Masala: Pure Ethereum VM and RPC with flexible backends, gas model

Implementation of Ethereum VM, to support investigations into hosting EVM and bytecode in a pure consensus-backed ledger such as Juno.

VM/Bytecode interpreter

Masala.VM houses the main interpreter, which sports a tight dispatch driven by the yellow paper spec ensuring that the stack interop is correct.

Showcases Haskell's superior numeric flexibility by leveraging Word256, Int256, Word8 and Word160 to represent the main EVM datatypes, with the respective newtypes U256, S256, U8 and Address supporting automatic JSON conversion.

Gas Models

Supports ethereum's complex gas model, as well as a FixedGasModel of one-unit-per-instruction.

Backend Polymorphism

VM Backend is represented as the MonadExt typeclass, with a basic implementation. This can easily be extended to write to a database, etc.

Because it's a transformer typeclass, it easily hoists into the RPC monad or runs standalone. Note however the transformer implementations only allow it to be the "inner" monad on the stack.

REPL/RPC

To run repl in GHCI, load module 'Masala.Repl', issue _repl, and enter RPC JSON calls.

Solidity code:
contract SimpleStorage2 {
   uint storedData;
   function set(uint x) {
       storedData = x;
   }
   function get() constant returns (uint retVal) {
       return storedData;
   }
}

ghci> :load Masala.Repl
Ok, modules loaded: Masala.VM, Masala.Instruction, Masala.Word, Masala.Ext.Simple, Masala.VM.Types, Masala.VM.Dispatch, Masala.VM.Memory, Masala.VM.Gas, Masala.RPC, Masala.Repl.
ghci> _repl
> {"method":"eth_sendTransaction","params":[{"from":"1e240","data":"0x606060405260908060106000396000f360606040526000357c01000000000000000000000000000000000000000000000000000000009004806360fe47b11460415780636d4ce63c14605257603f565b005b60506004803590602001506071565b005b605b600450607f565b6040518082815260200191505060405180910390f35b806000600050819055505b50565b60006000600050549050608d565b9056"}]}
sendTransaction: SendTran {stfrom = 1e240, stto = Nothing, stgas = Nothing, stgasPrice = Nothing, stvalue = Nothing, stdata = Just 0x606060405260908060106000396000f360606040526000357c01000000000000000000000000000000000000000000000000000000009004806360fe47b11460415780636d4ce63c14605257603f565b005b60506004803590602001506071565b005b605b600450607f565b6040518082815260200191505060405180910390f35b806000600050819055505b50565b60006000600050549050608d565b9056, stnonce = Nothing}
[...]
sendTransaction: Success, addr=1e241, output=[60,60,60,40,52,60,0,35,7c,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,90,4,80,63,60,fe,47,b1,14,60,41,57,80,63,6d,4c,e6,3c,14,60,52,57,60,3f,56,5b,0,5b,60,50,60,4,80,35,90,60,20,1,50,60,71,56,5b,0,5b,60,5b,60,4,50,60,7f,56,5b,60,40,51,80,82,81,52,60,20,1,91,50,50,60,40,51,80,91,3,90,f3,5b,80,60,0,60,0,50,81,90,55,50,5b,50,56,5b,60,0,60,0,60,0,50,54,90,50,60,8d,56,5b,90,56]
"Success, addr=1e241, acct=Just ExtAccount {code=*bytecode*, bal=0, addy=1e241, store=fromList []"
> {"method":"eth_call","params":[{"to":"1e241","data":"0x60fe47b1000000000000000000000000000000000000000000000000000000000000cafe"},"0x0"]}
[...]
call: Success, output=
> {"method":"eth_call","params":[{"to":"1e241","data":"0x6d4ce63c00000000000000000000000000000000000000000000000000000000"},"0x0"]}
[...]
call: Success, output=000000000000000000000000000000000000000000000000000000000000cafe

The repl implements an IORef state model suitable for plugging into a consensus state machine like Juno.

JSON Test Suite

A subset of the go and cpp tests (circa December 2015) are included, which are executed as an HSpec test.

Note that I extended the JSON format to include a "skip" key, for the tests which are intentionally unsupported. This includes some quirks of the go code test fixture, i.e. creating accounts on overflow, etc.