Validate host in SQLAlchemy URL helper

tests/unit/sqlalchemy/test_dialect.py

@@ -4,6 +4,7 @@
 from unittest import mock
 
 import pytest
+from sqlalchemy import exc
 from sqlalchemy.engine.url import make_url
 from sqlalchemy.engine.url import URL
 
@@ -314,3 +315,34 @@ def test_trino_connection_oauth2_auth():
     _, cparams = dialect.create_connect_args(url)
 
     assert isinstance(cparams['auth'], OAuth2Authentication)
+
+
+@pytest.mark.parametrize(
+    "host",
+    [
+        "https://trino.example.com",  # scheme prefix (the common mistake)
+        "http://trino.example.com",
+        "trino.example.com:443",      # port embedded in host
+        "trino.example.com/path",     # path embedded in host
+        "user@trino.example.com",     # credentials embedded in host
+        "::1",                        # unbracketed IPv6 literal
+    ],
+)
+def test_url_rejects_non_hostname_host(host):
+    with pytest.raises(exc.ArgumentError, match="host must be a hostname only"):
+        trino_url(host=host, port=443, user="user")
+
+
+@pytest.mark.parametrize(
+    "host",
+    [
+        "trino.example.com",
+        "localhost",
+        "192.168.0.1",
+        "[::1]",              # bracketed IPv6 literal
+        "host_with.dots-and_underscores",
+    ],
+)
+def test_url_accepts_bare_hostname(host):
+    # A valid host must round-trip through make_url without error.
+    assert make_url(trino_url(host=host, port=443, user="user")).host is not None

trino/sqlalchemy/util.py

@@ -6,6 +6,7 @@
 from typing import Tuple
 from typing import Union
 from urllib.parse import quote_plus
+from urllib.parse import urlparse
 
 from sqlalchemy import exc
 
@@ -14,6 +15,23 @@ def _rfc_1738_quote(text):
     return re.sub(r"[:@/]", lambda m: "%%%X" % ord(m.group(0)), text)
 
 
+def _assert_valid_host(host: str) -> None:
+    # Parse with a leading "//" so a bare hostname is treated as the authority
+    # rather than a path. `urlparse(host).scheme` catches an embedded scheme.
+    parsed = urlparse("//" + host)
+    try:
+        has_port = parsed.port is not None
+    except ValueError:
+        # A malformed port raises here.
+        has_port = True
+    if urlparse(host).scheme or has_port or parsed.path or parsed.username or parsed.password:
+        raise exc.ArgumentError(
+            f"host must be a hostname only, without a scheme, port, path, or credentials. Got {host!r}. "
+            "For example, use 'example.com' instead of 'https://example.com' and pass the port via the "
+            "'port' argument."
+        )
+
+
 def _url(
     host: str,
     port: Optional[int] = 8080,
@@ -56,6 +74,8 @@ def _url(
     if not host:
         raise exc.ArgumentError("host must be specified.")
 
+    _assert_valid_host(host)
+
     trino_url += host
 
     if not port: