diff --git a/requirements.txt b/requirements.txt
index e6a450fb..2535a552 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,26 +1,26 @@
 # Add here external Python modules dependencies, one per line. Module names
 # should match https://pypi.python.org/pypi names. For the full spec or
 # dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
 
 # Runtime dependencies
 beautifulsoup4
 Django >= 1.11.0, < 2.0
 djangorestframework >= 3.4.0
 django_webpack_loader
 django_js_reverse
 docutils
-file_magic >= 0.3.0
+python-magic >= 0.4.0
 htmlmin
 lxml
 pygments
 pypandoc
 python-dateutil
 pyyaml
 requests
 python-memcached
 
 # Doc dependencies
 sphinx
 sphinxcontrib-httpdomain
 
 
diff --git a/swh/web/browse/utils.py b/swh/web/browse/utils.py
index 181f005a..a0df55e6 100644
--- a/swh/web/browse/utils.py
+++ b/swh/web/browse/utils.py
@@ -1,1121 +1,1132 @@
 # Copyright (C) 2017-2019  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import base64
 from collections import defaultdict
 import magic
 import pypandoc
 import stat
 import textwrap
 
 from django.core.cache import cache
 from django.utils.safestring import mark_safe
 from django.utils.html import escape
 
 from importlib import reload
 
 from swh.model.identifiers import persistent_identifier
 from swh.web.common import highlightjs, service
 from swh.web.common.exc import NotFoundExc, http_status_code_message
 from swh.web.common.origin_visits import get_origin_visit
 from swh.web.common.utils import (
     reverse, format_utc_iso_date, get_swh_persistent_id,
     swh_object_icons
 )
 from swh.web.config import get_config
 
 
 def get_directory_entries(sha1_git):
     """Function that retrieves the content of a directory
     from the archive.
 
     The directories entries are first sorted in lexicographical order.
     Sub-directories and regular files are then extracted.
 
     Args:
         sha1_git: sha1_git identifier of the directory
 
     Returns:
         A tuple whose first member corresponds to the sub-directories list
         and second member the regular files list
 
     Raises:
         NotFoundExc if the directory is not found
     """
     cache_entry_id = 'directory_entries_%s' % sha1_git
     cache_entry = cache.get(cache_entry_id)
 
     if cache_entry:
         return cache_entry
 
     entries = list(service.lookup_directory(sha1_git))
     for e in entries:
         e['perms'] = stat.filemode(e['perms'])
         if e['type'] == 'rev':
             # modify dir entry name to explicitly show it points
             # to a revision
             e['name'] = '%s @ %s' % (e['name'], e['target'][:7])
 
     dirs = [e for e in entries if e['type'] in ('dir', 'rev')]
     files = [e for e in entries if e['type'] == 'file']
 
     dirs = sorted(dirs, key=lambda d: d['name'])
     files = sorted(files, key=lambda f: f['name'])
 
     cache.set(cache_entry_id, (dirs, files))
 
     return dirs, files
 
 
 def get_mimetype_and_encoding_for_content(content):
     """Function that returns the mime type and the encoding associated to
     a content buffer using the magic module under the hood.
 
     Args:
         content (bytes): a content buffer
 
     Returns:
         A tuple (mimetype, encoding), for instance ('text/plain', 'us-ascii'),
         associated to the provided content.
 
     """
-    while True:
-        try:
-            magic_result = magic.detect_from_content(content)
-            mime_type = magic_result.mime_type
-            encoding = magic_result.encoding
-            break
-        except Exception:
-            # workaround an issue with the magic module who can fail
-            # if detect_from_content is called multiple times in
-            # a short amount of time
-            reload(magic)
-
+    # https://pypi.org/project/python-magic/
+    # packaged as python3-magic in debian buster
+    if hasattr(magic, 'from_buffer'):
+        m = magic.Magic(mime=True, mime_encoding=True)
+        mime_encoding = m.from_buffer(content)
+        mime_type, encoding = mime_encoding.split(';')
+        encoding = encoding.replace(' charset=', '')
+    # https://pypi.org/project/file-magic/
+    # packaged as python3-magic in debian stretch
+    else:
+        # TODO: Remove that code when production environment is upgraded
+        #       to debian buster
+        while True:
+            try:
+                magic_result = magic.detect_from_content(content)
+                mime_type = magic_result.mime_type
+                encoding = magic_result.encoding
+                break
+            except Exception:
+                # workaround an issue with the magic module who can fail
+                # if detect_from_content is called multiple times in
+                # a short amount of time
+                reload(magic)
     return mime_type, encoding
 
 
 # maximum authorized content size in bytes for HTML display
 # with code highlighting
 content_display_max_size = get_config()['content_display_max_size']
 
 snapshot_content_max_size = get_config()['snapshot_content_max_size']
 
 
 def _re_encode_content(mimetype, encoding, content_data):
     # encode textual content to utf-8 if needed
     if mimetype.startswith('text/'):
         # probably a malformed UTF-8 content, re-encode it
         # by replacing invalid chars with a substitution one
         if encoding == 'unknown-8bit':
             content_data = content_data.decode('utf-8', 'replace')\
                                        .encode('utf-8')
         elif encoding not in ['utf-8', 'binary']:
             content_data = content_data.decode(encoding, 'replace')\
                                        .encode('utf-8')
     elif mimetype.startswith('application/octet-stream'):
         # file may detect a text content as binary
         # so try to decode it for display
         encodings = ['us-ascii']
         encodings += ['iso-8859-%s' % i for i in range(1, 17)]
         for encoding in encodings:
             try:
                 content_data = content_data.decode(encoding)\
                                            .encode('utf-8')
             except Exception:
                 pass
             else:
                 # ensure display in content view
                 mimetype = 'text/plain'
                 break
     return mimetype, content_data
 
 
 def request_content(query_string, max_size=content_display_max_size,
                     raise_if_unavailable=True, re_encode=True):
     """Function that retrieves a content from the archive.
 
     Raw bytes content is first retrieved, then the content mime type.
     If the mime type is not stored in the archive, it will be computed
     using Python magic module.
 
     Args:
         query_string: a string of the form "[ALGO_HASH:]HASH" where
             optional ALGO_HASH can be either ``sha1``, ``sha1_git``,
             ``sha256``, or ``blake2s256`` (default to ``sha1``) and HASH
             the hexadecimal representation of the hash value
         max_size: the maximum size for a content to retrieve (default to 1MB,
             no size limit if None)
 
     Returns:
         A tuple whose first member corresponds to the content raw bytes
         and second member the content mime type
 
     Raises:
         NotFoundExc if the content is not found
     """
     content_data = service.lookup_content(query_string)
     filetype = None
     language = None
     license = None
     # requests to the indexer db may fail so properly handle
     # those cases in order to avoid content display errors
     try:
         filetype = service.lookup_content_filetype(query_string)
         language = service.lookup_content_language(query_string)
         license = service.lookup_content_license(query_string)
     except Exception:
         pass
     mimetype = 'unknown'
     encoding = 'unknown'
     if filetype:
         mimetype = filetype['mimetype']
         encoding = filetype['encoding']
         # workaround when encountering corrupted data due to implicit
         # conversion from bytea to text in the indexer db (see T818)
         # TODO: Remove that code when all data have been correctly converted
         if mimetype.startswith('\\'):
             filetype = None
 
     content_data['error_code'] = 200
     content_data['error_message'] = ''
     content_data['error_description'] = ''
 
     if not max_size or content_data['length'] < max_size:
         try:
             content_raw = service.lookup_content_raw(query_string)
         except Exception as e:
             if raise_if_unavailable:
                 raise e
             else:
                 content_data['raw_data'] = None
                 content_data['error_code'] = 404
                 content_data['error_description'] = \
                     'The bytes of the content are currently not available in the archive.' # noqa
                 content_data['error_message'] = \
                     http_status_code_message[content_data['error_code']]
         else:
             content_data['raw_data'] = content_raw['data']
 
             if not filetype:
                 mimetype, encoding = \
                     get_mimetype_and_encoding_for_content(content_data['raw_data']) # noqa
 
             if re_encode:
                 mimetype, raw_data = _re_encode_content(
                     mimetype, encoding, content_data['raw_data'])
                 content_data['raw_data'] = raw_data
 
     else:
         content_data['raw_data'] = None
 
     content_data['mimetype'] = mimetype
     content_data['encoding'] = encoding
 
     if language:
         content_data['language'] = language['lang']
     else:
         content_data['language'] = 'not detected'
     if license:
         content_data['licenses'] = ', '.join(license['facts'][0]['licenses'])
     else:
         content_data['licenses'] = 'not detected'
 
     return content_data
 
 
 _browsers_supported_image_mimes = set(['image/gif', 'image/png',
                                        'image/jpeg', 'image/bmp',
                                        'image/webp', 'image/svg',
                                        'image/svg+xml'])
 
 
 def prepare_content_for_display(content_data, mime_type, path):
     """Function that prepares a content for HTML display.
 
     The function tries to associate a programming language to a
     content in order to perform syntax highlighting client-side
     using highlightjs. The language is determined using either
     the content filename or its mime type.
     If the mime type corresponds to an image format supported
     by web browsers, the content will be encoded in base64
     for displaying the image.
 
     Args:
         content_data (bytes): raw bytes of the content
         mime_type (string): mime type of the content
         path (string): path of the content including filename
 
     Returns:
         A dict containing the content bytes (possibly different from the one
         provided as parameter if it is an image) under the key 'content_data
         and the corresponding highlightjs language class under the
         key 'language'.
     """
 
     language = highlightjs.get_hljs_language_from_filename(path)
 
     if not language:
         language = highlightjs.get_hljs_language_from_mime_type(mime_type)
 
     if not language:
         language = 'nohighlight'
     elif mime_type.startswith('application/'):
         mime_type = mime_type.replace('application/', 'text/')
 
     if mime_type.startswith('image/'):
         if mime_type in _browsers_supported_image_mimes:
             content_data = base64.b64encode(content_data)
             content_data = content_data.decode('utf-8')
         else:
             content_data = None
 
     if mime_type.startswith('image/svg'):
         mime_type = 'image/svg+xml'
 
     return {'content_data': content_data,
             'language': language,
             'mimetype': mime_type}
 
 
 def process_snapshot_branches(snapshot):
     """
     Process a dictionary describing snapshot branches: extract those
     targeting revisions and releases, put them in two different lists,
     then sort those lists in lexicographical order of the branches' names.
 
     Args:
         snapshot_branches (dict): A dict describing the branches of a snapshot
             as returned for instance by
             :func:`swh.web.common.service.lookup_snapshot`
 
     Returns:
         tuple: A tuple whose first member is the sorted list of branches
             targeting revisions and second member the sorted list of branches
             targeting releases
     """
     snapshot_branches = snapshot['branches']
     branches = {}
     branch_aliases = {}
     releases = {}
     revision_to_branch = defaultdict(set)
     revision_to_release = defaultdict(set)
     release_to_branch = defaultdict(set)
     for branch_name, target in snapshot_branches.items():
         if not target:
             # FIXME: display branches with an unknown target anyway
             continue
         target_id = target['target']
         target_type = target['target_type']
         if target_type == 'revision':
             branches[branch_name] = {
                 'name': branch_name,
                 'revision': target_id,
             }
             revision_to_branch[target_id].add(branch_name)
         elif target_type == 'release':
             release_to_branch[target_id].add(branch_name)
         elif target_type == 'alias':
             branch_aliases[branch_name] = target_id
         # FIXME: handle pointers to other object types
 
     def _enrich_release_branch(branch, release):
         releases[branch] = {
             'name': release['name'],
             'branch_name': branch,
             'date': format_utc_iso_date(release['date']),
             'id': release['id'],
             'message': release['message'],
             'target_type': release['target_type'],
             'target': release['target'],
         }
 
     def _enrich_revision_branch(branch, revision):
         branches[branch].update({
             'revision': revision['id'],
             'directory': revision['directory'],
             'date': format_utc_iso_date(revision['date']),
             'message': revision['message']
         })
 
     releases_info = service.lookup_release_multiple(
         release_to_branch.keys()
     )
     for release in releases_info:
         branches_to_update = release_to_branch[release['id']]
         for branch in branches_to_update:
             _enrich_release_branch(branch, release)
         if release['target_type'] == 'revision':
             revision_to_release[release['target']].update(
                 branches_to_update
             )
 
     revisions = service.lookup_revision_multiple(
         set(revision_to_branch.keys()) | set(revision_to_release.keys())
     )
 
     for revision in revisions:
         if not revision:
             continue
         for branch in revision_to_branch[revision['id']]:
             _enrich_revision_branch(branch, revision)
         for release in revision_to_release[revision['id']]:
             releases[release]['directory'] = revision['directory']
 
     for branch_alias, branch_target in branch_aliases.items():
         if branch_target in branches:
             branches[branch_alias] = dict(branches[branch_target])
         else:
             snp = service.lookup_snapshot(snapshot['id'],
                                           branches_from=branch_target,
                                           branches_count=1)
             if snp and branch_target in snp['branches']:
 
                 if snp['branches'][branch_target] is None:
                     continue
 
                 target_type = snp['branches'][branch_target]['target_type']
                 target = snp['branches'][branch_target]['target']
                 if target_type == 'revision':
                     branches[branch_alias] = snp['branches'][branch_target]
                     revision = service.lookup_revision(target)
                     _enrich_revision_branch(branch_alias, revision)
                 elif target_type == 'release':
                     release = service.lookup_release(target)
                     _enrich_release_branch(branch_alias, release)
 
         if branch_alias in branches:
             branches[branch_alias]['name'] = branch_alias
 
     ret_branches = list(sorted(branches.values(), key=lambda b: b['name']))
     ret_releases = list(sorted(releases.values(), key=lambda b: b['name']))
 
     return ret_branches, ret_releases
 
 
 def get_snapshot_content(snapshot_id):
     """Returns the lists of branches and releases
     associated to a swh snapshot.
     That list is put in  cache in order to speedup the navigation
     in the swh-web/browse ui.
 
     .. warning:: At most 1000 branches contained in the snapshot
         will be returned for performance reasons.
 
     Args:
         snapshot_id (str): hexadecimal representation of the snapshot
             identifier
 
     Returns:
         A tuple with two members. The first one is a list of dict describing
         the snapshot branches. The second one is a list of dict describing the
         snapshot releases.
 
     Raises:
         NotFoundExc if the snapshot does not exist
     """
     cache_entry_id = 'swh_snapshot_%s' % snapshot_id
     cache_entry = cache.get(cache_entry_id)
 
     if cache_entry:
         return cache_entry['branches'], cache_entry['releases']
 
     branches = []
     releases = []
 
     if snapshot_id:
         snapshot = service.lookup_snapshot(
             snapshot_id, branches_count=snapshot_content_max_size)
         branches, releases = process_snapshot_branches(snapshot)
 
     cache.set(cache_entry_id, {
         'branches': branches,
         'releases': releases,
     })
 
     return branches, releases
 
 
 def get_origin_visit_snapshot(origin_info, visit_ts=None, visit_id=None,
                               snapshot_id=None):
     """Returns the lists of branches and releases
     associated to a swh origin for a given visit.
     The visit is expressed by a timestamp. In the latter case,
     the closest visit from the provided timestamp will be used.
     If no visit parameter is provided, it returns the list of branches
     found for the latest visit.
     That list is put in  cache in order to speedup the navigation
     in the swh-web/browse ui.
 
     .. warning:: At most 1000 branches contained in the snapshot
         will be returned for performance reasons.
 
     Args:
         origin_info (dict): a dict filled with origin information
             (id, url, type)
         visit_ts (int or str): an ISO date string or Unix timestamp to parse
         visit_id (int): optional visit id for disambiguation in case
             several visits have the same timestamp
 
     Returns:
         A tuple with two members. The first one is a list of dict describing
         the origin branches for the given visit.
         The second one is a list of dict describing the origin releases
         for the given visit.
 
     Raises:
         NotFoundExc if the origin or its visit are not found
     """
 
     visit_info = get_origin_visit(origin_info, visit_ts, visit_id, snapshot_id)
 
     return get_snapshot_content(visit_info['snapshot'])
 
 
 def gen_link(url, link_text=None, link_attrs=None):
     """
     Utility function for generating an HTML link to insert
     in Django templates.
 
     Args:
         url (str): an url
         link_text (str): optional text for the produced link,
             if not provided the url will be used
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="url">link_text</a>'
 
     """
     attrs = ' '
     if link_attrs:
         for k, v in link_attrs.items():
             attrs += '%s="%s" ' % (k, v)
     if not link_text:
         link_text = url
     link = '<a%shref="%s">%s</a>' \
         % (attrs, escape(url), escape(link_text))
     return mark_safe(link)
 
 
 def _snapshot_context_query_params(snapshot_context):
     query_params = None
     if snapshot_context and snapshot_context['origin_info']:
         origin_info = snapshot_context['origin_info']
         query_params = {'origin': origin_info['url']}
         if 'timestamp' in snapshot_context['url_args']:
             query_params['timestamp'] = \
                  snapshot_context['url_args']['timestamp']
         if 'visit_id' in snapshot_context['query_params']:
             query_params['visit_id'] = \
                 snapshot_context['query_params']['visit_id']
     elif snapshot_context:
         query_params = {'snapshot_id': snapshot_context['snapshot_id']}
     return query_params
 
 
 def gen_person_link(person_id, person_name, snapshot_context=None,
                     link_attrs=None):
     """
     Utility function for generating a link to a person HTML view
     to insert in Django templates.
 
     Args:
         person_id (int): a person id
         person_name (str): the associated person name
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="person_view_url">person_name</a>'
 
     """
     query_params = _snapshot_context_query_params(snapshot_context)
     person_url = reverse('browse-person', url_args={'person_id': person_id},
                          query_params=query_params)
     return gen_link(person_url, person_name or 'None', link_attrs)
 
 
 def gen_revision_url(revision_id, snapshot_context=None):
     """
     Utility function for generating an url to a revision.
 
     Args:
         revision_id (str): a revision id
         snapshot_context (dict): if provided, generate snapshot-dependent
             browsing url
 
     Returns:
         str: The url to browse the revision
 
     """
     query_params = _snapshot_context_query_params(snapshot_context)
 
     return reverse('browse-revision',
                    url_args={'sha1_git': revision_id},
                    query_params=query_params)
 
 
 def gen_revision_link(revision_id, shorten_id=False, snapshot_context=None,
                       link_text='Browse',
                       link_attrs={'class': 'btn btn-default btn-sm',
                                   'role': 'button'}):
     """
     Utility function for generating a link to a revision HTML view
     to insert in Django templates.
 
     Args:
         revision_id (str): a revision id
         shorten_id (boolean): whether to shorten the revision id to 7
             characters for the link text
         snapshot_context (dict): if provided, generate snapshot-dependent
             browsing link
         link_text (str): optional text for the generated link
             (the revision id will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         str: An HTML link in the form '<a href="revision_url">revision_id</a>'
 
     """
     if not revision_id:
         return None
 
     revision_url = gen_revision_url(revision_id, snapshot_context)
 
     if shorten_id:
         return gen_link(revision_url, revision_id[:7], link_attrs)
     else:
         if not link_text:
             link_text = revision_id
         return gen_link(revision_url, link_text, link_attrs)
 
 
 def gen_directory_link(sha1_git, snapshot_context=None, link_text='Browse',
                        link_attrs={'class': 'btn btn-default btn-sm',
                                    'role': 'button'}):
     """
     Utility function for generating a link to a directory HTML view
     to insert in Django templates.
 
     Args:
         sha1_git (str): directory identifier
         link_text (str): optional text for the generated link
             (the directory id will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="directory_view_url">link_text</a>'
 
     """
     if not sha1_git:
         return None
 
     query_params = _snapshot_context_query_params(snapshot_context)
 
     directory_url = reverse('browse-directory',
                             url_args={'sha1_git': sha1_git},
                             query_params=query_params)
 
     if not link_text:
         link_text = sha1_git
     return gen_link(directory_url, link_text, link_attrs)
 
 
 def gen_snapshot_link(snapshot_id, snapshot_context=None, link_text='Browse',
                       link_attrs={'class': 'btn btn-default btn-sm',
                                   'role': 'button'}):
     """
     Utility function for generating a link to a snapshot HTML view
     to insert in Django templates.
 
     Args:
         snapshot_id (str): snapshot identifier
         link_text (str): optional text for the generated link
             (the snapshot id will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="snapshot_view_url">link_text</a>'
 
     """
 
     query_params = _snapshot_context_query_params(snapshot_context)
 
     snapshot_url = reverse('browse-snapshot',
                            url_args={'snapshot_id': snapshot_id},
                            query_params=query_params)
     if not link_text:
         link_text = snapshot_id
     return gen_link(snapshot_url, link_text, link_attrs)
 
 
 def gen_content_link(sha1_git, snapshot_context=None, link_text='Browse',
                      link_attrs={'class': 'btn btn-default btn-sm',
                                  'role': 'button'}):
     """
     Utility function for generating a link to a content HTML view
     to insert in Django templates.
 
     Args:
         sha1_git (str): content identifier
         link_text (str): optional text for the generated link
             (the content sha1_git will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="content_view_url">link_text</a>'
 
     """
     if not sha1_git:
         return None
 
     query_params = _snapshot_context_query_params(snapshot_context)
 
     content_url = reverse('browse-content',
                           url_args={'query_string': 'sha1_git:' + sha1_git},
                           query_params=query_params)
     if not link_text:
         link_text = sha1_git
     return gen_link(content_url, link_text, link_attrs)
 
 
 def get_revision_log_url(revision_id, snapshot_context=None):
     """
     Utility function for getting the URL for a revision log HTML view
     (possibly in the context of an origin).
 
     Args:
         revision_id (str): revision identifier the history heads to
         snapshot_context (dict): if provided, generate snapshot-dependent
             browsing link
     Returns:
         The revision log view URL
     """
     query_params = {'revision': revision_id}
     if snapshot_context and snapshot_context['origin_info']:
         origin_info = snapshot_context['origin_info']
         url_args = {'origin_url': origin_info['url']}
         if 'timestamp' in snapshot_context['url_args']:
             url_args['timestamp'] = \
                 snapshot_context['url_args']['timestamp']
         if 'visit_id' in snapshot_context['query_params']:
             query_params['visit_id'] = \
                 snapshot_context['query_params']['visit_id']
         revision_log_url = reverse('browse-origin-log',
                                    url_args=url_args,
                                    query_params=query_params)
     elif snapshot_context:
         url_args = {'snapshot_id': snapshot_context['snapshot_id']}
         revision_log_url = reverse('browse-snapshot-log',
                                    url_args=url_args,
                                    query_params=query_params)
     else:
         revision_log_url = reverse('browse-revision-log',
                                    url_args={'sha1_git': revision_id})
     return revision_log_url
 
 
 def gen_revision_log_link(revision_id, snapshot_context=None,
                           link_text='Browse',
                           link_attrs={'class': 'btn btn-default btn-sm',
                                       'role': 'button'}):
     """
     Utility function for generating a link to a revision log HTML view
     (possibly in the context of an origin) to insert in Django templates.
 
     Args:
         revision_id (str): revision identifier the history heads to
         snapshot_context (dict): if provided, generate snapshot-dependent
             browsing link
         link_text (str): optional text to use for the generated link
             (the revision id will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form
         '<a href="revision_log_view_url">link_text</a>'
     """
     if not revision_id:
         return None
 
     revision_log_url = get_revision_log_url(revision_id, snapshot_context)
 
     if not link_text:
         link_text = revision_id
     return gen_link(revision_log_url, link_text, link_attrs)
 
 
 def gen_release_link(sha1_git, snapshot_context=None, link_text='Browse',
                      link_attrs={'class': 'btn btn-default btn-sm',
                                  'role': 'button'}):
     """
     Utility function for generating a link to a release HTML view
     to insert in Django templates.
 
     Args:
         sha1_git (str): release identifier
         link_text (str): optional text for the generated link
             (the release id will be used by default)
         link_attrs (dict): optional attributes (e.g. class)
             to add to the link
 
     Returns:
         An HTML link in the form '<a href="release_view_url">link_text</a>'
 
     """
 
     query_params = _snapshot_context_query_params(snapshot_context)
 
     release_url = reverse('browse-release',
                           url_args={'sha1_git': sha1_git},
                           query_params=query_params)
     if not link_text:
         link_text = sha1_git
     return gen_link(release_url, link_text, link_attrs)
 
 
 def format_log_entries(revision_log, per_page, snapshot_context=None):
     """
     Utility functions that process raw revision log data for HTML display.
     Its purpose is to:
 
         * add links to relevant browse views
         * format date in human readable format
         * truncate the message log
 
     Args:
         revision_log (list): raw revision log as returned by the swh-web api
         per_page (int): number of log entries per page
         snapshot_context (dict): if provided, generate snapshot-dependent
             browsing link
 
 
     """
     revision_log_data = []
     for i, rev in enumerate(revision_log):
         if i == per_page:
             break
         author_name = 'None'
         author_fullname = 'None'
         committer_fullname = 'None'
         if rev['author']:
             author_name = rev['author']['name'] or rev['author']['fullname']
             author_fullname = rev['author']['fullname']
         if rev['committer']:
             committer_fullname = rev['committer']['fullname']
         author_date = format_utc_iso_date(rev['date'])
         committer_date = format_utc_iso_date(rev['committer_date'])
 
         tooltip = 'revision %s\n' % rev['id']
         tooltip += 'author: %s\n' % author_fullname
         tooltip += 'author date: %s\n' % author_date
         tooltip += 'committer: %s\n' % committer_fullname
         tooltip += 'committer date: %s\n\n' % committer_date
         if rev['message']:
             tooltip += textwrap.indent(rev['message'], ' '*4)
 
         revision_log_data.append({
             'author': author_name,
             'id': rev['id'][:7],
             'message': rev['message'],
             'date': author_date,
             'commit_date': committer_date,
             'url': gen_revision_url(rev['id'], snapshot_context),
             'tooltip': tooltip
         })
     return revision_log_data
 
 
 # list of origin types that can be found in the swh archive
 # TODO: retrieve it dynamically in an efficient way instead
 #       of hardcoding it
 _swh_origin_types = ['git', 'svn', 'deb', 'hg', 'ftp', 'deposit',
                      'pypi', 'npm']
 
 
 def get_origin_info(origin_url, origin_type=None):
     """
     Get info about a software origin.
     Its main purpose is to automatically find an origin type
     when it is not provided as parameter.
 
     Args:
         origin_url (str): complete url of a software origin
         origin_type (str): optional origin type
 
     Returns:
         A dict with the following entries:
             * type: the origin type
             * url: the origin url
             * id: the internal id of the origin
     """
     if origin_type:
         return service.lookup_origin({'type': origin_type,
                                       'url': origin_url})
     else:
         for origin_type in _swh_origin_types:
             try:
                 origin_info = service.lookup_origin({'type': origin_type,
                                                      'url': origin_url})
                 return origin_info
             except Exception:
                 pass
     raise NotFoundExc('Origin with url %s not found!' % escape(origin_url))
 
 
 def get_snapshot_context(snapshot_id=None, origin_type=None, origin_url=None,
                          timestamp=None, visit_id=None):
     """
     Utility function to compute relevant information when navigating
     the archive in a snapshot context. The snapshot is either
     referenced by its id or it will be retrieved from an origin visit.
 
     Args:
         snapshot_id (str): hexadecimal representation of a snapshot identifier,
             all other parameters will be ignored if it is provided
         origin_type (str): the origin type (git, svn, deposit, ...)
         origin_url (str): the origin_url
             (e.g. https://github.com/(user)/(repo)/)
         timestamp (str): a datetime string for retrieving the closest
             visit of the origin
         visit_id (int): optional visit id for disambiguation in case
             of several visits with the same timestamp
 
     Returns:
         A dict with the following entries:
             * origin_info: dict containing origin information
             * visit_info: dict containing visit information
             * branches: the list of branches for the origin found
               during the visit
             * releases: the list of releases for the origin found
               during the visit
             * origin_browse_url: the url to browse the origin
             * origin_branches_url: the url to browse the origin branches
             * origin_releases_url': the url to browse the origin releases
             * origin_visit_url: the url to browse the snapshot of the origin
               found during the visit
             * url_args: dict containing url arguments to use when browsing in
               the context of the origin and its visit
 
     Raises:
         NotFoundExc: if no snapshot is found for the visit of an origin.
     """
     origin_info = None
     visit_info = None
     url_args = None
     query_params = {}
     branches = []
     releases = []
     browse_url = None
     visit_url = None
     branches_url = None
     releases_url = None
     swh_type = 'snapshot'
     if origin_url:
         swh_type = 'origin'
         origin_info = get_origin_info(origin_url, origin_type)
 
         visit_info = get_origin_visit(origin_info, timestamp, visit_id,
                                       snapshot_id)
         fmt_date = format_utc_iso_date(visit_info['date'])
         visit_info['fmt_date'] = fmt_date
         snapshot_id = visit_info['snapshot']
 
         if not snapshot_id:
             raise NotFoundExc('No snapshot associated to the visit of origin '
                               '%s on %s' % (escape(origin_url), fmt_date))
 
         # provided timestamp is not necessarily equals to the one
         # of the retrieved visit, so get the exact one in order
         # use it in the urls generated below
         if timestamp:
             timestamp = visit_info['date']
 
         branches, releases = \
             get_origin_visit_snapshot(origin_info, timestamp, visit_id,
                                       snapshot_id)
 
         url_args = {'origin_type': origin_type,
                     'origin_url': origin_info['url']}
 
         query_params = {'visit_id': visit_id}
 
         browse_url = reverse('browse-origin-visits',
                              url_args=url_args)
 
         if timestamp:
             url_args['timestamp'] = format_utc_iso_date(timestamp,
                                                         '%Y-%m-%dT%H:%M:%S')
         visit_url = reverse('browse-origin-directory',
                             url_args=url_args,
                             query_params=query_params)
         visit_info['url'] = visit_url
 
         branches_url = reverse('browse-origin-branches',
                                url_args=url_args,
                                query_params=query_params)
 
         releases_url = reverse('browse-origin-releases',
                                url_args=url_args,
                                query_params=query_params)
     elif snapshot_id:
         branches, releases = get_snapshot_content(snapshot_id)
         url_args = {'snapshot_id': snapshot_id}
         browse_url = reverse('browse-snapshot',
                              url_args=url_args)
         branches_url = reverse('browse-snapshot-branches',
                                url_args=url_args)
 
         releases_url = reverse('browse-snapshot-releases',
                                url_args=url_args)
 
     releases = list(reversed(releases))
 
     snapshot_size = service.lookup_snapshot_size(snapshot_id)
 
     is_empty = sum(snapshot_size.values()) == 0
 
     swh_snp_id = persistent_identifier('snapshot', snapshot_id)
 
     return {
         'swh_type': swh_type,
         'swh_object_id': swh_snp_id,
         'snapshot_id': snapshot_id,
         'snapshot_size': snapshot_size,
         'is_empty': is_empty,
         'origin_info': origin_info,
         # keep track if the origin type was provided as url argument
         'origin_type': origin_type,
         'visit_info': visit_info,
         'branches': branches,
         'releases': releases,
         'branch': None,
         'release': None,
         'browse_url': browse_url,
         'branches_url': branches_url,
         'releases_url': releases_url,
         'url_args': url_args,
         'query_params': query_params
     }
 
 
 # list of common readme names ordered by preference
 # (lower indices have higher priority)
 _common_readme_names = [
     "readme.markdown",
     "readme.md",
     "readme.rst",
     "readme.txt",
     "readme"
 ]
 
 
 def get_readme_to_display(readmes):
     """
     Process a list of readme files found in a directory
     in order to find the adequate one to display.
 
     Args:
         readmes: a list of dict where keys are readme file names and values
             are readme sha1s
 
     Returns:
         A tuple (readme_name, readme_sha1)
     """
     readme_name = None
     readme_url = None
     readme_sha1 = None
     readme_html = None
 
     lc_readmes = {k.lower(): {'orig_name': k, 'sha1': v}
                   for k, v in readmes.items()}
 
     # look for readme names according to the preference order
     # defined by the _common_readme_names list
     for common_readme_name in _common_readme_names:
         if common_readme_name in lc_readmes:
             readme_name = lc_readmes[common_readme_name]['orig_name']
             readme_sha1 = lc_readmes[common_readme_name]['sha1']
             readme_url = reverse('browse-content-raw',
                                  url_args={'query_string': readme_sha1},
                                  query_params={'re_encode': 'true'})
             break
 
     # otherwise pick the first readme like file if any
     if not readme_name and len(readmes.items()) > 0:
         readme_name = next(iter(readmes))
         readme_sha1 = readmes[readme_name]
         readme_url = reverse('browse-content-raw',
                              url_args={'query_string': readme_sha1},
                              query_params={'re_encode': 'true'})
 
     # convert rst README to html server side as there is
     # no viable solution to perform that task client side
     if readme_name and readme_name.endswith('.rst'):
         cache_entry_id = 'readme_%s' % readme_sha1
         cache_entry = cache.get(cache_entry_id)
 
         if cache_entry:
             readme_html = cache_entry
         else:
             try:
                 rst_doc = request_content(readme_sha1)
                 readme_html = pypandoc.convert_text(rst_doc['raw_data'],
                                                     'html', format='rst')
                 cache.set(cache_entry_id, readme_html)
             except Exception:
                 readme_html = 'Readme bytes are not available'
 
     return readme_name, readme_url, readme_html
 
 
 def get_swh_persistent_ids(swh_objects, snapshot_context=None):
     """
     Returns a list of dict containing info related to persistent
     identifiers of swh objects.
 
     Args:
         swh_objects (list): a list of dict with the following keys:
             * type: swh object type
                 (content/directory/release/revision/snapshot)
             * id: swh object id
         snapshot_context (dict): optional parameter describing the snapshot in
             which the object has been found
 
     Returns:
         list: a list of dict with the following keys:
             * object_type: the swh object type
                 (content/directory/release/revision/snapshot)
             * object_icon: the swh object icon to use in HTML views
             * swh_id: the computed swh object persistent identifier
             * swh_id_url: the url resolving the persistent identifier
             * show_options: boolean indicating if the persistent id options
                 must be displayed in persistent ids HTML view
     """
     swh_ids = []
     for swh_object in swh_objects:
         if not swh_object['id']:
             continue
         swh_id = get_swh_persistent_id(swh_object['type'], swh_object['id'])
         show_options = swh_object['type'] == 'content' or \
             (snapshot_context and snapshot_context['origin_info'] is not None)
 
         object_icon = swh_object_icons[swh_object['type']]
 
         swh_ids.append({
             'object_type': swh_object['type'],
             'object_icon': object_icon,
             'swh_id': swh_id,
             'swh_id_url': reverse('browse-swh-id',
                                   url_args={'swh_id': swh_id}),
             'show_options': show_options
         })
     return swh_ids