gracefully handle file open errors

cli/dcoscli/config/main.py

@@ -360,7 +360,7 @@ def _save_config_file(config_path, toml_config):
     """
 
     serial = toml.dumps(toml_config._dictionary)
-    with open(config_path, 'w') as config_file:
+    with util.open_file(config_path, 'w') as config_file:
         config_file.write(serial)
 
 

cli/dcoscli/marathon/main.py

@@ -289,8 +289,8 @@ def _get_resource(resource):
     :rtype: dict
     """
     if resource is not None:
-        with open(resource) as fd:
-            return util.load_json(fd)
+        with util.open_file(resource) as resource_file:
+            return util.load_json(resource_file)
 
     # Check that stdin is not tty
     if sys.stdin.isatty():

cli/dcoscli/package/main.py

@@ -246,11 +246,8 @@ def _user_options(path):
     if path is None:
         return {}
     else:
-        try:
-            with open(path) as options_file:
-                return util.load_json(options_file)
-        except IOError:
-            raise DCOSException('No such file: {}'.format(path))
+        with util.open_file(path) as options_file:
+            return util.load_json(options_file)
 
 
 def _confirm(prompt, yes):

cli/tests/integrations/test_package.py

@@ -385,7 +385,7 @@ def test_install_missing_options_file():
         returncode=1,
         stdout=b'We recommend a minimum of one node with at least 1 CPU and '
                b'2GB of RAM available for the Chronos Service.\n',
-        stderr=b"No such file: asdf.json\n")
+        stderr=b"Error opening file [asdf.json]: No such file or directory\n")
 
 
 def test_package_metadata():

dcos/auth.py

@@ -136,7 +136,7 @@ def _save_auth_keys(key_dict):
         toml_config[name] = python_value
 
     serial = toml.dumps(toml_config._dictionary)
-    with open(config_path, 'w') as config_file:
+    with util.open_file(config_path, 'w') as config_file:
         config_file.write(serial)
 
     return None

dcos/config.py

@@ -1,6 +1,7 @@
 import collections
 
 import toml
+from dcos import util
 
 
 def mutable_load_from_path(path):
@@ -12,7 +13,7 @@ def mutable_load_from_path(path):
     :rtype: MutableToml
     """
 
-    with open(path) as config_file:
+    with util.open_file(path) as config_file:
         return MutableToml(toml.loads(config_file.read()))
 
 
@@ -25,7 +26,7 @@ def load_from_path(path):
     :rtype: Toml
     """
 
-    with open(path) as config_file:
+    with util.open_file(path) as config_file:
         return Toml(toml.loads(config_file.read()))
 
 

dcos/package.py

@@ -630,18 +630,22 @@ def _acquire_file_lock(lock_file_path):
 
     :param lock_file_path: Path to the lock file
     :type lock_file_path: str
-    :returns: Lock file descriptor
+    :returns: Lock file
     :rtype: File
     """
 
-    lock_fd = open(lock_file_path, 'w')
+    try:
+        lock_file = open(lock_file_path, 'w')
+    except IOError as e:
+        raise util.io_exception(lock_file_path, e.errno)
+
     acquire_mode = portalocker.LOCK_EX | portalocker.LOCK_NB
 
     try:
-        portalocker.lock(lock_fd, acquire_mode)
-        return lock_fd
+        portalocker.lock(lock_file, acquire_mode)
+        return lock_file
     except portalocker.LockException:
-        lock_fd.close()
+        lock_file.close()
         raise DCOSException('Unable to acquire the package cache lock')
 
 
@@ -1036,11 +1040,9 @@ class Registry():
             raise DCOSException('Path [{}] is not a file'.format(index_path))
 
         try:
-            with open(index_path) as fd:
+            with util.open_file(index_path) as fd:
                 version_json = json.load(fd)
                 return version_json.get('version')
-        except IOError:
-            raise DCOSException('Unable to open file [{}]'.format(index_path))
         except ValueError:
             raise DCOSException('Unable to parse [{}]'.format(index_path))
 
@@ -1061,10 +1063,8 @@ class Registry():
             raise DCOSException('Path [{}] is not a file'.format(index_path))
 
         try:
-            with open(index_path) as fd:
+            with util.open_file(index_path) as fd:
                 return json.load(fd)
-        except IOError:
-            raise DCOSException('Unable to open file [{}]'.format(index_path))
         except ValueError:
             raise DCOSException('Unable to parse [{}]'.format(index_path))
 

dcos/subcommand.py

@@ -186,7 +186,7 @@ def _write_package_json(pkg, version):
 
     package_json = pkg.package_json(version)
 
-    with open(package_path, 'w') as package_file:
+    with util.open_file(package_path, 'w') as package_file:
         json.dump(package_json, package_file)
 
 
@@ -204,7 +204,7 @@ def _write_package_version(pkg, version):
 
     version_path = os.path.join(pkg_dir, 'version')
 
-    with open(version_path, 'w') as version_file:
+    with util.open_file(version_path, 'w') as version_file:
         version_file.write(version)
 
 
@@ -220,7 +220,7 @@ def _write_package_source(pkg):
 
     source_path = os.path.join(pkg_dir, 'source')
 
-    with open(source_path, 'w') as source_file:
+    with util.open_file(source_path, 'w') as source_file:
         source_file.write(pkg.registry.source.url)
 
 
@@ -447,5 +447,5 @@ class InstalledSubcommand(object):
         """
 
         package_json_path = os.path.join(self._dir(), 'package.json')
-        with open(package_json_path) as package_json_file:
+        with util.open_file(package_json_path) as package_json_file:
             return util.load_json(package_json_file)

dcos/util.py

@@ -15,7 +15,7 @@ import jsonschema
 import prettytable
 import pystache
 import six
-from dcos import config, constants
+from dcos import constants
 from dcos.errors import DCOSException
 
 
@@ -97,11 +97,8 @@ def read_file(path):
     if not os.path.isfile(path):
         raise DCOSException('Path [{}] is not a file'.format(path))
 
-    try:
-        with open(path) as fd:
-            return fd.read()
-    except IOError:
-        raise DCOSException('Unable to open file [{}]'.format(path))
+    with open_file(path) as file_:
+        return file_.read()
 
 
 def get_config():
@@ -110,6 +107,9 @@ def get_config():
     :rtype: Toml
     """
 
+    # avoid circular import
+    from dcos import config
+
     return config.load_from_path(
         os.environ[constants.DCOS_CONFIG_ENV])
 
@@ -509,4 +509,42 @@ def table(fields, objs, sortby=None):
     return tb
 
 
+@contextlib.contextmanager
+def open_file(path,  *args):
+    """Context manager that opens a file, and raises a DCOSException if
+    it fails.
+
+    :param path: file path
+    :type path: str
+    :param *args: other arguments to pass to `open`
+    :type *args: [str]
+    :returns: a context manager
+    :rtype: context manager
+    """
+
+    try:
+        file_ = open(path, *args)
+        yield file_
+    except IOError as e:
+        raise io_exception(path, e.errno)
+
+    file_.close()
+
+
+def io_exception(path, errno):
+    """Returns a DCOSException for when there is an error opening the
+    file at `path`
+
+    :param path: file path
+    :type path: str
+    :param errno: IO error number
+    :type errno: int
+    :returns: DCOSException
+    :rtype: DCOSException
+    """
+
+    return DCOSException('Error opening file [{}]: {}'.format(
+        path, os.strerror(errno)))
+
+
 logger = get_logger(__name__)

tests/test_util.py

@@ -1,4 +1,7 @@
 from dcos import util
+from dcos.errors import DCOSException
+
+import pytest
 
 
 def test_render_mustache_json():
@@ -16,3 +19,12 @@ def test_render_mustache_json():
     assert result.get('x') == xs
     assert result.get('y') == ys
     assert result.get('z') == z
+
+
+def test_open_file():
+    path = 'nonexistant_file_name.txt'
+    with pytest.raises(DCOSException) as excinfo:
+        with util.open_file(path):
+            pass
+    assert 'Error opening file [{}]: No such file or directory'.format(path) \
+        in str(excinfo.value)