Add abstract filesystem support to interface funcs

Add storage_backend as an optional parameter to functions in the interface
module which read files from the disk. When no argument is provided and
the default value of None is used, instantiate a FilesystemBackend and use
that to access files on the local filesystem.

Signed-off-by: Joshua Lock <jlock@vmware.com>

securesystemslib/interface.py

@@ -242,7 +242,8 @@ def generate_and_write_rsa_keypair(filepath=None, bits=DEFAULT_RSA_KEY_BITS,
 
 
 def import_rsa_privatekey_from_file(filepath, password=None,
-    scheme='rsassa-pss-sha256', prompt=False):
+    scheme='rsassa-pss-sha256', prompt=False,
+    storage_backend=None):
   """
   <Purpose>
     Import the PEM file in 'filepath' containing the private key.
@@ -272,6 +273,11 @@ def import_rsa_privatekey_from_file(filepath, password=None,
       If True the user is prompted for a passphrase to decrypt 'filepath'.
       Default is False.
 
+    storage_backend:
+      An object which implements
+      securesystemslib.storage.StorageBackendInterface. When no object is
+      passed a FilesystemStorageBackend will be instantiated and used.
+
   <Exceptions>
     ValueError, if 'password' is passed and 'prompt' is True.
 
@@ -344,9 +350,13 @@ def import_rsa_privatekey_from_file(filepath, password=None,
     logger.debug('No password was given. Attempting to import an'
         ' unencrypted file.')
 
+  if storage_backend is None:
+    storage_backend = securesystemslib.storage.FilesystemBackend()
+
   # Read the contents of 'filepath' that should be a PEM formatted private key.
-  with open(filepath, 'rb') as file_object:
-    pem_key = file_object.read().decode('utf-8')
+  file_object = storage_backend.get(filepath)
+  pem_key = file_object.read().decode('utf-8')
+  file_object.close()
 
   # Convert 'pem_key' to 'securesystemslib.formats.RSAKEY_SCHEMA' format.
   # Raise 'securesystemslib.exceptions.CryptoError' if 'pem_key' is invalid.
@@ -360,7 +370,8 @@ def import_rsa_privatekey_from_file(filepath, password=None,
 
 
 
-def import_rsa_publickey_from_file(filepath, scheme='rsassa-pss-sha256'):
+def import_rsa_publickey_from_file(filepath, scheme='rsassa-pss-sha256',
+    storage_backend=None):
   """
   <Purpose>
     Import the RSA key stored in 'filepath'.  The key object returned is in the
@@ -374,6 +385,11 @@ def import_rsa_publickey_from_file(filepath, scheme='rsassa-pss-sha256'):
     scheme:
       The signature scheme used by the imported key.
 
+    storage_backend:
+      An object which implements
+      securesystemslib.storage.StorageBackendInterface. When no object is
+      passed a FilesystemStorageBackend will be instantiated and used.
+
   <Exceptions>
     securesystemslib.exceptions.FormatError, if 'filepath' is improperly
     formatted.
@@ -397,10 +413,14 @@ def import_rsa_publickey_from_file(filepath, scheme='rsassa-pss-sha256'):
   # Is 'scheme' properly formatted?
   securesystemslib.formats.RSA_SCHEME_SCHEMA.check_match(scheme)
 
+  if storage_backend is None:
+    storage_backend = securesystemslib.storage.FilesystemBackend()
+
   # Read the contents of the key file that should be in PEM format and contains
   # the public portion of the RSA key.
-  with open(filepath, 'rb') as file_object:
-    rsa_pubkey_pem = file_object.read().decode('utf-8')
+  file_object = storage_backend.get(filepath)
+  rsa_pubkey_pem = file_object.read().decode('utf-8')
+  file_object.close()
 
   # Convert 'rsa_pubkey_pem' to 'securesystemslib.formats.RSAKEY_SCHEMA' format.
   try:
@@ -587,7 +607,8 @@ def import_ed25519_publickey_from_file(filepath):
 
 
 
-def import_ed25519_privatekey_from_file(filepath, password=None, prompt=False):
+def import_ed25519_privatekey_from_file(filepath, password=None, prompt=False,
+    storage_backend=None):
   """
   <Purpose>
     Import the encrypted ed25519 key file in 'filepath', decrypt it, and return
@@ -610,6 +631,11 @@ def import_ed25519_privatekey_from_file(filepath, password=None, prompt=False):
       If True the user is prompted for a passphrase to decrypt 'filepath'.
       Default is False.
 
+    storage_backend:
+      An object which implements
+      securesystemslib.storage.StorageBackendInterface. When no object is
+      passed a FilesystemStorageBackend will be instantiated and used.
+
   <Exceptions>
     securesystemslib.exceptions.FormatError, if the arguments are improperly
     formatted or the imported key object contains an invalid key type (i.e.,
@@ -634,6 +660,9 @@ def import_ed25519_privatekey_from_file(filepath, password=None, prompt=False):
   if password and prompt:
     raise ValueError("Passing 'password' and 'prompt' True is not allowed.")
 
+  if storage_backend is None:
+    storage_backend = securesystemslib.storage.FilesystemBackend()
+
   # If 'password' was passed check format and that it is not empty.
   if password is not None:
     securesystemslib.formats.PASSWORD_SCHEMA.check_match(password)
@@ -664,10 +693,11 @@ def import_ed25519_privatekey_from_file(filepath, password=None, prompt=False):
 
   # Finally, regardless of password, try decrypting the key, if necessary.
   # Otherwise, load it straight from the disk.
-  with open(filepath, 'rb') as file_object:
-    json_str = file_object.read()
-    return securesystemslib.keys.\
-           import_ed25519key_from_private_json(json_str, password=password)
+  file_object = storage_backend.get(filepath)
+  json_str = file_object.read()
+  file_object.close()
+  return securesystemslib.keys.\
+      import_ed25519key_from_private_json(json_str, password=password)
 
 
 
@@ -832,7 +862,8 @@ def import_ecdsa_publickey_from_file(filepath):
 
 
 
-def import_ecdsa_privatekey_from_file(filepath, password=None):
+def import_ecdsa_privatekey_from_file(filepath, password=None,
+    storage_backend=None):
   """
   <Purpose>
     Import the encrypted ECDSA key file in 'filepath', decrypt it, and return
@@ -850,6 +881,11 @@ def import_ecdsa_privatekey_from_file(filepath, password=None):
       encrypted key file 'filepath' must be decrypted before the ECDSA key
       object can be returned.
 
+    storage_backend:
+      An object which implements
+      securesystemslib.storage.StorageBackendInterface. When no object is
+      passed a FilesystemStorageBackend will be instantiated and used.
+
   <Exceptions>
     securesystemslib.exceptions.FormatError, if the arguments are improperly
     formatted or the imported key object contains an invalid key type (i.e.,
@@ -886,12 +922,16 @@ def import_ecdsa_privatekey_from_file(filepath, password=None):
   # Does 'password' have the correct format?
   securesystemslib.formats.PASSWORD_SCHEMA.check_match(password)
 
+  if storage_backend is None:
+    storage_backend = securesystemslib.storage.FilesystemBackend()
+
   # Store the encrypted contents of 'filepath' prior to calling the decryption
   # routine.
   encrypted_key = None
 
-  with open(filepath, 'rb') as file_object:
-    encrypted_key = file_object.read()
+  file_object = storage_backend.get(filepath)
+  encrypted_key = file_object.read()
+  file_object.close()
 
   # Decrypt the loaded key file, calling the 'cryptography' library to generate
   # the derived encryption key from 'password'.  Raise

tests/test_interface.py

@@ -218,8 +218,8 @@ def test_import_rsa_privatekey_from_file(self):
     # Non-existent key file.
     nonexistent_keypath = os.path.join(temporary_directory,
         'nonexistent_keypath')
-    self.assertRaises(IOError, interface.import_rsa_privatekey_from_file,
-        nonexistent_keypath, 'pw')
+    self.assertRaises(securesystemslib.exceptions.StorageError,
+        interface.import_rsa_privatekey_from_file, nonexistent_keypath, 'pw')
 
     # Invalid key file argument.
     invalid_keyfile = os.path.join(temporary_directory, 'invalid_keyfile')
@@ -252,8 +252,8 @@ def test_import_rsa_publickey_from_file(self):
     # Non-existent key file.
     nonexistent_keypath = os.path.join(temporary_directory,
         'nonexistent_keypath')
-    self.assertRaises(IOError, interface.import_rsa_publickey_from_file,
-        nonexistent_keypath)
+    self.assertRaises(securesystemslib.exceptions.StorageError,
+        interface.import_rsa_publickey_from_file, nonexistent_keypath)
 
     # Invalid key file argument.
     invalid_keyfile = os.path.join(temporary_directory, 'invalid_keyfile')
@@ -426,8 +426,9 @@ def test_import_ed25519_privatekey_from_file(self):
     # Non-existent key file.
     nonexistent_keypath = os.path.join(temporary_directory,
         'nonexistent_keypath')
-    self.assertRaises(IOError, interface.import_ed25519_privatekey_from_file,
-        nonexistent_keypath, 'pw')
+    self.assertRaises(securesystemslib.exceptions.StorageError,
+        interface.import_ed25519_privatekey_from_file, nonexistent_keypath,
+        'pw')
 
     # Invalid key file argument.
     invalid_keyfile = os.path.join(temporary_directory, 'invalid_keyfile')
@@ -576,8 +577,8 @@ def test_import_ecdsa_privatekey_from_file(self):
     # Test invalid argument.
     # Non-existent key file.
     nonexistent_keypath = os.path.join(temporary_directory, 'nonexistent_keypath')
-    self.assertRaises(IOError, interface.import_ecdsa_privatekey_from_file,
-        nonexistent_keypath, 'pw')
+    self.assertRaises(securesystemslib.exceptions.StorageError,
+        interface.import_ecdsa_privatekey_from_file, nonexistent_keypath, 'pw')
 
     # Invalid key file argument.
     invalid_keyfile = os.path.join(temporary_directory, 'invalid_keyfile')