Refactor HTTP request handling with RequestHandler base class

Introduce a new RequestHandler base class to introduce a shared session,
centralize HTTP request management and error handling across plugins.

Key changes:
- Add RequestHandler base class with a shared/cached session
- Convert TimeoutSession to use SingletonMeta for proper resource
  management
- Create LyricsRequestHandler subclass with lyrics-specific error
  handling
- Update MusicBrainzAPI to inherit from RequestHandler

beetsplug/_utils/requests.py

@@ -1,38 +1,149 @@
+from __future__ import annotations
+
 import atexit
+import threading
+from contextlib import contextmanager
+from functools import cached_property
 from http import HTTPStatus
+from typing import TYPE_CHECKING, Any, ClassVar, Generic, Protocol, TypeVar
 
 import requests
 
 from beets import __version__
 
-
-class HTTPNotFoundError(requests.exceptions.HTTPError):
-    pass
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
 
-class CaptchaError(requests.exceptions.HTTPError):
-    pass
+class BeetsHTTPError(requests.exceptions.HTTPError):
+    STATUS: ClassVar[HTTPStatus]
+
+    def __init__(self, *args, **kwargs) -> None:
+        super().__init__(
+            f"HTTP Error: {self.STATUS.value} {self.STATUS.phrase}",
+            *args,
+            **kwargs,
+        )
 
 
-class TimeoutSession(requests.Session):
+class HTTPNotFoundError(BeetsHTTPError):
+    STATUS = HTTPStatus.NOT_FOUND
+
+
+class Closeable(Protocol):
+    """Protocol for objects that have a close method."""
+
+    def close(self) -> None: ...
+
+
+C = TypeVar("C", bound=Closeable)
+
+
+class SingletonMeta(type, Generic[C]):
+    """Metaclass ensuring a single shared instance per class.
+
+    Creates one instance per class type on first instantiation, reusing it
+    for all subsequent calls. Automatically registers cleanup on program exit
+    for proper resource management.
+    """
+
+    _instances: ClassVar[dict[type[Any], Any]] = {}
+    _lock: ClassVar[threading.Lock] = threading.Lock()
+
+    def __call__(cls, *args: Any, **kwargs: Any) -> C:
+        if cls not in cls._instances:
+            with cls._lock:
+                if cls not in SingletonMeta._instances:
+                    instance = super().__call__(*args, **kwargs)
+                    SingletonMeta._instances[cls] = instance
+                    atexit.register(instance.close)
+        return SingletonMeta._instances[cls]
+
+
+class TimeoutSession(requests.Session, metaclass=SingletonMeta):
+    """HTTP session with automatic timeout and status checking.
+
+    Extends requests.Session to provide sensible defaults for beets HTTP
+    requests: automatic timeout enforcement, status code validation, and
+    proper user agent identification.
+    """
+
     def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
         self.headers["User-Agent"] = f"beets/{__version__} https://beets.io/"
 
-        @atexit.register
-        def close_session():
-            """Close the requests session on shut down."""
-            self.close()
-
     def request(self, *args, **kwargs):
-        """Wrap the request method to raise an exception on HTTP errors."""
+        """Execute HTTP request with automatic timeout and status validation.
+
+        Ensures all requests have a timeout (defaults to 10 seconds) and raises
+        an exception for HTTP error status codes.
+        """
         kwargs.setdefault("timeout", 10)
         r = super().request(*args, **kwargs)
-        if r.status_code == HTTPStatus.NOT_FOUND:
-            raise HTTPNotFoundError("HTTP Error: Not Found", response=r)
-        if 300 <= r.status_code < 400:
-            raise CaptchaError("Captcha is required", response=r)
-
         r.raise_for_status()
 
         return r
+
+
+class RequestHandler:
+    """Manages HTTP requests with custom error handling and session management.
+
+    Provides a reusable interface for making HTTP requests with automatic
+    conversion of standard HTTP errors to beets-specific exceptions. Supports
+    custom session types and error mappings that can be overridden by
+    subclasses.
+    """
+
+    session_type: ClassVar[type[TimeoutSession]] = TimeoutSession
+    explicit_http_errors: ClassVar[list[type[BeetsHTTPError]]] = [
+        HTTPNotFoundError
+    ]
+
+    @cached_property
+    def session(self) -> Any:
+        """Lazily initialize and cache the HTTP session."""
+        return self.session_type()
+
+    def status_to_error(
+        self, code: int
+    ) -> type[requests.exceptions.HTTPError] | None:
+        """Map HTTP status codes to beets-specific exception types.
+
+        Searches the configured explicit HTTP errors for a matching status code.
+        Returns None if no specific error type is registered for the given code.
+        """
+        return next(
+            (e for e in self.explicit_http_errors if e.STATUS == code), None
+        )
+
+    @contextmanager
+    def handle_http_error(self) -> Iterator[None]:
+        """Convert standard HTTP errors to beets-specific exceptions.
+
+        Wraps operations that may raise HTTPError, automatically translating
+        recognized status codes into their corresponding beets exception types.
+        Unrecognized errors are re-raised unchanged.
+        """
+        try:
+            yield
+        except requests.exceptions.HTTPError as e:
+            if beets_error := self.status_to_error(e.response.status_code):
+                raise beets_error(response=e.response) from e
+            raise
+
+    def request(self, method: str, *args, **kwargs) -> requests.Response:
+        """Perform HTTP request using the session with automatic error handling.
+
+        Delegates to the underlying session method while converting recognized
+        HTTP errors to beets-specific exceptions through the error handler.
+        """
+        with self.handle_http_error():
+            return getattr(self.session, method)(*args, **kwargs)
+
+    def get(self, *args, **kwargs) -> requests.Response:
+        """Perform HTTP GET request with automatic error handling."""
+        return self.request("get", *args, **kwargs)
+
+    def fetch_json(self, *args, **kwargs):
+        """Fetch and parse JSON data from an HTTP endpoint."""
+        return self.get(*args, **kwargs).json()

beetsplug/lyrics.py

@@ -26,7 +26,7 @@ from functools import cached_property, partial, total_ordering
 from html import unescape
 from itertools import groupby
 from pathlib import Path
-from typing import TYPE_CHECKING, Iterable, Iterator, NamedTuple
+from typing import TYPE_CHECKING, NamedTuple
 from urllib.parse import quote, quote_plus, urlencode, urlparse
 
 import langdetect
@@ -34,14 +34,17 @@ import requests
 from bs4 import BeautifulSoup
 from unidecode import unidecode
 
-import beets
 from beets import plugins, ui
 from beets.autotag.distance import string_dist
 from beets.util.config import sanitize_choices
 
-from ._utils.requests import CaptchaError, HTTPNotFoundError, TimeoutSession
+from ._utils.requests import HTTPNotFoundError, RequestHandler
 
 if TYPE_CHECKING:
+    from collections.abc import Iterable, Iterator
+
+    import confuse
+
     from beets.importer import ImportTask
     from beets.library import Item, Library
     from beets.logging import BeetsLogger as Logger
@@ -57,7 +60,9 @@ if TYPE_CHECKING:
 INSTRUMENTAL_LYRICS = "[Instrumental]"
 
 
-r_session = TimeoutSession()
+class CaptchaError(requests.exceptions.HTTPError):
+    def __init__(self, *args, **kwargs) -> None:
+        super().__init__("Captcha is required", *args, **kwargs)
 
 
 # Utilities.
@@ -153,9 +158,18 @@ def slug(text: str) -> str:
     return re.sub(r"\W+", "-", unidecode(text).lower().strip()).strip("-")
 
 
-class RequestHandler:
+class LyricsRequestHandler(RequestHandler):
     _log: Logger
 
+    def status_to_error(self, code: int) -> type[requests.HTTPError] | None:
+        if err := super().status_to_error(code):
+            return err
+
+        if 300 <= code < 400:
+            return CaptchaError
+
+        return None
+
     def debug(self, message: str, *args) -> None:
         """Log a debug message with the class name."""
         self._log.debug(f"{self.__class__.__name__}: {message}", *args)
@@ -185,7 +199,7 @@ class RequestHandler:
         """
         url = self.format_url(url, params)
         self.debug("Fetching HTML from {}", url)
-        r = r_session.get(url, **kwargs)
+        r = self.get(url, **kwargs)
         r.encoding = None
         return r.text
 
@@ -193,13 +207,13 @@ class RequestHandler:
         """Return JSON data from the given URL."""
         url = self.format_url(url, params)
         self.debug("Fetching JSON from {}", url)
-        return r_session.get(url, **kwargs).json()
+        return super().fetch_json(url, **kwargs)
 
     def post_json(self, url: str, params: JSONDict | None = None, **kwargs):
         """Send POST request and return JSON response."""
         url = self.format_url(url, params)
         self.debug("Posting JSON to {}", url)
-        return r_session.post(url, **kwargs).json()
+        return self.request("post", url, **kwargs).json()
 
     @contextmanager
     def handle_request(self) -> Iterator[None]:
@@ -218,8 +232,10 @@ class BackendClass(type):
         return cls.__name__.lower()
 
 
-class Backend(RequestHandler, metaclass=BackendClass):
-    def __init__(self, config, log):
+class Backend(LyricsRequestHandler, metaclass=BackendClass):
+    config: confuse.Subview
+
+    def __init__(self, config: confuse.Subview, log: Logger) -> None:
         self._log = log
         self.config = config
 
@@ -710,7 +726,7 @@ class Google(SearchBackend):
 
 
 @dataclass
-class Translator(RequestHandler):
+class Translator(LyricsRequestHandler):
     TRANSLATE_URL = "https://api.cognitive.microsofttranslator.com/translate"
     LINE_PARTS_RE = re.compile(r"^(\[\d\d:\d\d.\d\d\]|) *(.*)$")
     SEPARATOR = " | "
@@ -918,7 +934,7 @@ class RestFiles:
         ui.print_(textwrap.dedent(text))
 
 
-class LyricsPlugin(RequestHandler, plugins.BeetsPlugin):
+class LyricsPlugin(LyricsRequestHandler, plugins.BeetsPlugin):
     BACKEND_BY_NAME = {
         b.name: b for b in [LRCLib, Google, Genius, Tekstowo, MusiXmatch]
     }

beetsplug/musicbrainz.py

@@ -34,6 +34,7 @@ from beets.metadata_plugins import MetadataSourcePlugin
 from beets.util.id_extractors import extract_release_id
 
 from ._utils.requests import HTTPNotFoundError, TimeoutSession
+from .lyrics import RequestHandler
 
 if TYPE_CHECKING:
     from typing import Literal
@@ -58,10 +59,6 @@ FIELDS_TO_MB_KEYS = {
 }
 
 
-class LimiterTimeoutSession(LimiterMixin, TimeoutSession):
-    pass
-
-
 RELEASE_INCLUDES = [
     "artists",
     "media",
@@ -99,30 +96,36 @@ BROWSE_CHUNKSIZE = 100
 BROWSE_MAXTRACKS = 500
 
 
+class LimiterTimeoutSession(LimiterMixin, TimeoutSession):
+    pass
+
+
 @dataclass
-class MusicBrainzAPI:
+class MusicBrainzAPI(RequestHandler):
+    session_type = LimiterTimeoutSession
+
     api_host: str
     rate_limit: float
 
     @cached_property
     def session(self) -> LimiterTimeoutSession:
-        return LimiterTimeoutSession(per_second=self.rate_limit)
+        return self.session_type(per_second=self.rate_limit)
 
-    def _get(self, entity: str, **kwargs) -> JSONDict:
-        return self.session.get(
+    def get_entity(self, entity: str, **kwargs) -> JSONDict:
+        return self.fetch_json(
             f"{self.api_host}/ws/2/{entity}", params={**kwargs, "fmt": "json"}
-        ).json()
+        )
 
     def get_release(self, id_: str) -> JSONDict:
-        return self._get(f"release/{id_}", inc=" ".join(RELEASE_INCLUDES))
+        return self.get_entity(f"release/{id_}", inc=" ".join(RELEASE_INCLUDES))
 
     def get_recording(self, id_: str) -> JSONDict:
-        return self._get(f"recording/{id_}", inc=" ".join(TRACK_INCLUDES))
+        return self.get_entity(f"recording/{id_}", inc=" ".join(TRACK_INCLUDES))
 
     def browse_recordings(self, **kwargs) -> list[JSONDict]:
         kwargs.setdefault("limit", BROWSE_CHUNKSIZE)
         kwargs.setdefault("inc", BROWSE_INCLUDES)
-        return self._get("recording", **kwargs)["recordings"]
+        return self.get_entity("recording", **kwargs)["recordings"]
 
 
 def _preferred_alias(aliases: list[JSONDict]):
@@ -149,7 +152,7 @@ def _preferred_alias(aliases: list[JSONDict]):
             if (
                 alias["locale"] == locale
                 and alias.get("primary")
-                and alias.get("type", "").lower() not in ignored_alias_types
+                and (alias.get("type") or "").lower() not in ignored_alias_types
             ):
                 matches.append(alias)
 
@@ -790,7 +793,7 @@ class MusicBrainzPlugin(MetadataSourcePlugin):
         self._log.debug(
             "Searching for MusicBrainz {}s with: {!r}", query_type, query
         )
-        return self.api._get(
+        return self.api.get_entity(
             query_type, query=query, limit=self.config["search_limit"].get()
         )[f"{query_type}s"]
 

test/plugins/test_musicbrainz.py

@@ -1031,7 +1031,7 @@ class TestMusicBrainzPlugin(PluginMixin):
 
     def test_item_candidates(self, monkeypatch, mb):
         monkeypatch.setattr(
-            "beetsplug.musicbrainz.MusicBrainzAPI._get",
+            "beetsplug.musicbrainz.MusicBrainzAPI.fetch_json",
             lambda *_, **__: {"recordings": [self.RECORDING]},
         )
 
@@ -1042,7 +1042,7 @@ class TestMusicBrainzPlugin(PluginMixin):
 
     def test_candidates(self, monkeypatch, mb):
         monkeypatch.setattr(
-            "beetsplug.musicbrainz.MusicBrainzAPI._get",
+            "beetsplug.musicbrainz.MusicBrainzAPI.fetch_json",
             lambda *_, **__: {"releases": [{"id": self.mbid}]},
         )
         monkeypatch.setattr(