Fixes getStorageAt undeployed contract response

[weiihann]

Trie.Get by default returns no error and zero value for non-existent key. To check if a contract is deployed, we have no choice by to check if the nonce also exists (which is a redundant DB IO).

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 75.35%. Comparing base (e4240ac) to head (9e72cf1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
rpc/contract.go	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2250      +/-   ##
==========================================
+ Coverage   75.25%   75.35%   +0.09%     
==========================================
  Files         106      106              
  Lines       11229    11238       +9     
==========================================
+ Hits         8450     8468      +18     
+ Misses       2138     2133       -5     
+ Partials      641      637       -4     

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[IronGauntlets]

It seems to me that the problem you are describing would be better solved by returning an error from stateReader.ContractStorage when the key doesn't exist, right?

[weiihann]

It seems to me that the problem you are describing would be better solved by returning an error from stateReader.ContractStorage when the key doesn't exist, right?

If the key doesn't exist, it will return a zero value for ContractStorage (see Trie.Get). This behavior of Trie is correct because a non-existent key by default has a zero value, so we shouldn't modify it to return the key not found error.

The problem is that we need a way to check if a contract exists. Since we put contract fields (i.e. nonce, balance, storage) in different buckets, we have no choice but to add an additional DB lookup (in this case using ContractNonce) to check if a contract is deployed or not.

If we condensed the contract fields into a single bucket (see #2224), we only need to do a single DB lookup to check if a contract exists or not.