getdeps: introduce TransientFailure exception type

Summary:
The goal is to return an error code > 127 in the case of a
transient, retryable, infrastructure error.  This diff generates
those in the case of failure in downloading a URL or from interacting
with LFS.

Reviewed By: strager

Differential Revision: D15266838

fbshipit-source-id: 4f52a791320123968869032c37912dded464a86e

build/fbcode_builder/getdeps.py

@@ -16,6 +16,7 @@ import subprocess
 import sys
 
 from getdeps.buildopts import setup_build_options
+from getdeps.errors import TransientFailure
 from getdeps.load import load_project, manifests_in_dependency_order
 from getdeps.manifest import ManifestParser
 from getdeps.platform import HostType, context_from_host_tuple
@@ -407,7 +408,14 @@ def main():
         return 0
     try:
         return args.func(args)
-    except subprocess.CalledProcessError:
+    except TransientFailure as exc:
+        print("TransientFailure: %s" % str(exc))
+        # This return code is treated as a retryable transient infrastructure
+        # error by Facebook's internal CI, rather than eg: a build or code
+        # related error that needs to be fixed before progress can be made.
+        return 128
+    except subprocess.CalledProcessError as exc:
+        print("%s" % str(exc), file=sys.stderr)
         print("!! Failed", file=sys.stderr)
         return 1
 

build/fbcode_builder/getdeps/errors.py

@@ -0,0 +1,16 @@
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+
+class TransientFailure(Exception):
+    """ Raising this error causes getdeps to return with an error code
+    that Sandcastle will consider to be a retryable transient
+    infrastructure error """
+
+    pass

build/fbcode_builder/getdeps/fetcher.py

@@ -21,6 +21,7 @@ import zipfile
 
 from .copytree import prefetch_dir_if_eden
 from .envfuncs import Env
+from .errors import TransientFailure
 from .platform import is_windows
 from .runcmd import run_cmd
 
@@ -548,7 +549,13 @@ def download_url_to_file_with_progress(url, file_name):
 
     progress = Progress()
     start = time.time()
-    (_filename, headers) = urlretrieve(url, file_name, reporthook=progress.progress)
+    try:
+        (_filename, headers) = urlretrieve(url, file_name, reporthook=progress.progress)
+    except OSError as exc:
+        raise TransientFailure(
+            "Failed to download %s to %s: %s" % (url, file_name, str(exc))
+        )
+
     end = time.time()
     sys.stdout.write(" [Complete in %f seconds]\n" % (end - start))
     sys.stdout.flush()