implement asyncRecvMsg

asyncutils.nim

@@ -16,7 +16,8 @@ from posix import
   CMSG_FIRSTHDR,
   CMSG_LEN,
   CMSG_DATA,
-  sendmsg
+  sendmsg,
+  recvmsg
 
 ## asyncReadline as discussed at https://github.com/nim-lang/Nim/issues/11564
 proc asyncReadline*(): Future[string] =
@@ -90,3 +91,55 @@ proc asyncSendMsg*(fd: AsyncFD,
 
   addWrite(fd, cb)
   return retFuture
+
+proc asyncRecvMsg*(fd: AsyncFD,
+                   size: int): Future[tuple[data: string, ancillaryFd: Option[AsyncFD]]] =
+  var retFuture = newFuture[
+    tuple[data: string, ancillaryFd: Option[AsyncFD]]
+  ]("asyncRecvMsg")
+
+  proc cb(sock: AsyncFD): bool =
+    result = true
+
+    var dataBuffer = newString(size)
+    var iovec = IOVec(iov_base: dataBuffer.cstring,
+                      iov_len: dataBuffer.len.csize_t)
+    let cmsgBufferLen = CMSG_SPACE(sizeof(AsyncFD).csize_t)
+    let cmsgBuffer = newString(cmsgBufferLen)
+    var msg = Tmsghdr(msg_iov: addr iovec,
+                      msg_iovlen: 1,
+                      msg_control: cmsgBuffer.cstring,
+                      msg_controllen: cmsgBufferLen)
+    let cmsg: ptr Tcmsghdr = CMSG_FIRSTHDR(addr msg)
+    cmsg.cmsg_len = 0
+    cmsg.cmsg_level = 0
+    cmsg.cmsg_type = 0
+
+    let res = recvmsg(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
+      return
+
+    var ancillaryData = none(AsyncFD)
+    if cmsg.cmsg_len > 0:
+      if cmsg.cmsg_len == CMSG_LEN(sizeof(AsyncFD).csize_t) and
+         cmsg.cmsg_level == SOL_SOCKET and
+         cmsg.cmsg_type == SCM_RIGHTS:
+        var ancillaryFd: AsyncFD
+        copyMem(addr ancillaryFd, CMSG_DATA(cmsg), sizeof(AsyncFD))
+        ancillaryData = some(ancillaryFd)
+      else:
+        retFuture.fail(newException(ValueError, "unexpected ancillary data"))
+        return
+
+    dataBuffer.setLen(msg.msg_iov.iov_len)
+    retFuture.complete((dataBuffer, ancillaryData))
+
+  addRead(fd, cb)
+  return retFuture