Varint as an explicit type

moq-transport/src/coding/decode.rs

@@ -20,11 +20,11 @@ impl Decode for Bytes {
 #[async_trait]
 impl Decode for Vec<u8> {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let size = u64::decode(r).await?;
+		let size = VarInt::decode(r).await?;
 
 		// NOTE: we don't use with_capacity since size is from an untrusted source
 		let mut buf = Vec::new();
-		r.take(size).read_to_end(&mut buf).await?;
+		r.take(size.into()).read_to_end(&mut buf).await?;
 
 		Ok(buf)
 	}
@@ -38,17 +38,3 @@ impl Decode for String {
 		Ok(s)
 	}
 }
-
-#[async_trait]
-impl Decode for u64 {
-	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		VarInt::decode(r).await.map(Into::into)
-	}
-}
-
-#[async_trait]
-impl Decode for usize {
-	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		VarInt::decode(r).await.map(Into::into)
-	}
-}

moq-transport/src/coding/duration.rs

@@ -1,5 +1,6 @@
 use super::{Decode, Encode};
 
+use crate::coding::VarInt;
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
 
@@ -9,16 +10,15 @@ use std::time::Duration;
 impl Encode for Duration {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
 		let ms = self.as_millis();
-		let ms = u64::try_from(ms)?;
+		let ms = VarInt::try_from(ms)?;
 		ms.encode(w).await
 	}
 }
 
 #[async_trait]
 impl Decode for Duration {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let ms = u64::decode(r).await?;
-		let ms = ms;
-		Ok(Self::from_millis(ms))
+		let ms = VarInt::decode(r).await?;
+		Ok(Self::from_millis(ms.into()))
 	}
 }

moq-transport/src/coding/encode.rs

@@ -12,25 +12,22 @@ pub trait Encode: Sized {
 #[async_trait]
 impl Encode for Bytes {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		self.len().encode(w).await?;
-		w.write_all(self).await?;
-		Ok(())
+		self.as_ref().encode(w).await
 	}
 }
 
 #[async_trait]
 impl Encode for Vec<u8> {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		self.len().encode(w).await?;
-		w.write_all(self).await?;
-		Ok(())
+		self.as_slice().encode(w).await
 	}
 }
 
 #[async_trait]
 impl Encode for &[u8] {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		self.len().encode(w).await?;
+		let size: VarInt = self.len().try_into()?;
+		size.encode(w).await?;
 		w.write_all(self).await?;
 		Ok(())
 	}
@@ -42,17 +39,3 @@ impl Encode for String {
 		self.as_bytes().encode(w).await
 	}
 }
-
-#[async_trait]
-impl Encode for u64 {
-	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		VarInt::try_from(*self)?.encode(w).await
-	}
-}
-
-#[async_trait]
-impl Encode for usize {
-	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		VarInt::try_from(*self)?.encode(w).await
-	}
-}

moq-transport/src/coding/varint.rs

@@ -21,7 +21,22 @@ pub struct BoundsExceeded;
 // It would be neat if we could express to Rust that the top two bits are available for use as enum
 // discriminants
 #[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
-pub(crate) struct VarInt(u64);
+pub struct VarInt(u64);
+
+impl VarInt {
+	pub const MAX: Self = Self((1 << 62) - 1);
+
+	/// Construct a `VarInt` infallibly using the largest available type.
+	/// Larger values need to use `try_from` instead.
+	pub const fn from_u32(x: u32) -> Self {
+		Self(x as u64)
+	}
+
+	/// Extract the integer value
+	pub const fn into_inner(self) -> u64 {
+		self.0
+	}
+}
 
 impl From<VarInt> for u64 {
 	fn from(x: VarInt) -> Self {
@@ -35,6 +50,12 @@ impl From<VarInt> for usize {
 	}
 }
 
+impl From<VarInt> for u128 {
+	fn from(x: VarInt) -> Self {
+		x.0 as u128
+	}
+}
+
 impl From<u8> for VarInt {
 	fn from(x: u8) -> Self {
 		Self(x.into())
@@ -58,14 +79,27 @@ impl TryFrom<u64> for VarInt {
 
 	/// Succeeds iff `x` < 2^62
 	fn try_from(x: u64) -> Result<Self, BoundsExceeded> {
-		if x < 2u64.pow(62) {
+		if x <= Self::MAX.into_inner() {
 			Ok(Self(x))
 		} else {
 			Err(BoundsExceeded)
 		}
 	}
 }
 
+impl TryFrom<u128> for VarInt {
+	type Error = BoundsExceeded;
+
+	/// Succeeds iff `x` < 2^62
+	fn try_from(x: u128) -> Result<Self, BoundsExceeded> {
+		if x <= Self::MAX.into() {
+			Ok(Self(x as u64))
+		} else {
+			Err(BoundsExceeded)
+		}
+	}
+}
+
 impl TryFrom<usize> for VarInt {
 	type Error = BoundsExceeded;
 	/// Succeeds iff `x` < 2^62

moq-transport/src/control/announce_error.rs

@@ -1,4 +1,4 @@
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
@@ -10,7 +10,7 @@ pub struct AnnounceError {
 	pub track_namespace: String,
 
 	// An error code.
-	pub code: u64,
+	pub code: VarInt,
 
 	// An optional, human-readable reason.
 	pub reason: String,
@@ -20,7 +20,7 @@ pub struct AnnounceError {
 impl Decode for AnnounceError {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
 		let track_namespace = String::decode(r).await?;
-		let code = u64::decode(r).await?;
+		let code = VarInt::decode(r).await?;
 		let reason = String::decode(r).await?;
 
 		Ok(Self {

moq-transport/src/control/mod.rs

@@ -16,7 +16,7 @@ pub use subscribe::*;
 pub use subscribe_error::*;
 pub use subscribe_ok::*;
 
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use std::fmt;
@@ -35,9 +35,9 @@ macro_rules! message_types {
 		#[async_trait]
 		impl Decode for Message {
 			async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-				let t = u64::decode(r).await.context("failed to decode type")?;
+				let t = VarInt::decode(r).await.context("failed to decode type")?;
 
-				Ok(match u64::from(t) {
+				Ok(match t.into_inner() {
 					$($val => {
 						let msg = $name::decode(r).await.context(concat!("failed to decode ", stringify!($name)))?;
 						Self::$name(msg)
@@ -52,8 +52,7 @@ macro_rules! message_types {
 			async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
 				match self {
 					$(Self::$name(ref m) => {
-						let id: u64 = $val; // tell the compiler this is a u64
-						id.encode(w).await.context("failed to encode type")?;
+						VarInt::from_u32($val).encode(w).await.context("failed to encode type")?;
 						m.encode(w).await.context("failed to encode message")
 					},)*
 				}

moq-transport/src/control/subscribe.rs

@@ -1,4 +1,4 @@
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
@@ -7,7 +7,7 @@ use tokio::io::{AsyncRead, AsyncWrite};
 pub struct Subscribe {
 	// An ID we choose so we can map to the track_name.
 	// Proposal: https://github.com/moq-wg/moq-transport/issues/209
-	pub track_id: u64,
+	pub track_id: VarInt,
 
 	// The track namespace.
 	pub track_namespace: String,
@@ -19,7 +19,7 @@ pub struct Subscribe {
 #[async_trait]
 impl Decode for Subscribe {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let track_id = u64::decode(r).await?;
+		let track_id = VarInt::decode(r).await?;
 		let track_namespace = String::decode(r).await?;
 		let track_name = String::decode(r).await?;
 

moq-transport/src/control/subscribe_error.rs

@@ -1,4 +1,4 @@
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
@@ -8,10 +8,10 @@ pub struct SubscribeError {
 	// NOTE: No full track name because of this proposal: https://github.com/moq-wg/moq-transport/issues/209
 
 	// The ID for this track.
-	pub track_id: u64,
+	pub track_id: VarInt,
 
 	// An error code.
-	pub code: u64,
+	pub code: VarInt,
 
 	// An optional, human-readable reason.
 	pub reason: String,
@@ -20,8 +20,8 @@ pub struct SubscribeError {
 #[async_trait]
 impl Decode for SubscribeError {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let track_id = u64::decode(r).await?;
-		let code = u64::decode(r).await?;
+		let track_id = VarInt::decode(r).await?;
+		let code = VarInt::decode(r).await?;
 		let reason = String::decode(r).await?;
 
 		Ok(Self { track_id, code, reason })

moq-transport/src/control/subscribe_ok.rs

@@ -1,4 +1,4 @@
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use std::time::Duration;
 
@@ -10,7 +10,7 @@ pub struct SubscribeOk {
 	// NOTE: No full track name because of this proposal: https://github.com/moq-wg/moq-transport/issues/209
 
 	// The ID for this track.
-	pub track_id: u64,
+	pub track_id: VarInt,
 
 	// The subscription will end after this duration has elapsed.
 	// A value of zero is invalid.
@@ -20,7 +20,7 @@ pub struct SubscribeOk {
 #[async_trait]
 impl Decode for SubscribeOk {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let track_id = u64::decode(r).await?;
+		let track_id = VarInt::decode(r).await?;
 		let expires = Duration::decode(r).await?;
 		let expires = if expires == Duration::ZERO { None } else { Some(expires) };
 

moq-transport/src/data/header.rs

@@ -1,4 +1,4 @@
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
@@ -8,30 +8,30 @@ use tokio::io::{AsyncRead, AsyncWrite};
 pub struct Header {
 	// An ID for this track.
 	// Proposal: https://github.com/moq-wg/moq-transport/issues/209
-	pub track_id: u64,
+	pub track_id: VarInt,
 
 	// The group sequence number.
-	pub group_sequence: u64,
+	pub group_sequence: VarInt,
 
 	// The object sequence number.
-	pub object_sequence: u64,
+	pub object_sequence: VarInt,
 
 	// The priority/send order.
-	pub send_order: u64,
+	pub send_order: VarInt,
 }
 
 #[async_trait]
 impl Decode for Header {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let typ = u64::decode(r).await?;
-		anyhow::ensure!(typ == 0, "OBJECT type must be 0");
+		let typ = VarInt::decode(r).await?;
+		anyhow::ensure!(u64::from(typ) == 0, "OBJECT type must be 0");
 
 		// NOTE: size has been omitted
 
-		let track_id = u64::decode(r).await?;
-		let group_sequence = u64::decode(r).await?;
-		let object_sequence = u64::decode(r).await?;
-		let send_order = u64::decode(r).await?;
+		let track_id = VarInt::decode(r).await?;
+		let group_sequence = VarInt::decode(r).await?;
+		let object_sequence = VarInt::decode(r).await?;
+		let send_order = VarInt::decode(r).await?;
 
 		Ok(Self {
 			track_id,
@@ -45,7 +45,7 @@ impl Decode for Header {
 #[async_trait]
 impl Encode for Header {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		0u64.encode(w).await?;
+		VarInt::from_u32(0).encode(w).await?;
 		self.track_id.encode(w).await?;
 		self.group_sequence.encode(w).await?;
 		self.object_sequence.encode(w).await?;

moq-transport/src/setup/client.rs

@@ -1,5 +1,5 @@
 use super::{Role, Versions};
-use crate::coding::{Decode, Encode};
+use crate::coding::{Decode, Encode, VarInt};
 
 use async_trait::async_trait;
 use tokio::io::{AsyncRead, AsyncWrite};
@@ -26,8 +26,8 @@ pub struct Client {
 #[async_trait]
 impl Decode for Client {
 	async fn decode<R: AsyncRead + Unpin + Send>(r: &mut R) -> anyhow::Result<Self> {
-		let typ = u64::decode(r).await.context("failed to read type")?;
-		anyhow::ensure!(typ == 1, "client SETUP must be type 1");
+		let typ = VarInt::decode(r).await.context("failed to read type")?;
+		anyhow::ensure!(typ.into_inner() == 1, "client SETUP must be type 1");
 
 		let versions = Versions::decode(r).await.context("failed to read supported versions")?;
 		anyhow::ensure!(!versions.is_empty(), "client must support at least one version");
@@ -42,7 +42,7 @@ impl Decode for Client {
 #[async_trait]
 impl Encode for Client {
 	async fn encode<W: AsyncWrite + Unpin + Send>(&self, w: &mut W) -> anyhow::Result<()> {
-		1u64.encode(w).await?;
+		VarInt::from_u32(1).encode(w).await?;
 
 		anyhow::ensure!(!self.versions.is_empty(), "client must support at least one version");
 		self.versions.encode(w).await?;