Have all the special storage keys in a single place

[xlc]

I am working on a feature of Chopsticks to decode all the storage keys. There are some keys requires special handling as they are not included in metadata.

Currently we have

polkadot-sdk/substrate/primitives/storage/src/lib.rs

Lines 192 to 216 in 86228fa

	/// Wasm code of the runtime.
	///
	/// Stored as a raw byte vector. Required by substrate.
	pub const CODE: &[u8] = b":code";
	/// Number of wasm linear memory pages required for execution of the runtime.
	///
	/// The type of this value is encoded `u64`.
	pub const HEAP_PAGES: &[u8] = b":heappages";
	/// Current extrinsic index (u32) is stored under this key.
	///
	/// Encodes to `0x3a65787472696e7369635f696e646578`.
	pub const EXTRINSIC_INDEX: &[u8] = b":extrinsic_index";
	/// Current intra-block entropy (a universally unique `[u8; 32]` value) is stored here.
	///
	/// Encodes to `0x3a696e747261626c6f636b5f656e74726f7079`.
	pub const INTRABLOCK_ENTROPY: &[u8] = b":intrablock_entropy";
	/// Prefix of child storage keys.
	pub const CHILD_STORAGE_KEY_PREFIX: &[u8] = b":child_storage:";
	/// Prefix of the default child storage keys in the top trie.
	pub const DEFAULT_CHILD_STORAGE_KEY_PREFIX: &[u8] = b":child_storage:default:";

polkadot-sdk/substrate/frame/support/src/traits/metadata.rs

Lines 163 to 167 in 86228fa

	/// The storage key postfix that is used to store the [`StorageVersion`] per pallet.
	///
	/// The full storage key is built by using:
	/// Twox128([`PalletInfo::name`]) ++ Twox128([`STORAGE_VERSION_STORAGE_KEY_POSTFIX`])
	pub const STORAGE_VERSION_STORAGE_KEY_POSTFIX: &[u8] = b":__STORAGE_VERSION__:";

polkadot-sdk/substrate/frame/support/src/storage/transactional.rs

Lines 34 to 37 in 86228fa

	/// The key that is holds the current number of active layers.
	///
	/// Encodes to `0x3a7472616e73616374696f6e5f6c6576656c3a`.
	pub const TRANSACTION_LEVEL_KEY: &[u8] = b":transaction_level:";

polkadot-sdk/substrate/primitives/consensus/grandpa/src/lib.rs

Lines 65 to 67 in 86228fa

	/// The storage key for the current set of weighted Grandpa authorities.
	/// The value stored is an encoded VersionedAuthorityList.
	pub const GRANDPA_AUTHORITIES_KEY: &[u8] = b":grandpa_authorities";

polkadot-sdk/polkadot/primitives/src/v6/mod.rs

Lines 242 to 251 in 86228fa

	/// The upward message dispatch queue remaining capacity for the given para id.
	///
	/// The storage entry stores a tuple of two values:
	///
	/// - `count: u32`, the number of additional messages which may be enqueued for the given para,
	/// - `total_size: u32`, the total size of additional messages which may be enqueued for the
	/// given para.
	pub fn relay_dispatch_queue_remaining_capacity(para_id: Id) -> WellKnownKey<(u32, u32)> {
	(b":relay_dispatch_queue_remaining_capacity", para_id).encode().into()
	}

Please let me know if I missed anything

This makes it really hard to implement a generic and all-catching storage decoder. Can we move all the Substrate well known keys to sp_core::storage::well_known_keys? The polkadot one are all in a single place so that's good.

[xlc]

The key format is also inconsistent. Some of them are :xxx and some of them are :xxx: but I guess we are already too late to change them.

We should also update the docs to include encoded hex and the expected value type.

[bkchr]

The polkadot one are all in a single place so that's good.

The Polkadot ones are not special keys, these are just the normal FRAME storage keys.

[xlc]

:relay_dispatch_queue_remaining_capacity is definitely a special key but yeah everything else seems just storage keys encoded. Maybe we could refactor them in such why we code the string and have macro to convert them to hex in compile time? So it is more obvious where the hex is coming from.

[bkchr]

:relay_dispatch_queue_remaining_capacity

Ahh you got me :P

Maybe we could refactor them in such why we code the string and have macro to convert them to hex in compile time?

In a perfect way we would not need them at all. Or better abstracted. But we already have the hash macros, so it should actually work.

[ggwpez]

I think we should use storage_alias to have type safety.