nimbus-eth2/beacon_chain/libp2p_streams_backend.nim

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# TODO: How can this be tested?
proc uncompressFramedStream*(conn: Connection,
expectedSize: int): Future[Result[seq[byte], cstring]]
{.async.} =
var header: array[STREAM_HEADER.len, byte]
try:
await conn.readExactly(addr header[0], header.len)
except LPStreamEOFError, LPStreamIncompleteError:
return err "Unexpected EOF before snappy header"
if header != STREAM_HEADER.toOpenArrayByte(0, STREAM_HEADER.high):
return err "Incorrect snappy header"
var
uncompressedData = newSeq[byte](MAX_UNCOMPRESSED_DATA_LEN)
frameData = newSeq[byte](MAX_COMPRESSED_DATA_LEN)
output = newSeqOfCap[byte](expectedSize)
while output.len < expectedSize:
var frameHeader: array[4, byte]
try:
await conn.readExactly(addr frameHeader[0], frameHeader.len)
except LPStreamEOFError, LPStreamIncompleteError:
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return err "no snappy frame"
let x = uint32.fromBytesLE frameHeader
let id = x and 0xFF
let dataLen = (x shr 8).int
if dataLen > MAX_COMPRESSED_DATA_LEN:
return err "invalid snappy frame length"
if dataLen > 0:
try:
await conn.readExactly(addr frameData[0], dataLen)
except LPStreamEOFError, LPStreamIncompleteError:
return err "Incomplete snappy frame"
if id == COMPRESSED_DATA_IDENTIFIER:
if dataLen < 4:
return err "Snappy frame size too low to contain CRC checksum"
let
crc = uint32.fromBytesLE frameData.toOpenArray(0, 3)
remaining = expectedSize - output.len
chunkLen = min(remaining, uncompressedData.len)
# Grab up to MAX_UNCOMPRESSED_DATA_LEN bytes, but no more than remains
# according to the expected size. If it turns out that the uncompressed
# data is longer than that, snappyUncompress will fail and we will not
# decompress the chunk at all, instead reporting failure.
let
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# The `int` conversion below is safe, because `uncompressedLen` is
# bounded to `chunkLen` (which in turn is bounded by `MAX_CHUNK_SIZE`).
# TODO: Use a range type for the parameter.
uncompressedLen = int snappyUncompress(
frameData.toOpenArray(4, dataLen - 1),
uncompressedData.toOpenArray(0, chunkLen - 1))
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if uncompressedLen == 0:
return err "Failed to decompress snappy frame"
doAssert output.len + uncompressedLen <= expectedSize,
"enforced by `remains` limit above"
if not checkCrc(uncompressedData.toOpenArray(0, uncompressedLen-1), crc):
return err "Snappy content CRC checksum failed"
output.add uncompressedData.toOpenArray(0, uncompressedLen-1)
elif id == UNCOMPRESSED_DATA_IDENTIFIER:
if dataLen < 4:
return err "Snappy frame size too low to contain CRC checksum"
if output.len + dataLen - 4 > expectedSize:
return err "Too much data"
let crc = uint32.fromBytesLE frameData.toOpenArray(0, 3)
if not checkCrc(frameData.toOpenArray(4, dataLen - 1), crc):
return err "Snappy content CRC checksum failed"
output.add frameData.toOpenArray(4, dataLen-1)
elif id < 0x80:
# Reserved unskippable chunks (chunk types 0x02-0x7f)
# if we encounter this type of chunk, stop decoding
# the spec says it is an error
return err "Invalid snappy chunk type"
else:
# Reserved skippable chunks (chunk types 0x80-0xfe)
# including STREAM_HEADER (0xff) should be skipped
continue
return ok output
proc readChunkPayload(conn: Connection, peer: Peer,
MsgType: type): Future[NetRes[MsgType]] {.async.} =
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let sm = now(chronos.Moment)
let size =
try: await conn.readVarint()
except LPStreamEOFError: #, LPStreamIncompleteError, InvalidVarintError
# TODO compiler error - haha, uncaught exception
# Error: unhandled exception: closureiters.nim(322, 17) `c[i].kind == nkType` [AssertionError]
return neterr UnexpectedEOF
except LPStreamIncompleteError:
return neterr UnexpectedEOF
except InvalidVarintError:
return neterr UnexpectedEOF
if size > MAX_CHUNK_SIZE:
return neterr SizePrefixOverflow
if size == 0:
return neterr ZeroSizePrefix
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# The `size.int` conversion is safe because `size` is bounded to `MAX_CHUNK_SIZE`
let data = await conn.uncompressFramedStream(size.int)
if data.isOk:
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# `10` is the maximum size of variable integer on wire, so error could
# not be significant.
peer.updateNetThroughput(now(chronos.Moment) - sm,
uint64(10 + size))
return ok SSZ.decode(data.get(), MsgType)
else:
debug "Snappy decompression/read failed", msg = $data.error, conn
return neterr InvalidSnappyBytes
proc readResponseChunk(conn: Connection, peer: Peer,
MsgType: typedesc): Future[NetRes[MsgType]] {.async.} =
try:
var responseCodeByte: byte
try:
await conn.readExactly(addr responseCodeByte, 1)
except LPStreamEOFError, LPStreamIncompleteError:
return neterr PotentiallyExpectedEOF
static: assert ResponseCode.low.ord == 0
if responseCodeByte > ResponseCode.high.byte:
return neterr InvalidResponseCode
let responseCode = ResponseCode responseCodeByte
case responseCode:
of InvalidRequest, ServerError:
let errorMsgChunk = await readChunkPayload(conn, peer, ErrorMsg)
let errorMsg = if errorMsgChunk.isOk: errorMsgChunk.value
else: return err(errorMsgChunk.error)
return err Eth2NetworkingError(kind: ReceivedErrorResponse,
responseCode: responseCode,
errorMsg: errorMsg)
of Success:
discard
return await readChunkPayload(conn, peer, MsgType)
except LPStreamEOFError, LPStreamIncompleteError:
return neterr UnexpectedEOF
proc readResponse(conn: Connection, peer: Peer,
MsgType: type, timeout: Duration): Future[NetRes[MsgType]] {.async.} =
when MsgType is seq:
type E = ElemType(MsgType)
var results: MsgType
while true:
# Because we interleave networking with response processing, it may
# happen that reading all chunks takes longer than a strict dealine
# timeout would allow, so we allow each chunk a new timeout instead.
# The problem is exacerbated by the large number of round-trips to the
# poll loop that each future along the way causes.
trace "reading chunk", conn
let nextFut = conn.readResponseChunk(peer, E)
if not await nextFut.withTimeout(timeout):
return neterr(ReadResponseTimeout)
let nextRes = nextFut.read()
if nextRes.isErr:
if nextRes.error.kind == PotentiallyExpectedEOF:
trace "EOF chunk", conn, err = nextRes.error
return ok results
trace "Error chunk", conn, err = nextRes.error
return err nextRes.error
else:
trace "Got chunk", conn
results.add nextRes.value
else:
let nextFut = conn.readResponseChunk(peer, MsgType)
if not await nextFut.withTimeout(timeout):
return neterr(ReadResponseTimeout)
return nextFut.read()