Deprecation of get_state_item

[melpadden]

From Rasikh via Telegram:

The deprecation of state_get_item breaks all of our stuff as the js sdk breaks with it. There's no backwards compatibility or easy way to migrate to query_global_state
https://github.com/casper-network/casper-node/blob/e4e700e4dbbb14f4e0732c4444d978f821003775/resources/test/rpc_schema_hashing.json#L1295

This breaks paradiso indexing, our offchain infra and all fm offchain infra
If there's a good branch (we don't see one on the repo) to test the migration on we can go for that, but for rn we're not sure what to do
We had some downtime yesterday as the validation cloud guys when building from source to upgrade their rpc pulled this in and it broke our stuff (not their fault, someone merged this in already and that's not their fault). They reverted versions for us but this is already in the master branch

[melpadden]

TL;DR; We'll put it back in for RC3

With regards to state_get_item, this method has been deprecated for quite some time now. To be precise, 16 months ago.
https://github.com/casper-network/casper-node/blob/bad6b5b35274ad1a66654f159ed56a3e6ff6c87e/resources/test/rpc_schema_hashing.json

However, in looking through the release notes, it appears that this change did not make it into any formal communication. Therefore we will be reinstating the function to the API surface, in the Condor RC3 release.

That said, the function will still be marked as deprecated, and will be marked as obsolete in some future release, and eventually deleted. With that in mind, we are providing a short guide to effectively migrating from the deprecated function to the new one.

In terms of the branch to use for migration, the branch for the second release candidate for 2.0 (i.e. the current one) is called release-2.0.0-rc2.

https://github.com/casper-network/casper-node/tree/release-2.0.0-rc2

Future release candidates, including the aforementioned RC3, will follow the same naming convention.

Migration of existing code:
Here is the GetItemParams struct, which is the input parameter for get_state_item:

pub struct GetItemParams {
/// Hash of the state root.
pub state_root_hash: Digest,
/// casper_types::Key as formatted string.
pub key: String,
/// The path components starting from the key as base.
#[serde(default)]
pub path: Vec<String>,
}

Here is the QueryGlobalStateParams struct, input to the query_global_state method:

pub struct QueryGlobalStateParams {
/// The identifier used for the query. If none is passed
/// the tip of the chain will be used.
pub state_identifier: Option<GlobalStateIdentifier>,
/// casper_types::Key as formatted string.
pub key: String,
/// The path components starting from the key as base.
#[serde(default)]
pub path: Vec<String>,
}

Here is the GlobalStateIdentifier enumeration

pub enum GlobalStateIdentifier {
/// Query using a block hash.
BlockHash(BlockHash),
/// Query using a block height.
BlockHeight(u64),
/// Query using the state root hash.
StateRootHash(Digest),
}

The main difference between the old GetItemParams and the new QueryGlobalStateParams is that there are now multiple ways to specify the global state identifier. This adds flexibility without removing any of the old functionality.

To call the query_global_state method, using the state_root_hash, pass the root hash as follows

  state_identifier = Some(GlobalStateIdentifier::StateRootHash(<the hash>))
  //Instead of: 
  state_root_hash = <the hash>

N.B.
In the event that the state identifier is not provided, the node will look up the tip of the chain, and use the root hash from there.