Connection::parse rejects URLs without a host

[PuercoPop]

Ej. the URL postgresql:://myuser@/mydb is rejected by rust-postgres but is accepted by psql. ej. The following command succeds

$ psql -d postgresql:://myuser@/mydb.

But when calling Client::connect("postgresql:://myuser@/mydb", NoTls) we get

Error: DBerror(Error { kind: Config, cause: Some("host missing") })

From the PostgreSQL documentation this is a valid URL. Quoting relevant sections below:

In particular, a Unix-domain socket connection is chosen if the host part is either empty or looks like an absolute path name

And the grammar marks the host as optional as well

postgresql://[userspec@][hostspec][/dbname][?paramspec] ... and hostspec is:

[host][:port][,...]

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I looked briefly into how would fixing the issue would look like and iiuc I need to make the following test pass.

// tokio-postgres/tests/test/parse.rs
    #[cfg(unix)]
    check(
        "postgresql://user@/mydb",
        Config::new().user("user").host_path("/tmp").dbname("mydb"),
    );

One point of contention is what should the host_path be set to if the host is omitted. The documentation above only talks above standard unix-domain socket directory. The following link suggests that it should be /tmp on a vanilla PostgreSQL install. But that Debian and derivatives use /var/run/postgresql. In NixOS (my scenario) the default unix-domain socket directory is /run/postgresql. :shrug:

---

Note that although I encountered this error in production it is not a blocker as the workaround is straightforward.

[sfackler]

The Unix socket fallback is not implemented in this library - in libpq it depends on knowledge of the Postgres Unix socket directory which is set at Postgres compilation time and varies between distros.

[PuercoPop]

@sfackler Ok, so should I close the issue? Is it worth it detect that syntax was used and notify the that that syntax is not supported?

[sfackler]

Yeah unfortunately there isn't really anything we can do to make this work like it does for libpq.