nim-codex/codex/erasure/erasure.nim

277 lines
8.7 KiB
Nim

## Nim-Codex
## Copyright (c) 2022 Status Research & Development GmbH
## Licensed under either of
## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
## * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.
import pkg/upraises
push: {.upraises: [].}
import std/sequtils
import pkg/chronos
import pkg/chronicles
import ../manifest
import ../stores
import ../blocktype as bt
import ./backend
export backend
logScope:
topics = "codex erasure"
type
## Encode a manifest into one that is erasure protected.
##
## The new manifest has K `blocks` that are encoded into
## additional M `parity` blocks. The resulting dataset
## is padded with empty blocks if it doesn't have a square
## shape.
##
## NOTE: The padding blocks could be excluded
## from transmission, but they aren't for now.
##
## The resulting dataset is logically divided into rows
## where a row is made up of B blocks. There are then,
## K + M = N rows in total, each of length B blocks. Rows
## are assumed to be of the same number of (B) blocks.
##
## The encoding is systematic and the rows can be
## read sequentially by any node without decoding.
##
## Decoding is possible with any K rows or partial K
## columns (with up to M blocks missing per column),
## or any combination there of.
##
EncoderProvider* = proc(size, blocks, parity: int): EncoderBackend
{.raises: [Defect], noSideEffect.}
DecoderProvider* = proc(size, blocks, parity: int): DecoderBackend
{.raises: [Defect], noSideEffect.}
Erasure* = ref object
encoderProvider*: EncoderProvider
decoderProvider*: DecoderProvider
store*: BlockStore
proc encode*(
self: Erasure,
manifest: Manifest,
blocks: int,
parity: int): Future[?!Manifest] {.async.} =
## Encode a manifest into one that is erasure protected.
##
## `manifest` - the original manifest to be encoded
## `blocks` - the number of blocks to be encoded - K
## `parity` - the number of parity blocks to generate - M
##
logScope:
original_cid = manifest.cid.get()
original_len = manifest.len
blocks = blocks
parity = parity
trace "Erasure coding manifest", blocks, parity
without var encoded =? Manifest.new(manifest, blocks, parity), error:
trace "Unable to create manifest", msg = error.msg
return error.failure
logScope:
steps = encoded.steps
rounded_blocks = encoded.rounded
new_manifest = encoded.len
var
encoder = self.encoderProvider(manifest.blockSize, blocks, parity)
try:
for i in 0..<encoded.steps:
# TODO: Don't allocate a new seq every time, allocate once and zero out
var
data = newSeq[seq[byte]](blocks) # number of blocks to encode
parityData = newSeqWith[seq[byte]](parity, newSeq[byte](manifest.blockSize))
# calculate block indexes to retrieve
blockIdx = toSeq(countup(i, encoded.rounded - 1, encoded.steps))
# request all blocks from the store
dataBlocks = await allFinished(
blockIdx.mapIt( self.store.getBlock(encoded[it]) ))
# TODO: this is a tight blocking loop so we sleep here to allow
# other events to be processed, this should be addressed
# by threading
await sleepAsync(10.millis)
for j in 0..<blocks:
let idx = blockIdx[j]
if idx < manifest.len:
without blk =? (await dataBlocks[j]), error:
trace "Unable to retrieve block", error = error.msg
return failure error
trace "Encoding block", cid = blk.cid, pos = idx
shallowCopy(data[j], blk.data)
else:
trace "Padding with empty block", pos = idx
data[j] = newSeq[byte](manifest.blockSize)
trace "Erasure coding data", data = data.len, parity = parityData.len
let res = encoder.encode(data, parityData);
if res.isErr:
trace "Unable to encode manifest!", error = $res.error
return failure($res.error)
for j in 0..<parity:
let idx = encoded.rounded + blockIdx[j]
without blk =? bt.Block.new(parityData[j]), error:
trace "Unable to create parity block", err = error.msg
return failure(error)
trace "Adding parity block", cid = blk.cid, pos = idx
encoded[idx] = blk.cid
if isErr (await self.store.putBlock(blk)):
trace "Unable to store block!", cid = blk.cid
return failure("Unable to store block!")
except CancelledError as exc:
trace "Erasure coding encoding cancelled"
raise exc # cancellation needs to be propagated
except CatchableError as exc:
trace "Erasure coding encoding error", exc = exc.msg
return failure(exc)
finally:
encoder.release()
return encoded.success
proc decode*(
self: Erasure,
encoded: Manifest): Future[?!Manifest] {.async.} =
## Decode a protected manifest into it's original
## manifest
##
## `encoded` - the encoded (protected) manifest to
## be recovered
##
logScope:
steps = encoded.steps
rounded_blocks = encoded.rounded
new_manifest = encoded.len
var
decoder = self.decoderProvider(encoded.blockSize, encoded.K, encoded.M)
try:
for i in 0..<encoded.steps:
# TODO: Don't allocate a new seq every time, allocate once and zero out
let
# calculate block indexes to retrieve
blockIdx = toSeq(countup(i, encoded.len - 1, encoded.steps))
# request all blocks from the store
pendingBlocks = blockIdx.mapIt(
self.store.getBlock(encoded[it]) # Get the data blocks (first K)
)
# TODO: this is a tight blocking loop so we sleep here to allow
# other events to be processed, this should be addressed
# by threading
await sleepAsync(10.millis)
var
data = newSeq[seq[byte]](encoded.K) # number of blocks to encode
parityData = newSeq[seq[byte]](encoded.M)
recovered = newSeqWith[seq[byte]](encoded.K, newSeq[byte](encoded.blockSize))
idxPendingBlocks = pendingBlocks # copy futures to make using with `one` easier
emptyBlock = newSeq[byte](encoded.blockSize)
resolved = 0
while true:
# Continue to receive blocks until we have just enough for decoding
# or no more blocks can arrive
if (resolved >= encoded.K) or (idxPendingBlocks.len == 0):
break
let
done = await one(idxPendingBlocks)
idx = pendingBlocks.find(done)
idxPendingBlocks.del(idxPendingBlocks.find(done))
without blk =? (await done), error:
trace "Failed retrieving block", error = error.msg
continue
if idx >= encoded.K:
trace "Retrieved parity block", cid = blk.cid, idx
shallowCopy(parityData[idx - encoded.K], if blk.isEmpty: emptyBlock else: blk.data)
else:
trace "Retrieved data block", cid = blk.cid, idx
shallowCopy(data[idx], if blk.isEmpty: emptyBlock else: blk.data)
resolved.inc
let
dataPieces = data.filterIt( it.len > 0 ).len
parityPieces = parityData.filterIt( it.len > 0 ).len
if dataPieces >= encoded.K:
trace "Retrieved all the required data blocks", data = dataPieces, parity = parityPieces
continue
trace "Erasure decoding data", data = dataPieces, parity = parityPieces
if (
let err = decoder.decode(data, parityData, recovered);
err.isErr):
trace "Unable to decode manifest!", err = $err.error
return failure($err.error)
for i in 0..<encoded.K:
if data[i].len <= 0:
without blk =? bt.Block.new(recovered[i]), error:
trace "Unable to create block!", exc = error.msg
return failure(error)
trace "Recovered block", cid = blk.cid
if isErr (await self.store.putBlock(blk)):
trace "Unable to store block!", cid = blk.cid
return failure("Unable to store block!")
except CancelledError as exc:
trace "Erasure coding decoding cancelled"
raise exc # cancellation needs to be propagated
except CatchableError as exc:
trace "Erasure coding decoding error", exc = exc.msg
return failure(exc)
finally:
decoder.release()
without decoded =? Manifest.new(blocks = encoded.blocks[0..<encoded.originalLen]), error:
return error.failure
return decoded.success
proc start*(self: Erasure) {.async.} =
return
proc stop*(self: Erasure) {.async.} =
return
proc new*(
T: type Erasure,
store: BlockStore,
encoderProvider: EncoderProvider,
decoderProvider: DecoderProvider): Erasure =
Erasure(
store: store,
encoderProvider: encoderProvider,
decoderProvider: decoderProvider)