Support unix domain socket connections

[mp911de]

It would make sense to support unix domain sockets as connection addresses in addition to host/port-based addressing.

Using PostgresqlConnectionConfiguration, we could introduce a socket(…) configuration method to configure the socket endpoint.

For PostgresqlConnectionFactoryProvider, we could have a Option.valueOf("socket") that configures the socket to use.

Probably we don't have a good way how to configure the socket using URL-based connection strings as we assume <host>[/<database>] as pattern. The path does not provide any information about whether the last segment is a database name or whether it belongs to the socket. At configuration time, the socket might not even be available so a exists check cannot be used to disambiguate the string.

Related issue: spring-projects/spring-data-r2dbc#192

[mirromutth]

How about r2dbc:postgresql:unix:///absolute/path/to/xxx.sock[/<database>]? Relative path will like r2dbc:postgresql:unix://relative/path/to/xxx.sock[/<database>] or r2dbc:postgresql:unix://./relative/path/to/xxx.sock[/<database>] (In other words, protocol is unix, path end by last .sock)

May be useful: SSLSessionHandlerAdapter#operationComplete() cast the type of channel.remoteAddress() result to be InetSocketAddress when SSLMode is VERIFY_FULL, because it need verify the hostname.

So, VERIFY_FULL should be unavailable when using unix domain socket.

[mp911de]

Although MySQL uses the .sock scheme, there's really nothing that would enforce it. So let's keep the URL variant out of scope for now. I was also wondering about SSL. Probably we don't need SSL, I haven't investigated yet what the database does if SSL is available or whether it's possible to use client certificates over unix domain sockets. Likely, SSL and domain sockets do not make sense.

[jvz]

Did you ever decide on a URL syntax for this feature?

[mp911de]

The format is: r2dbc:postgresql:///foo?socket=/tmp/.s.PGSQL.5432