nim-libp2p/libp2p/stream/bufferstream.nim

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## Nim-LibP2P
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## Copyright (c) 2019 Status Research & Development GmbH
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## 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 std/strformat
import stew/byteutils
import chronos, chronicles, metrics
import ../stream/connection
import ./streamseq
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when chronicles.enabledLogLevel == LogLevel.TRACE:
import oids
export connection
logScope:
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topics = "libp2p bufferstream"
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const
BufferStreamTrackerName* = "BufferStream"
type
BufferStream* = ref object of Connection
readQueue*: AsyncQueue[seq[byte]] # read queue for managing backpressure
readBuf*: StreamSeq # overflow buffer for readOnce
pushing*: bool # number of ongoing push operations
reading*: bool # is there an ongoing read? (only allow one)
pushedEof*: bool # eof marker has been put on readQueue
returnedEof*: bool # 0-byte readOnce has been completed
func shortLog*(s: BufferStream): auto =
if s.isNil: "BufferStream(nil)"
elif s.peerInfo.isNil: $s.oid
else: &"{shortLog(s.peerInfo.peerId)}:{s.oid}"
chronicles.formatIt(BufferStream): shortLog(it)
proc len*(s: BufferStream): int =
s.readBuf.len + (if s.readQueue.len > 0: s.readQueue[0].len() else: 0)
method initStream*(s: BufferStream) =
if s.objName.len == 0:
s.objName = "BufferStream"
procCall Connection(s).initStream()
s.readQueue = newAsyncQueue[seq[byte]](1)
trace "BufferStream created", s
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proc newBufferStream*(timeout: Duration = DefaultConnectionTimeout): BufferStream =
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new result
result.timeout = timeout
result.initStream()
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method pushData*(s: BufferStream, data: seq[byte]) {.base, async.} =
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## Write bytes to internal read buffer, use this to fill up the
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## buffer with data.
##
## `pushTo` will block if the queue is full, thus maintaining backpressure.
##
doAssert(not s.pushing,
&"Only one concurrent push allowed for stream {s.shortLog()}")
if s.isClosed or s.pushedEof:
raise newLPStreamEOFError()
if data.len == 0:
return # Don't push 0-length buffers, these signal EOF
# We will block here if there is already data queued, until it has been
# processed
try:
s.pushing = true
trace "Pushing data", s, data = data.len
await s.readQueue.addLast(data)
finally:
s.pushing = false
method pushEof*(s: BufferStream) {.base, async.} =
if s.pushedEof:
return
doAssert(not s.pushing,
&"Only one concurrent push allowed for stream {s.shortLog()}")
s.pushedEof = true
# We will block here if there is already data queued, until it has been
# processed
try:
s.pushing = true
trace "Pushing EOF", s
await s.readQueue.addLast(Eof)
finally:
s.pushing = false
method atEof*(s: BufferStream): bool =
s.isEof and s.readBuf.len == 0
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method readOnce*(s: BufferStream,
pbytes: pointer,
nbytes: int):
Future[int] {.async.} =
doAssert(nbytes > 0, "nbytes must be positive integer")
doAssert(not s.reading,
&"Only one concurrent read allowed for stream {s.shortLog()}")
if s.returnedEof:
raise newLPStreamEOFError()
var
p = cast[ptr UncheckedArray[byte]](pbytes)
# First consume leftovers from previous read
var rbytes = s.readBuf.consumeTo(toOpenArray(p, 0, nbytes - 1))
if rbytes < nbytes and not s.isEof:
# There's space in the buffer - consume some data from the read queue
s.reading = true
let buf =
try:
await s.readQueue.popFirst()
except CatchableError as exc:
# When an exception happens here, the Bufferstream is effectively
# broken and no more reads will be valid - for now, return EOF if it's
# called again, though this is not completely true - EOF represents an
# "orderly" shutdown and that's not what happened here..
s.returnedEof = true
raise exc
finally:
s.reading = false
if buf.len == 0:
# No more data will arrive on read queue
trace "EOF", s
s.isEof = true
else:
let remaining = min(buf.len, nbytes - rbytes)
toOpenArray(p, rbytes, nbytes - 1)[0..<remaining] =
buf.toOpenArray(0, remaining - 1)
rbytes += remaining
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if remaining < buf.len:
trace "add leftovers", s, len = buf.len - remaining
s.readBuf.add(buf.toOpenArray(remaining, buf.high))
if s.isEof and s.readBuf.len() == 0:
# We can clear the readBuf memory since it won't be used any more
s.readBuf = StreamSeq()
s.activity = true
# We want to return 0 exactly once - after that, we'll start raising instead -
# this is a bit nuts in a mixed exception / return value world, but allows the
# consumer of the stream to rely on the 0-byte read as a "regular" EOF marker
# (instead of _sometimes_ getting an exception).
s.returnedEof = rbytes == 0
return rbytes
method closeImpl*(s: BufferStream): Future[void] =
## close the stream and clear the buffer
trace "Closing BufferStream", s, len = s.len
# First, make sure any new calls to `readOnce` and `pushData` etc will fail -
# there may already be such calls in the event queue however
s.isEof = true
s.readBuf = StreamSeq()
s.pushedEof = true
# Essentially we need to handle the following cases
#
# - If a push was in progress but no reader is
# attached we need to pop the queue
# - If a read was in progress without without a
# push/data we need to push the Eof marker to
# notify the reader that the channel closed
#
# In all other cases, there should be a data to complete
# a read or enough room in the queue/buffer to complete a
# push.
#
# State | Q Empty | Q Full
# ------------|----------|-------
# Reading | Push Eof | Na
# Pushing | Na | Pop
if not(s.reading and s.pushing):
if s.reading:
if s.readQueue.empty():
# There is an active reader
s.readQueue.addLastNoWait(Eof)
elif s.pushing:
if not s.readQueue.empty():
discard s.readQueue.popFirstNoWait()
trace "Closed BufferStream", s
procCall Connection(s).closeImpl() # noraises, nocancels