Clarify enr content value format

[mattsse]

This states:

enr/src/builder.rs

Lines 18 to 20 in 83cd989

	/// The key-value pairs for the ENR record.
	/// Values are stored as RLP encoded bytes.
	content: BTreeMap<Key, Bytes>,

This will add any encodable value encoded as rlp to the map:

enr/src/builder.rs

Lines 45 to 56 in 83cd989

	/// Adds an arbitrary key-value to the `ENRBuilder`.
	pub fn add_value<T: Encodable>(&mut self, key: impl AsRef<[u8]>, value: &T) -> &mut Self {
	let mut out = BytesMut::new();
	value.encode(&mut out);
	self.add_value_rlp(key, out.freeze())
	}
	/// Adds an arbitrary key-value where the value is raw RLP encoded bytes.
	pub fn add_value_rlp(&mut self, key: impl AsRef<[u8]>, rlp: Bytes) -> &mut Self {
	self.content.insert(key.as_ref().to_vec(), rlp);
	self
	}

on build this check ensures that all values are rlp(bytes):

enr/src/builder.rs

Lines 159 to 162 in 83cd989

	// Sanitize all data, ensuring all RLP data is correctly formatted.
	for value in self.content.values() {
	Bytes::decode(&mut value.as_ref())?;
	}

on reth, this test currently fails because the value is rlp(forkId)

https://github.com/paradigmxyz/reth/blob/bc2634981e2fdca2d968b1dc63d3ca9a716c93e4/crates/net/discv4/src/proto.rs#L660-L664

If all values should be rlp(bytes) where bytes itself can be rlp(forkid), should add_value then insert self.add_value_rlp(key, alloy_rlp::encode(&out)) ?

enr/src/builder.rs

Lines 45 to 50 in 83cd989

	/// Adds an arbitrary key-value to the `ENRBuilder`.
	pub fn add_value<T: Encodable>(&mut self, key: impl AsRef<[u8]>, value: &T) -> &mut Self {
	let mut out = BytesMut::new();
	value.encode(&mut out);
	self.add_value_rlp(key, out.freeze())
	}

[AgeManning]

To be generic across all types we store the underlying data as bytes and convert to specific types later one.

The general spec indicates an RLP list of k,v: https://github.com/ethereum/devp2p/blob/master/enr.md#rlp-encoding

In principle, it should work for any object that is RLP encodable. In your test could you not just put the fork_id into add_value() and it will be encoded as every other type that is rlp encodeable and stored in the ENR.

Your suggestion would be to double rlp-encode objects right?
Currently we are just rlp-encoding the types and storing the bytes of the rlp-encoded object, which seems sensible to me.

Unless the .build() fails on normal types, it should be the case that all rlp-bytes can be decoded as bytes right?