JDK-8233191 : MulticastSocket joinGroup/leaveGroup do not specify their behavior when the outgoing interface has not been set
  • Type: Bug
  • Component: core-libs
  • Sub-Component: java.net
  • Affected Version: 14
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2019-10-30
  • Updated: 2020-02-12
  • Resolved: 2019-12-09
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JDK 14
14 b27Fixed
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The 2-arg joinGroup/leaveGroup methods are specified to use the interface set by setNetworkInterface (or setInterface) when invoked with netIf==null. These methods do not specify how they should behave when the outgoing interface for multicast datagrams has not been set. It would not be unreasonable for these methods to throw SocketException although this would be a small behavioral compatibility issue as the long standing (and unspecified behavior) has been to pick a random interface.

While in the area, the getNetworkInterface (and getInterface) do not specify what they return when an outgoing interface for multicast datagrams has not been set. The long standing behavior has been to return a "useless" network interface (or anyLocalAddress).

URL: https://hg.openjdk.java.net/jdk/jdk/rev/8df91a722672 User: pconcannon Date: 2019-12-09 15:58:42 +0000

Implementing JDK-8233191 will be much easier once JDK-8233307 has been fixed.

Isn't there (or shouldn't there be) different behaviors depending on IPv4/IPv6? I mean - IPv6 addresses (bind address / group address) may have a scope that could influence which network interface gets picked?