Utilize free atoms when writing; Fix meta atom writing

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+- **MP4**: Padding atoms (`free`) are used when writing
+
+### Fixed
+- **MP4**: `meta` atoms are written correctly
+
 ## [0.5.0] - 2022-02-20
 
 ### Added

src/mp4/ilst/mod.rs

@@ -439,8 +439,10 @@ fn item_key_to_ident(key: &ItemKey) -> Option<AtomIdentRef<'_>> {
 
 #[cfg(test)]
 mod tests {
-	use crate::mp4::{AdvisoryRating, Atom, AtomData, AtomIdent, Ilst};
-	use crate::{ItemKey, Tag, TagExt, TagType};
+	use crate::mp4::{AdvisoryRating, Atom, AtomData, AtomIdent, Ilst, Mp4File};
+	use crate::tag_utils::test_utils::read_path;
+	use crate::{Accessor, AudioFile, ItemKey, Tag, TagExt, TagType};
+	use std::io::{Cursor, Read, Seek, SeekFrom, Write};
 
 	fn read_ilst(path: &str) -> Ilst {
 		let tag = crate::tag_utils::test_utils::read_path(path);
@@ -506,7 +508,7 @@ mod tests {
 			AtomData::UTF8(String::from("Foo title")),
 		));
 
-		let tag = crate::tag_utils::test_utils::read_path("tests/tags/assets/test.ilst");
+		let tag = crate::tag_utils::test_utils::read_path("tests/tags/assets/ilst/test.ilst");
 
 		let parsed_tag = super::read::parse_ilst(&mut &tag[..], tag.len() as u64).unwrap();
 
@@ -515,7 +517,7 @@ mod tests {
 
 	#[test]
 	fn ilst_re_read() {
-		let parsed_tag = read_ilst("tests/tags/assets/test.ilst");
+		let parsed_tag = read_ilst("tests/tags/assets/ilst/test.ilst");
 
 		let mut writer = Vec::new();
 		parsed_tag.dump_to(&mut writer).unwrap();
@@ -529,7 +531,7 @@ mod tests {
 
 	#[test]
 	fn ilst_to_tag() {
-		let tag_bytes = crate::tag_utils::test_utils::read_path("tests/tags/assets/test.ilst");
+		let tag_bytes = crate::tag_utils::test_utils::read_path("tests/tags/assets/ilst/test.ilst");
 
 		let ilst = super::read::parse_ilst(&mut &tag_bytes[..], tag_bytes.len() as u64).unwrap();
 
@@ -595,7 +597,7 @@ mod tests {
 
 	#[test]
 	fn issue_34() {
-		let ilst = read_ilst("tests/tags/assets/issue_34.ilst");
+		let ilst = read_ilst("tests/tags/assets/ilst/issue_34.ilst");
 
 		verify_atom(
 			&ilst,
@@ -614,7 +616,7 @@ mod tests {
 
 	#[test]
 	fn advisory_rating() {
-		let ilst = read_ilst("tests/tags/assets/advisory_rating.ilst");
+		let ilst = read_ilst("tests/tags/assets/ilst/advisory_rating.ilst");
 
 		verify_atom(
 			&ilst,
@@ -624,4 +626,53 @@ mod tests {
 
 		assert_eq!(ilst.advisory_rating(), Some(AdvisoryRating::Explicit));
 	}
+
+	#[test]
+	fn trailing_padding() {
+		const ILST_START: usize = 97;
+		const ILST_END: usize = 131;
+		const PADDING_SIZE: usize = 990;
+
+		let file_bytes = read_path("tests/files/assets/ilst_trailing_padding.m4a");
+		assert!(Mp4File::read_from(&mut Cursor::new(&file_bytes), false).is_ok());
+
+		let ilst_bytes = &file_bytes[ILST_START..ILST_END];
+
+		let old_free_size =
+			u32::from_be_bytes(file_bytes[ILST_END..ILST_END + 4].try_into().unwrap());
+		assert_eq!(old_free_size, PADDING_SIZE as u32);
+
+		let mut ilst = super::read::parse_ilst(&mut &*ilst_bytes, ilst_bytes.len() as u64).unwrap();
+
+		let mut file = tempfile::tempfile().unwrap();
+		file.write_all(&file_bytes).unwrap();
+		file.seek(SeekFrom::Start(0)).unwrap();
+
+		ilst.set_title(String::from("Exactly 21 Characters"));
+		ilst.save_to(&mut file).unwrap();
+
+		// Now verify the free atom
+		file.seek(SeekFrom::Start(0)).unwrap();
+
+		let mut file_bytes = Vec::new();
+		file.read_to_end(&mut file_bytes).unwrap();
+
+		// 24 (atom + data) + title string (21)
+		let new_data_size = 24_u32 + 21;
+		let new_ilst_end = ILST_END + new_data_size as usize;
+
+		let file_atom = &file_bytes[new_ilst_end..new_ilst_end + 8];
+
+		match file_atom {
+			[size @ .., b'f', b'r', b'e', b'e'] => assert_eq!(
+				old_free_size - new_data_size,
+				u32::from_be_bytes(size.try_into().unwrap())
+			),
+			_ => unreachable!(),
+		}
+
+		// Verify we can re-read the file
+		file.seek(SeekFrom::Start(0)).unwrap();
+		assert!(Mp4File::read_from(&mut file, false).is_ok());
+	}
 }

src/mp4/ilst/read.rs

@@ -172,8 +172,8 @@ fn parse_int(bytes: &[u8]) -> Result<i32> {
 	Ok(match bytes.len() {
 		1 => i32::from(bytes[0]),
 		2 => i32::from(i16::from_be_bytes([bytes[0], bytes[1]])),
-		3 => i32::from_be_bytes([0, bytes[0], bytes[1], bytes[2]]) as i32,
-		4 => i32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]) as i32,
+		3 => i32::from_be_bytes([0, bytes[0], bytes[1], bytes[2]]),
+		4 => i32::from_be_bytes([bytes[0], bytes[1], bytes[2], bytes[3]]),
 		_ => {
 			return Err(LoftyError::new(ErrorKind::BadAtom(
 				"Unexpected atom size for type \"BE signed integer\"",

src/mp4/ilst/write.rs

@@ -1,8 +1,10 @@
 use super::{AtomDataRef, IlstRef};
-use crate::error::{FileEncodingError, Result};
+use crate::error::{ErrorKind, FileEncodingError, LoftyError, Result};
+use crate::macros::try_vec;
+use crate::mp4::atom_info::{AtomIdent, AtomInfo};
 use crate::mp4::ilst::{AtomIdentRef, AtomRef};
 use crate::mp4::moov::Moov;
-use crate::mp4::read::{nested_atom, verify_mp4};
+use crate::mp4::read::{atom_tree, nested_atom, verify_mp4};
 use crate::types::file::FileType;
 use crate::types::picture::{MimeType, Picture};
 
@@ -36,75 +38,45 @@ pub(in crate) fn write_to(data: &mut File, tag: &mut IlstRef<'_>) -> Result<()>
 	}
 
 	// Total size of new atoms
-	let new_udta_size;
+	let mut new_udta_size;
 	// Size of the existing udta atom
 	let mut existing_udta_size = 0;
 
 	// ilst is nested in udta.meta, so we need to check what atoms actually exist
 	if let Some(udta) = udta {
-		if let Some(meta) = nested_atom(&mut cursor, udta.len, b"meta")? {
+		existing_udta_size = udta.len;
+		new_udta_size = existing_udta_size;
+
+		let meta = nested_atom(&mut cursor, udta.len, b"meta")?;
+		match meta {
+			Some(meta) => {
 				// Skip 4 bytes
 				// Version (1)
 				// Flags   (3)
 				cursor.seek(SeekFrom::Current(4))?;
 
-			let replacement;
-			let range;
-			let existing_ilst_size;
-
-			let existing_ilst = nested_atom(&mut cursor, meta.len - 4, b"ilst")?;
-
-			match existing_ilst {
-				Some(existing) => {
-					replacement = if remove_tag { Vec::new() } else { ilst };
-
-					range = existing.start as usize..(existing.start + existing.len) as usize;
-					existing_ilst_size = existing.len as u64;
+				// We can use the existing `udta` and `meta` atoms
+				save_to_existing(
+					&mut cursor,
+					(meta, udta),
+					&mut new_udta_size,
+					ilst,
+					remove_tag,
+				)?
 			},
+			// Nothing to do
+			None if remove_tag => return Ok(()),
+			// We have to create the `meta` atom
 			None => {
-					// Nothing to do
-					if remove_tag {
-						return Ok(());
-					}
-
-					let meta_end = (meta.start + meta.len) as usize;
-
-					replacement = ilst;
-					range = meta_end..meta_end;
-					existing_ilst_size = 0;
-				},
-			}
-
 				existing_udta_size = udta.len;
 
-			let new_meta_size = (meta.len - existing_ilst_size) + replacement.len() as u64;
-			new_udta_size = (udta.len - meta.len) + new_meta_size;
-
-			cursor.get_mut().splice(range, replacement);
-
-			cursor.seek(SeekFrom::Start(meta.start))?;
-			write_size(meta.start, new_meta_size, meta.extended, &mut cursor)?;
-
-			cursor.seek(SeekFrom::Start(udta.start))?;
-			write_size(udta.start, new_udta_size, udta.extended, &mut cursor)?;
-		} else {
-			// Nothing to do
-			if remove_tag {
-				return Ok(());
-			}
-
-			existing_udta_size = udta.len;
-
-			// `meta` + `ilst`
-			let capacity = 8 + ilst.len();
+				// `meta` (12) + `ilst`
+				let capacity = 12 + ilst.len();
 				let buf = Vec::with_capacity(capacity);
 
 				let mut bytes = Cursor::new(buf);
-			bytes.write_all(&[0, 0, 0, 0, b'm', b'e', b't', b'a'])?;
+				create_meta(&mut bytes, &ilst)?;
 
-			write_size(0, ilst.len() as u64 + 8, false, &mut bytes)?;
-
-			bytes.write_all(&ilst)?;
 				let bytes = bytes.into_inner();
 
 				new_udta_size = udta.len + bytes.len() as u64;
@@ -115,38 +87,30 @@ pub(in crate) fn write_to(data: &mut File, tag: &mut IlstRef<'_>) -> Result<()>
 				cursor
 					.get_mut()
 					.splice(udta.start as usize..udta.start as usize, bytes);
+			},
 		}
 	} else {
-		// `udta` + `meta` + `ilst`
-		let capacity = 16 + ilst.len();
+		// We have to create the `udta` atom
+
+		// `udta` + `meta` (12) + `hdlr` (33) + `ilst`
+		let capacity = 53 + ilst.len();
 		let buf = Vec::with_capacity(capacity);
 
 		let mut bytes = Cursor::new(buf);
-		bytes.write_all(&[
-			0, 0, 0, 0, b'u', b'd', b't', b'a', 0, 0, 0, 0, b'm', b'e', b't', b'a',
-		])?;
+		bytes.write_all(&[0, 0, 0, 0, b'u', b'd', b't', b'a'])?;
+
+		create_meta(&mut bytes, &ilst)?;
 
 		// udta size
+		bytes.seek(SeekFrom::Start(0))?;
 		write_size(0, ilst.len() as u64 + 8, false, &mut bytes)?;
 
-		// meta size
-		write_size(
-			bytes.seek(SeekFrom::Current(0))?,
-			ilst.len() as u64,
-			false,
-			&mut bytes,
-		)?;
-
-		bytes.seek(SeekFrom::End(0))?;
-		bytes.write_all(&ilst)?;
-
 		let bytes = bytes.into_inner();
 
 		new_udta_size = bytes.len() as u64;
 
-		cursor
-			.get_mut()
-			.splice((moov.start + 8) as usize..(moov.start + 8) as usize, bytes);
+		let udta_pos = (moov.start + 8) as usize;
+		cursor.get_mut().splice(udta_pos..udta_pos, bytes);
 	}
 
 	cursor.seek(SeekFrom::Start(moov.start))?;
@@ -166,6 +130,141 @@ pub(in crate) fn write_to(data: &mut File, tag: &mut IlstRef<'_>) -> Result<()>
 	Ok(())
 }
 
+fn save_to_existing(
+	cursor: &mut Cursor<Vec<u8>>,
+	(meta, udta): (AtomInfo, AtomInfo),
+	new_udta_size: &mut u64,
+	ilst: Vec<u8>,
+	remove_tag: bool,
+) -> Result<()> {
+	let replacement;
+	let range;
+
+	let (ilst_idx, tree) = atom_tree(cursor, meta.len - 4, b"ilst")?;
+
+	if tree.is_empty() {
+		// Nothing to do
+		if remove_tag {
+			return Ok(());
+		}
+
+		let meta_end = (meta.start + meta.len) as usize;
+
+		replacement = ilst;
+		range = meta_end..meta_end;
+	} else {
+		let existing_ilst = &tree[ilst_idx];
+		let existing_ilst_size = existing_ilst.len;
+
+		let mut range_start = existing_ilst.start;
+		let range_end = existing_ilst.start + existing_ilst_size;
+
+		if remove_tag {
+			// We just need to strip out the `ilst` atom
+
+			replacement = Vec::new();
+			range = range_start as usize..range_end as usize;
+		} else {
+			// Check for some padding atoms we can utilize
+			let mut available_space = existing_ilst_size;
+
+			// Check for one directly before the `ilst` atom
+			if ilst_idx > 0 {
+				let previous_atom = &tree[ilst_idx - 1];
+
+				if previous_atom.ident == AtomIdent::Fourcc(*b"free") {
+					range_start = previous_atom.start;
+					available_space += previous_atom.len;
+				}
+			}
+
+			// And after
+			if ilst_idx != tree.len() - 1 {
+				let next_atom = &tree[ilst_idx + 1];
+
+				if next_atom.ident == AtomIdent::Fourcc(*b"free") {
+					available_space += next_atom.len;
+				}
+			}
+
+			let ilst_len = ilst.len() as u64;
+
+			// Check if we have enough padding to fit the `ilst` atom and a new `free` atom
+			if available_space > ilst_len && available_space - ilst_len > 8 {
+				// We have enough space to make use of the padding
+
+				let remaining_space = available_space - ilst_len;
+				if remaining_space > u64::from(u32::MAX) {
+					return Err(LoftyError::new(ErrorKind::TooMuchData));
+				}
+
+				let remaining_space = remaining_space as u32;
+
+				cursor.seek(SeekFrom::Start(range_start))?;
+				cursor.write_all(&ilst)?;
+
+				// Write the remaining padding
+				cursor.write_u32::<BigEndian>(remaining_space)?;
+				cursor.write_all(b"free")?;
+				cursor.write_all(&try_vec![1; (remaining_space - 8) as usize])?;
+
+				return Ok(());
+			}
+
+			replacement = ilst;
+			range = range_start as usize..range_end as usize;
+		}
+	}
+
+	let new_meta_size = (meta.len - range.len() as u64) + replacement.len() as u64;
+
+	// Replace the `ilst` atom
+	cursor.get_mut().splice(range, replacement);
+
+	if new_meta_size != meta.len {
+		// We need to change the `meta` and `udta` atom sizes
+
+		*new_udta_size = (udta.len - meta.len) + new_meta_size;
+
+		cursor.seek(SeekFrom::Start(meta.start))?;
+		write_size(meta.start, new_meta_size, meta.extended, cursor)?;
+
+		cursor.seek(SeekFrom::Start(udta.start))?;
+		write_size(udta.start, *new_udta_size, udta.extended, cursor)?;
+	}
+
+	Ok(())
+}
+
+fn create_meta(cursor: &mut Cursor<Vec<u8>>, ilst: &[u8]) -> Result<()> {
+	const HDLR_SIZE: u64 = 33;
+
+	let start = cursor.stream_position()?;
+	// meta atom
+	cursor.write_all(&[0, 0, 0, 0, b'm', b'e', b't', b'a', 0, 0, 0, 0])?;
+
+	// hdlr atom
+	cursor.write_u32::<BigEndian>(0)?;
+	cursor.write_all(b"hdlr")?;
+	cursor.write_u64::<BigEndian>(0)?;
+	cursor.write_all(b"mdirappl")?;
+	cursor.write_all(&[0, 0, 0, 0, 0, 0, 0, 0, 0])?;
+
+	cursor.seek(SeekFrom::Start(start))?;
+
+	let meta_size = 4 + HDLR_SIZE + ilst.len() as u64;
+	write_size(start, meta_size, false, cursor)?;
+
+	// Seek to `hdlr` size
+	let hdlr_size_pos = cursor.seek(SeekFrom::Current(4))?;
+	write_size(hdlr_size_pos, HDLR_SIZE, false, cursor)?;
+
+	cursor.seek(SeekFrom::End(0))?;
+	cursor.write_all(ilst)?;
+
+	Ok(())
+}
+
 fn write_size(start: u64, size: u64, extended: bool, writer: &mut Cursor<Vec<u8>>) -> Result<()> {
 	if size > u64::from(u32::MAX) {
 		// 0001 (identifier) ????????

src/mp4/read.rs

@@ -98,3 +98,36 @@ where
 
 	Ok(ret)
 }
+
+// Creates a tree of nested atoms
+pub(crate) fn atom_tree<R>(data: &mut R, len: u64, up_to: &[u8]) -> Result<(usize, Vec<AtomInfo>)>
+where
+	R: Read + Seek,
+{
+	let mut read = 8;
+	let mut found_idx: usize = 0;
+	let mut buf = Vec::new();
+
+	let mut i = 0;
+
+	while read < len {
+		let atom = AtomInfo::read(data)?;
+
+		skip_unneeded(data, atom.extended, atom.len)?;
+		read += atom.len;
+
+		if let AtomIdent::Fourcc(ref fourcc) = atom.ident {
+			i += 1;
+
+			if fourcc == up_to {
+				found_idx = i;
+			}
+
+			buf.push(atom);
+		}
+	}
+
+	found_idx = found_idx.saturating_sub(1);
+
+	Ok((found_idx, buf))
+}

tests/files/mp4.rs

@@ -27,6 +27,7 @@ fn write() {
 
 	// Now reread the file
 	file.seek(SeekFrom::Start(0)).unwrap();
+
 	let mut tagged_file = lofty::read_from(&mut file, false).unwrap();
 
 	crate::set_artist!(tagged_file, tag_mut, TagType::Mp4Ilst, "Bar artist", 1 => file, "Foo artist");