fix(server): properly detect remote_server URL scheme instead of substring match

CHANGELOG.md

@@ -38,6 +38,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/2.0.0/),
 - Fixed a bug in `LanguageTool._query_server` where `RateLimitError` was only raised when the rate-limit response body was invalid JSON, a valid JSON body with status 426 was silently returned as data instead (for now, the body from LanguageTool for rate-limiting responses is "Upgrade Required", which is not valid JSON, but this may change in the future).
 - Fixed a bug in `LanguageTool._terminate_server` where `_RUNNING_SERVER_PROCESSES.remove()` could raise `ValueError` if the server process was not yet in the list or was no longer in it.
 - Fixed a missing warning when downloading a LanguageTool zip file (with `LanguageTool` or `LocalLanguageTool`) without an available SHA-256 checksum. Now a `RuntimeWarning` is emitted in this case.
+- Fixed `remote_server` URL scheme detection in `language_tool_python.server.LanguageTool`, which used a fragile substring check (`"http" in remote_server`) and could misidentify a host containing "http" in its name (e.g. `myhttpserver.example.com`) as already having a scheme. `parse_url` now correctly recognises `scheme://` URLs, bare `scheme:` URLs (e.g. `http:example.com`, `ftp:example.com`), and protocol-relative URLs (`//host`). Only `http`/`https` are accepted, raising `ValueError` otherwise (unsupported scheme, empty URL, or missing host), and warning via `RuntimeWarning` when `http://` is added by default.
 
 ### Removed
 - **Breaking:** Removed all functions and classes previously deprecated in v3.3.0:

src/language_tool_python/_internals/utils.py

@@ -3,9 +3,11 @@
 import logging
 import math
 import os
+import re
 import urllib.parse
 from pathlib import Path
-from typing import Protocol, runtime_checkable
+from typing import Protocol, cast, runtime_checkable
+from warnings import warn
 
 import psutil
 
@@ -28,22 +30,70 @@
 
 LTP_PATH_ENV_VAR = "LTP_PATH"  # LanguageTool download path
 
+_SUPPORTED_URL_SCHEMES = frozenset({"http", "https"})
+
+# Matches an explicit "scheme://" prefix, capturing the scheme name.
+_URL_SCHEME_RE = re.compile(r"^([a-zA-Z][a-zA-Z0-9+.-]*)://")
+
+# Matches an explicit "scheme:" prefix that lacks the "//" authority marker
+# (RFC 3986's scheme:opaque form, e.g. "ftp:example.com" or "mailto:a@b.com").
+_EXPLICIT_SCHEME_NO_SLASH_RE = re.compile(r"^([a-zA-Z][a-zA-Z0-9+.-]*):(?!\d)")
+
+
+def _check_supported_scheme(scheme: str) -> None:
+    """Raise ValueError if ``scheme`` is not one of the supported URL schemes."""
+    if scheme not in _SUPPORTED_URL_SCHEMES:
+        err = (
+            f"Unsupported URL scheme {scheme!r}. Only 'http' and 'https' are supported."
+        )
+        raise ValueError(err)
+
 
 def parse_url(url_str: str) -> str:
     """Parse the given URL string and ensure it has a scheme.
 
-    If the input URL string does not contain 'http', 'http://' is prepended to it. The
-    function then parses the URL and returns its canonical form.
-
     :param url_str: The URL string to be parsed.
     :type url_str: str
     :return: The parsed URL in its canonical form.
     :rtype: str
+    :raises ValueError: If ``url_str`` is empty (or only whitespace), uses an
+        unsupported scheme, or has no host.
     """
-    if "http" not in url_str:
-        url_str = "http://" + url_str
+    stripped = url_str.strip()
+    if not stripped:
+        err = "The URL must not be empty."
+        raise ValueError(err)
+
+    scheme_match = _URL_SCHEME_RE.match(stripped)
+    if scheme_match is not None:
+        # scheme is present and followed by "//"
+        scheme = cast("str", scheme_match.group(1)).lower()
+        _check_supported_scheme(scheme)
+    else:
+        explicit_scheme_match = _EXPLICIT_SCHEME_NO_SLASH_RE.match(stripped)
+        if explicit_scheme_match is not None:
+            # scheme is present but not followed by "//"
+            scheme = cast("str", explicit_scheme_match.group(1)).lower()
+            _check_supported_scheme(scheme)
+            stripped = scheme + stripped[explicit_scheme_match.end(1) :]
+        else:
+            # scheme is missing, so we default to "http://" and issue a warning
+            prefix = "http:" if stripped.startswith("//") else "http://"
+            stripped = prefix + stripped
+            warn(
+                "No scheme was specified in the URL, so the unsecure 'http://' "
+                "scheme was used by default. It is recommended to explicitly set the "
+                "protocol ('http://' or 'https://') yourself in the URL.",
+                RuntimeWarning,
+                stacklevel=2,
+            )
+
+    parsed = urllib.parse.urlparse(stripped)
+    if not parsed.hostname:
+        err = f"The URL {stripped!r} must include a host."
+        raise ValueError(err)
 
-    return urllib.parse.urlparse(url_str).geturl()
+    return parsed.geturl()
 
 
 def get_env_int(env_var: str, default: int) -> int:

tests/unit/test_internals_utils.py

@@ -40,15 +40,125 @@ def test_https_url_unchanged(self) -> None:
         assert parse_url("https://example.com") == "https://example.com"
 
     def test_adds_http_scheme(self) -> None:
-        """A host:port string without a scheme gets http:// prepended."""
-        result = parse_url("localhost:8081")
-        assert result.startswith("http://")
-        assert "localhost" in result
+        """A host:port string without a scheme gets http:// prepended and warns."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("localhost:8081")
+        assert result == "http://localhost:8081"
 
     def test_canonical_form(self) -> None:
         """An already-complete URL with trailing slash is returned unchanged."""
         assert parse_url("http://localhost:8081/") == "http://localhost:8081/"
 
+    def test_host_containing_http_substring_is_prefixed(self) -> None:
+        """A schemeless host containing 'http' in its name still gets prefixed."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("myhttpserver.example.com")
+        assert result == "http://myhttpserver.example.com"
+
+    def test_host_with_port_and_path(self) -> None:
+        """A schemeless host:port/path string is prefixed and preserved."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("example.com:8081/api")
+        assert result == "http://example.com:8081/api"
+
+    def test_uppercase_scheme_is_normalised(self) -> None:
+        """An uppercase scheme is recognised and normalised to lowercase."""
+        assert parse_url("HTTP://example.com") == "http://example.com"
+
+    def test_mixed_case_https_scheme_is_normalised(self) -> None:
+        """A mixed-case https scheme is recognised and normalised to lowercase."""
+        assert parse_url("HTTPS://example.com") == "https://example.com"
+
+    def test_strips_surrounding_whitespace(self) -> None:
+        """Leading and trailing whitespace around the URL is ignored."""
+        assert parse_url("  http://example.com  ") == "http://example.com"
+
+    def test_empty_string_raises(self) -> None:
+        """An empty URL string raises ValueError."""
+        with pytest.raises(ValueError, match="must not be empty"):
+            parse_url("")
+
+    def test_whitespace_only_raises(self) -> None:
+        """A whitespace-only URL string raises ValueError."""
+        with pytest.raises(ValueError, match="must not be empty"):
+            parse_url("   ")
+
+    def test_unsupported_scheme_raises(self) -> None:
+        """An explicit, unsupported scheme (e.g. ftp) raises ValueError."""
+        with pytest.raises(ValueError, match="Unsupported URL scheme 'ftp'"):
+            parse_url("ftp://example.com")
+
+    def test_file_scheme_raises(self) -> None:
+        """An explicit file:// scheme raises ValueError instead of passing through."""
+        with pytest.raises(ValueError, match="Unsupported URL scheme 'file'"):
+            parse_url("file:///etc/passwd")
+
+    def test_scheme_without_host_raises(self) -> None:
+        """A scheme with no host raises ValueError."""
+        with pytest.raises(ValueError, match="must include a host"):
+            parse_url("http://")
+
+    def test_scheme_with_empty_host_and_port_raises(self) -> None:
+        """A scheme with a port but no host raises ValueError."""
+        with pytest.raises(ValueError, match="must include a host"):
+            parse_url("http://:8081")
+
+    def test_error_message_strips_whitespace(self) -> None:
+        """The host-missing error message does not leak surrounding whitespace."""
+        with pytest.raises(
+            ValueError, match=r"^The URL 'http://:8081' must include a host\.$"
+        ):
+            parse_url("  http://:8081  ")
+
+    def test_protocol_relative_url_gets_http_scheme(self) -> None:
+        """A protocol-relative URL (//host) is given an http:// scheme, not mangled."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("//example.com:8081")
+        assert result == "http://example.com:8081"
+
+    def test_explicit_scheme_without_slashes_raises_clean_message(self) -> None:
+        """An RFC 3986 scheme:opaque form (no host) raises with a clean message."""
+        with pytest.raises(
+            ValueError, match=r"^The URL 'http:example\.com' must include a host\.$"
+        ):
+            parse_url("http:example.com")
+
+    def test_uppercase_explicit_scheme_without_slashes_raises(self) -> None:
+        """An uppercase scheme:opaque form is treated the same as lowercase."""
+        with pytest.raises(ValueError, match="must include a host"):
+            parse_url("HTTPS:example.com")
+
+    def test_schemeless_host_port_unaffected_by_scheme_without_slash_detection(
+        self,
+    ) -> None:
+        """A schemeless host:port input is still treated as schemeless."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("localhost:8081")
+        assert result == "http://localhost:8081"
+
+    def test_schemeless_host_port_path_unaffected_by_scheme_without_slash_detection(
+        self,
+    ) -> None:
+        """A schemeless host:port/path input is still treated as schemeless."""
+        with pytest.warns(RuntimeWarning, match="No scheme was specified"):
+            result = parse_url("example.com:8081/api")
+        assert result == "http://example.com:8081/api"
+
+    def test_ftp_scheme_without_slashes_raises_unsupported(self) -> None:
+        """An unsupported scheme:opaque form (ftp:) raises Unsupported URL scheme."""
+        with pytest.raises(ValueError, match="Unsupported URL scheme 'ftp'"):
+            parse_url("ftp:example.com")
+
+    def test_mailto_scheme_without_slashes_raises_unsupported(self) -> None:
+        """An unsupported scheme:opaque form (mailto:) raises Unsupported URL scheme."""
+        with pytest.raises(ValueError, match="Unsupported URL scheme 'mailto'"):
+            parse_url("mailto:a@b.com")
+
+    def test_ws_scheme_without_slashes_raises_unsupported(self) -> None:
+        """An unsupported scheme:opaque form (ws:) raises Unsupported URL scheme."""
+        with pytest.raises(ValueError, match="Unsupported URL scheme 'ws'"):
+            parse_url("ws:example.com")
+
 
 class TestGetEnvInt:
     """Tests for get_env_int() environment variable reader."""