EBML: Stub implement Segment parsing

Signed-off-by: Serial <69764315+Serial-ATA@users.noreply.github.com>

Author: Serial-ATA

lofty_attr/src/lib.rs

@@ -134,7 +134,7 @@ pub fn ebml_master_elements(input: TokenStream) -> TokenStream {
 	});
 
 	TokenStream::from(quote! {
-		#[derive(Copy, Clone, Eq, PartialEq)]
+		#[derive(Copy, Clone, Eq, PartialEq, Debug)]
 		pub(crate) enum ElementIdent {
 			#( #identifiers_iter ),*
 		}

src/ebml/read.rs

@@ -1,5 +1,8 @@
+mod segment;
+
 use super::EbmlFile;
-use crate::ebml::element_reader::{ElementIdent, ElementReader, ElementReaderYield};
+use crate::ebml::element_reader::{ElementHeader, ElementIdent, ElementReader, ElementReaderYield};
+use crate::ebml::vint::VInt;
 use crate::ebml::EbmlProperties;
 use crate::error::Result;
 use crate::macros::decode_err;
@@ -15,35 +18,38 @@ where
 	// new ones all scattered throughout the file
 	let mut properties = EbmlProperties::default();
 
+	let mut ebml_tag = None;
+
 	let mut element_reader = ElementReader::new(reader);
 
 	// First we need to go through the elements in the EBML master element
 	read_ebml_header(&mut element_reader, parse_options, &mut properties)?;
 
 	loop {
-		let ident;
-		let data_ty;
-		let size;
-
 		let res = element_reader.next()?;
 		match res {
-			ElementReaderYield::Master(_) => continue,
-			ElementReaderYield::Child((child, size_)) => {
-				ident = child.ident;
-				data_ty = child.data_type;
-				size = size_;
+			ElementReaderYield::Master((ElementIdent::Segment, _)) => {
+				ebml_tag = segment::read_from(&mut element_reader, parse_options, &mut properties)?;
+				break;
 			},
-			ElementReaderYield::Unknown(element) => {
-				log::debug!("Encountered unknown EBML element: {}", element.id.0);
-				element_reader.skip(element.size.value())?;
+			// CRC-32 (0xBF) and Void (0xEC) elements can occur at the top level.
+			// This is valid, and we can just skip them.
+			ElementReaderYield::Unknown(ElementHeader {
+				id: VInt(id @ (0xBF | 0xEC)),
+				size,
+			}) => {
+				log::debug!("Skipping global element: {:X}", id);
+				element_reader.skip(size.value())?;
 				continue;
 			},
-			ElementReaderYield::Eof => break,
+			_ => {
+				decode_err!(@BAIL Ebml, "File does not contain a segment element")
+			},
 		}
 	}
 
 	Ok(EbmlFile {
-		ebml_tag: None,
+		ebml_tag,
 		properties,
 	})
 }
@@ -78,7 +84,7 @@ where
 			},
 			ElementReaderYield::Unknown(element) => {
 				log::debug!(
-					"Encountered unknown EBML element in header: {}",
+					"Encountered unknown EBML element in header: {:X}",
 					element.id.0
 				);
 				element_reader.skip(element.size.value())?;

src/ebml/read/segment.rs

@@ -0,0 +1,58 @@
+use crate::ebml::element_reader::{ElementIdent, ElementReader, ElementReaderYield};
+use crate::ebml::properties::EbmlProperties;
+use crate::ebml::tag::EbmlTag;
+use crate::error::Result;
+use crate::macros::decode_err;
+use crate::probe::ParseOptions;
+
+use std::io::{Read, Seek};
+
+pub(super) fn read_from<R>(
+	element_reader: &mut ElementReader<R>,
+	_parse_options: ParseOptions,
+	_properties: &mut EbmlProperties,
+) -> Result<Option<EbmlTag>>
+where
+	R: Read + Seek,
+{
+	element_reader.lock();
+
+	let mut tags = None;
+
+	loop {
+		let res = element_reader.next()?;
+		match res {
+			ElementReaderYield::Master((id, size)) => match id {
+				ElementIdent::Info => todo!("Support segment.Info"),
+				ElementIdent::Cluster => todo!("Support segment.Cluster"),
+				ElementIdent::Tracks => todo!("Support segment.Tracks"),
+				ElementIdent::Tags => todo!("Support segment.Tags"),
+				ElementIdent::Attachments => todo!("Support segment.Attachments"),
+				ElementIdent::Chapters => todo!("Support segment.Chapters"),
+				_ => {
+					// We do not end up using information from all of the segment
+					// elements, so we can just skip any useless ones.
+
+					log::debug!("Skipping EBML master element: {:?}", id);
+					element_reader.skip(size)?;
+					element_reader.goto_previous_master()?;
+					continue;
+				},
+			},
+			ElementReaderYield::Unknown(element) => {
+				log::debug!("Skipping unknown EBML element: {:X}", element.id.0);
+				element_reader.skip(element.size.value())?;
+				continue;
+			},
+			ElementReaderYield::Eof => {
+				element_reader.unlock();
+				break;
+			},
+			_ => {
+				decode_err!(@BAIL Ebml, "Segment element should only contain master elements")
+			},
+		}
+	}
+
+	Ok(tags)
+}