nixguix: Deal with connection error with server

When that arises, we skip the origins.

Related to T3781

swh/lister/nixguix/lister.py

@@ -25,7 +25,7 @@ from typing import Any, Dict, Iterator, List, Optional, Tuple, Union
 from urllib.parse import urlparse
 
 import requests
-from requests.exceptions import InvalidSchema, SSLError
+from requests.exceptions import ConnectionError, InvalidSchema, SSLError
 
 from swh.core.github.utils import GitHubSession
 from swh.core.tarball import MIMETYPE_TO_ARCHIVE_FORMAT
@@ -143,7 +143,7 @@ def is_tarball(urls: List[str], request: Optional[Any] = None) -> Tuple[bool, st
 
         try:
             response = request.head(url)
-        except (InvalidSchema, SSLError):
+        except (InvalidSchema, SSLError, ConnectionError):
             raise ArtifactNatureUndetected(
                 f"Cannot determine artifact type from url <{url}>"
             )

swh/lister/nixguix/tests/data/guix-swh_sources.json

@@ -20,6 +20,13 @@
       ],
       "integrity": "sha256-bss09x9yOnuW+Q5BHHjf8nNcCNxCKMdl9/2/jKSFcrQ="
     },
+    {
+      "type": "url",
+      "urls": [
+        "https://git-tails.immerda.ch/onioncircuits"
+      ],
+      "integrity": "sha256-lV3xiWUZmSnt4LW0ni/sUyC/bbtaxkTzvFLFtJKLuI4="
+    },
     {
       "type": "url",
       "urls": [ "unknown://example.org/wrong-scheme-so-skipped.txt" ],

swh/lister/nixguix/tests/test_lister.py

@@ -11,6 +11,7 @@ from typing import Dict, List
 
 import pytest
 import requests
+from requests.exceptions import ConnectionError, InvalidSchema, SSLError
 
 from swh.lister import TARBALL_EXTENSIONS
 from swh.lister.nixguix.lister import (
@@ -229,16 +230,21 @@ def test_lister_nixguix_mostly_noop(datadir, swh_scheduler, requests_mock):
         "https://crates.io/api/v1/0.1.5/no-extension-and-head-404-so-skipped",
         status_code=404,
     )
-    # Will raise for that origin, this will get ignored as we cannot determine anything
+    # Invalid schema for that origin (and no extension), so skip origin
     # from its name
     requests_mock.head(
         "ftp://ftp.ourproject.org/file-with-no-extension",
-        exc=requests.exceptions.InvalidSchema,
+        exc=InvalidSchema,
     )
-    # Cannot communicate with an expired cert so skip
+    # Cannot communicate with an expired cert, so skip origin
     requests_mock.head(
         "https://code.9front.org/hg/plan9front",
-        exc=requests.exceptions.SSLError,
+        exc=SSLError,
+    )
+    # Cannot connect to the site, so skip origin
+    requests_mock.head(
+        "https://git-tails.immerda.ch/onioncircuits",
+        exc=ConnectionError,
     )
 
     listed_result = lister.run()