moq-transport: MaxSubscribeId message coding

draft-06

encode/decode support for MaxSubscribeId

MAX_SUBSCRIBE_ID control message

- [PR 491](moq-wg/moq-transport#491)
- [PR 528](moq-wg/moq-transport#528)
- [§6.16](https://www.ietf.org/archive/id/draft-ietf-moq-transport-06.html#section-6.16)

Just parsing for the control message so far, not wired up anywhere yet,
will need error codes

moq-transport/src/message/max_subscribe_id.rs

@@ -0,0 +1,24 @@
+use crate::coding::{Decode, DecodeError, Encode, EncodeError};
+
+/// Sent by the publisher to update the max allowed subscription ID for the session.
+#[derive(Clone, Debug)]
+pub struct MaxSubscribeId {
+	/// The max allowed subscription ID
+	pub id: u64,
+}
+
+impl Decode for MaxSubscribeId {
+	fn decode<R: bytes::Buf>(r: &mut R) -> Result<Self, DecodeError> {
+		let id = u64::decode(r)?;
+
+		Ok(Self { id })
+	}
+}
+
+impl Encode for MaxSubscribeId {
+	fn encode<W: bytes::BufMut>(&self, w: &mut W) -> Result<(), EncodeError> {
+		self.id.encode(w)?;
+
+		Ok(())
+	}
+}

moq-transport/src/message/mod.rs

@@ -39,6 +39,7 @@ mod announce_ok;
 mod filter_type;
 mod go_away;
 mod group_order;
+mod max_subscribe_id;
 mod publisher;
 mod subscribe;
 mod subscribe_done;
@@ -62,6 +63,7 @@ pub use announce_ok::*;
 pub use filter_type::*;
 pub use go_away::*;
 pub use group_order::*;
+pub use max_subscribe_id::*;
 pub use publisher::*;
 pub use subscribe::*;
 pub use subscribe_done::*;
@@ -182,6 +184,7 @@ message_types! {
 	SubscribeOk = 0x4,
 	SubscribeError = 0x5,
 	SubscribeDone = 0xb,
+	MaxSubscribeId = 0x15,
 
 	// ANNOUNCE family, sent by publisher
 	Announce = 0x6,