VorbisComments: Support current/total TRACKNUMBER fields

Closes: #499

lofty/src/ogg/read.rs

@@ -4,6 +4,7 @@ use crate::config::{ParseOptions, ParsingMode};
 use crate::error::{ErrorKind, LoftyError, Result};
 use crate::macros::{decode_err, err, parse_mode_choice};
 use crate::picture::{MimeType, Picture, PictureInformation, PictureType};
+use crate::tag::Accessor;
 use crate::util::text::{utf16_decode, utf8_decode, utf8_decode_str};
 
 use std::borrow::Cow;
@@ -167,6 +168,32 @@ where
 					},
 				}
 			},
+			// Support the case of TRACKNUMBER being equal to current/total
+			k if k.eq_ignore_ascii_case(b"TRACKNUMBER") => {
+				match utf8_decode_str(value) {
+					Ok(value) => {
+						let mut value_split = value.splitn(2, '/');
+						let track_number: Option<u32> =
+							value_split.next().and_then(|b| b.parse().ok());
+						let track_total: Option<u32> =
+							value_split.next().and_then(|b| b.parse().ok());
+						if let Some(n) = track_number {
+							tag.set_track(n);
+						}
+						if let Some(n) = track_total {
+							tag.set_track_total(n);
+						}
+					},
+					Err(e) => {
+						if parse_mode == ParsingMode::Strict {
+							return Err(e);
+						}
+
+						log::warn!("Non UTF-8 value found, discarding field {key:?}");
+						continue;
+					},
+				}
+			},
 			// The valid range is 0x20..=0x7D not including 0x3D
 			k if k.iter().all(|c| (b' '..=b'}').contains(c) && *c != b'=') => {
 				// SAFETY: We just verified that all of the bytes fall within the subset of ASCII

lofty/tests/files/ogg.rs

@@ -167,6 +167,20 @@ fn flac_with_id3v2() {
 	assert!(flac_file.vorbis_comments().is_some());
 }
 
+// case TRACKNUMBER=11/22 (current/total)
+#[test_log::test]
+fn opus_issue_499() {
+	use lofty::ogg::OpusFile;
+
+	let file = std::fs::read("tests/files/assets/issue_499.opus").unwrap();
+	let opus_file =
+		OpusFile::read_from(&mut std::io::Cursor::new(file), ParseOptions::new()).unwrap();
+
+	let comments = opus_file.vorbis_comments();
+	assert_eq!(comments.track(), Some(11));
+	assert_eq!(comments.track_total(), Some(22));
+}
+
 #[test_log::test]
 fn flac_remove_id3v2() {
 	crate::remove_tag!("tests/files/assets/flac_with_id3v2.flac", TagType::Id3v2);