io: Impl Length for mutable refs

Author: Serial-ATA

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- **Length**: `impl<T: Length> Truncate for &mut T` ([PR](https://github.com/Serial-ATA/lofty-rs/pull/387))
+
 ## [0.19.1] - 2024-04-26
 
 ### Added
@@ -726,7 +729,8 @@ See [ogg_pager's changelog](ogg_pager/CHANGELOG.md).
 ### Removed
 - `ErrorKind::BadExtension`
 
-[Unreleased]: https://github.com/Serial-ATA/lofty-rs/compare/0.19.1...HEAD
+[Unreleased]: https://github.com/Serial-ATA/lofty-rs/compare/0.19.2...HEAD
+[0.19.2]: https://github.com/Serial-ATA/lofty-rs/compare/0.19.1...0.19.2
 [0.19.1]: https://github.com/Serial-ATA/lofty-rs/compare/0.19.0...0.19.1
 [0.19.0]: https://github.com/Serial-ATA/lofty-rs/compare/0.18.2...0.19.0
 [0.18.2]: https://github.com/Serial-ATA/lofty-rs/compare/0.18.1...0.18.2

lofty/src/iff/wav/tag/write.rs

@@ -124,7 +124,7 @@ pub(super) fn create_riff_info(
 		bytes.extend(terminator);
 	}
 
-	let packet_size = bytes.len() - 4;
+	let packet_size = Vec::len(bytes) - 4;
 
 	if packet_size > u32::MAX as usize {
 		err!(TooMuchData);

lofty/src/mp4/ilst/mod.rs

@@ -599,7 +599,7 @@ impl SplitTag for Ilst {
 					ItemValue::Text(text)
 				},
 				// We have to special case track/disc numbers since they are stored together
-				AtomData::Unknown { code: 0, data } if data.len() >= 6 => {
+				AtomData::Unknown { code: 0, data } if Vec::len(data) >= 6 => {
 					if let AtomIdent::Fourcc(ref fourcc) = ident {
 						match fourcc {
 							b"trkn" => {

lofty/src/util/io.rs

@@ -29,6 +29,17 @@ impl<T> SeekStreamLen for T where T: Seek {}
 ///
 /// Take great care in implementing this for downstream types, as Lofty will assume that the
 /// container has the new length specified. If this assumption were to be broken, files **will** become corrupted.
+///
+/// # Examples
+///
+/// ```rust
+/// use lofty::io::Truncate;
+///
+/// let mut data = vec![1, 2, 3, 4, 5];
+/// data.truncate(3);
+///
+/// assert_eq!(data, vec![1, 2, 3]);
+/// ```
 pub trait Truncate {
 	/// The error type of the truncation operation
 	type Error: Into<LoftyError>;
@@ -107,6 +118,15 @@ where
 ///
 /// Take great care in implementing this for downstream types, as Lofty will assume that the
 /// container has the exact length specified. If this assumption were to be broken, files **may** become corrupted.
+///
+/// # Examples
+///
+/// ```rust
+/// use lofty::io::Length;
+///
+/// let data = vec![1, 2, 3, 4, 5];
+/// assert_eq!(data.len(), 5);
+/// ```
 pub trait Length {
 	/// The error type of the length operation
 	type Error: Into<LoftyError>;
@@ -176,6 +196,17 @@ where
 	}
 }
 
+impl<T> Length for &mut T
+where
+	T: Length,
+{
+	type Error = <T as Length>::Error;
+
+	fn len(&self) -> Result<u64, Self::Error> {
+		Length::len(*self)
+	}
+}
+
 /// Provides a set of methods to read and write to a file-like object
 ///
 /// This is a combination of the [`Read`], [`Write`], [`Seek`], [`Truncate`], and [`Length`] traits.
@@ -284,4 +315,40 @@ mod tests {
 		let current_file_contents = reader.into_inner();
 		assert_eq!(current_file_contents, test_asset_contents());
 	}
+
+	#[test]
+	fn io_save_using_references() {
+		struct File {
+			buf: Vec<u8>,
+		}
+
+		let mut f = File {
+			buf: std::fs::read(TEST_ASSET).unwrap(),
+		};
+
+		// Same test as above, but using references instead of owned values
+		let mut file = file();
+		alter_tag(&mut file);
+
+		{
+			let mut reader = Cursor::new(&mut f.buf);
+			file.save_to(&mut reader, WriteOptions::new().preferred_padding(0))
+				.expect("Failed to save to vec");
+		}
+
+		{
+			let mut reader = Cursor::new(&f.buf[..]);
+			file = MpegFile::read_from(&mut reader, ParseOptions::new()).unwrap();
+			revert_tag(&mut file);
+		}
+
+		{
+			let mut reader = Cursor::new(&mut f.buf);
+			file.save_to(&mut reader, WriteOptions::new().preferred_padding(0))
+				.expect("Failed to save to vec");
+		}
+
+		let current_file_contents = f.buf;
+		assert_eq!(current_file_contents, test_asset_contents());
+	}
 }