punchd/asyncutils.nim

import asyncdispatch, threadpool, osproc
from os import
  osLastError,
  newOsError
from posix import
  SOL_SOCKET,
  SCM_RIGHTS,
  EINTR,
  EWOULDBLOCK,
  EAGAIN,
  IOVec,
  Tmsghdr,
  Tcmsghdr,
  SocketHandle,
  CMSG_SPACE,
  CMSG_FIRSTHDR,
  CMSG_LEN,
  CMSG_DATA,
  sendmsg

## asyncReadline as discussed at https://github.com/nim-lang/Nim/issues/11564
proc asyncReadline*(): Future[string] =
  let event = newAsyncEvent()
  let future = newFuture[string]("asyncReadline")
  proc readlineBackground(event: AsyncEvent): string =
    result = stdin.readline()
    event.trigger()
  let flowVar = spawn readlineBackground(event)
  proc callback(fd: AsyncFD): bool =
    future.complete(^flowVar)
    true                                                                                
  addEvent(event, callback)
  return future

proc asyncExecCmd*(command: string): Future[int] =
  let event = newAsyncEvent()
  let future = newFuture[int]("asyncExecCmd")
  proc execCmdBackground(event: AsyncEvent, command: string): int =
    result = execCmd(command)
    event.trigger()
  let flowVar = spawn execCmdBackground(event, command)
  proc callback(fd: AsyncFD): bool =
    future.complete(^flowVar)
    true                                                                                
  addEvent(event, callback)
  return future

proc asyncSendMsg*(fd: AsyncFD,
                   data: string,
                   fds: openArray[AsyncFD] = []): Future[void] =
  var retFuture = newFuture[void]("asyncSendMsg")

  proc cb(sock: AsyncFD): bool =
    # FIXME: if file descriptors are given in fds, check if sock is a unix socket
    result = true

    # sendmsg needs an array of iovec structs as described in the writev(2) man
    # page. The message is passed as a msghdr struct which may contain ancillary
    # data, see sendmsg(2) man page. We use ancillary data exclusively for
    # passing file descriptors if any are given in fds.
    var iovec = IOVec(iov_base: data.cstring,
                      iov_len: data.len.csize_t)
    var msg = Tmsghdr(msg_iov: addr iovec,
                      msg_iovlen: 1)
    if fds.len > 0:
      # assemble ancillary data, see cmsg(3) man page
      let cmsgBufferLen = CMSG_SPACE(sizeof(AsyncFD).csize_t * fds.len.csize_t)
      let cmsgBuffer = newString(cmsgBufferLen)
      msg.msg_control = cmsgBuffer.cstring
      msg.msg_controllen = cmsgBufferLen
      let cmsg: ptr Tcmsghdr = CMSG_FIRSTHDR(addr msg)
      cmsg.cmsg_len = CMSG_LEN(sizeof(AsyncFD).csize_t * fds.len.csize_t)
      cmsg.cmsg_level = SOL_SOCKET
      cmsg.cmsg_type = SCM_RIGHTS
      copyMem(CMSG_DATA(cmsg), unsafeAddr fds[0], sizeof(AsyncFD) * fds.len)

    let res = sendmsg(sock.SocketHandle, addr msg, 0)
    if res < 0:
      let lastError = osLastError()
      if lastError.int32 != EINTR and
         lastError.int32 != EWOULDBLOCK and
         lastError.int32 != EAGAIN:
        retFuture.fail(newOSError(lastError))
      else:
        result = false
    else:
      retFuture.complete()

  addWrite(fd, cb)
  return retFuture