Move HTTP-date formatting utils to `utils.http_date`

4 files changed, 37 insertions, 16 deletions

diff --git a/doc/extdev/deprecated.rst b/doc/extdev/deprecated.rst
index f613bc8e8..78eda5111 100644
--- a/doc/extdev/deprecated.rst
+++ b/doc/extdev/deprecated.rst
@@ -22,6 +22,16 @@ The following is a list of deprecated interfaces.
      - Removed
      - Alternatives
 
+   * - ``sphinx.util.epoch_to_rfc1123``
+     - 6.1
+     - 8.0
+     - ``sphinx.util.http_date.epoch_to_rfc1123``
+
+   * - ``sphinx.util.rfc1123_to_epoch``
+     - 6.1
+     - 8.0
+     - ``sphinx.util.http_date.rfc1123_to_epoch``
+
    * - ``sphinx.util.status_iterator``
      - 6.1
      - 8.0
diff --git a/sphinx/transforms/post_transforms/images.py b/sphinx/transforms/post_transforms/images.py
index acf3ba486..1871a0f9c 100644
--- a/sphinx/transforms/post_transforms/images.py
+++ b/sphinx/transforms/post_transforms/images.py
@@ -12,7 +12,8 @@ from docutils import nodes
 from sphinx.application import Sphinx
 from sphinx.locale import __
 from sphinx.transforms import SphinxTransform
-from sphinx.util import epoch_to_rfc1123, logging, requests, rfc1123_to_epoch, sha1
+from sphinx.util import logging, requests, sha1
+from sphinx.util.http_date import epoch_to_rfc1123, rfc1123_to_epoch
 from sphinx.util.images import get_image_extension, guess_mimetype, parse_data_uri
 from sphinx.util.osutil import ensuredir
 
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index 6f742cfe5..f17d4e7a5 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -10,10 +10,8 @@ import sys
 import tempfile
 import traceback
 import warnings
-from datetime import datetime
 from importlib import import_module
 from os import path
-from time import mktime, strptime
 from typing import IO, TYPE_CHECKING, Any, Iterable
 from urllib.parse import parse_qsl, quote_plus, urlencode, urlsplit, urlunsplit
 
@@ -21,6 +19,7 @@ from sphinx.deprecation import RemovedInSphinx70Warning, deprecated_alias
 from sphinx.errors import ExtensionError, FiletypeNotFoundError, SphinxParallelError
 from sphinx.locale import __
 from sphinx.util import display as _display
+from sphinx.util import http_date as _http_date
 from sphinx.util import logging
 from sphinx.util.console import strip_colors
 from sphinx.util.matching import patfilter  # noqa: F401
@@ -444,19 +443,6 @@ def isurl(url: str) -> bool:
     return bool(url) and '://' in url
 
 
-def epoch_to_rfc1123(epoch: float) -> str:
-    """Convert datetime format epoch to RFC1123."""
-    from babel.dates import format_datetime
-
-    dt = datetime.fromtimestamp(epoch)
-    fmt = 'EEE, dd LLL yyyy hh:mm:ss'
-    return format_datetime(dt, fmt, locale='en') + ' GMT'
-
-
-def rfc1123_to_epoch(rfc1123: str) -> float:
-    return mktime(strptime(rfc1123, '%a, %d %b %Y %H:%M:%S %Z'))
-
-
 def xmlname_checker() -> re.Pattern:
     # https://www.w3.org/TR/REC-xml/#NT-Name
     name_start_chars = [
@@ -491,6 +477,8 @@ deprecated_alias('sphinx.util',
                      'status_iterator': _display.status_iterator,
                      'SkipProgressMessage': _display.SkipProgressMessage,
                      'progress_message': _display.progress_message,
+                     'epoch_to_rfc1123': _http_date.epoch_to_rfc1123,
+                     'rfc1123_to_epoch': _http_date.rfc1123_to_epoch,
                  },
                  RemovedInSphinx70Warning,
                  {
@@ -498,4 +486,6 @@ deprecated_alias('sphinx.util',
                      'status_iterator': 'sphinx.util.display.status_iterator',
                      'SkipProgressMessage': 'sphinx.util.display.SkipProgressMessage',
                      'progress_message': 'sphinx.util.display.progress_message',
+                     'epoch_to_rfc1123': 'sphinx.http_date.epoch_to_rfc1123',
+                     'rfc1123_to_epoch': 'sphinx.http_date.rfc1123_to_epoch',
                  })
diff --git a/sphinx/util/http_date.py b/sphinx/util/http_date.py
new file mode 100644
index 000000000..e3c452419
--- /dev/null
+++ b/sphinx/util/http_date.py
@@ -0,0 +1,20 @@
+"""Convert times to and from HTTP-date serialisations.
+
+Reference: https://www.rfc-editor.org/rfc/rfc7231#section-7.1.1.1
+"""
+
+import time
+from email.utils import formatdate, parsedate
+
+
+def epoch_to_rfc1123(epoch: float) -> str:
+    """Return HTTP-date string from epoch offset."""
+    return formatdate(epoch, usegmt=True)
+
+
+def rfc1123_to_epoch(rfc1123: str) -> float:
+    """Return epoch offset from HTTP-date string."""
+    t = parsedate(rfc1123)
+    if t:
+        return time.mktime(t)
+    raise ValueError