Unix domain sockets (UDS, AF_UNIX) in System.inheritedChannel() and elsewhere in Java

[Alan Bateman]

On 21/07/2019 11:01, František Kučera wrote:
> I would also prefer String or Path in the Java API but 
> sockaddr_un.sun_path is defined in the POSIX standard as a byte array 
> and it might be not only a file path but there are also "abstract" 
> paths which have no representation on the filesystem – they start with 
> \0 null-byte and the abstract path is the whole rest of the array. So 
> lossless mapping between byte arrays and strings will be difficult or 
> maybe impossible (the "@" character is sometimes used in the UI 
> instead of the \0 but "@" is also valid character on the filesystem 
> path, so there are ambiguities).  Although Java Sting can hold the \0 
> bytes, depending on local encoding there might be edge cases where the 
> path is a valid byte array (sun_path) and is addressable from the 
> POSIX API but is not a valid String in given encoding. Maybe there 
> might be subclasses for abstract and non-abstract addresses... but in 
> the prototype, I looked for the simplest solution (but buggy, I know, 
> it e.g. includes all the \0s in the toString() representation).
The implementation of Path on Unix systems uses bytes so will preserve 
the original file path, you just need to be careful to avoid Path -> 
String round trips.

> :
>
> The System.inheritedChannel() is in the Java base – there might be 
> some indirect/optional dependency from the base to the module. Idea: 
> create an SPI interface with methods canCreateChannel(fd) and 
> createChannel(fd); the new module will implement this interface for 
> AF_UNIX file descriptors; and the System.inheritedChannel() will 
> lookup implementations of this interface and try to get the channel 
> from them; and if no implementation will return a channel, it will 
> fallback to the current implementation. Is it possible solution?
>
> May the java.net.UnixSocketAddress and 
> java.net.StandardProtocolFamily.UNIX stay where they are?
For the prototype then you should be able to put UnixSocketAddress and 
UnixProtocolFamily in jdk.net too. On naming, one of the discussion 
points will be whether it should be LocalSocketAddress as PF_UNIX is 
deprecated in favor of PF_LOCAL on some systems. A bigger discussion 
point will be whether to introduce new channel types rather than trying 
to have alternative implementations of 
SocketChannel/ServerSocketChannel. The approach that we've been taking 
with the RDMA API is to use the existing API and have the factory 
methods that that create the RDMA socket channel specify the differences.

>
> My primary goal was to fix the wrong addresses (random IP and port) 
> returned from System.inheritedChannel() 
If fd 0 is a Unix domain socket then inheritedChannel should return 
null. Are you sure you it's returning a SocketChannel to something that 
is not a stream or datagram socket? If so then then this is a bug that 
should be looked into.

-Alan