Fix getTransactionCount leading zeros in hex string

[natanrolnik]

As described here (emphasis mine):

When encoding QUANTITIES (integers, numbers): encode as hex, prefix with "0x", the most compact representation (slight exception: zero should be represented as "0x0").

The implementation of getTransactionCount would encode numbers including a leading zero, for example: 4 would become 0x04 instead of the correct way 0x4.

This PR fixes it, and also fixes the function hexWithoutLeadingZeroes in lib/utils/to.js to correctly convert 0 to 0x0 instead of 0x (which would lead to an exception in Web3js when creating a BigNumber, more specifically at line 363).

I tried to add a test for this change, but as Web3 already returns the decoded number, I wasn't able to find the right place to check that the hex string is returned correctly.

Related issues and PRs that might related to this PR:

• Fixes Quantities such as from eth_getTransactionCount have leading zeroes ganache-cli-archive#220;
• Relates to Allow leading zeros when parsing hex strings. hyperledger-web3j/web3j#23, probably allowing to revert it;
• Similar to Incorrect Hex Encoding for Quantities ethereumjs/ethereumjs-tx#51

[natanrolnik]

Removed because it's already present at line 12

[attente]

Hello, thank you for working on this! Would you mind also merging in some tests I wrote for this?

kinecosystem#2

[natanrolnik]

@attente thanks for writing the tests. Merged.

[benjamincburns]

@natanrolnik & @attente thanks for teaming up on this one!

[FutureOfAI]

I have same problem as you, can you help me how to deal with leading zero in raw-transaction?
My raw transaction is: f86b0285012a05f2008261a8948b733353ce21ebd8eb5ffd9f49d57830942e88158769ec95a3fa70008025a04f9dd75069b51d36ec47b5bf68e6c45f8b854cf17a661e734e7a7c651240eeaca00044280475c3d355c44829ac93118b4ebe044356185c1c08724c8bcfebbd4b3d

including:
R is 4f9dd75069b51d36ec47b5bf68e6c45f8b854cf17a661e734e7a7c651240eeac
S is 0044280475c3d355c44829ac93118b4ebe044356185c1c08724c8bcfebbd4b3d
How can I deal with leading zero, and how can I reconstruction raw-transaction after correct it?
Does the process like this:
RLP{ RLP(nonce) + RLP(Gas price) + RLP(Gas limit) + RLP(to address) + RLP(value) + RLP(data) + V + [a0 + FixLeadingZero(R)] + [a0 + FixLeadingZero(S)] }