8236184: (dc) IP_MULTICAST_* and IP_TOS socket options not effective

[Daniel Fuchs]

Hi Alan,

DatagramChannelImpl:

  382             // remaining options don't need any special handling
  383             Net.setSocketOption(fd, family, name, value);
  384             if (needToSetIPv4Option) {
  385                 try {
  386                     Net.setSocketOption(fd, 
StandardProtocolFamily.INET, name, value);
  387                 } catch (IOException ignore) { }
  388             }

If family == StandardProtocolFamily.INET && needToSetIPv4Option
won't that set the option twice?

If this is impossible - maybe an assert could make it explicit:
    assert family != StandardProtocolFamily.INET || !needToSetIPv4Option


Otherwise looks reasonable to me.
Does the new test pass reliably on macOS? We already have some
multicast tests in the ProblemList.txt for that platform.

best regards,

-- daniel

On 18/12/2019 17:47, Alan Bateman wrote:
> 
> This is another update to the DatagramChannel implementation so that it 
> can be used by the upcoming re-implementation of DatagramSocket and 
> MulticastSocket.
> 
> DatagramChannel has good multicast support but some of the IP_ socket 
> options are only are effective for IPv6 datagrams when the channel's 
> socket is IPv6, e.g. IP_MUILTICAST_IF sets the outgoing multicast 
> interface for IPv6 multicast datagrams but not IPv4 multicast datagrams. 
> The javadoc is clear that many aspects of multicasting are platform 
> dependent and all of the IP_ socket options are clear that it is 
> platform specific as to whether they apply to IPv4 datagrams when the 
> socket is IPv6. So not a concern for DatagramChannel as the protocol 
> family is specified as creation time. However it is a concern for code 
> using the existing MulticastSocket API as the protocol family cannot be 
> specified.
> 
> The patch proposed here updates DatagramChannel's setOption 
> implementation to set both the IPv4 and IPv6 sockets on platforms that 
> support this. For example, setOption(IP_MULTICAST_TTL, 8) will attempt 
> to set both IP_TOS and IPV6_TCLASS when the socket is IPv6 on platforms 
> that allow IP_TOS to set the ToS field of IPv4 datagrams sent with the 
> socket. Legacy networking has been doing the same on Linux for many 
> releases. The change does the same on Windows, something legacy 
> networking doesn't need to do because MulticastSocket uses two sockets 
> on Windows.
> 
> The webrev with the changes is here:
>    http://cr.openjdk.java.net/~alanb/8236184/webrev/
> 
> Testing these changes is difficult and requires using tcpdump/equivalent 
> to look at the network. However we can test IP_MULTICAST_LOOP so I've 
> added a test for that.
> 
> 
> -Alan