Merge pull request #2273 from VickyMerzOwn/develop

enhancement: Add from_data() method to MetaFile

Author: Lukas Pühringer

tests/test_api.py

@@ -34,6 +34,7 @@
     Delegations,
     Key,
     Metadata,
+    MetaFile,
     Root,
     Signature,
     Snapshot,
@@ -725,6 +726,29 @@ def test_targetfile_from_data(self) -> None:
         targetfile_from_data = TargetFile.from_data(target_file_path, data)
         targetfile_from_data.verify_length_and_hashes(data)
 
+    def test_metafile_from_data(self) -> None:
+        data = b"Inline test content"
+
+        # Test with a valid hash algorithm
+        metafile = MetaFile.from_data(1, data, ["sha256"])
+        metafile.verify_length_and_hashes(data)
+
+        # Test with an invalid hash algorithm
+        with self.assertRaises(ValueError):
+            metafile = MetaFile.from_data(1, data, ["invalid_algorithm"])
+            metafile.verify_length_and_hashes(data)
+
+        self.assertEqual(
+            metafile,
+            MetaFile(
+                1,
+                19,
+                {
+                    "sha256": "fcee2e6d56ab08eab279016f7db7e4e1d172ccea78e15f4cf8bd939991a418fa"
+                },
+            ),
+        )
+
     def test_targetfile_get_prefixed_paths(self) -> None:
         target = TargetFile(100, {"sha256": "abc", "md5": "def"}, "a/b/f.ext")
         self.assertEqual(

tuf/api/metadata.py

@@ -900,6 +900,41 @@ def _validate_length(length: int) -> None:
         if length < 0:
             raise ValueError(f"Length must be >= 0, got {length}")
 
+    @staticmethod
+    def _get_length_and_hashes(
+        data: Union[bytes, IO[bytes]], hash_algorithms: Optional[List[str]]
+    ) -> Tuple[int, Dict[str, str]]:
+        """Calculate length and hashes of ``data``."""
+        if isinstance(data, bytes):
+            length = len(data)
+        else:
+            data.seek(0, io.SEEK_END)
+            length = data.tell()
+
+        hashes = {}
+
+        if hash_algorithms is None:
+            hash_algorithms = [sslib_hash.DEFAULT_HASH_ALGORITHM]
+
+        for algorithm in hash_algorithms:
+            try:
+                if isinstance(data, bytes):
+                    digest_object = sslib_hash.digest(algorithm)
+                    digest_object.update(data)
+                else:
+                    digest_object = sslib_hash.digest_fileobject(
+                        data, algorithm
+                    )
+            except (
+                sslib_exceptions.UnsupportedAlgorithmError,
+                sslib_exceptions.FormatError,
+            ) as e:
+                raise ValueError(f"Unsupported algorithm '{algorithm}'") from e
+
+            hashes[algorithm] = digest_object.hexdigest()
+
+        return (length, hashes)
+
 
 class MetaFile(BaseFile):
     """A container with information about a particular metadata file.
@@ -966,6 +1001,28 @@ def from_dict(cls, meta_dict: Dict[str, Any]) -> "MetaFile":
         # All fields left in the meta_dict are unrecognized.
         return cls(version, length, hashes, meta_dict)
 
+    @classmethod
+    def from_data(
+        cls,
+        version: int,
+        data: Union[bytes, IO[bytes]],
+        hash_algorithms: List[str],
+    ) -> "MetaFile":
+        """Creates MetaFile object from bytes.
+        This constructor should only be used if hashes are wanted.
+        By default, MetaFile(ver) should be used.
+        Args:
+            version: Version of the metadata file.
+            data: Metadata bytes that the metafile represents.
+            hash_algorithms: Hash algorithms to create the hashes with. If not
+            specified, the securesystemslib default hash algorithm is used.
+        Raises:
+            ValueError: The hash algorithms list contains an unsupported
+            algorithm.
+        """
+        length, hashes = cls._get_length_and_hashes(data, hash_algorithms)
+        return cls(version, length, hashes)
+
     def to_dict(self) -> Dict[str, Any]:
         """Return the dictionary representation of self."""
         res_dict: Dict[str, Any] = {
@@ -1693,34 +1750,7 @@ def from_data(
             ValueError: The hash algorithms list contains an unsupported
                 algorithm.
         """
-        if isinstance(data, bytes):
-            length = len(data)
-        else:
-            data.seek(0, io.SEEK_END)
-            length = data.tell()
-
-        hashes = {}
-
-        if hash_algorithms is None:
-            hash_algorithms = [sslib_hash.DEFAULT_HASH_ALGORITHM]
-
-        for algorithm in hash_algorithms:
-            try:
-                if isinstance(data, bytes):
-                    digest_object = sslib_hash.digest(algorithm)
-                    digest_object.update(data)
-                else:
-                    digest_object = sslib_hash.digest_fileobject(
-                        data, algorithm
-                    )
-            except (
-                sslib_exceptions.UnsupportedAlgorithmError,
-                sslib_exceptions.FormatError,
-            ) as e:
-                raise ValueError(f"Unsupported algorithm '{algorithm}'") from e
-
-            hashes[algorithm] = digest_object.hexdigest()
-
+        length, hashes = cls._get_length_and_hashes(data, hash_algorithms)
         return cls(length, hashes, target_file_path)
 
     def verify_length_and_hashes(self, data: Union[bytes, IO[bytes]]) -> None: