Add database creation code

src/postgres.rs

@@ -8,6 +8,8 @@ pub(crate) enum Error {
     NoRolCreateDb,
     #[error("user does not have permission `rolcreaterole`")]
     NoRolCreateRole,
+    #[error("not a valid identifier: {0}")]
+    InvalidIdent(String),
     #[error(transparent)]
     PostgresError(#[from] tokio_postgres::Error),
 }
@@ -80,4 +82,45 @@ impl PostgresConnection {
 
         Ok(())
     }
+
+    pub(crate) async fn create_instance(
+        &self,
+        role_name: &str,
+        role_password: &str,
+        db_name: &str,
+    ) -> Result<(), Error> {
+        assert_valid_ident(role_name)?;
+        assert_valid_ident(db_name)?;
+
+        // Create role if it does not exist yet.
+        if self.client.query_opt("SELECT usename FROM pg_user WHERE usename = $1;", &[&role_name]).await?.is_none() {
+            // User does not exist, ensure we create it.
+            let create_role_sql = format!("CREATE ROLE {} NOCREATEDB NOCREATEROLE NOINHERIT LOGIN NOREPLICATION NOBYPASSRLS CONNECTION LIMIT 8 PASSWORD $1;", role_name);
+            self.client.execute(&create_role_sql, &[&role_name, &role_password]).await?;
+        };
+
+        // Same for database, only create if not existent yet.
+        if self.client.query_opt("SELECT datname FROM pg_database WHERE datname = $1", &[&db_name]).await?.is_none() {
+            let create_db_sql = format!("CREATE DATABASE {} WITH OWNER = {};", db_name, role_name);
+            self.client.execute(&create_db_sql, &[]).await?;
+        }
+
+        Ok(())
+    }
+}
+
+fn valid_ident(input: &str) -> bool {
+    let Some(first) = input.chars().next() else { return false; }
+
+    if !first.is_alphabetic() {
+        return false;
+    }
+
+    input.chars().all(|c| c.is_alphanumeric() || c == '_' || c == '$')
+}
+
+fn assert_valid_ident(input: &str) -> Result<(), Error> {
+    if !valid_ident(input) {
+       Err(Error::InvalidIdent(input.to_owned()))
+    }  else {Ok(())}
 }