better handling of http header for remote files

rocrate/model/file.py

@@ -20,10 +20,10 @@
 # limitations under the License.
 
 from pathlib import Path
+import requests
 import shutil
 import urllib.request
 import warnings
-from http.client import HTTPResponse
 from io import BytesIO, StringIO
 
 from .file_or_dir import FileOrDir
@@ -48,19 +48,20 @@ def write(self, base_path):
                 out_file.write(self.source.getvalue())
         elif is_url(str(self.source)):
             if self.fetch_remote or self.validate_url:
-                with urllib.request.urlopen(self.source) as response:
-                    if self.validate_url:
-                        if isinstance(response, HTTPResponse):
+                if self.validate_url:
+                    if self.source.startswith("http"):
+                        with requests.head(self.source) as response:
                             self._jsonld.update({
-                                'contentSize': response.getheader('Content-Length'),
-                                'encodingFormat': response.getheader('Content-Type')
+                                'contentSize': response.headers.get('Content-Length'),
+                                'encodingFormat': response.headers.get('Content-Type')
                             })
                         if not self.fetch_remote:
-                            self._jsonld['sdDatePublished'] = iso_now()
-                    if self.fetch_remote:
-                        out_file_path.parent.mkdir(parents=True, exist_ok=True)
-                        urllib.request.urlretrieve(response.url, out_file_path)
-                        self._jsonld['contentUrl'] = str(self.source)
+                            date_published = response.headers.get("Last-Modified", iso_now())
+                            self._jsonld['sdDatePublished'] = date_published
+                if self.fetch_remote:
+                    out_file_path.parent.mkdir(parents=True, exist_ok=True)
+                    urllib.request.urlretrieve(self.source, out_file_path)
+                    self._jsonld['contentUrl'] = str(self.source)
         elif self.source is None:
             # Allows to record a File entity whose @id does not exist, see #73
             warnings.warn(f"No source for {self.id}")