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// Package chunk provides a heap of chunks so that larger in-order chunks can be
// processed more easily, e.g., for verifying ranged inclusion proofs and
// batching file writes. For how to implement the heap interface, see:
// https://pkg.go.dev/container/heap#Interface
//
// Idea to use a heap from:
// https://github.com/aarongable/ctaudit
package chunk
import (
"container/heap"
"crypto/sha256"
)
// Chunk holds the SANs of a consecutive range of downloaded leaves. The start
// index and associated leaf hashes are included so that they can be verified.
type Chunk struct {
Start int64 // index of first leaf in this chunk
LeafHashes [][sha256.Size]byte // in-order leaf hashes in this chunk
SANs []string // sans of all leaves in this chunk
Notes []string // notes about this chunk, e.g., errors
}
// ChunkHeap is a min-heap of chunks wrt. to start indices. Use TPush() and
// TPop() to to push/pop chunks without having to worry about type casts.
type ChunkHeap []*Chunk
// TPop pops a chunk from the heap
func (h *ChunkHeap) TPop() *Chunk {
x := heap.Pop(h)
return x.(*Chunk)
}
// TPush pushes a chunk to the heap
func (h *ChunkHeap) TPush(c *Chunk) {
heap.Push(h, c)
}
// Sequence checks if the next pop would provide a chunk starting at index
// start. If so, the heap is also re-organized so that the popped chunk will be
// as large as possible (i.e., in-order chunks are merged to a single chunk).
func (h *ChunkHeap) Sequence(start int64) bool {
if len(*h) == 0 {
return false
}
// See if we have the next in-order chunk ready
s := h.TPop()
if start != s.Start {
h.TPush(s)
return false
}
// See if we can make a larger in-order chunk
for len(*h) > 0 {
c := h.TPop()
if c.Start != s.Start+int64(len(s.LeafHashes)) {
h.TPush(c)
break
}
s.LeafHashes = append(s.LeafHashes, c.LeafHashes...)
s.SANs = append(s.SANs, c.SANs...)
s.Notes = append(s.Notes, c.Notes...)
}
// Put back the largest in-order chunk we have
h.TPush(s)
return true
}
//
// Implement the heap interface
//
func (h ChunkHeap) Len() int { return len(h) }
func (h ChunkHeap) Less(i, j int) bool { return h[i].Start < h[j].Start }
func (h ChunkHeap) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
func (h *ChunkHeap) Push(x any) {
*h = append(*h, x.(*Chunk))
}
func (h *ChunkHeap) Pop() any {
old := *h
n := len(old)
x := old[n-1]
old[n-1] = nil // avoid memory leak
*h = old[:n-1]
return x
}
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