fix: validate address format in _parse_address with clear errors

Previously, bare hostnames without port caused confusing ValueError
about unpacking. Now raises clear messages for missing port, invalid
port, and malformed IPv6 brackets.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqliteclient/connection.py

@@ -13,12 +13,28 @@ def _parse_address(address: str) -> tuple[str, int]:
     """Parse a host:port address string, handling IPv6 brackets."""
     if address.startswith("["):
         # Bracketed IPv6: [host]:port
+        if "]:" not in address:
+            raise ValueError(
+                f"Invalid IPv6 address format: expected '[host]:port', got {address!r}"
+            )
         bracket_end = address.index("]")
         host = address[1:bracket_end]
         port_str = address[bracket_end + 2:]  # Skip ']:
     else:
+        if ":" not in address:
+            raise ValueError(
+                f"Invalid address format: expected 'host:port', got {address!r}"
+            )
         host, port_str = address.rsplit(":", 1)
-    return host, int(port_str)
+
+    try:
+        port = int(port_str)
+    except ValueError:
+        raise ValueError(
+            f"Invalid port in address {address!r}: {port_str!r} is not a number"
+        ) from None
+
+    return host, port
 
 
 class DqliteConnection:

tests/test_connection.py

@@ -29,6 +29,24 @@ def test_ipv6_full_bracketed(self) -> None:
 
         assert _parse_address("[2001:db8::1]:9001") == ("2001:db8::1", 9001)
 
+    def test_bare_hostname_raises(self) -> None:
+        from dqliteclient.connection import _parse_address
+
+        with pytest.raises(ValueError, match="expected.*host:port"):
+            _parse_address("localhost")
+
+    def test_invalid_port_raises(self) -> None:
+        from dqliteclient.connection import _parse_address
+
+        with pytest.raises(ValueError, match="not a number"):
+            _parse_address("localhost:abc")
+
+    def test_ipv6_no_port_raises(self) -> None:
+        from dqliteclient.connection import _parse_address
+
+        with pytest.raises(ValueError, match="expected.*host.*port"):
+            _parse_address("[::1]")
+
 
 class TestDqliteConnection:
     def test_init(self) -> None: