Is flags={SocketFlag.Peek} buggy or am I missing something ?

[void09]

I have this code with asyncSocket on linux:
    
    
    while true:
      var msgSize = ""
      while msgSize.len == 0:
          try:
            msgSize = await asocket.recv(4, flags={SocketFlag.Peek})
            await sleepAsync(200)
          except ...
        try:
          resp = await asocket.recv(4 + msg2Int(msgSize))
        (proces message...)
    
    Run

This works as expected, until I get a larger message (16kB, confirmed with 
wireshark that I actually receive it). What happens is that it gets stuck on 
recv the first 4 bytes in peek mode, it stays at 0, even though I have not 
gotten the data out of the socket buffer. If I remove the Peek flag, and adjust 
the code (remove +4 from the second recv size), I get the expected data.

<https://man7.org/linux/man-pages/man2/recv.2.html> :
    

MSG_PEEK
    This flag causes the receive operation to return data from the beginning of 
the receive queue without removing that data from the queue. Thus, a subsequent 
receive call will return the same data.

Any idea what could be going on ?