POA-Ethereum Bridge

This is software to be operated by POA bridge validators to faciliate proof-of-authority based briding of POA to tokens on an another Ethereum-based blockchain.

The validators work with POA bridge contracts to convert ether on one chain into the same amount of ERC20 tokens on the other and back.

This software works in conjunction with other projects:

• POA Bridge UI
• POA Bridge Smart Contracts
• POA Bridge Monitoring service
• POA Bridge Deployment scripts

Functionality

The bridge connects two chains (home and foreign). When a user deposits ether into the bridge contract contract on home they get the same amount of ERC20 tokens on foreign, and they can convert them back as well.

Deposit

Withdraw

How to build

Requires rust and cargo: installation instructions.

Requires solc to be in $PATH: installation instructions.

Assuming you've cloned the bridge (git clone git@github.com:poanetwork/poa-bridge.git), run

cd poa-bridge
make

and install ../target/release/bridge in your $PATH.

Running

bridge --config config.toml --database db.toml

• --config - location of the configuration file. configuration file must exist
• --database - location of the database file.

Bridge forces TLS for RPC connections by default. However, in some limited scenarios (like local testing), this might be undesirable. In this case, you can use --allow-insecure-rpc-endpoints option to allow non-TLS endpoints to be used. Ensure, however, that this option is not going to be used in production.

Exit Status Codes

Code	Meaning
0	Success
1	Unknwon error
2	I/O error
3	Shutdown requested
4	Insufficient funds
5	Gas too low
6	Gas price is too low
7	Nonce reused
10	Cannot connect
11	Connection lost
12	Bridge crashed
20	RPC error

Configuration file example

keystore = "/path/to/keystore"

[home]
account = "0x006e27b6a72e1f34c626762f3c4761547aff1421"
rpc_host = "http://localhost"
rpc_port = 8545
required_confirmations = 0
password = "home_password.txt"
default_gas_price = 1_000_000_000 # 1 GWEI

[foreign]
account = "0x006e27b6a72e1f34c626762f3c4761547aff1421"
rpc_host = "http://localhost"
rpc_port = 9545
required_confirmations = 0
gas_price_oracle_url = "https://gasprice.poa.network"
gas_price_speed = "instant"
default_gas_price = 10_000_000_000 # 10 GWEI
password = "foreign_password.txt"

[authorities]
required_signatures = 2

[transactions]
deposit_relay = { gas = 3000000 }
withdraw_relay = { gas = 3000000 }
withdraw_confirm = { gas = 3000000 }

Options

• keystore - path to a keystore directory with JSON keys

home/foreign options

• home/foreign.account - authority address on the home (required)
• home/foreign.rpc_host - RPC host (required)
• home/foreign.rpc_port - RPC port (defaults to 8545)
• home/foreign.required_confirmations - number of confirmation required to consider transaction final on home (default: 12)
• home/foreign.poll_interval - specify how often home node should be polled for changes (in seconds, default: 1)
• home/foreign.request_timeout - specify request timeout (in seconds, default: 3600)
• home/foreign.password - path to the file containing a password for the validator's account (to decrypt the key from the keystore)
• home/foreign.gas_price_oracle_url - the URL used to query the current gas-price for the home and foreign nodes, this service is known as the gas-price Oracle. This config option defaults to None if not supplied in the User's config TOML file. If this config value is None, no Oracle gas-price querying will occur, resulting in the config value for home/foreign.default_gas_price being used for all gas-prices.
• home/foreign.gas_price_timeout - the number of seconds to wait for an HTTP response from the gas price oracle before using the default gas price. Defaults to 10 seconds.
• home/foreign.gas_price_speed - retrieve the gas-price corresponding to this speed when querying from an Oracle. Defaults to fast. The available values are: "instant", "fast", "standard", and "slow".
• home/foreign.default_gas_price - the default gas price (in WEI) used in transactions with the home or foreign nodes. The default_gas_price is used when the Oracle cannot be reached. The default value is 15_000_000_000 WEI (ie. 15 GWEI).
• home/foreign.concurrent_http_requests - the number of concurrent HTTP requests allowed in-flight (default: 64)

authorities options

• authorities.account - all authorities (required)

transaction options

• transaction.deposit_relay.gas - specify how much gas should be consumed by deposit relay
• transaction.withdraw_confirm.gas - specify how much gas should be consumed by withdraw confirm
• transaction.withdraw_relay.gas - specify how much gas should be consumed by withdraw relay

Database file format

home_contract_address = "0x49edf201c1e139282643d5e7c6fb0c7219ad1db7"
foreign_contract_address = "0x49edf201c1e139282643d5e7c6fb0c7219ad1db8"
checked_deposit_relay = 120
checked_withdraw_relay = 121
checked_withdraw_confirm = 121

all fields are required

• home_contract_address - address of the bridge contract on home chain
• foreign_contract_address - address of the bridge contract on foreign chain
• checked_deposit_relay - number of the last block for which an authority has relayed deposits to the foreign
• checked_withdraw_relay - number of the last block for which an authority has relayed withdraws to the home
• checked_withdraw_confirm - number of the last block for which an authority has confirmed withdraw