Override the raise_for_status method for silencing logs

closes pulp#518

CHANGES/518.bugfix

@@ -0,0 +1 @@
+Silenced redundant logs when downloading signatures.

pulp_container/app/downloaders.py

@@ -165,6 +165,22 @@ def auth_header(token, basic_auth):
         return {}
 
 
+class NoAuthSignatureDownloader(HttpDownloader):
+    """A downloader class suited for signature downloads."""
+
+    def raise_for_status(self, response):
+        """Log an error only if the status code of the response is not equal to 404.
+
+        Status codes equal to 404 signify that a signature could not be found on the server. This
+        case is still valid because it is not possible to determine the number of signatures
+        beforehand.
+        """
+        if response.status == 404:
+            raise FileNotFoundError()
+        else:
+            response.raise_for_status()
+
+
 class NoAuthDownloaderFactory(DownloaderFactory):
     """
     A downloader factory without any preset auth configuration, TLS or basic auth.

pulp_container/app/models.py

@@ -323,7 +323,13 @@ def noauth_download_factory(self):
         try:
             return self._noauth_download_factory
         except AttributeError:
-            self._noauth_download_factory = downloaders.NoAuthDownloaderFactory(self)
+            self._noauth_download_factory = downloaders.NoAuthDownloaderFactory(
+                self,
+                downloader_overrides={
+                    "http": downloaders.NoAuthSignatureDownloader,
+                    "https": downloaders.NoAuthSignatureDownloader,
+                }
+            )
             return self._noauth_download_factory
 
     def get_downloader(self, remote_artifact=None, url=None, **kwargs):

pulp_container/app/tasks/sync_stages.py

@@ -525,14 +525,14 @@ async def create_signatures(self, man_dc, signature_source):
                 signature_downloader = self.remote.get_noauth_downloader(url=signature_url)
                 try:
                     signature_download_result = await signature_downloader.run()
-                except aiohttp.client_exceptions.ClientResponseError as exc:
-                    if exc.status != 404:
-                        log.info(
-                            "{} is not accessible, can't sync an image signature. "
-                            "Error: {} {}".format(signature_url, exc.status, exc.message)
-                        )
+                except FileNotFoundError:
                     # 404 is fine, it means there are no or no more signatures available
                     break
+                except aiohttp.client_exceptions.ClientResponseError as exc:
+                    log.info(
+                        "{} is not accessible, can't sync an image signature. "
+                        "Error: {} {}".format(signature_url, exc.status, exc.message)
+                    )
 
                 with open(signature_download_result.path, "rb") as f:
                     signature_raw = f.read()