Web3 filter proxy

[p4u]

When deploying the Vocdoni smart contracts to mainnet, we will need to provide Web3 access for Archive Nodes in order to let the eligible voters fetch their ethereum storage proofs when using the Vocdoni Bridge

Running an Archive Node is very expensive (around 200€/month), so the access to them should be limited for vocdoni only usage, else we'll end up with thousands of queries not related to vocdoni that will probably occupy the node resources.

To limit the queries we need to build an intermediate proxy between the client and the web3 archive-node. This proxy will needs to:

1. Filter for type of queries required by Vocdoni (so only allow those from a whitelist)
2. On eth_getProof and eth_call allow only querying those contracts that have an active voting process

Current list of queries that should be allowed:

• eth_syncing
• eth_getBlockByNumber
• eth_getProof
• eth_call
• eth_chainId

Here an existing proxy implementation that could be used as basis https://github.com/gochain/rpc-proxy

eth_call

Here an eth_call example query.

{
	"id": 346,
	"jsonrpc": "2.0",
	"method": "eth_call",
	"params": [
		{
			"data": "0x8eaa6ac097500c591f7636cc303ef0fd49ada268c30cffbf5881f5cdc774e41d103a764e",
			"to": "0x8770c609905df85dcdd6a5bc35a181471e297e73"
		},
		"latest"
	]
}

The to parameter is the contract to query. The proxy should filter to allow only queries to an existing Vocdoni smart contract.

eth_getProof

An example for eth_getProof JSON call:

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "eth_getProof",
  "params": [
    "0x7F0d15C7FAae65896648C8273B6d7E43f58Fa842",
    [  "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421" ],
    "latest"
  ]
}

The first argument of params is the contract address on which the storage proof will be retrieved. The last one latest is the block number to which the proof wants to be fetched.

The Web3 proxy should also listen for processNewProcess event, as the Oracle does. And in case of censusOrigin=ERC20 include the contract address and block number to the whitelist.

When a getProof query is received, check that contract and block-number are whitelisted, else return an error.

[vdo]

a maybe viable option is to increase the window of historic data that geth saves in memory, here:

https://github.com/ethereum/go-ethereum/blob/2fc465a7be6f29f75f0528d7867fe3e5f49c4e65/core/blockchain.go#L92

We could just increase, or parametrize it so we can save a month or two of state data to execute eth_getProof

[p4u]

If that works it would be amazing. A cheap way to have a storage-proof ethereum node. So we don't need the full archive stuff. We might send a PR to go-ethereum to make this const configurable via flag, thus we don't need to fork go-ethereum.

In any case the proxy is complementary to that solution. So @vdo if you can test it and report on this thread the results, that would be amazing.

[brickpop]

So far, the methods that we are using are:

• eth_syncing (dvote-js)
• eth_getProof (storage-proofs-eth-js)
• eth_getBlockByNumber (storage-proofs-eth-js)

[p4u]

updated in the description! thanks @brickpop