upload: add connection exceptions to upload retry protocol

tests/test_repository.py

@@ -269,6 +269,49 @@ def test_upload_retry(tmpdir, default_repo, caplog):
     ]
 
 
+def test_upload_retry_on_connection_error(tmpdir, default_repo, caplog):
+    default_repo.disable_progress_bar = True
+
+    default_repo.session = pretend.stub(
+        post=pretend.raiser(requests.exceptions.ConnectionError)
+    )
+
+    fakefile = tmpdir.join("fake.whl")
+    fakefile.write(".")
+
+    package = pretend.stub(
+        safe_name="fake",
+        metadata=pretend.stub(version="2.12.0"),
+        basefilename="fake.whl",
+        filename=str(fakefile),
+        metadata_dictionary=lambda: {"name": "fake"},
+    )
+
+    # Upload with default max_redirects of 5
+    default_repo.upload(package)
+
+    assert caplog.messages == [
+        (
+            'ConnectionError raised.\n'
+            f"Package upload appears to have failed. Retry {i} of 5."
+        )
+        for i in range(1, 6)
+    ]
+
+    caplog.clear()
+
+    # Upload with custom max_redirects of 3
+    default_repo.upload(package, 3)
+
+    assert caplog.messages == [
+        (
+            'ConnectionError raised.\n'
+            f"Package upload appears to have failed. Retry {i} of 3."
+        )
+        for i in range(1, 4)
+    ]
+
+
 @pytest.mark.parametrize(
     "package_meta,repository_url,release_urls",
     [

twine/repository.py

@@ -183,21 +183,31 @@ def upload(
     ) -> requests.Response:
         number_of_redirects = 0
         while number_of_redirects < max_redirects:
-            resp = self._upload(package)
-
-            if resp.status_code == requests.codes.OK:
-                return resp
-            if 500 <= resp.status_code < 600:
+            try:
+                resp = self._upload(package)
+            except (
+                requests.exceptions.ConnectionError,
+                requests.exceptions.ConnectTimeout,
+            ) as exc:
                 number_of_redirects += 1
                 logger.warning(
-                    f'Received "{resp.status_code}: {resp.reason}"'
+                    f"{exc.__class__.__name__} raised."
                     "\nPackage upload appears to have failed."
                     f" Retry {number_of_redirects} of {max_redirects}."
                 )
+                continue
             else:
-                return resp
-
-        return resp
+                if resp.status_code == requests.codes.OK:
+                    return resp
+                if 500 <= resp.status_code < 600:
+                    number_of_redirects += 1
+                    logger.warning(
+                        f'Received "{resp.status_code}: {resp.reason}"'
+                        "\nPackage upload appears to have failed."
+                        f" Retry {number_of_redirects} of {max_redirects}."
+                    )
+                else:
+                    return resp
 
     def package_is_uploaded(
         self, package: package_file.PackageFile, bypass_cache: bool = False