New API: Add TargetFile class

Add a new TargetFile class to tuf.api.metadata module make Targets
class to use it.
This class will contain information about the "targets" field
from targets.json

Also, update the tests for that change.

Signed-off-by: Martin Vrachev <[email protected]>

tests/test_api.py

@@ -37,7 +37,8 @@ def setUpModule():
         Root,
         Snapshot,
         Timestamp,
-        Targets
+        Targets,
+        TargetInfo
     )
 
     from securesystemslib.interface import (
@@ -324,15 +325,12 @@ def test_metadata_targets(self):
             "sha512": "ef5beafa16041bcdd2937140afebd485296cd54f7348ecd5a4d035c09759608de467a7ac0eb58753d0242df873c305e8bffad2454aa48f44480f15efae1cacd0"
         },
 
-        fileinfo = {
-            'hashes': hashes,
-            'length': 28
-        }
+        fileinfo = TargetInfo(length=28, hashes=hashes)
 
         # Assert that data is not aleady equal
         self.assertNotEqual(targets.signed.targets[filename], fileinfo)
         # Update an already existing fileinfo
-        targets.signed.update(filename, fileinfo)
+        targets.signed.update(filename, fileinfo.to_dict())
         # Verify that data is updated
         self.assertEqual(targets.signed.targets[filename], fileinfo)
 

tuf/api/metadata.py

@@ -570,22 +570,66 @@ def update(
         self.meta[metadata_fn] = MetadataInfo(version, length, hashes)
 
 
+class TargetInfo:
+    """A container with information about a particular target file.
+    Instances of TargetInfo are used as values in a dictionary
+    called "targets" in Targets.
+
+    Attributes:
+        length: An integer indicating the length of the target file.
+        hashes: A dictionary containing hash algorithms and the
+            hashes resulted from applying them over the target file::
+
+                'hashes': {
+                    '<HASH ALGO 1>': '<TARGET FILE HASH 1>',
+                    '<HASH ALGO 2>': '<TARGET FILE HASH 2>',
+                    ...
+                }
+
+        custom: An optional dictionary which may include version numbers,
+            dependencies, or any other data that the application wants
+            to include to describe the target file::
+
+                'custom': {
+                    'type': 'metadata',
+                    'file_permissions': '0644',
+                    ...
+                } // optional
+
+    """
+
+    def __init__(self, length: int, hashes: JsonDict,
+            custom: Optional[JsonDict] = None) -> None:
+        self.length = length
+        self.hashes = hashes
+        self.custom = custom
+
+
+    def __eq__(self, other: 'TargetInfo') -> bool:
+        """Compare objects by their values instead of by their addresses."""
+        return (self.length == other.length and
+                self.hashes == other.hashes and
+                self.custom == other.custom)
+
+
+    def to_dict(self) -> JsonDict:
+        """Returns the JSON-serializable dictionary representation of self. """
+        json_dict = {'length': self.length, 'hashes': self.hashes}
+
+        if self.custom is not None:
+            json_dict['custom'] = self.custom
+
+        return json_dict
+
+
 class Targets(Signed):
     """A container for the signed part of targets metadata.
 
     Attributes:
         targets: A dictionary that contains information about target files::
 
             {
-                '<TARGET FILE NAME>': {
-                    'length': <TARGET FILE SIZE>,
-                    'hashes': {
-                        '<HASH ALGO 1>': '<TARGET FILE HASH 1>',
-                        '<HASH ALGO 2>': '<TARGETS FILE HASH 2>',
-                        ...
-                    },
-                    'custom': <CUSTOM OPAQUE DICT> // optional
-                },
+                '<TARGET FILE NAME>': <TargetInfo INSTANCE>,
                 ...
             }
 
@@ -629,25 +673,41 @@ class Targets(Signed):
     # pylint: disable=too-many-arguments
     def __init__(
             self, _type: str, version: int, spec_version: str,
-            expires: datetime, targets: JsonDict, delegations: JsonDict
-            ) -> None:
+            expires: datetime, targets: Dict[str, TargetInfo],
+            delegations: JsonDict) -> None:
         super().__init__(_type, version, spec_version, expires)
-        # TODO: Add class for meta
         self.targets = targets
+
+        # TODO: Add Key and Role classes
         self.delegations = delegations
 
 
+    @classmethod
+    def from_dict(cls, signed_dict: JsonDict) -> 'Targets':
+        """Creates Targets object from its JSON/dict representation. """
+        for target_path in signed_dict['targets'].keys():
+            signed_dict['targets'][target_path] = TargetInfo(
+                    **signed_dict['targets'][target_path])
+
+        return super().from_dict(signed_dict)
+
+
     # Serialization.
     def to_dict(self) -> JsonDict:
         """Returns the JSON-serializable dictionary representation of self. """
         json_dict = super().to_dict()
+        target_dict = {}
+        for target_path, target_file_obj in self.targets.items():
+            target_dict[target_path] = target_file_obj.to_dict()
+
         json_dict.update({
-            'targets': self.targets,
+            'targets': target_dict,
             'delegations': self.delegations,
         })
         return json_dict
 
     # Modification.
     def update(self, filename: str, fileinfo: JsonDict) -> None:
         """Assigns passed target file info to meta dict. """
-        self.targets[filename] = fileinfo
+        self.targets[filename] = TargetInfo(fileinfo['length'],
+            fileinfo['hashes'], fileinfo.get('custom'))