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.
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## This module implements an asynchronous buffer stream
## which emulates physical async IO.
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##
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## The stream is based on the standard library's `Deque`,
## which is itself based on a ring buffer.
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##
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## It works by exposing a regular LPStream interface and
## a method ``pushTo`` to push data to the internal read
## buffer; as well as a handler that can be registered
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## that gets triggered on every write to the stream. This
## allows using the buffered stream as a sort of proxy,
## which can be consumed as a regular LPStream but allows
## injecting data for reads and intercepting writes.
##
## Another notable feature is that the stream is fully
## ordered and asynchronous. Reads are queued up in order
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## and are suspended when not enough data available. This
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## allows preserving backpressure while maintaining full
## asynchrony. Both writing to the internal buffer with
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## ``pushTo`` as well as reading with ``read*` methods,
## will suspend until either the amount of elements in the
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## buffer goes below ``maxSize`` or more data becomes available.
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import deques, math
import chronos, chronicles, metrics
import ../stream/connection
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when chronicles.enabledLogLevel == LogLevel.TRACE:
import oids
export connection
logScope:
topics = "bufferstream"
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const
DefaultBufferSize* = 1024
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const
BufferStreamTrackerName* = "libp2p.bufferstream"
type
BufferStreamTracker* = ref object of TrackerBase
opened*: uint64
closed*: uint64
proc setupBufferStreamTracker(): BufferStreamTracker {.gcsafe.}
proc getBufferStreamTracker(): BufferStreamTracker {.gcsafe.} =
result = cast[BufferStreamTracker](getTracker(BufferStreamTrackerName))
if isNil(result):
result = setupBufferStreamTracker()
proc dumpTracking(): string {.gcsafe.} =
var tracker = getBufferStreamTracker()
result = "Opened buffers: " & $tracker.opened & "\n" &
"Closed buffers: " & $tracker.closed
proc leakTransport(): bool {.gcsafe.} =
var tracker = getBufferStreamTracker()
result = (tracker.opened != tracker.closed)
proc setupBufferStreamTracker(): BufferStreamTracker =
result = new BufferStreamTracker
result.opened = 0
result.closed = 0
result.dump = dumpTracking
result.isLeaked = leakTransport
addTracker(BufferStreamTrackerName, result)
type
# TODO: figure out how to make this generic to avoid casts
WriteHandler* = proc (data: seq[byte]): Future[void] {.gcsafe.}
BufferStream* = ref object of Connection
maxSize*: int # buffer's max size in bytes
readBuf: Deque[byte] # this is a ring buffer based dequeue
readReqs*: Deque[Future[void]] # use dequeue to fire reads in order
dataReadEvent*: AsyncEvent # event triggered when data has been consumed from the internal buffer
writeHandler*: WriteHandler # user provided write callback
writeLock*: AsyncLock # write lock to guarantee ordered writes
lock: AsyncLock # pushTo lock to guarantee ordered reads
piped: BufferStream # a piped bufferstream instance
AlreadyPipedError* = object of CatchableError
NotWritableError* = object of CatchableError
proc newAlreadyPipedError*(): ref CatchableError {.inline.} =
result = newException(AlreadyPipedError, "stream already piped")
proc newNotWritableError*(): ref CatchableError {.inline.} =
result = newException(NotWritableError, "stream is not writable")
proc requestReadBytes(s: BufferStream): Future[void] =
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## create a future that will complete when more
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## data becomes available in the read buffer
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result = newFuture[void]()
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s.readReqs.addLast(result)
# trace "requestReadBytes(): added a future to readReqs", oid = s.oid
method initStream*(s: BufferStream) =
if s.objName.len == 0:
s.objName = "BufferStream"
procCall Connection(s).initStream()
inc getBufferStreamTracker().opened
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proc initBufferStream*(s: BufferStream,
handler: WriteHandler = nil,
size: int = DefaultBufferSize) =
s.initStream()
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s.maxSize = if isPowerOfTwo(size): size else: nextPowerOfTwo(size)
s.readBuf = initDeque[byte](s.maxSize)
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s.readReqs = initDeque[Future[void]]()
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s.dataReadEvent = newAsyncEvent()
s.lock = newAsyncLock()
s.writeLock = newAsyncLock()
if not(isNil(handler)):
s.writeHandler = proc (data: seq[byte]) {.async, gcsafe.} =
defer:
s.writeLock.release()
# Using a lock here to guarantee
# proper write ordering. This is
# specially important when
# implementing half-closed in mplex
# or other functionality that requires
# strict message ordering
await s.writeLock.acquire()
await handler(data)
trace "created bufferstream", oid = $s.oid
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proc newBufferStream*(handler: WriteHandler = nil,
size: int = DefaultBufferSize,
timeout: Duration = DefaultConnectionTimeout): BufferStream =
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new result
result.timeout = timeout
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result.initBufferStream(handler, size)
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proc popFirst*(s: BufferStream): byte =
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result = s.readBuf.popFirst()
s.dataReadEvent.fire()
proc popLast*(s: BufferStream): byte =
result = s.readBuf.popLast()
s.dataReadEvent.fire()
proc shrink(s: BufferStream, fromFirst = 0, fromLast = 0) =
s.readBuf.shrink(fromFirst, fromLast)
s.dataReadEvent.fire()
proc len*(s: BufferStream): int = s.readBuf.len
method pushTo*(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.
##
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## This method is async and will wait until all data has been
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## written to the internal buffer; this is done so that backpressure
## is preserved.
##
if s.atEof:
raise newLPStreamEOFError()
defer:
# trace "ended", size = s.len
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s.lock.release()
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await s.lock.acquire()
var index = 0
while not s.closed():
while index < data.len and s.readBuf.len < s.maxSize:
s.readBuf.addLast(data[index])
inc(index)
# trace "pushTo()", msg = "added " & $s.len & " bytes to readBuf", oid = s.oid
# resolve the next queued read request
if s.readReqs.len > 0:
s.readReqs.popFirst().complete()
# trace "pushTo(): completed a readReqs future", oid = s.oid
if index >= data.len:
return
# if we couldn't transfer all the data to the
# internal buf wait on a read event
await s.dataReadEvent.wait()
s.dataReadEvent.clear()
proc drainBuffer*(s: BufferStream) {.async.} =
## wait for all data in the buffer to be consumed
##
trace "draining buffer", len = s.len
while s.len > 0:
await s.dataReadEvent.wait()
s.dataReadEvent.clear()
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method readOnce*(s: BufferStream,
pbytes: pointer,
nbytes: int):
Future[int] {.async.} =
if s.atEof:
raise newLPStreamEOFError()
if s.len() == 0:
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await s.requestReadBytes()
var index = 0
var size = min(nbytes, s.len)
let output = cast[ptr UncheckedArray[byte]](pbytes)
s.activity = true # reset activity flag
while s.len() > 0 and index < size:
output[index] = s.popFirst()
inc(index)
return size
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method write*(s: BufferStream, msg: seq[byte]) {.async.} =
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## Write sequence of bytes ``sbytes`` of length ``msglen`` to writer
## stream ``wstream``.
##
## Sequence of bytes ``sbytes`` must not be zero-length.
##
## If ``msglen < 0`` whole sequence ``sbytes`` will be writen to stream.
## If ``msglen > len(sbytes)`` only ``len(sbytes)`` bytes will be written to
## stream.
##
if s.closed:
raise newLPStreamClosedError()
if isNil(s.writeHandler):
raise newNotWritableError()
s.activity = true # reset activity flag
await s.writeHandler(msg)
# TODO: move pipe routines out
proc pipe*(s: BufferStream,
target: BufferStream): BufferStream =
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## pipe the write end of this stream to
## be the source of the target stream
##
## Note that this only works with the LPStream
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## interface methods `read*` and `write` are
## piped.
##
if not(isNil(s.piped)):
raise newAlreadyPipedError()
s.piped = target
let oldHandler = target.writeHandler
proc handler(data: seq[byte]) {.async, closure, gcsafe.} =
if not isNil(oldHandler):
await oldHandler(data)
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# if we're piping to self,
# then add the data to the
# buffer directly and fire
# the read event
if s == target:
for b in data:
s.readBuf.addLast(b)
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# notify main loop of available
# data
s.dataReadEvent.fire()
else:
await target.pushTo(data)
s.writeHandler = handler
result = target
proc `|`*(s: BufferStream, target: BufferStream): BufferStream =
## pipe operator to make piping less verbose
pipe(s, target)
method close*(s: BufferStream) {.async, gcsafe.} =
try:
## close the stream and clear the buffer
if not s.isClosed:
trace "closing bufferstream", oid = $s.oid
s.isEof = true
for r in s.readReqs:
if not(isNil(r)) and not(r.finished()):
r.fail(newLPStreamEOFError())
s.dataReadEvent.fire()
s.readBuf.clear()
await procCall Connection(s).close()
inc getBufferStreamTracker().closed
trace "bufferstream closed", oid = $s.oid
else:
trace "attempt to close an already closed bufferstream", trace = getStackTrace()
except CancelledError as exc:
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raise exc
except CatchableError as exc:
trace "error closing buffer stream", exc = exc.msg