356 lines
11 KiB
Nim
356 lines
11 KiB
Nim
## Nim-LibP2P
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## Copyright (c) 2019 Status Research & Development GmbH
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## Licensed under either of
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## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
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## * MIT license ([LICENSE-MIT](LICENSE-MIT))
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## at your option.
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## This file may not be copied, modified, or distributed except according to
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## those terms.
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## This module implements an asynchronous buffer stream
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## which emulates physical async IO.
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##
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## The stream is based on the standard library's `Deque`,
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## 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
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## a method ``pushTo`` to push data to the internal read
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## buffer; as well as a handler that can be registrered
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## that gets triggered on every write to the stream. This
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## allows using the buffered stream as a sort of proxy,
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## which can be consumed as a regular LPStream but allows
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## injecting data for reads and intercepting writes.
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##
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## Another notable feature is that the stream is fully
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## 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
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## asynchrony. Both writting to the internal buffer with
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## ``pushTo`` as well as reading with ``read*` methods,
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## 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
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import chronos
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import ../stream/lpstream
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const DefaultBufferSize* = 1024
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type
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# TODO: figure out how to make this generic to avoid casts
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WriteHandler* = proc (data: seq[byte]): Future[void]
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BufferStream* = ref object of LPStream
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maxSize*: int # buffer's max size in bytes
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readBuf: Deque[byte] # this is a ring buffer based dequeue, this makes it perfect as the backing store here
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readReqs: Deque[Future[void]] # use dequeue to fire reads in order
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dataReadEvent: AsyncEvent
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writeHandler*: WriteHandler
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lock: AsyncLock
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isPiped: bool
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AlreadyPipedError* = object of CatchableError
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NotWritableError* = object of CatchableError
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proc newAlreadyPipedError*(): ref Exception {.inline.} =
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result = newException(AlreadyPipedError, "stream already piped")
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proc newNotWritableError*(): ref Exception {.inline.} =
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result = newException(NotWritableError, "stream is not writable")
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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)
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proc initBufferStream*(s: BufferStream,
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handler: WriteHandler = nil,
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size: int = DefaultBufferSize) =
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s.maxSize = if isPowerOfTwo(size): size else: nextPowerOfTwo(size)
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s.readBuf = initDeque[byte](s.maxSize)
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s.readReqs = initDeque[Future[void]]()
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s.dataReadEvent = newAsyncEvent()
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s.lock = newAsyncLock()
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s.writeHandler = handler
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s.closeEvent = newAsyncEvent()
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proc newBufferStream*(handler: WriteHandler = nil,
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size: int = DefaultBufferSize): BufferStream =
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new result
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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()
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s.dataReadEvent.fire()
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proc popLast*(s: BufferStream): byte =
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result = s.readBuf.popLast()
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s.dataReadEvent.fire()
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proc shrink(s: BufferStream, fromFirst = 0, fromLast = 0) =
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s.readBuf.shrink(fromFirst, fromLast)
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s.dataReadEvent.fire()
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proc len*(s: BufferStream): int = s.readBuf.len
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proc pushTo*(s: BufferStream, data: seq[byte]) {.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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##
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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
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## is preserved.
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##
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try:
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await s.lock.acquire()
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var index = 0
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while true:
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while index < data.len and s.readBuf.len < s.maxSize:
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s.readBuf.addLast(data[index])
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inc(index)
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# resolve the next queued read request
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if s.readReqs.len > 0:
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s.readReqs.popFirst().complete()
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if index >= data.len:
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return
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# if we couldn't transfer all the data to the
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# internal buf wait on a read event
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await s.dataReadEvent.wait()
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s.dataReadEvent.clear()
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finally:
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s.lock.release()
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method read*(s: BufferStream, n = -1): Future[seq[byte]] {.async.} =
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## Read all bytes (n <= 0) or exactly `n` bytes from buffer
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##
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## This procedure allocates buffer seq[byte] and return it as result.
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##
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var size = if n > 0: n else: s.readBuf.len()
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var index = 0
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while index < size:
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while s.readBuf.len() > 0 and index < size:
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result.add(s.popFirst())
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inc(index)
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if index < size:
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await s.requestReadBytes()
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method readExactly*(s: BufferStream,
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pbytes: pointer,
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nbytes: int):
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Future[void] {.async.} =
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## Read exactly ``nbytes`` bytes from read-only stream ``rstream`` and store
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## it to ``pbytes``.
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##
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## If EOF is received and ``nbytes`` is not yet read, the procedure
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## will raise ``LPStreamIncompleteError``.
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##
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var buff = await s.read(nbytes)
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if nbytes > buff.len():
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raise newLPStreamIncompleteError()
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copyMem(pbytes, addr buff[0], nbytes)
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method readLine*(s: BufferStream,
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limit = 0,
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sep = "\r\n"):
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Future[string] {.async.} =
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## Read one line from read-only stream ``rstream``, where ``"line"`` is a
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## sequence of bytes ending with ``sep`` (default is ``"\r\n"``).
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##
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## If EOF is received, and ``sep`` was not found, the method will return the
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## partial read bytes.
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##
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## If the EOF was received and the internal buffer is empty, return an
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## empty string.
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##
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## If ``limit`` more then 0, then result string will be limited to ``limit``
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## bytes.
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##
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result = ""
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var lim = if limit <= 0: -1 else: limit
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var state = 0
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var index = 0
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index = 0
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while index < s.readBuf.len:
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let ch = char(s.readBuf[index])
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if sep[state] == ch:
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inc(state)
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if state == len(sep):
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s.shrink(index + 1)
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break
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else:
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state = 0
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result.add(ch)
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if len(result) == lim:
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s.shrink(index + 1)
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break
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inc(index)
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method readOnce*(s: BufferStream,
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pbytes: pointer,
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nbytes: int):
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Future[int] {.async.} =
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## Perform one read operation on read-only stream ``rstream``.
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##
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## If internal buffer is not empty, ``nbytes`` bytes will be transferred from
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## internal buffer, otherwise it will wait until some bytes will be received.
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##
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if s.readBuf.len == 0:
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await s.requestReadBytes()
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var len = if nbytes > s.readBuf.len: s.readBuf.len else: nbytes
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await s.readExactly(pbytes, len)
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result = len
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method readUntil*(s: BufferStream,
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pbytes: pointer,
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nbytes: int,
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sep: seq[byte]):
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Future[int] {.async.} =
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## Read data from the read-only stream ``rstream`` until separator ``sep`` is
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## found.
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##
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## On success, the data and separator will be removed from the internal
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## buffer (consumed). Returned data will include the separator at the end.
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##
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## If EOF is received, and `sep` was not found, procedure will raise
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## ``LPStreamIncompleteError``.
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##
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## If ``nbytes`` bytes has been received and `sep` was not found, procedure
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## will raise ``LPStreamLimitError``.
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##
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## Procedure returns actual number of bytes read.
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##
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var
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dest = cast[ptr UncheckedArray[byte]](pbytes)
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state = 0
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k = 0
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let datalen = s.readBuf.len()
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if datalen == 0 and s.readBuf.len() == 0:
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raise newLPStreamIncompleteError()
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var index = 0
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while index < datalen:
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let ch = s.readBuf[index]
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if sep[state] == ch:
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inc(state)
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else:
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state = 0
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if k < nbytes:
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dest[k] = ch
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inc(k)
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else:
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raise newLPStreamLimitError()
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if state == len(sep):
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break
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inc(index)
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if state == len(sep):
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s.shrink(index + 1)
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result = k
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else:
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s.shrink(datalen)
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method write*(s: BufferStream,
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pbytes: pointer,
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nbytes: int): Future[void] =
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## Consume (discard) all bytes (n <= 0) or ``n`` bytes from read-only stream
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## ``rstream``.
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##
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## Return number of bytes actually consumed (discarded).
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##
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var buf: seq[byte] = newSeq[byte](nbytes)
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copyMem(addr buf[0], pbytes, nbytes)
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if not isNil(s.writeHandler):
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result = s.writeHandler(buf)
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method write*(s: BufferStream,
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msg: string,
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msglen = -1): Future[void] =
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## Write string ``sbytes`` of length ``msglen`` to writer stream ``wstream``.
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##
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## String ``sbytes`` must not be zero-length.
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##
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## If ``msglen < 0`` whole string ``sbytes`` will be writen to stream.
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## If ``msglen > len(sbytes)`` only ``len(sbytes)`` bytes will be written to
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## stream.
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##
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var buf = ""
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shallowCopy(buf, if msglen > 0: msg[0..<msglen] else: msg)
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if not isNil(s.writeHandler):
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result = s.writeHandler(cast[seq[byte]](buf))
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method write*(s: BufferStream,
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msg: seq[byte],
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msglen = -1): Future[void] =
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## Write sequence of bytes ``sbytes`` of length ``msglen`` to writer
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## stream ``wstream``.
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##
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## Sequence of bytes ``sbytes`` must not be zero-length.
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##
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## If ``msglen < 0`` whole sequence ``sbytes`` will be writen to stream.
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## If ``msglen > len(sbytes)`` only ``len(sbytes)`` bytes will be written to
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## stream.
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##
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var buf: seq[byte]
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shallowCopy(buf, if msglen > 0: msg[0..<msglen] else: msg)
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if not isNil(s.writeHandler):
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result = s.writeHandler(buf)
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proc pipe*(s: BufferStream,
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target: BufferStream): BufferStream =
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## pipe the write end of this stream to
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## be the source of the target stream
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##
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## Note that this only works with the LPStream
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## interface methods `read*` and `write` are
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## piped.
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##
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if s.isPiped:
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raise newAlreadyPipedError()
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s.isPiped = true
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let oldHandler = target.writeHandler
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proc handler(data: seq[byte]) {.async, closure.} =
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if not isNil(oldHandler):
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await oldHandler(data)
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# if we're piping to self,
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# then add the data to the
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# buffer directly and fire
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# the read event
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if s == target:
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for b in data:
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s.readBuf.addLast(b)
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# notify main loop of available
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# data
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s.dataReadEvent.fire()
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else:
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await target.pushTo(data)
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s.writeHandler = handler
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result = target
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proc `|`*(s: BufferStream, target: BufferStream): BufferStream =
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## pipe operator to make piping less verbose
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pipe(s, target)
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method close*(s: BufferStream) {.async.} =
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## close the stream and clear the buffer
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for r in s.readReqs:
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if not(isNil(r)) and not(r.finished()):
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r.cancel()
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s.dataReadEvent.fire()
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s.readBuf.clear()
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s.closeEvent.fire()
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s.isClosed = true
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