eth_api: Implement get_storage method

[dutterbutter]

Description:

We need to implement the get_storage method, which will be responsible for fetching the storage value from a position in a contract.

/// Retrieves the storage value from a position in a contract.
fn get_storage(&self, address: H160, position: U256, block: Option<BlockIdentifier>) -> jsonrpc_core::BoxFuture<jsonrpc_core::Result<Option<H256>>> {
    not_implemented("get_storage")
}

Expected response

Command:

# Note: Using mainnet URL for demonstration purposes
curl -X POST https://mainnet.era.zksync.io \
     -H "Content-Type: application/json" \
     --data '{
       "jsonrpc": "2.0",
       "id": 1,
       "method": "eth_getStorageAt",
       "params": ["0x123456789abcdef123456789abcdef1234567890", "0x0", "latest"]
     }'

Response:

{"jsonrpc":"2.0","result":"0x0000000000000000000000000000000000000000000000000000000000000000","id":1}

Requirements:

1. Implement the Method:

   • This method should take in three parameters: an H160 address, a U256 position, and an optional BlockIdentifier to specify the block from which the storage should be retrieved.
   • It should return an Option<H256> value representing the storage at the specified position.

2. Unit Tests:

   • Write unit tests to ensure that the get_storage method is functioning correctly.
   • Ensure that any potential exceptions and errors, like an invalid address or position, are correctly handled.

3. Inline Documentation:

   • Add inline Rust documentation (/// comments) detailing the purpose and usage of the get_storage method.
   • Include any relevant information about the return values and potential errors/exceptions.

Task Checklist:

• Implement the get_storage method.
• Write unit tests for the get_storage method.
• Add inline documentation for the get_storage method.

Additional Notes:

If you're an external contributor looking to take on this issue, please comment below to let us know you're working on it. If you need further clarification on the requirements or need assistance with anything related to the implementation, feel free to ask!

[nbaztec]

@MexicanAce I see that currently we do not have a storage (root) per block and only a 1-tier storage. For implementing eth_getStorageAt we also have the additional block parameter to get storage at a height. Do we have an intention of supporting a per height storage?

[georgewhewell]

@MexicanAce I see that currently we do not have a storage (root) per block and only a 1-tier storage. For implementing eth_getStorageAt we also have the additional block parameter to get storage at a height. Do we have an intention of supporting a per height storage?

imo yes, it's quite important- it would be very confusing for people debug issues that arise when using tooling which expects this parameter to be respected and it is not. other dev nodes (e.g anvil) do implement this