fix @eas342's bug - which was that, if a partial file was detected and

continuation was set to False (which is the case - MAST hard-codes
that), no download was being done - we were only retrieving the header,
not the data

Author: keflavich

astroquery/query.py

@@ -412,7 +412,6 @@ def _download_file(self, url, local_filepath, timeout=None, auth=None,
         verbose : bool
             Whether to show download progress. Defaults to True.
         """
-
         if head_safe:
             response = self._session.request("HEAD", url,
                                              timeout=timeout, stream=True,
@@ -442,6 +441,7 @@ def _download_file(self, url, local_filepath, timeout=None, auth=None,
                          .format(local_filepath, existing_file_length))
                 return
             elif existing_file_length == 0:
+                log.info(f"Found existing {local_filepath} file with length 0.  Overwriting.")
                 open_mode = 'wb'
                 if head_safe:
                     response = self._session.request(method, url,
@@ -459,6 +459,7 @@ def _download_file(self, url, local_filepath, timeout=None, auth=None,
                 end = "{0}".format(length-1) if length is not None else ""
                 self._session.headers['Range'] = "bytes={0}-{1}".format(existing_file_length,
                                                                         end)
+                log.debug(f"Continuing with range={self._session.headers['Range']}")
 
                 response = self._session.request(method, url,
                                                  timeout=timeout, stream=True,
@@ -471,8 +472,16 @@ def _download_file(self, url, local_filepath, timeout=None, auth=None,
                 statinfo = os.stat(local_filepath)
                 if statinfo.st_size != length:
                     log.warning(f"Found cached file {local_filepath} with size {statinfo.st_size} "
-                                f"that is different from expected size {length}")
+                                f"that is different from expected size {length}.  ")
+                    if continuation:
+                        log.warning(
+                                "Continuation was requested but is not possible because "
+                                "'Accepts-Ranges' is not in the response headers.")
                     open_mode = 'wb'
+                    response = self._session.request(method, url,
+                                                    timeout=timeout, stream=True,
+                                                    auth=auth, **kwargs)
+                    response.raise_for_status()
                 else:
                     log.info("Found cached file {0} with expected size {1}."
                              .format(local_filepath, statinfo.st_size))
@@ -493,7 +502,7 @@ def _download_file(self, url, local_filepath, timeout=None, auth=None,
         blocksize = astropy.utils.data.conf.download_block_size
 
         log.debug(f"Downloading URL {url} to {local_filepath} with size {length} "
-                  f"by blocks of {blocksize}")
+                  f"by blocks of {blocksize} with open_mode={open_mode}")
 
         bytes_read = 0