bsc/cmd/evm/README.md

## EVM state transition tool

The `evm t8n` tool is a stateless state transition utility. It is a utility
which can

1. Take a prestate, including
- Accounts,
- Block context information,
- Previous blockshashes (*optional)
2. Apply a set of transactions,
3. Apply a mining-reward (*optional),
4. And generate a post-state, including
- State root, transaction root, receipt root,
- Information about rejected transactions,
- Optionally: a full or partial post-state dump

## Specification

The idea is to specify the behaviour of this binary very _strict_, so that other
node implementors can build replicas based on their own state-machines, and the
state generators can swap between a `geth`-based implementation and a `parityvm`-based
implementation.

### Command line params

Command line params that has to be supported are
```

   --trace                            Output full trace logs to files <txhash>.jsonl
   --trace.nomemory                   Disable full memory dump in traces
   --trace.nostack                    Disable stack output in traces
   --trace.noreturndata               Disable return data output in traces
   --output.basedir value             Specifies where output files are placed. Will be created if it does not exist.
   --output.alloc alloc               Determines where to put the alloc of the post-state.
                                      `stdout` - into the stdout output
                                      `stderr` - into the stderr output
   --output.result result             Determines where to put the result (stateroot, txroot etc) of the post-state.
                                      `stdout` - into the stdout output
                                      `stderr` - into the stderr output
   --output.body value                If set, the RLP of the transactions (block body) will be written to this file.
   --input.txs stdin                  stdin or file name of where to find the transactions to apply. If the file prefix is '.rlp', then the data is interpreted as an RLP list of signed transactions.The '.rlp' format is identical to the output.body format. (default: "txs.json")
   --state.fork value                 Name of ruleset to use.
   --state.chainid value              ChainID to use (default: 1)
   --state.reward value               Mining reward. Set to -1 to disable (default: 0)

```

### Error codes and output

All logging should happen against the `stderr`.
There are a few (not many) errors that can occur, those are defined below.

#### EVM-based errors (`2` to `9`)

- Other EVM error. Exit code `2`
- Failed configuration: when a non-supported or invalid fork was specified. Exit code `3`.
- Block history is not supplied, but needed for a `BLOCKHASH` operation. If `BLOCKHASH`
  is invoked targeting a block which history has not been provided for, the program will
  exit with code `4`.

#### IO errors (`10`-`20`)

- Invalid input json: the supplied data could not be marshalled.
  The program will exit with code `10`
- IO problems: failure to load or save files, the program will exit with code `11`

## Examples
### Basic usage

Invoking it with the provided example files
```
./evm t8n --input.alloc=./testdata/1/alloc.json --input.txs=./testdata/1/txs.json --input.env=./testdata/1/env.json
```
Two resulting files:

`alloc.json`:
```json
{
 "0x8a8eafb1cf62bfbeb1741769dae1a9dd47996192": {
  "balance": "0xfeed1a9d",
  "nonce": "0x1"
 },
 "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
  "balance": "0x5ffd4878be161d74",
  "nonce": "0xac"
 },
 "0xc94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
  "balance": "0xa410"
 }
}
```
`result.json`:
```json
{
 "stateRoot": "0x84208a19bc2b46ada7445180c1db162be5b39b9abc8c0a54b05d32943eae4e13",
 "txRoot": "0xc4761fd7b87ff2364c7c60b6c5c8d02e522e815328aaea3f20e3b7b7ef52c42d",
 "receiptRoot": "0x056b23fbba480696b65fe5a59b8f2148a1299103c4f57df839233af2cf4ca2d2",
 "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
 "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
 "receipts": [
  {
   "root": "0x",
   "status": "0x1",
   "cumulativeGasUsed": "0x5208",
   "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
   "logs": null,
   "transactionHash": "0x0557bacce3375c98d806609b8d5043072f0b6a8bae45ae5a67a00d3a1a18d673",
   "contractAddress": "0x0000000000000000000000000000000000000000",
   "gasUsed": "0x5208",
   "blockHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
   "transactionIndex": "0x0"
  }
 ],
 "rejected": [
  {
   "index": 1,
   "error": "nonce too low: address 0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192, tx: 0 state: 1"
  }
 ]
}
```

We can make them spit out the data to e.g. `stdout` like this:
```
./evm t8n --input.alloc=./testdata/1/alloc.json --input.txs=./testdata/1/txs.json --input.env=./testdata/1/env.json --output.result=stdout --output.alloc=stdout
```
Output:
```json
{
 "alloc": {
  "0x8a8eafb1cf62bfbeb1741769dae1a9dd47996192": {
   "balance": "0xfeed1a9d",
   "nonce": "0x1"
  },
  "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
   "balance": "0x5ffd4878be161d74",
   "nonce": "0xac"
  },
  "0xc94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
   "balance": "0xa410"
  }
 },
 "result": {
  "stateRoot": "0x84208a19bc2b46ada7445180c1db162be5b39b9abc8c0a54b05d32943eae4e13",
  "txRoot": "0xc4761fd7b87ff2364c7c60b6c5c8d02e522e815328aaea3f20e3b7b7ef52c42d",
  "receiptRoot": "0x056b23fbba480696b65fe5a59b8f2148a1299103c4f57df839233af2cf4ca2d2",
  "logsHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
  "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  "receipts": [
   {
    "root": "0x",
    "status": "0x1",
    "cumulativeGasUsed": "0x5208",
    "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
    "logs": null,
    "transactionHash": "0x0557bacce3375c98d806609b8d5043072f0b6a8bae45ae5a67a00d3a1a18d673",
    "contractAddress": "0x0000000000000000000000000000000000000000",
    "gasUsed": "0x5208",
    "blockHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "transactionIndex": "0x0"
   }
  ],
  "rejected": [
   {
    "index": 1,
    "error": "nonce too low: address 0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192, tx: 0 state: 1"
   }
  ]
 }
}
```

## About Ommers

Mining rewards and ommer rewards might need to be added. This is how those are applied:

- `block_reward` is the block mining reward for the miner (`0xaa`), of a block at height `N`.
- For each ommer (mined by `0xbb`), with blocknumber `N-delta`
  - (where `delta` is the difference between the current block and the ommer)
  - The account `0xbb` (ommer miner) is awarded `(8-delta)/ 8 * block_reward`
  - The account `0xaa` (block miner) is awarded `block_reward / 32`

To make `state_t8n` apply these, the following inputs are required:

- `state.reward`
  - For ethash, it is `5000000000000000000` `wei`,
  - If this is not defined, mining rewards are not applied,
  - A value of `0` is valid, and causes accounts to be 'touched'.
- For each ommer, the tool needs to be given an `address` and a `delta`. This
  is done via the `env`.

Note: the tool does not verify that e.g. the normal uncle rules apply,
and allows e.g two uncles at the same height, or the uncle-distance. This means that
the tool allows for negative uncle reward (distance > 8)

Example:
`./testdata/5/env.json`:
```json
{
  "currentCoinbase": "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
  "currentDifficulty": "0x20000",
  "currentGasLimit": "0x750a163df65e8a",
  "currentNumber": "1",
  "currentTimestamp": "1000",
  "ommers": [
    {"delta":  1, "address": "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb" },
    {"delta":  2, "address": "0xcccccccccccccccccccccccccccccccccccccccc" }
  ]
}
```
When applying this, using a reward of `0x80`
Output:
```json
{
 "alloc": {
  "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa": {
   "balance": "0x88"
  },
  "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb": {
   "balance": "0x70"
  },
  "0xcccccccccccccccccccccccccccccccccccccccc": {
   "balance": "0x60"
  }
 }
}
```
### Future EIPS

It is also possible to experiment with future eips that are not yet defined in a hard fork.
Example, putting EIP-1344 into Frontier:
```
./evm t8n --state.fork=Frontier+1344 --input.pre=./testdata/1/pre.json --input.txs=./testdata/1/txs.json --input.env=/testdata/1/env.json
```

### Block history

The `BLOCKHASH` opcode requires blockhashes to be provided by the caller, inside the `env`.
If a required blockhash is not provided, the exit code should be `4`:
Example where blockhashes are provided:
```
./evm --verbosity=1 t8n --input.alloc=./testdata/3/alloc.json --input.txs=./testdata/3/txs.json --input.env=./testdata/3/env.json  --trace
INFO [07-27|11:53:40.960] Trie dumping started                     root=b7341d..857ea1
INFO [07-27|11:53:40.960] Trie dumping complete                    accounts=3 elapsed="103.298µs"
INFO [07-27|11:53:40.960] Wrote file                               file=alloc.json
INFO [07-27|11:53:40.960] Wrote file                               file=result.json

```

```
cat trace-0-0x72fadbef39cd251a437eea619cfeda752271a5faaaa2147df012e112159ffb81.jsonl | grep BLOCKHASH -C2
```
```
{"pc":0,"op":96,"gas":"0x5f58ef8","gasCost":"0x3","memory":"0x","memSize":0,"stack":[],"returnData":"0x","depth":1,"refund":0,"opName":"PUSH1","error":""}
{"pc":2,"op":64,"gas":"0x5f58ef5","gasCost":"0x14","memory":"0x","memSize":0,"stack":["0x1"],"returnData":"0x","depth":1,"refund":0,"opName":"BLOCKHASH","error":""}
{"pc":3,"op":0,"gas":"0x5f58ee1","gasCost":"0x0","memory":"0x","memSize":0,"stack":["0xdac58aa524e50956d0c0bae7f3f8bb9d35381365d07804dd5b48a5a297c06af4"],"returnData":"0x","depth":1,"refund":0,"opName":"STOP","error":""}
{"output":"","gasUsed":"0x17","time":156276}
```

In this example, the caller has not provided the required blockhash:
```
./evm t8n --input.alloc=./testdata/4/alloc.json --input.txs=./testdata/4/txs.json --input.env=./testdata/4/env.json --trace
ERROR(4): getHash(3) invoked, blockhash for that block not provided
```
Error code: 4

### Chaining

Another thing that can be done, is to chain invocations:
```
./evm t8n --input.alloc=./testdata/1/alloc.json --input.txs=./testdata/1/txs.json --input.env=./testdata/1/env.json --output.alloc=stdout | ./evm t8n --input.alloc=stdin --input.env=./testdata/1/env.json --input.txs=./testdata/1/txs.json
INFO [07-27|11:53:41.049] rejected tx                              index=1 hash=0557ba..18d673 from=0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192 error="nonce too low: address 0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192, tx: 0 state: 1"
INFO [07-27|11:53:41.050] Trie dumping started                     root=84208a..ae4e13
INFO [07-27|11:53:41.050] Trie dumping complete                    accounts=3 elapsed="59.412µs"
INFO [07-27|11:53:41.050] Wrote file                               file=result.json
INFO [07-27|11:53:41.051] rejected tx                              index=0 hash=0557ba..18d673 from=0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192 error="nonce too low: address 0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192, tx: 0 state: 1"
INFO [07-27|11:53:41.051] rejected tx                              index=1 hash=0557ba..18d673 from=0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192 error="nonce too low: address 0x8A8eAFb1cf62BfBeb1741769DAE1a9dd47996192, tx: 0 state: 1"
INFO [07-27|11:53:41.052] Trie dumping started                     root=84208a..ae4e13
INFO [07-27|11:53:41.052] Trie dumping complete                    accounts=3 elapsed="45.734µs"
INFO [07-27|11:53:41.052] Wrote file                               file=alloc.json
INFO [07-27|11:53:41.052] Wrote file                               file=result.json

```
What happened here, is that we first applied two identical transactions, so the second one was rejected.
Then, taking the poststate alloc as the input for the next state, we tried again to include
the same two transactions: this time, both failed due to too low nonce.

In order to meaningfully chain invocations, one would need to provide meaningful new `env`, otherwise the
actual blocknumber (exposed to the EVM) would not increase.

### Transactions in RLP form

It is possible to provide already-signed transactions as input to, using an `input.txs` which ends with the `rlp` suffix.
The input format for RLP-form transactions is _identical_ to the _output_ format for block bodies. Therefore, it's fully possible
to use the evm to go from `json` input to `rlp` input.

The following command takes **json** the transactions in `./testdata/13/txs.json` and signs them. After execution, they are output to `signed_txs.rlp`.:
```
./evm t8n --state.fork=London --input.alloc=./testdata/13/alloc.json --input.txs=./testdata/13/txs.json --input.env=./testdata/13/env.json --output.result=alloc_jsontx.json --output.body=signed_txs.rlp
INFO [07-27|11:53:41.124] Trie dumping started                     root=e4b924..6aef61
INFO [07-27|11:53:41.124] Trie dumping complete                    accounts=3 elapsed="94.284µs"
INFO [07-27|11:53:41.125] Wrote file                               file=alloc.json
INFO [07-27|11:53:41.125] Wrote file                               file=alloc_jsontx.json
INFO [07-27|11:53:41.125] Wrote file                               file=signed_txs.rlp

```

The `output.body` is the rlp-list of transactions, encoded in hex and placed in a string a'la `json` encoding rules:
```
cat signed_txs.rlp
"0xf8d2b86702f864010180820fa08284d09411111111111111111111111111111111111111118080c001a0b7dfab36232379bb3d1497a4f91c1966b1f932eae3ade107bf5d723b9cb474e0a06261c359a10f2132f126d250485b90cf20f30340801244a08ef6142ab33d1904b86702f864010280820fa08284d09411111111111111111111111111111111111111118080c080a0d4ec563b6568cd42d998fc4134b36933c6568d01533b5adf08769270243c6c7fa072bf7c21eac6bbeae5143371eef26d5e279637f3bd73482b55979d76d935b1e9"
```

We can use `rlpdump` to check what the contents are:
```
rlpdump -hex $(cat signed_txs.rlp | jq -r )
[
  02f864010180820fa08284d09411111111111111111111111111111111111111118080c001a0b7dfab36232379bb3d1497a4f91c1966b1f932eae3ade107bf5d723b9cb474e0a06261c359a10f2132f126d250485b90cf20f30340801244a08ef6142ab33d1904,
  02f864010280820fa08284d09411111111111111111111111111111111111111118080c080a0d4ec563b6568cd42d998fc4134b36933c6568d01533b5adf08769270243c6c7fa072bf7c21eac6bbeae5143371eef26d5e279637f3bd73482b55979d76d935b1e9,
]
```
Now, we can now use those (or any other already signed transactions), as input, like so:
```
./evm t8n --state.fork=London --input.alloc=./testdata/13/alloc.json --input.txs=./signed_txs.rlp --input.env=./testdata/13/env.json --output.result=alloc_rlptx.json
INFO [07-27|11:53:41.253] Trie dumping started                     root=e4b924..6aef61
INFO [07-27|11:53:41.253] Trie dumping complete                    accounts=3 elapsed="128.445µs"
INFO [07-27|11:53:41.253] Wrote file                               file=alloc.json
INFO [07-27|11:53:41.255] Wrote file                               file=alloc_rlptx.json

```

You might have noticed that the results from these two invocations were stored in two separate files.
And we can now finally check that they match.
```
cat alloc_jsontx.json | jq .stateRoot && cat alloc_rlptx.json | jq .stateRoot
"0xe4b924a6adb5959fccf769d5b7bb2f6359e26d1e76a2443c5a91a36d826aef61"
"0xe4b924a6adb5959fccf769d5b7bb2f6359e26d1e76a2443c5a91a36d826aef61"
```