Add DistributionMetadata.read_pkg_file

This is the baseline, unchanged from the version in distutils.dist, to
be modified before patching.

setuptools/dist.py

@@ -53,6 +53,59 @@ def get_metadata_version(dist_md):
     return StrictVersion('1.0')
 
 
+def read_pkg_file(self, file):
+    """Reads the metadata values from a file object."""
+    msg = message_from_file(file)
+
+    def _read_field(name):
+        value = msg[name]
+        if value == 'UNKNOWN':
+            return None
+        return value
+
+    def _read_list(name):
+        values = msg.get_all(name, None)
+        if values == []:
+            return None
+        return values
+
+    metadata_version = msg['metadata-version']
+    self.name = _read_field('name')
+    self.version = _read_field('version')
+    self.description = _read_field('summary')
+    # we are filling author only.
+    self.author = _read_field('author')
+    self.maintainer = None
+    self.author_email = _read_field('author-email')
+    self.maintainer_email = None
+    self.url = _read_field('home-page')
+    self.license = _read_field('license')
+
+    if 'download-url' in msg:
+        self.download_url = _read_field('download-url')
+    else:
+        self.download_url = None
+
+    self.long_description = _read_field('description')
+    self.description = _read_field('summary')
+
+    if 'keywords' in msg:
+        self.keywords = _read_field('keywords').split(',')
+
+    self.platforms = _read_list('platform')
+    self.classifiers = _read_list('classifier')
+
+    # PEP 314 - these fields only exist in 1.1
+    if metadata_version == '1.1':
+        self.requires = _read_list('requires')
+        self.provides = _read_list('provides')
+        self.obsoletes = _read_list('obsoletes')
+    else:
+        self.requires = None
+        self.provides = None
+        self.obsoletes = None
+
+
 # Based on Python 3.5 version
 def write_pkg_file(self, file):
     """Write the PKG-INFO format data to a file object.