Replaceing the metadata parser from packaging.metadata

Replace parse_email() + Metadata.from_raw() with Metadata.from_email() for simpler code and proper validation. Use parse_metadata() helper where appropriate and fix empty metadata error handling.

Fixes: #561

Signed-off-by: Lalatendu Mohanty <lmohanty@redhat.com>

Author: LalatenduMohanty

src/fromager/bootstrapper.py

@@ -10,7 +10,6 @@
 import tempfile
 import typing
 import zipfile
-from email.parser import BytesParser
 from urllib.parse import urlparse
 
 from packaging.requirements import Requirement
@@ -907,10 +906,8 @@ def _get_version_from_package_metadata(
             config_settings=pbi.config_settings,
         )
         metadata_filename = source_dir.parent / metadata_dir_base / "METADATA"
-        with open(metadata_filename, "rb") as f:
-            p = BytesParser()
-            metadata = p.parse(f, headersonly=True)
-        return Version(metadata["Version"])
+        metadata = dependencies.parse_metadata(metadata_filename)
+        return metadata.version
 
     def _resolve_prebuilt_with_history(
         self,

src/fromager/candidate.py

@@ -2,12 +2,10 @@
 import datetime
 import logging
 import typing
-from email.message import EmailMessage, Message
-from email.parser import BytesParser
 from io import BytesIO
-from typing import TYPE_CHECKING
 from zipfile import ZipFile
 
+from packaging.metadata import Metadata
 from packaging.requirements import Requirement
 from packaging.utils import BuildTag, canonicalize_name
 from packaging.version import Version
@@ -16,13 +14,6 @@
 
 logger = logging.getLogger(__name__)
 
-# fix for runtime errors caused by inheriting classes that are generic in stubs but not runtime
-# https://mypy.readthedocs.io/en/latest/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime
-if TYPE_CHECKING:
-    Metadata = Message[str, str]
-else:
-    Metadata = Message
-
 
 @dataclasses.dataclass(frozen=True, order=True, slots=True, repr=False, kw_only=True)
 class Candidate:
@@ -73,11 +64,10 @@ def metadata(self) -> Metadata:
         return self._metadata
 
     def _get_dependencies(self) -> typing.Iterable[Requirement]:
-        deps = self.metadata.get_all("Requires-Dist", [])
+        deps = self.metadata.requires_dist or []
         extras = self.extras if self.extras else [""]
 
-        for d in deps:
-            r = Requirement(d)
+        for r in deps:
             if r.marker is None:
                 yield r
             else:
@@ -95,7 +85,8 @@ def dependencies(self) -> list[Requirement]:
 
     @property
     def requires_python(self) -> str | None:
-        return self.metadata.get("Requires-Python")
+        spec = self.metadata.requires_python
+        return str(spec) if spec is not None else None
 
 
 def get_metadata_for_wheel(url: str, metadata_url: str | None = None) -> Metadata:
@@ -107,7 +98,7 @@ def get_metadata_for_wheel(url: str, metadata_url: str | None = None) -> Metadat
         metadata_url: Optional URL of the metadata file (PEP 658)
 
     Returns:
-        Parsed metadata as a Message object
+        Parsed metadata as a Metadata object
     """
     # Try PEP 658 metadata endpoint first if available
     if metadata_url:
@@ -119,8 +110,7 @@ def get_metadata_for_wheel(url: str, metadata_url: str | None = None) -> Metadat
             response.raise_for_status()
 
             # Parse metadata directly from the response content
-            p = BytesParser()
-            metadata = p.parse(BytesIO(response.content), headersonly=True)
+            metadata = Metadata.from_email(response.content)
             logger.debug(f"Successfully retrieved metadata via PEP 658 for {url}")
             return metadata
 
@@ -136,8 +126,8 @@ def get_metadata_for_wheel(url: str, metadata_url: str | None = None) -> Metadat
     with ZipFile(BytesIO(data)) as z:
         for n in z.namelist():
             if n.endswith(".dist-info/METADATA"):
-                p = BytesParser()
-                return p.parse(z.open(n), headersonly=True)
+                metadata_content = z.read(n)
+                return Metadata.from_email(metadata_content)
 
-    # If we didn't find the metadata, return an empty dict
-    return EmailMessage()
+    # If we didn't find the metadata, raise an error
+    raise ValueError(f"Could not find METADATA file in wheel: {url}")

tests/test_pep658_support.py

@@ -56,10 +56,11 @@ def test_get_metadata_with_pep658_success(self, mock_session) -> None:
         metadata = get_metadata_for_wheel(wheel_url, metadata_url)
 
         # Verify the metadata was parsed correctly
-        assert metadata["Name"] == "test-package"
-        assert metadata["Version"] == "1.0.0"
-        assert metadata["Summary"] == "A test package"
-        assert "requests >= 2.0.0" in metadata.get_all("Requires-Dist", [])
+        assert metadata.name == "test-package"
+        assert str(metadata.version) == "1.0.0"
+        assert metadata.summary == "A test package"
+        assert metadata.requires_dist is not None
+        assert any(str(req) == "requests>=2.0.0" for req in metadata.requires_dist)
 
         # Verify only the metadata URL was called, not the wheel URL
         mock_session.get.assert_called_once_with(metadata_url)