diff --git a/swh/loader/package/npm.py b/swh/loader/package/npm.py
index 96de129..c5dfe40 100644
--- a/swh/loader/package/npm.py
+++ b/swh/loader/package/npm.py
@@ -1,301 +1,340 @@
 # Copyright (C) 2019  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
 
 import json
 import logging
 import os
 import re
 
 from codecs import BOM_UTF8
 from typing import Any, Dict, Generator, Mapping, Sequence, Tuple, Optional
 
 import chardet
 import iso8601
 
 from swh.model.identifiers import normalize_timestamp
 from swh.loader.package.loader import PackageLoader
 from swh.loader.package.utils import api_info, release_name
 
 
 logger = logging.getLogger(__name__)
 
 
 _EMPTY_AUTHOR = {'fullname': b'', 'name': None, 'email': None}
 
 # https://github.com/jonschlinkert/author-regex
 _author_regexp = r'([^<(]+?)?[ \t]*(?:<([^>(]+?)>)?[ \t]*(?:\(([^)]+?)\)|$)'
 
 
 class NpmLoader(PackageLoader):
     visit_type = 'npm'
 
     def __init__(self, package_name, package_url, package_metadata_url):
         super().__init__(url=package_url)
         self.provider_url = package_metadata_url
 
         self._info = None
         self._versions = None
 
         # if package_url is None:
         #     package_url = 'https://www.npmjs.com/package/%s' % package_name
         # if package_metadata_url is None:
         #     package_metadata_url = 'https://replicate.npmjs.com/%s/' %\
         #                             quote(package_name, safe='')
 
     @property
     def info(self) -> Dict:
         """Return the project metadata information (fetched from npm registry)
 
         """
         if not self._info:
             self._info = api_info(self.provider_url)
         return self._info
 
     def get_versions(self) -> Sequence[str]:
         return sorted(list(self.info['versions'].keys()))
 
     def get_default_version(self) -> str:
         return self.info['dist-tags'].get('latest', '')
 
     def get_package_info(self, version: str) -> Generator[
             Tuple[str, Mapping[str, Any]], None, None]:
         meta = self.info['versions'][version]
         url = meta['dist']['tarball']
         p_info = {
             'url': url,
             'filename': os.path.basename(url),
             'raw': meta,
         }
         yield release_name(version), p_info
 
     def resolve_revision_from(
             self, known_artifacts: Dict, artifact_metadata: Dict) \
             -> Optional[bytes]:
-        shasum = artifact_metadata['dist']['shasum']
-        for rev_id, known_artifact in known_artifacts.items():
-            original_artifact = known_artifact['original_artifact'][0]
-            if shasum == original_artifact['checksums']['sha1']:
-                return rev_id
-        return None
+        return artifact_to_revision_id(known_artifacts, artifact_metadata)
 
     def build_revision(
             self, a_metadata: Dict, uncompressed_path: str) -> Dict:
         i_metadata = extract_intrinsic_metadata(uncompressed_path)
         # from intrinsic metadata
         author = extract_npm_package_author(i_metadata)
         message = i_metadata['version'].encode('ascii')
 
         # from extrinsic metadata
 
         # No date available in intrinsic metadata: retrieve it from the API
         # metadata, using the version number that the API claims this package
         # has.
         extrinsic_version = a_metadata['version']
         date = self.info['time'][extrinsic_version]
         date = iso8601.parse_date(date)
         date = normalize_timestamp(int(date.timestamp()))
 
         return {
             'type': 'tar',
             'message': message,
             'author': author,
             'date': date,
             'committer': author,
             'committer_date': date,
             'parents': [],
             'metadata': {
                 'intrinsic': {
                     'tool': 'package.json',
                     'raw': i_metadata,
                 },
                 'extrinsic': {
                     'provider': self.provider_url,
                     'when': self.visit_date.isoformat(),
                     'raw': a_metadata,
                 },
             },
         }
 
 
+def artifact_to_revision_id(
+        known_artifacts: Dict, artifact_metadata: Dict) -> Optional[bytes]:
+    """Given metadata artifact, solves the associated revision id.
+
+    The following code allows to deal with 2 metadata formats:
+
+    - old format sample:
+
+        {
+            'package_source': {
+                'sha1': '05181c12cd8c22035dd31155656826b85745da37',
+            }
+        }
+
+    - new format sample:
+
+        {
+            'original_artifact': [{
+                'checksums': {
+                    'sha256': "6975816f2c5ad4046acc676ba112f2fff945b01522d63948531f11f11e0892ec",  # noqa
+                    ...
+                },
+            }],
+            ...
+        }
+
+    """
+    shasum = artifact_metadata['dist']['shasum']
+    for rev_id, known_artifact in known_artifacts.items():
+        known_original_artifact = known_artifact.get('original_artifact')
+        if not known_original_artifact:
+            # previous loader-npm version kept original artifact elsewhere
+            known_original_artifact = known_artifact.get('package_source')
+            if not known_original_artifact:
+                continue
+            original_hash = known_original_artifact['sha1']
+        else:
+            assert isinstance(known_original_artifact, list)
+            original_hash = known_original_artifact[0]['checksums']['sha1']
+        if shasum == original_hash:
+            return rev_id
+    return None
+
+
 def parse_npm_package_author(author_str):
     """
     Parse npm package author string.
 
     It works with a flexible range of formats, as detailed below::
 
         name
         name <email> (url)
         name <email>(url)
         name<email> (url)
         name<email>(url)
         name (url) <email>
         name (url)<email>
         name(url) <email>
         name(url)<email>
         name (url)
         name(url)
         name <email>
         name<email>
         <email> (url)
         <email>(url)
         (url) <email>
         (url)<email>
         <email>
         (url)
 
     Args:
         author_str (str): input author string
 
     Returns:
         dict: A dict that may contain the following keys:
             * name
             * email
             * url
 
     """
     author = {}
     matches = re.findall(_author_regexp,
                          author_str.replace('<>', '').replace('()', ''),
                          re.M)
     for match in matches:
         if match[0].strip():
             author['name'] = match[0].strip()
         if match[1].strip():
             author['email'] = match[1].strip()
         if match[2].strip():
             author['url'] = match[2].strip()
     return author
 
 
 def extract_npm_package_author(package_json):
     """
     Extract package author from a ``package.json`` file content and
     return it in swh format.
 
     Args:
         package_json (dict): Dict holding the content of parsed
             ``package.json`` file
 
     Returns:
         dict: A dict with the following keys:
             * fullname
             * name
             * email
 
     """
 
     def _author_str(author_data):
         if type(author_data) is dict:
             author_str = ''
             if 'name' in author_data:
                 author_str += author_data['name']
             if 'email' in author_data:
                 author_str += ' <%s>' % author_data['email']
             return author_str
         elif type(author_data) is list:
             return _author_str(author_data[0]) if len(author_data) > 0 else ''
         else:
             return author_data
 
     author_data = {}
     for author_key in ('author', 'authors'):
         if author_key in package_json:
             author_str = _author_str(package_json[author_key])
             author_data = parse_npm_package_author(author_str)
 
     name = author_data.get('name')
     email = author_data.get('email')
 
     fullname = None
 
     if name and email:
         fullname = '%s <%s>' % (name, email)
     elif name:
         fullname = name
 
     if not fullname:
         return _EMPTY_AUTHOR
 
     if fullname:
         fullname = fullname.encode('utf-8')
 
     if name:
         name = name.encode('utf-8')
 
     if email:
         email = email.encode('utf-8')
 
     return {'fullname': fullname, 'name': name, 'email': email}
 
 
 def _lstrip_bom(s, bom=BOM_UTF8):
     if s.startswith(bom):
         return s[len(bom):]
     else:
         return s
 
 
 def load_json(json_bytes):
     """
     Try to load JSON from bytes and return a dictionary.
 
     First try to decode from utf-8. If the decoding failed,
     try to detect the encoding and decode again with replace
     error handling.
 
     If JSON is malformed, an empty dictionary will be returned.
 
     Args:
         json_bytes (bytes): binary content of a JSON file
 
     Returns:
         dict: JSON data loaded in a dictionary
     """
     json_data = {}
     try:
         json_str = _lstrip_bom(json_bytes).decode('utf-8')
     except UnicodeDecodeError:
         encoding = chardet.detect(json_bytes)['encoding']
         if encoding:
             json_str = json_bytes.decode(encoding, 'replace')
     try:
         json_data = json.loads(json_str)
     except json.decoder.JSONDecodeError:
         pass
     return json_data
 
 
 def extract_intrinsic_metadata(dir_path: str) -> Dict:
     """Given an uncompressed path holding the pkginfo file, returns a
        pkginfo parsed structure as a dict.
 
        The release artifact contains at their root one folder. For example:
        $ tar tvf zprint-0.0.6.tar.gz
        drwxr-xr-x root/root         0 2018-08-22 11:01 zprint-0.0.6/
        ...
 
     Args:
 
         dir_path (str): Path to the uncompressed directory
                         representing a release artifact from npm.
 
     Returns:
         the pkginfo parsed structure as a dict if any or None if
         none was present.
 
     """
     # Retrieve the root folder of the archive
     if not os.path.exists(dir_path):
         return {}
     lst = os.listdir(dir_path)
     if len(lst) == 0:
         return {}
     project_dirname = lst[0]
     package_json_path = os.path.join(dir_path, project_dirname, 'package.json')
     if not os.path.exists(package_json_path):
         return {}
     with open(package_json_path, 'rb') as package_json_file:
         package_json_bytes = package_json_file.read()
         return load_json(package_json_bytes)
diff --git a/swh/loader/package/tests/test_npm.py b/swh/loader/package/tests/test_npm.py
index 0b38cca..de0648e 100644
--- a/swh/loader/package/tests/test_npm.py
+++ b/swh/loader/package/tests/test_npm.py
@@ -1,584 +1,661 @@
 # Copyright (C) 2019  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
 
 
 import json
 import os
 import pytest
 
 from swh.model.hashutil import hash_to_bytes
 
 from swh.loader.package.npm import (
-    parse_npm_package_author, extract_npm_package_author
+    parse_npm_package_author, extract_npm_package_author,
+    artifact_to_revision_id
 )
 from swh.loader.package.tests.common import (
     check_snapshot, check_metadata_paths, get_stats
 )
 
 from swh.loader.package.npm import NpmLoader
 
 
 def _parse_author_string_test(author_str, expected_result):
     assert parse_npm_package_author(author_str) == expected_result
     assert parse_npm_package_author(' %s' % author_str) == expected_result
     assert parse_npm_package_author('%s ' % author_str) == expected_result
 
 
 def test_parse_npm_package_author():
     _parse_author_string_test(
         'John Doe',
         {
             'name': 'John Doe'
         }
     )
 
     _parse_author_string_test(
         '<john.doe@foo.bar>',
         {
             'email': 'john.doe@foo.bar'
         }
     )
 
     _parse_author_string_test(
         '(https://john.doe)',
         {
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe <john.doe@foo.bar>',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar'
         }
     )
 
     _parse_author_string_test(
         'John Doe<john.doe@foo.bar>',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar'
         }
     )
 
     _parse_author_string_test(
         'John Doe (https://john.doe)',
         {
             'name': 'John Doe',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe(https://john.doe)',
         {
             'name': 'John Doe',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         '<john.doe@foo.bar> (https://john.doe)',
         {
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         '(https://john.doe) <john.doe@foo.bar>',
         {
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe <john.doe@foo.bar> (https://john.doe)',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe (https://john.doe) <john.doe@foo.bar>',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe<john.doe@foo.bar> (https://john.doe)',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe<john.doe@foo.bar>(https://john.doe)',
         {
             'name': 'John Doe',
             'email': 'john.doe@foo.bar',
             'url': 'https://john.doe'
         }
     )
 
     _parse_author_string_test('', {})
     _parse_author_string_test('<>', {})
     _parse_author_string_test(' <>', {})
     _parse_author_string_test('<>()', {})
     _parse_author_string_test('<> ()', {})
     _parse_author_string_test('()', {})
     _parse_author_string_test(' ()', {})
 
     _parse_author_string_test(
         'John Doe <> ()',
         {
             'name': 'John Doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe <>',
         {
             'name': 'John Doe'
         }
     )
 
     _parse_author_string_test(
         'John Doe ()',
         {
             'name': 'John Doe'
         }
     )
 
 
 def test_extract_npm_package_author(datadir):
     package_metadata_filepath = os.path.join(
         datadir, 'https_replicate.npmjs.com', 'org_visit1')
 
     with open(package_metadata_filepath) as json_file:
         package_metadata = json.load(json_file)
 
     extract_npm_package_author(package_metadata['versions']['0.0.2']) == \
         {
             'fullname': b'mooz <stillpedant@gmail.com>',
             'name': b'mooz',
             'email': b'stillpedant@gmail.com'
         }
 
     assert (
         extract_npm_package_author(package_metadata['versions']['0.0.3']) ==
         {
             'fullname': b'Masafumi Oyamada <stillpedant@gmail.com>',
             'name': b'Masafumi Oyamada',
             'email': b'stillpedant@gmail.com'
         }
     )
 
     package_json = json.loads('''
     {
         "name": "highlightjs-line-numbers.js",
         "version": "2.7.0",
         "description": "Highlight.js line numbers plugin.",
         "main": "src/highlightjs-line-numbers.js",
         "dependencies": {},
         "devDependencies": {
             "gulp": "^4.0.0",
             "gulp-rename": "^1.4.0",
             "gulp-replace": "^0.6.1",
             "gulp-uglify": "^1.2.0"
         },
         "repository": {
             "type": "git",
             "url": "https://github.com/wcoder/highlightjs-line-numbers.js.git"
         },
         "author": "Yauheni Pakala <evgeniy.pakalo@gmail.com>",
         "license": "MIT",
         "bugs": {
             "url": "https://github.com/wcoder/highlightjs-line-numbers.js/issues"
         },
         "homepage": "http://wcoder.github.io/highlightjs-line-numbers.js/"
     }''') # noqa
 
     assert extract_npm_package_author(package_json) == \
         {
             'fullname': b'Yauheni Pakala <evgeniy.pakalo@gmail.com>',
             'name': b'Yauheni Pakala',
             'email': b'evgeniy.pakalo@gmail.com'
         }
 
     package_json = json.loads('''
     {
         "name": "3-way-diff",
         "version": "0.0.1",
         "description": "3-way diffing of JavaScript objects",
         "main": "index.js",
         "authors": [
             {
                 "name": "Shawn Walsh",
                 "url": "https://github.com/shawnpwalsh"
             },
             {
                 "name": "Markham F Rollins IV",
                 "url": "https://github.com/mrollinsiv"
             }
         ],
         "keywords": [
             "3-way diff",
             "3 way diff",
             "three-way diff",
             "three way diff"
         ],
         "devDependencies": {
             "babel-core": "^6.20.0",
             "babel-preset-es2015": "^6.18.0",
             "mocha": "^3.0.2"
         },
         "dependencies": {
             "lodash": "^4.15.0"
         }
     }''')
 
     assert extract_npm_package_author(package_json) == \
         {
             'fullname': b'Shawn Walsh',
             'name': b'Shawn Walsh',
             'email': None
         }
 
     package_json = json.loads('''
     {
         "name": "yfe-ynpm",
         "version": "1.0.0",
         "homepage": "http://gitlab.ywwl.com/yfe/yfe-ynpm",
         "repository": {
             "type": "git",
             "url": "git@gitlab.ywwl.com:yfe/yfe-ynpm.git"
         },
         "author": [
             "fengmk2 <fengmk2@gmail.com> (https://fengmk2.com)",
             "xufuzi <xufuzi@ywwl.com> (https://7993.org)"
         ],
         "license": "MIT"
     }''')
 
     assert extract_npm_package_author(package_json) == \
         {
             'fullname': b'fengmk2 <fengmk2@gmail.com>',
             'name': b'fengmk2',
             'email': b'fengmk2@gmail.com'
         }
 
     package_json = json.loads('''
     {
         "name": "umi-plugin-whale",
         "version": "0.0.8",
         "description": "Internal contract component",
         "authors": {
             "name": "xiaohuoni",
             "email": "448627663@qq.com"
         },
         "repository": "alitajs/whale",
         "devDependencies": {
             "np": "^3.0.4",
             "umi-tools": "*"
         },
         "license": "MIT"
     }''')
 
     assert extract_npm_package_author(package_json) == \
         {
             'fullname': b'xiaohuoni <448627663@qq.com>',
             'name': b'xiaohuoni',
             'email': b'448627663@qq.com'
         }
 
 
 def normalize_hashes(hashes):
     if isinstance(hashes, str):
         return hash_to_bytes(hashes)
     if isinstance(hashes, list):
         return [hash_to_bytes(x) for x in hashes]
     return {hash_to_bytes(k): hash_to_bytes(v) for k, v in hashes.items()}
 
 
 _expected_new_contents_first_visit = normalize_hashes([
     '4ce3058e16ab3d7e077f65aabf855c34895bf17c',
     '858c3ceee84c8311adc808f8cdb30d233ddc9d18',
     '0fa33b4f5a4e0496da6843a38ff1af8b61541996',
     '85a410f8ef8eb8920f2c384a9555566ad4a2e21b',
     '9163ac8025923d5a45aaac482262893955c9b37b',
     '692cf623b8dd2c5df2c2998fd95ae4ec99882fb4',
     '18c03aac6d3e910efb20039c15d70ab5e0297101',
     '41265c42446aac17ca769e67d1704f99e5a1394d',
     '783ff33f5882813dca9239452c4a7cadd4dba778',
     'b029cfb85107aee4590c2434a3329bfcf36f8fa1',
     '112d1900b4c2e3e9351050d1b542c9744f9793f3',
     '5439bbc4bd9a996f1a38244e6892b71850bc98fd',
     'd83097a2f994b503185adf4e719d154123150159',
     'd0939b4898e83090ee55fd9d8a60e312cfadfbaf',
     'b3523a26f7147e4af40d9d462adaae6d49eda13e',
     'cd065fb435d6fb204a8871bcd623d0d0e673088c',
     '2854a40855ad839a54f4b08f5cff0cf52fca4399',
     'b8a53bbaac34ebb8c6169d11a4b9f13b05c583fe',
     '0f73d56e1cf480bded8a1ecf20ec6fc53c574713',
     '0d9882b2dfafdce31f4e77fe307d41a44a74cefe',
     '585fc5caab9ead178a327d3660d35851db713df1',
     'e8cd41a48d79101977e3036a87aeb1aac730686f',
     '5414efaef33cceb9f3c9eb5c4cc1682cd62d14f7',
     '9c3cc2763bf9e9e37067d3607302c4776502df98',
     '3649a68410e354c83cd4a38b66bd314de4c8f5c9',
     'e96ed0c091de1ebdf587104eaf63400d1974a1fe',
     '078ca03d2f99e4e6eab16f7b75fbb7afb699c86c',
     '38de737da99514de6559ff163c988198bc91367a',
 ])
 
 _expected_new_directories_first_visit = normalize_hashes([
     '3370d20d6f96dc1c9e50f083e2134881db110f4f',
     '42753c0c2ab00c4501b552ac4671c68f3cf5aece',
     'd7895533ef5edbcffdea3f057d9fef3a1ef845ce',
     '80579be563e2ef3e385226fe7a3f079b377f142c',
     '3b0ddc6a9e58b4b53c222da4e27b280b6cda591c',
     'bcad03ce58ac136f26f000990fc9064e559fe1c0',
     '5fc7e82a1bc72e074665c6078c6d3fad2f13d7ca',
     'e3cd26beba9b1e02f6762ef54bd9ac80cc5f25fd',
     '584b5b4b6cf7f038095e820b99386a9c232de931',
     '184c8d6d0d242f2b1792ef9d3bf396a5434b7f7a',
     'bb5f4ee143c970367eb409f2e4c1104898048b9d',
     '1b95491047add1103db0dfdfa84a9735dcb11e88',
     'a00c6de13471a2d66e64aca140ddb21ef5521e62',
     '5ce6c1cd5cda2d546db513aaad8c72a44c7771e2',
     'c337091e349b6ac10d38a49cdf8c2401ef9bb0f2',
     '202fafcd7c0f8230e89d5496ad7f44ab12b807bf',
     '775cc516543be86c15c1dc172f49c0d4e6e78235',
     'ff3d1ead85a14f891e8b3fa3a89de39db1b8de2e',
 ])
 
 _expected_new_revisions_first_visit = normalize_hashes({
     'd8a1c7474d2956ac598a19f0f27d52f7015f117e':
     '42753c0c2ab00c4501b552ac4671c68f3cf5aece',
     '5f9eb78af37ffd12949f235e86fac04898f9f72a':
     '3370d20d6f96dc1c9e50f083e2134881db110f4f',
     'ba019b192bdb94bd0b5bd68b3a5f92b5acc2239a':
     'd7895533ef5edbcffdea3f057d9fef3a1ef845ce'}
 )
 
 
 def package_url(package):
     return 'https://www.npmjs.com/package/%s' % package
 
 
 def package_metadata_url(package):
     return 'https://replicate.npmjs.com/%s/' % package
 
 
 def test_revision_metadata_structure(swh_config, requests_mock_datadir):
     package = 'org'
     loader = NpmLoader(package,
                        package_url(package),
                        package_metadata_url(package))
 
     actual_load_status = loader.load()
     assert actual_load_status['status'] == 'eventful'
     assert actual_load_status['snapshot_id'] is not None
 
     expected_revision_id = hash_to_bytes(
         'd8a1c7474d2956ac598a19f0f27d52f7015f117e')
     revision = list(loader.storage.revision_get([expected_revision_id]))[0]
 
     assert revision is not None
 
     check_metadata_paths(revision['metadata'], paths=[
         ('intrinsic.tool', str),
         ('intrinsic.raw', dict),
         ('extrinsic.provider', str),
         ('extrinsic.when', str),
         ('extrinsic.raw', dict),
         ('original_artifact', list),
     ])
 
     for original_artifact in revision['metadata']['original_artifact']:
         check_metadata_paths(original_artifact, paths=[
             ('filename', str),
             ('length', int),
             ('checksums', dict),
         ])
 
 
 def test_npm_loader_first_visit(swh_config, requests_mock_datadir):
 
     package = 'org'
     loader = NpmLoader(package,
                        package_url(package),
                        package_metadata_url(package))
 
     actual_load_status = loader.load()
     expected_snapshot_id = 'd0587e1195aed5a8800411a008f2f2d627f18e2d'
     assert actual_load_status == {
         'status': 'eventful',
         'snapshot_id': expected_snapshot_id
     }
 
     stats = get_stats(loader.storage)
 
     assert {
         'content': len(_expected_new_contents_first_visit),
         'directory': len(_expected_new_directories_first_visit),
         'origin': 1,
         'origin_visit': 1,
         'person': 2,
         'release': 0,
         'revision': len(_expected_new_revisions_first_visit),
         'skipped_content': 0,
         'snapshot': 1,
     } == stats
 
     assert len(list(loader.storage.content_get(
         _expected_new_contents_first_visit))) == len(
             _expected_new_contents_first_visit)
 
     assert list(loader.storage.directory_missing(
         _expected_new_directories_first_visit)) == []
 
     assert list(loader.storage.revision_missing(
         _expected_new_revisions_first_visit)) == []
 
     expected_snapshot = {
         'id': expected_snapshot_id,
         'branches': {
             'HEAD': {
                 'target': 'releases/0.0.4',
                 'target_type': 'alias'
             },
             'releases/0.0.2': {
                 'target': 'd8a1c7474d2956ac598a19f0f27d52f7015f117e',
                 'target_type': 'revision'
             },
             'releases/0.0.3': {
                 'target': '5f9eb78af37ffd12949f235e86fac04898f9f72a',
                 'target_type': 'revision'
             },
             'releases/0.0.4': {
                 'target': 'ba019b192bdb94bd0b5bd68b3a5f92b5acc2239a',
                 'target_type': 'revision'
             }
         }
     }
     check_snapshot(expected_snapshot, loader.storage)
 
 
 def test_npm_loader_incremental_visit(
         swh_config, requests_mock_datadir_visits):
     package = 'org'
     url = package_url(package)
     metadata_url = package_metadata_url(package)
     loader = NpmLoader(package, url, metadata_url)
 
     actual_load_status = loader.load()
     assert actual_load_status['status'] == 'eventful'
     assert actual_load_status['status'] is not None
     origin_visit = list(loader.storage.origin_visit_get(url))[-1]
     assert origin_visit['status'] == 'full'
     assert origin_visit['type'] == 'npm'
 
     stats = get_stats(loader.storage)
 
     assert {
         'content': len(_expected_new_contents_first_visit),
         'directory': len(_expected_new_directories_first_visit),
         'origin': 1,
         'origin_visit': 1,
         'person': 2,
         'release': 0,
         'revision': len(_expected_new_revisions_first_visit),
         'skipped_content': 0,
         'snapshot': 1,
     } == stats
 
     loader._info = None  # reset loader internal state
     actual_load_status2 = loader.load()
     assert actual_load_status2['status'] == 'eventful'
     snap_id2 = actual_load_status2['snapshot_id']
     assert snap_id2 is not None
     assert snap_id2 != actual_load_status['snapshot_id']
 
     origin_visit2 = list(loader.storage.origin_visit_get(url))[-1]
     assert origin_visit2['status'] == 'full'
     assert origin_visit2['type'] == 'npm'
 
     stats = get_stats(loader.storage)
 
     assert {  # 3 new releases artifacts
         'content': len(_expected_new_contents_first_visit) + 14,
         'directory': len(_expected_new_directories_first_visit) + 15,
         'origin': 1,
         'origin_visit': 2,
         'person': 2,
         'release': 0,
         'revision': len(_expected_new_revisions_first_visit) + 3,
         'skipped_content': 0,
         'snapshot': 2,
     } == stats
 
     urls = [
         m.url for m in requests_mock_datadir_visits.request_history
         if m.url.startswith('https://registry.npmjs.org')
     ]
     assert len(urls) == len(set(urls))  # we visited each artifact once across
 
 
 @pytest.mark.usefixtures('requests_mock_datadir')
 def test_npm_loader_version_divergence(swh_config):
     package = '@aller_shared'
     url = package_url(package)
     loader = NpmLoader(package, url, package_metadata_url(package))
 
     actual_load_status = loader.load()
     assert actual_load_status['status'] == 'eventful'
     assert actual_load_status['status'] is not None
     origin_visit = list(loader.storage.origin_visit_get(url))[-1]
     assert origin_visit['status'] == 'full'
     assert origin_visit['type'] == 'npm'
 
     stats = get_stats(loader.storage)
 
     assert {  # 1 new releases artifacts
         'content': 534,
         'directory': 153,
         'origin': 1,
         'origin_visit': 1,
         'person': 1,
         'release': 0,
         'revision': 2,
         'skipped_content': 0,
         'snapshot': 1,
     } == stats
 
     expected_snapshot = {
         'id': 'b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92',
         'branches': {
             'HEAD': {
                 'target_type': 'alias',
                 'target': 'releases/0.1.0'
             },
             'releases/0.1.0': {
                 'target_type': 'revision',
                 'target': '845673bfe8cbd31b1eaf757745a964137e6f9116',
             },
             'releases/0.1.1-alpha.14': {
                 'target_type': 'revision',
                 'target': '05181c12cd8c22035dd31155656826b85745da37',
             },
         },
     }
     check_snapshot(expected_snapshot, loader.storage)
+
+
+def test_npm_artifact_to_revision_id_none():
+    """Current loader version should stop soon if nothing can be found
+
+    """
+    artifact_metadata = {
+        'dist': {
+            'shasum': '05181c12cd8c22035dd31155656826b85745da37',
+        },
+    }
+
+    known_artifacts = {
+        'b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92': {},
+    }
+
+    assert artifact_to_revision_id(known_artifacts, artifact_metadata) is None
+
+
+def test_npm_artifact_to_revision_id_old_loader_version():
+    """Current loader version should solve old metadata scheme
+
+    """
+    artifact_metadata = {
+        'dist': {
+            'shasum': '05181c12cd8c22035dd31155656826b85745da37',
+        }
+    }
+
+    known_artifacts = {
+        hash_to_bytes('b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92'): {
+            'package_source': {
+                'sha1': "something-wrong"
+            }
+        },
+        hash_to_bytes('845673bfe8cbd31b1eaf757745a964137e6f9116'): {
+            'package_source': {
+                'sha1': '05181c12cd8c22035dd31155656826b85745da37',
+            }
+        }
+
+    }
+
+    assert artifact_to_revision_id(known_artifacts, artifact_metadata) \
+        == hash_to_bytes('845673bfe8cbd31b1eaf757745a964137e6f9116')
+
+
+def test_npm_artifact_to_revision_id_current_loader_version():
+    """Current loader version should be able to solve current metadata scheme
+
+    """
+    artifact_metadata = {
+        'dist': {
+            'shasum': '05181c12cd8c22035dd31155656826b85745da37',
+        }
+    }
+
+    known_artifacts = {
+        hash_to_bytes('b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92'): {
+            'original_artifact': [{
+                'checksums': {
+                    'sha1': "05181c12cd8c22035dd31155656826b85745da37"
+                },
+            }],
+        },
+        hash_to_bytes('845673bfe8cbd31b1eaf757745a964137e6f9116'): {
+            'original_artifact': [{
+                'checksums': {
+                    'sha1': 'something-wrong'
+                },
+            }],
+        },
+    }
+
+    assert artifact_to_revision_id(known_artifacts, artifact_metadata) \
+        == hash_to_bytes('b11ebac8c9d0c9e5063a2df693a18e3aba4b2f92')