nimbus-eth2/beacon_chain/networking/network_metadata_downloads.nim

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# beacon_chain
# Copyright (c) 2023 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
import
std/uri,
stew/io2, chronos, chronos/apps/http/httpclient, snappy,
../spec/digest
import network_metadata
export network_metadata
type
HttpFetchError* = object of CatchableError
status*: int
DigestMismatchError* = object of CatchableError
proc downloadFile(url: Uri): Future[seq[byte]] {.async.} =
var httpSession = HttpSessionRef.new()
let response = await httpSession.fetch(url)
if response[0] == 200:
return response[1]
else:
raise (ref HttpFetchError)(
msg: "Unexpected status code " & $response[0] & " when fetching " & $url,
status: response[0])
proc fetchBytes*(metadata: GenesisMetadata,
genesisStateUrlOverride = none(Uri)): Future[seq[byte]] {.async.} =
case metadata.kind
of NoGenesis:
raiseAssert "fetchBytes should be called only when metadata.hasGenesis is true"
of BakedIn:
result = @(metadata.bakedBytes)
of BakedInUrl:
result = await downloadFile(genesisStateUrlOverride.get(parseUri metadata.url))
# Under the built-in default URL, we serve a snappy-encoded BeaconState in order
# to reduce the size of the downloaded file with roughly 50% (this precise ratio
# depends on the number of validator recors). The user is still free to provide
# any URL which may serve an uncompressed state (e.g. a Beacon API endpoint)
#
# Since a SSZ-encoded BeaconState will start with a LittleEndian genesis time
# (64 bits) while a snappy framed stream will always start with a fixed header
# that will decoded as a timestamp with the value 5791996851603375871 (year 2153).
#
# TODO: A more complete solution will implement compression on the HTTP level,
# by relying on the Content-Encoding header to determine the compression
# algorithm. The detection method used here will not interfere with such
# an implementation and it may remain useful when dealing with misconfigured
# HTTP servers.
if result.isSnappyFramedStream:
result = decodeFramed(result)
if eth2digest(result) != metadata.digest:
raise (ref DigestMismatchError)(
msg: "The downloaded genesis state cannot be verified (checksum mismatch)")
of UserSuppliedFile:
result = readAllBytes(metadata.path).tryGet()
proc sourceDesc*(metadata: GenesisMetadata): string =
case metadata.kind
of NoGenesis:
"no genesis"
of BakedIn:
metadata.networkName
of BakedInUrl:
metadata.url
of UserSuppliedFile:
metadata.path
when isMainModule:
let holeskyMetadata = getMetadataForNetwork("holesky")
io2.writeFile(
"holesky-genesis.ssz",
waitFor holeskyMetadata.genesis.fetchBytes()
).expect("success")