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# nimbus-eth1
# Copyright (c) 2021 Status Research & Development GmbH
# Licensed under either of
# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
# http://www.apache.org/licenses/LICENSE-2.0)
# * MIT license ([LICENSE-MIT](LICENSE-MIT) or
# http://opensource.org/licenses/MIT)
# at your option. This file may not be copied, modified, or distributed
# except according to those terms.
## Aristo DB -- Patricia Trie traversal
## ====================================
##
## This module provides tools to visit leaf vertices in a monotone order,
## increasing or decreasing. These tools are intended for
## * boundary proof verification
## * step along leaf vertices in sorted order
## * tree/trie consistency checks when debugging
##
{.push raises: [].}
import
std/tables,
eth/[common, trie/nibbles],
results,
"."/[aristo_desc, aristo_get, aristo_hike, aristo_path]
# ------------------------------------------------------------------------------
# Private helpers
# ------------------------------------------------------------------------------
proc `<=`(a, b: NibblesSeq): bool =
## Compare nibbles, different lengths are padded to the right with zeros
let abMin = min(a.len, b.len)
for n in 0 ..< abMin:
if a[n] < b[n]:
return true
if b[n] < a[n]:
return false
# otherwise a[n] == b[n]
# Assuming zero for missing entries
if b.len < a.len:
for n in abMin + 1 ..< a.len:
if 0 < a[n]:
return false
true
proc `<`(a, b: NibblesSeq): bool =
not (b <= a)
# ------------------
proc branchNibbleMin*(vtx: VertexRef; minInx: int8): int8 =
## Find the least index for an argument branch `vtx` link with index
## greater or equal the argument `nibble`.
if vtx.vType == Branch:
for n in minInx .. 15:
if vtx.bVid[n].isValid:
return n
-1
proc branchNibbleMax*(vtx: VertexRef; maxInx: int8): int8 =
## Find the greatest index for an argument branch `vtx` link with index
## less or equal the argument `nibble`.
if vtx.vType == Branch:
for n in maxInx.countDown 0:
if vtx.bVid[n].isValid:
return n
-1
# ------------------
proc toTLeafTiePayload(hike: Hike): (LeafTie,PayloadRef) =
## Shortcut for iterators. This function will gloriously crash unless the
## `hike` argument is complete.
(LeafTie(root: hike.root, path: hike.to(NibblesSeq).pathToTag.value),
hike.legs[^1].wp.vtx.lData)
# ------------------------------------------------------------------------------
# Private functions
# ------------------------------------------------------------------------------
proc complete(
hike: Hike; # Partially expanded chain of vertices
vid: VertexID; # Start ID
db: AristoDbRef; # Database layer
hikeLenMax: static[int]; # Beware of loops (if any)
doLeast: static[bool]; # Direction: *least* or *most*
): Result[Hike,(VertexID,AristoError)] =
## Extend `hike` using least or last vertex without recursion.
if not vid.isValid:
return err((VertexID(0),NearbyVidInvalid))
var
vid = vid
vtx = db.getVtx vid
uHike = Hike(root: hike.root, legs: hike.legs)
if not vtx.isValid:
return err((vid,GetVtxNotFound))
while uHike.legs.len < hikeLenMax:
var leg = Leg(wp: VidVtxPair(vid: vid, vtx: vtx), nibble: -1)
case vtx.vType:
of Leaf:
uHike.legs.add leg
return ok(uHike) # done
of Extension:
vid = vtx.eVid
if vid.isValid:
vtx = db.getVtx vid
if vtx.isValid:
uHike.legs.add leg
continue
return err((vid,NearbyExtensionError)) # Oops, no way
of Branch:
when doLeast:
leg.nibble = vtx.branchNibbleMin 0
else:
leg.nibble = vtx.branchNibbleMax 15
if 0 <= leg.nibble:
vid = vtx.bVid[leg.nibble]
vtx = db.getVtx vid
if vtx.isValid:
uHike.legs.add leg
continue
return err((leg.wp.vid,NearbyBranchError)) # Oops, no way
err((VertexID(0),NearbyNestingTooDeep))
proc zeroAdjust(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
doLeast: static[bool]; # Direction: *least* or *most*
): Result[Hike,(VertexID,AristoError)] =
## Adjust empty argument path to the first vertex entry to the right. Ths
## applies is the argument `hike` is before the first entry in the database.
## The result is a hike which is aligned with the first entry.
proc accept(p: Hike; pfx: NibblesSeq): bool =
when doLeast:
p.tail <= pfx
else:
pfx <= p.tail
proc branchBorderNibble(w: VertexRef; n: int8): int8 =
when doLeast:
w.branchNibbleMin n
else:
w.branchNibbleMax n
proc toHike(pfx: NibblesSeq, root: VertexID, db: AristoDbRef): Hike =
when doLeast:
pfx.pathPfxPad(0).hikeUp(root, db).to(Hike)
else:
pfx.pathPfxPad(255).hikeUp(root, db).to(Hike)
if 0 < hike.legs.len:
return ok(hike)
let root = db.getVtx hike.root
if root.isValid:
block fail:
var pfx: NibblesSeq
case root.vType:
of Branch:
# Find first non-dangling link and assign it
if hike.tail.len == 0:
break fail
let n = root.branchBorderNibble hike.tail[0].int8
if n < 0:
# Before or after the database range
return err((hike.root,NearbyBeyondRange))
pfx = @[n.byte].initNibbleRange.slice(1)
of Extension:
let ePfx = root.ePfx
# Must be followed by a branch vertex
if hike.tail.len < 2 or not hike.accept(ePfx):
break fail
let vtx = db.getVtx root.eVid
if not vtx.isValid:
break fail
let ePfxLen = ePfx.len
if hike.tail.len <= ePfxLen:
return err((root.eVid,NearbyPathTailInxOverflow))
let tailPfx = hike.tail.slice(0,ePfxLen)
when doLeast:
if ePfx < tailPfx:
return err((root.eVid,NearbyBeyondRange))
else:
if tailPfx < ePfx:
return err((root.eVid,NearbyBeyondRange))
pfx = ePfx
of Leaf:
pfx = root.lPfx
if not hike.accept(pfx):
# Before or after the database range
return err((hike.root,NearbyBeyondRange))
var newHike = pfx.toHike(hike.root, db)
if 0 < newHike.legs.len:
return ok(newHike)
err((VertexID(0),NearbyEmptyHike))
proc finalise(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
moveRight: static[bool]; # Direction of next vertex
): Result[Hike,(VertexID,AristoError)] =
## Handle some pathological cases after main processing failed
proc beyond(p: Hike; pfx: NibblesSeq): bool =
when moveRight:
pfx < p.tail
else:
p.tail < pfx
proc branchBorderNibble(w: VertexRef): int8 =
when moveRight:
w.branchNibbleMax 15
else:
w.branchNibbleMin 0
# Just for completeness (this case should have been handled, already)
if hike.legs.len == 0:
return err((VertexID(0),NearbyEmptyHike))
# Check whether the path is beyond the database range
if 0 < hike.tail.len: # nothing to compare against, otherwise
let top = hike.legs[^1]
# Note that only a `Branch` vertices has a non-zero nibble
if 0 <= top.nibble and top.nibble == top.wp.vtx.branchBorderNibble:
# Check the following up vertex
let
vid = top.wp.vtx.bVid[top.nibble]
vtx = db.getVtx vid
if not vtx.isValid:
return err((vid,NearbyDanglingLink))
var pfx: NibblesSeq
case vtx.vType:
of Leaf:
pfx = vtx.lPfx
of Extension:
pfx = vtx.ePfx
of Branch:
pfx = @[vtx.branchBorderNibble.byte].initNibbleRange.slice(1)
if hike.beyond pfx:
return err((vid,NearbyBeyondRange))
# Pathological cases
# * finalise right: nfffff.. for n < f or
# * finalise left: n00000.. for 0 < n
if hike.legs[0].wp.vtx.vType == Branch or
(1 < hike.legs.len and hike.legs[1].wp.vtx.vType == Branch):
return err((VertexID(0),NearbyFailed)) # no more vertices
err((hike.legs[^1].wp.vid,NearbyUnexpectedVtx)) # error
proc nearbyNext(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
hikeLenMax: static[int]; # Beware of loops (if any)
moveRight: static[bool]; # Direction of next vertex
): Result[Hike,(VertexID,AristoError)] =
## Unified implementation of `nearbyRight()` and `nearbyLeft()`.
proc accept(nibble: int8): bool =
## Accept `nibble` unless on boundaty dependent on `moveRight`
when moveRight:
nibble < 15
else:
0 < nibble
proc accept(p: Hike; pfx: NibblesSeq): bool =
when moveRight:
p.tail <= pfx
else:
pfx <= p.tail
proc branchNibbleNext(w: VertexRef; n: int8): int8 =
when moveRight:
w.branchNibbleMin(n + 1)
else:
w.branchNibbleMax(n - 1)
# Some easy cases
let hike = ? hike.zeroAdjust(db, doLeast=moveRight)
if hike.legs[^1].wp.vtx.vType == Extension:
let vid = hike.legs[^1].wp.vtx.eVid
return hike.complete(vid, db, hikeLenMax, doLeast=moveRight)
var
uHike = hike
start = true
while 0 < uHike.legs.len:
let top = uHike.legs[^1]
case top.wp.vtx.vType:
of Leaf:
return ok(uHike)
of Branch:
if top.nibble < 0 or uHike.tail.len == 0:
return err((top.wp.vid,NearbyUnexpectedVtx))
of Extension:
uHike.tail = top.wp.vtx.ePfx & uHike.tail
uHike.legs.setLen(uHike.legs.len - 1)
continue
var
step = top
let
uHikeLen = uHike.legs.len # in case of backtracking
uHikeTail = uHike.tail # in case of backtracking
# Look ahead checking next vertex
if start:
let vid = top.wp.vtx.bVid[top.nibble]
if not vid.isValid:
return err((top.wp.vid,NearbyDanglingLink)) # error
let vtx = db.getVtx vid
if not vtx.isValid:
return err((vid,GetVtxNotFound)) # error
case vtx.vType
of Leaf:
if uHike.accept vtx.lPfx:
return uHike.complete(vid, db, hikeLenMax, doLeast=moveRight)
of Extension:
if uHike.accept vtx.ePfx:
return uHike.complete(vid, db, hikeLenMax, doLeast=moveRight)
of Branch:
let nibble = uHike.tail[0].int8
if start and accept nibble:
# Step down and complete with a branch link on the child vertex
step = Leg(wp: VidVtxPair(vid: vid, vtx: vtx), nibble: nibble)
uHike.legs.add step
# Find the next item to the right/left of the current top entry
let n = step.wp.vtx.branchNibbleNext step.nibble
if 0 <= n:
uHike.legs[^1].nibble = n
return uHike.complete(
step.wp.vtx.bVid[n], db, hikeLenMax, doLeast=moveRight)
if start:
# Retry without look ahead
start = false
# Restore `uPath` (pop temporary extra step)
if uHikeLen < uHike.legs.len:
uHike.legs.setLen(uHikeLen)
uHike.tail = uHikeTail
else:
# Pop current `Branch` vertex on top and append nibble to `tail`
uHike.tail = @[top.nibble.byte].initNibbleRange.slice(1) & uHike.tail
uHike.legs.setLen(uHike.legs.len - 1)
# End while
# Handle some pathological cases
hike.finalise(db, moveRight)
proc nearbyNextLeafTie(
lty: LeafTie; # Some `Patricia Trie` path
db: AristoDbRef; # Database layer
hikeLenMax: static[int]; # Beware of loops (if any)
moveRight:static[bool]; # Direction of next vertex
): Result[HashID,(VertexID,AristoError)] =
## Variant of `nearbyNext()`, convenience wrapper
let hike = ? lty.hikeUp(db).to(Hike).nearbyNext(db, hikeLenMax, moveRight)
if 0 < hike.legs.len:
if hike.legs[^1].wp.vtx.vType != Leaf:
return err((hike.legs[^1].wp.vid,NearbyLeafExpected))
let rc = hike.legsTo(NibblesSeq).pathToKey
if rc.isOk:
return ok rc.value.to(HashID)
return err((VertexID(0),rc.error))
err((VertexID(0),NearbyLeafExpected))
# ------------------------------------------------------------------------------
# Public functions, moving and right boundary proof
# ------------------------------------------------------------------------------
proc right*(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
): Result[Hike,(VertexID,AristoError)] =
## Extends the maximally extended argument vertices `hike` to the right (i.e.
## with non-decreasing path value). This function does not backtrack if
## there are dangling links in between. It will return an error in that case.
##
## If there is no more leaf vertices to the right of the argument `hike`, the
## particular error code `NearbyBeyondRange` is returned.
##
## This code is intended to be used for verifying a left-bound proof to
## verify that there is no leaf vertex *right* of a boundary path value.
hike.nearbyNext(db, 64, moveRight=true)
proc right*(
lty: LeafTie; # Some `Patricia Trie` path
db: AristoDbRef; # Database layer
): Result[LeafTie,(VertexID,AristoError)] =
## Variant of `nearbyRight()` working with a `HashID` argument instead
## of a `Hike`.
ok LeafTie(
root: lty.root,
path: ? lty.nearbyNextLeafTie(db, 64, moveRight=true))
iterator right*(
db: AristoDbRef; # Database layer
start = low(LeafTie); # Before or at first value
): (LeafTie,PayloadRef) =
## Traverse the sub-trie implied by the argument `start` with increasing
## order.
var
hike = start.hikeUp(db).to(Hike)
rc = hike.right db
while rc.isOK:
hike = rc.value
let (key, pyl) = hike.toTLeafTiePayload
yield (key, pyl)
if high(HashID) <= key.path:
break
# Increment `key` by one and update `hike`. In many cases, the current
# `hike` can be modified and re-used which saves some database lookups.
block:
let tail = hike.legs[^1].wp.vtx.lPfx
if 0 < tail.len:
let topNibble = tail[tail.len - 1]
if topNibble < 15:
let newNibble = @[topNibble+1].initNibbleRange.slice(1)
hike.tail = tail.slice(0, tail.len - 1) & newNibble
hike.legs.setLen(hike.legs.len - 1)
break
if 1 < tail.len:
let nxtNibble = tail[tail.len - 2]
if nxtNibble < 15:
let dblNibble = @[((nxtNibble+1) shl 4) + 0].initNibbleRange
hike.tail = tail.slice(0, tail.len - 2) & dblNibble
hike.legs.setLen(hike.legs.len - 1)
break
# Fall back to default method
hike = (key + 1).hikeUp(db).to(Hike)
rc = hike.right db
# End while
# ----------------
proc left*(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
): Result[Hike,(VertexID,AristoError)] =
## Similar to `nearbyRight()`.
##
## This code is intended to be used for verifying a right-bound proof to
## verify that there is no leaf vertex *left* to a boundary path value.
hike.nearbyNext(db, 64, moveRight=false)
proc left*(
lty: LeafTie; # Some `Patricia Trie` path
db: AristoDbRef; # Database layer
): Result[LeafTie,(VertexID,AristoError)] =
## Similar to `nearbyRight()` for `HashID` argument instead of a `Hike`.
ok LeafTie(
root: lty.root,
path: ? lty.nearbyNextLeafTie(db, 64, moveRight=false))
iterator left*(
db: AristoDbRef; # Database layer
start = high(LeafTie); # Before or at first value
): (LeafTie,PayloadRef) =
## Traverse the sub-trie implied by the argument `start` with decreasing
## order. It will stop at any error. In order to reproduce an error, one
## can run the function `left()` on the last returned `LiefTie` item with
## the `path` field decremented by `1`.
var
hike = start.hikeUp(db).to(Hike)
rc = hike.left db
while rc.isOK:
hike = rc.value
let (key, pyl) = hike.toTLeafTiePayload
yield (key, pyl)
if key.path <= low(HashID):
break
# Decrement `key` by one and update `hike`. In many cases, the current
# `hike` can be modified and re-used which saves some database lookups.
block:
let tail = hike.legs[^1].wp.vtx.lPfx
if 0 < tail.len:
let topNibble = tail[tail.len - 1]
if 0 < topNibble:
let newNibble = @[topNibble - 1].initNibbleRange.slice(1)
hike.tail = tail.slice(0, tail.len - 1) & newNibble
hike.legs.setLen(hike.legs.len - 1)
break
if 1 < tail.len:
let nxtNibble = tail[tail.len - 2]
if 0 < nxtNibble:
let dblNibble = @[((nxtNibble-1) shl 4) + 15].initNibbleRange
hike.tail = tail.slice(0, tail.len - 2) & dblNibble
hike.legs.setLen(hike.legs.len - 1)
break
# Fall back to default method
hike = (key - 1).hikeUp(db).to(Hike)
rc = hike.left db
# End while
# ------------------------------------------------------------------------------
# Public debugging helpers
# ------------------------------------------------------------------------------
proc rightMissing*(
hike: Hike; # Partially expanded chain of vertices
db: AristoDbRef; # Database layer
): Result[bool,AristoError] =
## Returns `true` if the maximally extended argument vertex `hike` is the
## right most on the hexary trie database. It verifies that there is no more
## leaf entry to the right of the argument `hike`. This function is an
## alternative to
## ::
## let rc = path.nearbyRight(db)
## if rc.isOk:
## # not at the end => false
## ...
## elif rc.error != NearbyBeyondRange:
## # problem with database => error
## ...
## else:
## # no nore vertices => true
## ...
## and is intended mainly for debugging.
if hike.legs.len == 0:
return err(NearbyEmptyHike)
if 0 < hike.tail.len:
return err(NearbyPathTailUnexpected)
let top = hike.legs[^1]
if top.wp.vtx.vType != Branch or top.nibble < 0:
return err(NearbyBranchError)
let vid = top.wp.vtx.bVid[top.nibble]
if not vid.isValid:
return err(NearbyDanglingLink) # error
let vtx = db.getVtx vid
if not vtx.isValid:
return err(GetVtxNotFound) # error
case vtx.vType
of Leaf:
return ok(vtx.lPfx < hike.tail)
of Extension:
return ok(vtx.ePfx < hike.tail)
of Branch:
return ok(vtx.branchNibbleMin(hike.tail[0].int8) < 0)
# ------------------------------------------------------------------------------
# End
# ------------------------------------------------------------------------------
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