ethlite

Eth(ereum) Lite

ethlite - light-weight machinery to query / call ethereum (blockchain contract) services via json-rpc (incl. tuple support)

• home :: github.com/rubycocos/blockchain
• bugs :: github.com/rubycocos/blockchain/issues
• gem :: rubygems.org/gems/ethlite
• rdoc :: rubydoc.info/gems/ethlite

Usage

Step 0: Setup JSON RPC Client

Let's use the simple (built-in) JSON RPC client. Get the eth node uri via the INFURA_URI enviroment variable / key e.g. https://mainnet.infura.io/v3/<YOUR_KEY_HERE>:

ETH_NODE  = JsonRpc.new( ENV['INFURA_URI'] )

Do-It-Yourself (DIY) JSON RPC eth_call With "Hand-Coded" To-The-Metal ABI Encoding/Decoding

Let's try to build a JSON-RPC request from scratch calling a (constant/read-only/view) blockchain contract method via eth_call.

Let's try function tokenURI(uint256 tokenId) returns (string) that lets you request the metdata uri for a (non-fungible) token.

Let's try the Moonbirds contract @ 0x23581767a106ae21c074b2276d25e5c3e136a68b:

## contract address - let's try moonbirds
contract_address = '0x23581767a106ae21c074b2276d25e5c3e136a68b'

token_ids = (0..9)
token_ids.each do |token_id|

  puts "==> calling tokenURI(#{token_id})..."
  tokenURI = eth_call( ETH_NODE, contract_address,
                         'tokenURI', ['uint256'], ['string'],
                         [token_id] )
  puts "   ...returns: #{tokenURI}"
end

And the "magic" hand-coded to-the-metal eth_call machinery:

## construct a json-rpc call from scratch
def eth_call( rpc,
              contract_address,
              name, inputs, outputs,
              args )

  ## binary encode method sig(nature)
  signature      = "#{name}(#{inputs.join(',')})"
  signature_hash =  Ethlite::Utils.encode_hex(
                        Ethlite::Utils.keccak256(signature)[0,4])

  pp signature
  # => "tokenURI(uint256)"
  pp signature_hash
  # => "c87b56dd"

  ## binary encode method arg(ument)s
  args_encoded = Ethlite::Utils.encode_hex(
                   ABI.encode( inputs, args) )

  data = '0x' + signature_hash + args_encoded

  ## json-rpc  method and params
  method =  'eth_call'
  params =  [{ to:   contract_address,
              data: data},
            'latest'
            ]

  ## do the json-rpc request
  response = rpc.request( method, params )

  puts "response:"
  pp response

  ## decode binary result (returned as a hex string starting with 0x)
  bin = Ethlite::Utils.decode_hex( response )
  result =  ABI.decode( outputs, bin )
  result.length  == 1 ? result[0] : result
end

resulting in (with debug json rpc request/reponse output):

calling tokenURI(0)... json_rpc POST payload request:

{"jsonrpc":"2.0",
 "method":"eth_call",
 "params":[
    {"to":"0x23581767a106ae21c074b2276d25e5c3e136a68b",
     "data":"0xc87b56dd0000000000000000000000000000000000000000000000000000000000000000"},
    "latest"],
  "id":1
}

json_rpc response:

{"jsonrpc":"2.0",
 "id":1,"result":"0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000003a68747470733a2f2f6c6976652d2d2d6d657461646174612d35636f767071696a61612d75632e612e72756e2e6170702f6d657461646174612f30000000000000"
}

...returns: https://live---metadata-5covpqijaa-uc.a.run.app/metadata/0

calling tokenURI(1)... json_rpc POST payload request:

{"jsonrpc":"2.0",
 "method":"eth_call",
 "params":[
  {"to":"0x23581767a106ae21c074b2276d25e5c3e136a68b",
   "data":"0xc87b56dd0000000000000000000000000000000000000000000000000000000000000001"},
   "latest"],
  "id":2
}

json_rpc response:

{"jsonrpc":"2.0",
 "id":2,"result":"0x0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000003a68747470733a2f2f6c6976652d2d2d6d657461646174612d35636f767071696a61612d75632e612e72756e2e6170702f6d657461646174612f31000000000000"
}

...returns: https://live---metadata-5covpqijaa-uc.a.run.app/metadata/1

JSON RPC eth_call With ContractMethod Helper

Let's retry using the convenience builtin ContractMethod helper:

## contract address - let's try moonbirds
contract_address = '0x23581767a106ae21c074b2276d25e5c3e136a68b'

ETH_tokenURI = Ethlite::ContractMethod.new( 'tokenURI',
                                             inputs: ['uint256'],
                                             outputs: ['string'] )

token_ids = (0..9)
token_ids.each do |token_id|
  puts "==> tokenURI(#{token_id}) returns:"
  pp ETH_tokenURI.do_call( ETH_NODE, contract_address, [token_id] )
end

resulting in:

==> tokenURI(0) returns:
"https://live---metadata-5covpqijaa-uc.a.run.app/metadata/0"
==> tokenURI(1) returns:
"https://live---metadata-5covpqijaa-uc.a.run.app/metadata/1"
==> tokenURI(2) returns:
"https://live---metadata-5covpqijaa-uc.a.run.app/metadata/3"
...

And so on and so forth.

License

The scripts are dedicated to the public domain. Use it as you please with no restrictions whatsoever.

Questions? Comments?

Post them on the D.I.Y. Punk (Pixel) Art reddit. Thanks.