns whether or not two chain views are the same. Uninitialized
|
||
|
|
// views (tip set to nil) are considered equal.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Equals(other *chainView) bool {
|
||
|
|
c.mtx.Lock()
|
||
|
|
other.mtx.Lock()
|
||
|
|
equals := len(c.nodes) == len(other.nodes) && c.tip() == other.tip()
|
||
|
|
other.mtx.Unlock()
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return equals
|
||
|
|
}
|
||
|
|
|
||
|
|
// contains returns whether or not the chain view contains the passed block
|
||
|
|
// node. This only differs from the exported version in that it is up to the
|
||
|
|
// caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) contains(node *blockNode) bool {
|
||
|
|
return c.nodeByHeight(node.height) == node
|
||
|
|
}
|
||
|
|
|
||
|
|
// Contains returns whether or not the chain view contains the passed block
|
||
|
|
// node.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Contains(node *blockNode) bool {
|
||
|
|
c.mtx.Lock()
|
||
|
|
contains := c.contains(node)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return contains
|
||
|
|
}
|
||
|
|
|
||
|
|
// next returns the successor to the provided node for the chain view. It will
|
||
|
|
// return nil if there is no successor or the provided node is not part of the
|
||
|
|
// view. This only differs from the exported version in that it is up to the
|
||
|
|
// caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// See the comment on the exported function for more details.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) next(node *blockNode) *blockNode {
|
||
|
|
if node == nil || !c.contains(node) {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
return c.nodeByHeight(node.height + 1)
|
||
|
|
}
|
||
|
|
|
||
|
|
// Next returns the successor to the provided node for the chain view. It will
|
||
|
|
// return nil if there is no successfor or the provided node is not part of the
|
||
|
|
// view.
|
||
|
|
//
|
||
|
|
// For example, assume a block chain with a side chain as depicted below:
|
||
|
|
// genesis -> 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8
|
||
|
|
// \-> 4a -> 5a -> 6a
|
||
|
|
//
|
||
|
|
// Further, assume the view is for the longer chain depicted above. That is to
|
||
|
|
// say it consists of:
|
||
|
|
// genesis -> 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8
|
||
|
|
//
|
||
|
|
// Invoking this function with block node 5 would return block node 6 while
|
||
|
|
// invoking it with block node 5a would return nil since that node is not part
|
||
|
|
// of the view.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) Next(node *blockNode) *blockNode {
|
||
|
|
c.mtx.Lock()
|
||
|
|
next := c.next(node)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return next
|
||
|
|
}
|
||
|
|
|
||
|
|
// findFork returns the final common block between the provided node and the
|
||
|
|
// the chain view. It will return nil if there is no common block. This only
|
||
|
|
// differs from the exported version in that it is up to the caller to ensure
|
||
|
|
// the lock is held.
|
||
|
|
//
|
||
|
|
// See the exported FindFork comments for more details.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) findFork(node *blockNode) *blockNode {
|
||
|
|
// No fork point for node that doesn't exist.
|
||
|
|
if node == nil {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
// When the height of the passed node is higher than the height of the
|
||
|
|
// tip of the current chain view, walk backwards through the nodes of
|
||
|
|
// the other chain until the heights match (or there or no more nodes in
|
||
|
|
// which case there is no common node between the two).
|
||
|
|
//
|
||
|
|
// NOTE: This isn't strictly necessary as the following section will
|
||
|
|
// find the node as well, however, it is more efficient to avoid the
|
||
|
|
// contains check since it is already known that the common node can't
|
||
|
|
// possibly be past the end of the current chain view. It also allows
|
||
|
|
// this code to take advantage of any potential future optimizations to
|
||
|
|
// the Ancestor function such as using an O(log n) skip list.
|
||
|
|
chainHeight := c.height()
|
||
|
|
if node.height > chainHeight {
|
||
|
|
node = node.Ancestor(chainHeight)
|
||
|
|
}
|
||
|
|
|
||
|
|
// Walk the other chain backwards as long as the current one does not
|
||
|
|
// contain the node or there are no more nodes in which case there is no
|
||
|
|
// common node between the two.
|
||
|
|
for node != nil && !c.contains(node) {
|
||
|
|
node = node.parent
|
||
|
|
}
|
||
|
|
|
||
|
|
return node
|
||
|
|
}
|
||
|
|
|
||
|
|
// FindFork returns the final common block between the provided node and the
|
||
|
|
// the chain view. It will return nil if there is no common block.
|
||
|
|
//
|
||
|
|
// For example, assume a block chain with a side chain as depicted below:
|
||
|
|
// genesis -> 1 -> 2 -> ... -> 5 -> 6 -> 7 -> 8
|
||
|
|
// \-> 6a -> 7a
|
||
|
|
//
|
||
|
|
// Further, assume the view is for the longer chain depicted above. That is to
|
||
|
|
// say it consists of:
|
||
|
|
// genesis -> 1 -> 2 -> ... -> 5 -> 6 -> 7 -> 8.
|
||
|
|
//
|
||
|
|
// Invoking this function with block node 7a would return block node 5 while
|
||
|
|
// invoking it with block node 7 would return itself since it is already part of
|
||
|
|
// the branch formed by the view.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) FindFork(node *blockNode) *blockNode {
|
||
|
|
c.mtx.Lock()
|
||
|
|
fork := c.findFork(node)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return fork
|
||
|
|
}
|
||
|
|
|
||
|
|
// blockLocator returns a block locator for the passed block node. The passed
|
||
|
|
// node can be nil in which case the block locator for the current tip
|
||
|
|
// associated with the view will be returned. This only differs from the
|
||
|
|
// exported version in that it is up to the caller to ensure the lock is held.
|
||
|
|
//
|
||
|
|
// See the exported BlockLocator function comments for more details.
|
||
|
|
//
|
||
|
|
// This function MUST be called with the view mutex locked (for reads).
|
||
|
|
func (c *chainView) blockLocator(node *blockNode) BlockLocator {
|
||
|
|
// Use the current tip if requested.
|
||
|
|
if node == nil {
|
||
|
|
node = c.tip()
|
||
|
|
}
|
||
|
|
if node == nil {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
|
||
|
|
// Calculate the max number of entries that will ultimately be in the
|
||
|
|
// block locator. See the description of the algorithm for how these
|
||
|
|
// numbers are derived.
|
||
|
|
var maxEntries uint8
|
||
|
|
if node.height <= 12 {
|
||
|
|
maxEntries = uint8(node.height) + 1
|
||
|
|
} else {
|
||
|
|
// Requested hash itself + previous 10 entries + genesis block.
|
||
|
|
// Then floor(log2(height-10)) entries for the skip portion.
|
||
|
|
adjustedHeight := uint32(node.height) - 10
|
||
|
|
maxEntries = 12 + fastLog2Floor(adjustedHeight)
|
||
|
|
}
|
||
|
|
locator := make(BlockLocator, 0, maxEntries)
|
||
|
|
|
||
|
|
step := int32(1)
|
||
|
|
for node != nil {
|
||
|
|
locator = append(locator, &node.hash)
|
||
|
|
|
||
|
|
// Nothing more to add once the genesis block has been added.
|
||
|
|
if node.height == 0 {
|
||
|
|
break
|
||
|
|
}
|
||
|
|
|
||
|
|
// Calculate height of previous node to include ensuring the
|
||
|
|
// final node is the genesis block.
|
||
|
|
height := node.height - step
|
||
|
|
if height < 0 {
|
||
|
|
height = 0
|
||
|
|
}
|
||
|
|
|
||
|
|
// When the node is in the current chain view, all of its
|
||
|
|
// ancestors must be too, so use a much faster O(1) lookup in
|
||
|
|
// that case. Otherwise, fall back to walking backwards through
|
||
|
|
// the nodes of the other chain to the correct ancestor.
|
||
|
|
if c.contains(node) {
|
||
|
|
node = c.nodes[height]
|
||
|
|
} else {
|
||
|
|
node = node.Ancestor(height)
|
||
|
|
}
|
||
|
|
|
||
|
|
// Once 11 entries have been included, start doubling the
|
||
|
|
// distance between included hashes.
|
||
|
|
if len(locator) > 10 {
|
||
|
|
step *= 2
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return locator
|
||
|
|
}
|
||
|
|
|
||
|
|
// BlockLocator returns a block locator for the passed block node. The passed
|
||
|
|
// node can be nil in which case the block locator for the current tip
|
||
|
|
// associated with the view will be returned.
|
||
|
|
//
|
||
|
|
// See the BlockLocator type for details on the algorithm used to create a block
|
||
|
|
// locator.
|
||
|
|
//
|
||
|
|
// This function is safe for concurrent access.
|
||
|
|
func (c *chainView) BlockLocator(node *blockNode) BlockLocator {
|
||
|
|
c.mtx.Lock()
|
||
|
|
locator := c.blockLocator(node)
|
||
|
|
c.mtx.Unlock()
|
||
|
|
return locator
|
||
|
|
}
|