pile-audio refactor

crates/pile-flac/src/blocks/header.rs

@@ -0,0 +1,87 @@
+//! FLAC metablock headers. See spec.
+use std::fmt::Debug;
+
+use crate::{FlacDecodeError, FlacEncodeError};
+
+/// A type of flac metadata block
+#[expect(missing_docs)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum FlacMetablockType {
+	Streaminfo,
+	Padding,
+	Application,
+	Seektable,
+	VorbisComment,
+	Cuesheet,
+	Picture,
+}
+
+impl FlacMetablockType {
+	/// Read and parse a metablock header from the given reader.
+	/// Returns (block_type, block_data_length, is_last)
+	pub(crate) fn from_id(id: u8) -> Result<Self, FlacDecodeError> {
+		return Ok(match id & 0b01111111 {
+			0 => FlacMetablockType::Streaminfo,
+			1 => FlacMetablockType::Padding,
+			2 => FlacMetablockType::Application,
+			3 => FlacMetablockType::Seektable,
+			4 => FlacMetablockType::VorbisComment,
+			5 => FlacMetablockType::Cuesheet,
+			6 => FlacMetablockType::Picture,
+			x => return Err(FlacDecodeError::BadMetablockType(x)),
+		});
+	}
+}
+
+/// The header of a flac metadata block
+#[derive(Debug, Clone)]
+pub struct FlacMetablockHeader {
+	/// The type of block this is
+	pub block_type: FlacMetablockType,
+
+	/// The length of this block, in bytes
+	/// (not including this header)
+	pub length: u32,
+
+	/// If true, this is the last metadata block
+	pub is_last: bool,
+}
+
+impl FlacMetablockHeader {
+	/// Try to decode the given bytes as a flac metablock header
+	pub fn decode(header: &[u8]) -> Result<Self, FlacDecodeError> {
+		if header.len() != 4 {
+			return Err(FlacDecodeError::MalformedBlock);
+		}
+
+		return Ok(Self {
+			block_type: FlacMetablockType::from_id(header[0])?,
+			length: u32::from_be_bytes([0, header[1], header[2], header[3]]),
+			is_last: header[0] & 0b10000000 == 0b10000000,
+		});
+	}
+}
+
+impl FlacMetablockHeader {
+	/// Try to encode this header
+	pub fn encode(&self, target: &mut impl std::io::Write) -> Result<(), FlacEncodeError> {
+		let mut block_type = match self.block_type {
+			FlacMetablockType::Streaminfo => 0,
+			FlacMetablockType::Padding => 1,
+			FlacMetablockType::Application => 2,
+			FlacMetablockType::Seektable => 3,
+			FlacMetablockType::VorbisComment => 4,
+			FlacMetablockType::Cuesheet => 5,
+			FlacMetablockType::Picture => 6,
+		};
+
+		if self.is_last {
+			block_type |= 0b1000_0000;
+		};
+
+		let x = self.length.to_be_bytes();
+		target.write_all(&[block_type, x[1], x[2], x[3]])?;
+
+		return Ok(());
+	}
+}