nim-libp2p/libp2p/stream/streamseq.nim

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import stew/bitops2
{.push raises: [Defect].}
type
StreamSeq* = object
# Seq adapted to the stream use case where we add data at the back and
# consume at the front in chunks. A bit like a deque but contiguous memory
# area - will try to avoid moving data unless it has to, subject to buffer
# space. The assumption is that data is typically consumed fully.
#
# See also asio::stream_buf
buf: seq[byte] # Data store
rpos: int # Reading position - valid data starts here
wpos: int # Writing position - valid data ends here
template len*(v: StreamSeq): int =
v.wpos - v.rpos
func grow(v: var StreamSeq, n: int) =
if v.rpos == v.wpos:
# All data has been consumed, reset positions
v.rpos = 0
v.wpos = 0
if v.buf.len - v.wpos < n:
if v.rpos > 0:
# We've consumed some data so we'll try to move that data to the beginning
# of the buffer, hoping that this will clear up enough capacity to avoid
# reallocation
moveMem(addr v.buf[0], addr v.buf[v.rpos], v.wpos - v.rpos)
v.wpos -= v.rpos
v.rpos = 0
if v.buf.len - v.wpos >= n:
return
# TODO this is inefficient - `setLen` will copy all data of buf, even though
# we know that only a part of it contains "valid" data
v.buf.setLen(nextPow2(max(64, v.wpos + n).uint64).int)
template prepare*(v: var StreamSeq, n: int): var openArray[byte] =
## Return a buffer that is at least `n` bytes long
mixin grow
v.grow(n)
v.buf.toOpenArray(v.wpos, v.buf.len - 1)
template commit*(v: var StreamSeq, n: int) =
## Mark `n` bytes in the buffer returned by `prepare` as ready for reading
v.wpos += n
func add*(v: var StreamSeq, data: openArray[byte]) =
## Add data - the equivalent of `buf.prepare(n) = data; buf.commit(n)`
if data.len > 0:
v.grow(data.len)
copyMem(addr v.buf[v.wpos], unsafeAddr data[0], data.len)
v.commit(data.len)
template data*(v: StreamSeq): openArray[byte] =
# Data that is ready to be consumed
# TODO a double-hash comment here breaks compile (!)
v.buf.toOpenArray(v.rpos, v.wpos - 1)
template toOpenArray*(v: StreamSeq, b, e: int): openArray[byte] =
# Data that is ready to be consumed
# TODO a double-hash comment here breaks compile (!)
v.buf.toOpenArray(v.rpos + b, v.rpos + e - b)
func consume*(v: var StreamSeq, n: int) =
## Mark `n` bytes that were returned via `data` as consumed
v.rpos += n
func consumeTo*(v: var StreamSeq, buf: var openArray[byte]): int =
let bytes = min(buf.len, v.len)
if bytes > 0:
copyMem(addr buf[0], addr v.buf[v.rpos], bytes)
v.consume(bytes)
bytes
func clear*(v: var StreamSeq) =
v.consume(v.len)
func assign*(v: var StreamSeq, buf: openArray[byte]) =
v.clear()
v.add(buf)