only support sending one fd

asyncutils.nim

@@ -1,4 +1,4 @@
-import asyncdispatch, threadpool, osproc
+import asyncdispatch, threadpool, osproc, options
 from os import
   osLastError,
   newOsError
@@ -47,32 +47,34 @@ proc asyncExecCmd*(command: string): Future[int] =
 
 proc asyncSendMsg*(fd: AsyncFD,
                    data: string,
-                   fds: openArray[AsyncFD] = []): Future[void] =
+                   ancillaryData: Option[AsyncFD] = none(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
+    # FIXME: if file descriptor is given in ancillaryData, 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.
+    # passing a file descriptor if one is given in ancillaryData.
     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:
+    if ancillaryData.isSome:
       # assemble ancillary data, see cmsg(3) man page
-      let cmsgBufferLen = CMSG_SPACE(sizeof(AsyncFD).csize_t * fds.len.csize_t)
+      let cmsgBufferLen = CMSG_SPACE(sizeof(AsyncFD).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_len = CMSG_LEN(sizeof(AsyncFD).csize_t)
       cmsg.cmsg_level = SOL_SOCKET
       cmsg.cmsg_type = SCM_RIGHTS
-      copyMem(CMSG_DATA(cmsg), unsafeAddr fds[0], sizeof(AsyncFD) * fds.len)
+      var ancillaryFd = ancillaryData.get
+      copyMem(CMSG_DATA(cmsg), addr ancillaryFd, sizeof(AsyncFD))
 
     let res = sendmsg(sock.SocketHandle, addr msg, 0)
     if res < 0: