# Premix

> Premix is **pre**mium gasoline **mix**ed with lubricant oil and it is
used in two-stroke internal combustion engines. It tends to produce a lot of
smoke.

This Premix is a block validation debugging tool for the Nimbus Ethereum
client. Premix will query transaction execution steps from other Ethereum
clients and compare them with those generated by Nimbus. It will then produce a
web page to present comparison results that can be inspected by the developer
to pinpoint the faulty instruction.

Premix will also produce a test case for the specific problematic transaction,
complete with a database snapshot to execute transaction validation in
isolation. This test case can then be integrated with the Nimbus project's test
suite.

![screenshot](assets/images/premix_screenshot.png)

## Requirements

Before you can use the Premix debugging tool there are several things you need
to prepare. The first requirement is a recent version of `geth` installed from
[source](https://github.com/ethereum/go-ethereum/releases) or
[binary](https://ethereum.github.io/go-ethereum/downloads/). The minimum
required version is 1.8.18. Beware that version 1.8.x contains bugs in
transaction tracer, upgrade it to 1.9.x soon after it has been released.
Afterwards, you can run it with this command:

```bash
geth --rpc --rpcapi eth,debug --syncmode full --gcmode=archive
```

You need to run it until it fully syncs past the problematic block you want to
debug (you might need to do it on an empty db, because some geth versions will
keep on doing a fast sync if that's what was done before). After that, you can
stop it by pressing `CTRL-C` and rerun it with the additional flag `--maxpeers
0` if you want it to stop syncing
- or just let it run as is if you want to keep syncing.

The next requirement is building Nimbus and Premix:

```bash
# in the top-level directory:
make
```

After that, you can run Nimbus with this command:

```bash
./build/nimbus --prune:archive --port:30304
```

Nimbus will try to sync up to the problematic block, then stop and execute
Premix which will then load a report page in your default browser. If it fails
to do that, you can see the report page by manually opening
`premix/index.html`.

In your browser, you can explore the tracing result and find where the problem is.

## Tools

### Premix

Premix is the main debugging tool. It produces reports that can be viewed in
a browser and serialised debug data that can be consumed by the `debug` tool.
Premix consumes data produced by either `nimbus`, `persist`, or `dumper`.

You can run it manually using this command:

```bash
./build/premix debug*.json
```

### Persist

Because the Nimbus P2P layer still contains bugs, you may become impatient when
trying to sync blocks. In the `./premix` directory, you can find a `persist`
tool. It will help you sync relatively quicker because it will bypass the P2P
layer and download blocks from `geth` via `rpc-api`.

When it encounters a problematic block during syncing, it will stop and produce
debugging data just like Nimbus does.

```bash
./build/persist [--dataDir:your_database_directory] [--head: blockNumber] [--maxBlocks: number] [--numCommits: number]
```

### Debug

In the same `./premix` directory you'll find the `debug` tool that you can use
to process previously generated debugging info in order to work with one block
and one transaction at a time instead of multiple confusing blocks and
transactions.

```bash
./build/debug block*.json
```

where `block*.json` contains the database snapshot needed to debug a single
block produced by the Premix tool.

### Dumper

Dumper was designed specifically to produce debugging data that can be further
processed by Premix from information already stored in database. It will create
tracing information for a single block if that block has been already
persisted.

If you want to generate debugging data, it's better to use the Persist tool.
The data generated by Dumper is usually used to debug Premix features in
general and the report page logic in particular.

```bash
# usage:
./build/dumper [--datadir:your_path] --head:blockNumber
```

### Hunter

Hunter's purpose is to track down problematic blocks and create debugging info
associated with them. It will not access your on-disk database, because it has
its own prestate construction code.

Hunter will download all it needs from geth, just make sure your geth version
is at least 1.8.18.

Hunter depends on
`eth_getProof`[(EIP1186)](https://github.com/ethereum/EIPs/issues/1186). Make
sure your installed `geth` supports this functionality (older versions don't
have this implemented).

```bash
# usage:
./build/hunter --head:blockNumber --maxBlocks:number
```

`blockNumber` is the starting block where the hunt begins.

`maxBlocks` is the number of problematic blocks you want to capture before
stopping the hunt.

### Regress

Regress is an offline block validation tool. It will not download block
information from anywhere like Persist tool. Regress will validate your
already persisted block in database. It will try to find any regression
introduced either by bugfixing or refactoring.

```bash
# usage:
./build/regress [--dataDir:your_db_path] --head:blockNumber
```