t}` (macOS when installed through Homebrew)
* `/tmp/.s.PGSQL.{port}` (default otherwise)

This depends on the value of `port` being correct.
If Postgres is using a port other than the default (`5432`), `port` must be set.

If no Unix domain socket is found, `localhost` is assumed.

Note: this description is updated on a best-effort basis.
See `default_host()` in the same source file as this method for the current behavior.

# Note: SSL
## Root Certs
If `sslrootcert` is not set, the default root certificates used depends on Cargo features:

* If `tls-native-tls` is enabled, the system root certificates are used.
* If `tls-rustls-native-roots` is enabled, the system root certificates are used.
* Otherwise, TLS roots are populated using the [`webpki-roots`] crate.

## Environment Variables
Unlike with `libpq`, the following environment variables may be _either_
a path to a file _or_ a string value containing a [PEM-encoded value][rfc7468]:

* `PGSSLROOTCERT`
* `PGSSLCERT`
* `PGSSLKEY`

If the string begins with the standard `-----BEGIN <CERTIFICATE | PRIVATE KEY>-----` header
and ends with the standard `-----END <CERTIFICATE | PRIVATE KEY>-----` footer,
it is parsed directly.

This behavior is _only_ implemented for the environment variables, not the URL parameters.

Note: passing the SSL private key via environment variable may be a security risk.

# Note: Unix Domain Sockets
If you want to connect to Postgres over a Unix domain socket, you can pass the path
to the _directory_ containing the socket as the `host` parameter.

The final path to the socket will be `{host}/.s.PGSQL.{port}` as is standard for Postgres.

If you're passing the domain socket path as the host segment of the URL, forward slashes
in the path must be [percent-encoded] (replacing `/` with `%2F`), e.g.:

```text
postgres://%2Fvar%2Frun%2Fpostgresql/dbname

Different port:
postgres://%2Fvar%2Frun%2Fpostgresql:5433/dbname

With username and password:
postgres://user:password@%2Fvar%2Frun%2Fpostgresql/dbname

With username and password, and different port:
postgres://user:password@%2Fvar%2Frun%2Fpostgresql:5432/dbname
```

Instead, the hostname can be passed in the query segment of the URL,
which does not require forward-slashes to be percent-encoded
(however, [other characters are][percent-encoded]):

```text
postgres:dbname?host=/var/run/postgresql

Different port:
postgres://:5433/dbname?host=/var/run/postgresql

With username and password:
postgres://user:password@/dbname?host=/var/run/postgresql

With username and password, and different port:
postgres://user:password@:5433/dbname?host=/var/run/postgresql
```

# Example

```rust,no_run
use sqlx::{Connection, ConnectOptions};
use sqlx::postgres::{PgConnectOptions, PgConnection, PgPool, PgSslMode};

# async fn example() -> sqlx::Result<()> {
// URL connection string
let conn = PgConnection::connect("postgres://localhost/mydb").await?;

// Manually-constructed options
let conn = PgConnectOptions::new()
    .host("secret-host")
    .port(2525)
    .username("secret-user")
    .password("secret-password")
    .ssl_mode(PgSslMode::Require)
    .connect()
    .await?;

// Modifying options parsed from a string
let mut opts: PgConnectOptions = "postgres://localhost/mydb".parse()?;

// Change the log verbosity level for queries.
// Information about SQL queries is logged at `DEBUG` level by default.
opts = opts.log_statements(log::LevelFilter::Trace);

let pool = PgPool::connect_with(opts).await?;
# Ok(())
# }
```

[percent-encoded]: https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding
[`passfile`]: https://www.postgresql.org/docs/current/libpq-pgpass.html
[libpq-connstring]: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING
[libpq-params]: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS
[libpq-envars]: https://www.postgresql.org/docs/current/libpq-envars.html
[rfc7468]: https://datatracker.ietf.org/doc/html/rfc7468
[`webpki-roots`]: https://docs.rs/webpki-roots