Replace AU metadata parser with our own implementation

The sunau stdlib module will be removed in Python 3.13.

xl/metadata/__init__.py

@@ -38,6 +38,7 @@
     aiff,
     ape,
     asf,
+    au,
     flac,
     mka,
     mod,
@@ -64,7 +65,7 @@
     'ape'   : ape.MonkeysFormat,
     'amf'   : mod.ModFormat,
     'asf'   : asf.AsfFormat,
-    'au'    : wav.WavFormat,
+    'au'    : au.AuFormat,
     'dsm'   : mod.ModFormat,
     'far'   : mod.ModFormat,
     'flac'  : flac.FlacFormat,

xl/metadata/au.py

@@ -0,0 +1,87 @@
+# Copyright (C) 2024  Johannes Sasongko <johannes sasongko org>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+#
+# The developers of the Exaile media player hereby grant permission
+# for non-GPL compatible GStreamer and Exaile plugins to be used and
+# distributed together with GStreamer and Exaile. This permission is
+# above and beyond the permissions granted by the GPL license by which
+# Exaile is covered. If you modify this code, you may extend this
+# exception to your version of the code, but you are not obligated to
+# do so. If you do not wish to do so, delete this exception statement
+# from your version.
+
+
+import io
+import os
+import struct
+from typing import Tuple
+
+from xl.metadata._base import BaseFormat, NotReadable
+
+
+class AuFormat(BaseFormat):
+    writable = False
+
+    def load(self):
+        try:
+            with open(self.loc, 'rb', buffering=0) as f:
+                file_size = os.stat(f.fileno()).st_size
+                bitrate, length = _read_metadata(f, file_size)
+        except IOError:
+            raise NotReadable
+        self.mutagen = {'__bitrate': bitrate, '__length': length}
+
+
+def _read_metadata(f: io.FileIO, file_size: int) -> Tuple[float, float]:
+    """
+    :return: bitrate, length
+    """
+
+    # See https://en.wikipedia.org/wiki/Au_file_format
+
+    try:
+        header = f.read(24)
+    except IOError:
+        return -1, -1
+
+    # > = big-endian; I = uint32
+    magic, data_offset, data_size, encoding, sample_rate, channels = struct.unpack(
+        '>IIIIII', header
+    )
+    if magic != 0x2E736E64:  # '.snd'
+        return -1, -1
+
+    # Data size can be unknown (uint32_max) or wrong; try to guess it
+    data_size = min(data_size, file_size - data_offset)
+
+    # fmt: off
+    ENCODING_WIDTHS = {
+        1: 1,
+        2: 1, 3: 2, 4: 3, 5: 4,
+        6: 4, 7: 8,
+        11: 1, 12: 2, 13: 3, 14: 4,
+        18: 2, 19: 2, 20: 2,
+        27: 1,
+    }
+    # fmt: on
+    try:
+        sample_width = ENCODING_WIDTHS[encoding]
+    except KeyError:
+        return -1, -1
+
+    byterate = sample_rate * sample_width * channels
+    return byterate * 8, data_size / byterate

xl/metadata/wav.py

@@ -26,29 +26,22 @@
 
 
 import wave
-import sunau
-import os
 
 from xl.metadata._base import BaseFormat, NotReadable
 
-type_map = {"au": sunau, "wav": wave}
-
 
 class WavFormat(BaseFormat):
     writable = False
 
     def load(self):
-        ext = os.path.splitext(self.loc)[1][1:].lower()
-        opener = type_map[ext]
-
         try:
             fp = open(self.loc, 'rb')
         except IOError:
             raise NotReadable
 
         try:
             with fp:
-                f = opener.open(fp)
+                f = wave.open(fp)
                 length = f.getnframes() // f.getframerate()
             self.mutagen = {'__bitrate': -1, '__length': length}
         except (IOError, KeyError):