swh.models.hashutil: Add persistent identifier function

Related T335
Related T933

swh/model/identifiers.py

-# Copyright (C) 2015  The Software Heritage developers
+# Copyright (C) 2015-2018  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -8,6 +8,14 @@ import datetime
 from functools import lru_cache
 
 from .hashutil import hash_data, hash_git_data, DEFAULT_ALGORITHMS
+from .hashutil import hash_to_hex
+
+
+SNAPSHOT = 'snapshot'
+REVISION = 'revision'
+RELEASE = 'release'
+DIRECTORY = 'directory'
+CONTENT = 'content'
 
 
 @lru_cache()
@@ -584,3 +592,47 @@ def snapshot_identifier(snapshot, *, ignore_unresolved=False):
                                    for name, target in unresolved))
 
     return identifier_to_str(hash_git_data(b''.join(lines), 'snapshot'))
+
+
+def persistent_identifier(type, hash):
+    """Compute persistent identifier as per the documentation.
+
+    Source: https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html  # noqa
+
+    Args:
+        type (str): Object type
+        hash (str): Object hash
+
+    Returns:
+        Persistent identifier as string.
+
+    """
+    _map = {
+        SNAPSHOT: 'snp',
+        RELEASE: 'rel',
+        REVISION: 'rev',
+        DIRECTORY: 'dir',
+        CONTENT: 'cnt',
+    }
+    _hash = hash_to_hex(hash)
+
+    return 'swh:1:%s:%s' % (_map[type], _hash)
+
+
+def parse_persistent_identifier(persistent_id):
+    """Parse swh's persistent identifier.
+
+    Args:
+        persistent_id (str): A persistent identifier
+
+    Returns:
+        dict with keys namespace, scheme_version, object_type, object_id
+
+    """
+    data = persistent_id.split(':')
+    return {
+        'namespace': data[0],  # should be 'swh'
+        'scheme_version': data[1],
+        'object_type': data[2],
+        'object_id': data[3],
+    }

swh/model/tests/test_identifiers.py

-# Copyright (C) 2015-2017  The Software Heritage developers
+# Copyright (C) 2015-2018  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -11,6 +11,9 @@ from nose.tools import istest
 
 from swh.model import hashutil, identifiers
 
+from swh.model.identifiers import SNAPSHOT, RELEASE, REVISION, DIRECTORY
+from swh.model.identifiers import CONTENT
+
 
 class UtilityFunctionsIdentifier(unittest.TestCase):
     def setUp(self):
@@ -768,3 +771,43 @@ class SnapshotIdentifier(unittest.TestCase):
             identifiers.snapshot_identifier(self.all_types),
             identifiers.identifier_to_str(self.all_types['id']),
         )
+
+    def test_persistent_identifier(self):
+        for full_type, _hash, expected_persistent_id in [
+                (SNAPSHOT, hashutil.hash_to_bytes(
+                    'c7c108084bc0bf3d81436bf980b46e98bd338453'),
+                 'swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453'),
+                (RELEASE, '22ece559cc7cc2364edc5e5593d63ae8bd229f9f',
+                 'swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f'),
+                (REVISION, '309cf2674ee7a0749978cf8265ab91a60aea0f7d',
+                 'swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d'),
+                (DIRECTORY, 'd198bc9d7a6bcf6db04f476d29314f157507d505',
+                 'swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505'),
+                (CONTENT, '94a9ed024d3859793618152ea559a168bbcbb5e2',
+                 'swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2')
+        ]:
+            actual_value = identifiers.persistent_identifier(
+                full_type, _hash)
+            self.assertEquals(actual_value, expected_persistent_id)
+
+    def test_parse_persistent_identifier(self):
+        for pid, _type, _hash in [
+                ('swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2', 'cnt',
+                 '94a9ed024d3859793618152ea559a168bbcbb5e2'),
+                ('swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505', 'dir',
+                 'd198bc9d7a6bcf6db04f476d29314f157507d505'),
+                ('swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d', 'rev',
+                 '309cf2674ee7a0749978cf8265ab91a60aea0f7d'),
+                ('swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f', 'rel',
+                 '22ece559cc7cc2364edc5e5593d63ae8bd229f9f'),
+                ('swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453', 'snp',
+                 'c7c108084bc0bf3d81436bf980b46e98bd338453'),
+        ]:
+            expected_result = {
+                'namespace': 'swh',
+                'scheme_version': '1',
+                'object_type': _type,
+                'object_id': _hash,
+            }
+            actual_result = identifiers.parse_persistent_identifier(pid)
+            self.assertEquals(actual_result, expected_result)