EVM Gateway

EVM Gateway enables seamless interaction with EVM on Flow, mirroring the experience of engaging with any other EVM blockchain.

EVM Gateway implements the Ethereum JSON-RPC API for EVM on Flow which conforms to the Ethereum JSON-RPC specification. The EVM Gateway is tailored for integration with the EVM environment on the Flow blockchain. Rather than implementing the full geth stack, the JSON-RPC API available in EVM Gateway is a lightweight implementation that uses Flow's underlying consensus and smart contract language, Cadence, to handle calls received by the EVM Gateway. For those interested in the underlying implementation details, please refer to the FLIP #243 (EVM Gateway) and FLIP #223 (EVM on Flow Core) improvement proposals.

EVM Gateway is compatible with the majority of standard Ethereum JSON-RPC APIs allowing seamless integration with existing Ethereum-compatible web3 tools via HTTP. EVM Gateway honors Ethereum's JSON-RPC namespace system, grouping RPC methods into categories based on their specific purpose. Each method name is constructed using the namespace, an underscore, and the specific method name in that namespace. For example, the eth_call method is located within the eth namespace. See below for details on methods currently supported or planned.

Design

The basic design of the EVM Gateway consists of a couple of components:

• Event Ingestion Engine: this component listens to all Cadence events that are emitted by the EVM core, which can be identified by the special event type ID evm.TransactionExecuted and evm.BlockExecuted and decodes and index the data they contain in the payloads.
• Flow Requester: this component knows how to submit transactions to Flow AN to change the EVM state. What happens behind the scenes is that EVM gateway will receive an EVM transaction payload, which will get wrapped in a Cadence transaction that calls EVM contract with that payload and then the EVM core will execute the transaction and change the state.
• JSON RPC API: this is the client API component that implements all the API according to the JSON RPC API specification.

Building

Manual Build

We recommend using Docker to run the EVM Gateway, as detailed in the subsequent section. Alternatively, if you decide to build the binary manually, you can do so by running:

# Make sure you pull the latest changes before running `make build`
git pull origin main
git fetch origin --tags

make build

To view the binary version:

./flow-evm-gateway version

To view all the available flags for running the EVM Gateway Node:

./flow-evm-gateway help run

The binary can then be run by passing the necessary flags:

./flow-evm-gateway run {flags}

To run a local version for development, with the necessary flags set:

make start-local-bin

Running

Operating an EVM Gateway is straightforward. It can either be deployed locally alongside the Flow emulator or configured to connect with any active Flow networks supporting EVM. Given that the EVM Gateway depends solely on Access Node APIs, it is compatible with any networks offering this API access.

Running Locally

Start Emulator

To run the gateway locally you need to start the Flow Emulator:

flow emulator

Make sure flow.json has the emulator account configured to address and private key we will use for starting gateway bellow.

Please refer to the configuration section and read through all the configuration flags before proceeding.

Then you can start the EVM Gateway with:

make start-local

Note that the gateway will be starting from the latest emulator block, so if the emulator is run before any transactions happen in the meantime, the gateway will not fetch those historical blocks & transactions. This will be improved soon.

In the example above we set coa-address value to the service account of the emulator, the same as coa-key. This account will by default be funded with Flow which is a requirement. For coinbase we can use whichever valid EVM address. It's not really useful when running locally besides collecting fees. We also allow for the coa-resource-create to auto-create resources needed on start-up on the coa account in order to operate the gateway. gas-price is set at 0 so we don't have to fund EOA accounts. We can set it higher but keep in mind you will then need funded accounts for interacting with EVM.

With Docker

Run the following commands:

cd dev

docker build -t onflow/flow-evm-gateway .

docker run -d -p 127.0.0.1:8545:8545 onflow/flow-evm-gateway

Verify To verify the service is up and running:

curl -XPOST 'localhost:8545'  --header 'Content-Type: application/json' --data-raw '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

it should return:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x2"
}

Running on Testnet

Running against the testnet with a local build can be done by pointing the gateway to the testnet ANs and providing the correct configuration. Please refer to the configuration section and read through all the configuration flags before proceeding.

Below is an example configuration for running against testnet, with an already created testnet account.

./flow-evm-gateway run \
--access-node-grpc-host=access.devnet.nodes.onflow.org:9000 \
--access-node-spork-hosts=access-001.devnet51.nodes.onflow.org:9000 \
--flow-network-id=flow-testnet \
--init-cadence-height=211176670 \
--ws-enabled=true \
--coa-resource-create=false \
--coinbase=FACF71692421039876a5BB4F10EF7A439D8ef61E \
--coa-address=0x62631c28c9fc5a91 \
--coa-key=2892fba444f1d5787739708874e3b01160671924610411ac787ac1379d420f49 \
--gas-price=100

The --init-cadence-height is the Flow block height to start indexing from. To index the full EVM state, from its beginning, the proper value for this flag is 211176670. This is the height where the EVM contract was first deployed on testnet, and this is where the EVM state starts from.

If you wish to test this out with your own Access Node, simply set --access-node-grpc-host to the location where it is hosted. Note: You need to make sure that your Access Node has indexed at least up to Flow block height 211176670.

For the --gas-price, feel free to experiment with different values.

The --coinbase can be any EOA address.

To generate your own --coa-key and --coa-address, run:

# Install Flow CLI, if you do not already have it installed
sh -ci "$(curl -fsSL https://raw.githubusercontent.com/onflow/flow-cli/master/install.sh)"

flow-c1 keys generate

This will output something similar to:

🔴️ Store private key safely and don't share with anyone!
Private Key 		 3cf8334d.....95c3c54a28e4ad1
Public Key 		 33a13ade6....85f1b49a197747
Mnemonic 		 often scare peanut ... boil corn change
Derivation Path 	 m/44'/539'/0'/0/0
Signature Algorithm 	 ECDSA_P256

Visit https://faucet.flow.com/, and use the generated Public Key, to create and fund your Flow account. Make sure to use the Flow address and the Private Key for the --coa-address & --coa-key flags.

Once the EVM Gateway is up and running, verify that indexing works with:

curl -s -XPOST 'localhost:8545' --header 'Content-Type: application/json' --data-raw '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Should return a response similar to:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x68"
}

Running on Mainnet

Running the EVM gateway for mainnet requires additional security and stability measures which are described in this document: https://flowfoundation.notion.site/EVM-Gateway-Deployment-3c41da6710af40acbaf971e22ce0a9fd?pvs=74

For mainnet, the Flow block height where the EVM state starts from is 85981134. To index the full EVM state, use this value for the --init-cadence-height flag.

Configuration Flags

The application can be configured using the following flags at runtime:

Flag	Default Value	Description
database-dir	./db	Path to the directory for the database
rpc-host	""	Host for the RPC API server
rpc-port	8545	Port for the RPC API server
ws-enabled	false	Enable websocket connections
access-node-grpc-host	localhost:3569	Host to the flow access node gRPC API
access-node-spork-hosts	""	Previous spork AN hosts, defined as a comma-separated list (e.g. "host-1.com,host2.com")
flow-network-id	flow-emulator	Flow network ID (options: flow-emulator, flow-testnet, flow-mainnet)
coinbase	""	Coinbase address to use for fee collection
init-cadence-height	0	Cadence block height to start indexing; avoid using on a new network
gas-price	1	Static gas price for EVM transactions
coa-address	""	Flow address holding COA account for submitting transactions
coa-key	""	Private key for the COA address used for transactions
coa-key-file	""	Path to a JSON file of COA keys for key-rotation (exclusive with coa-key flag)
coa-resource-create	false	Auto-create the COA resource if it doesn't exist in the Flow COA account
coa-cloud-kms-project-id	""	Project ID for KMS keys (e.g. flow-evm-gateway)
coa-cloud-kms-location-id	""	Location ID for KMS key ring (e.g. 'global')
coa-cloud-kms-key-ring-id	""	Key ring ID for KMS keys (e.g. 'tx-signing')
coa-cloud-kms-keys	""	KMS keys and versions, comma-separated (e.g. "gw-key-6@1,gw-key-7@1")
log-level	debug	Log verbosity level (debug, info, warn, error, fatal, panic)
log-writer	stderr	Output method for logs (stderr, console)
stream-limit	10	Rate-limit for client events sent per second
rate-limit	50	Requests per second limit for clients over any protocol (ws/http)
address-header	""	Header for client IP when server is behind a proxy
heartbeat-interval	100	Interval for AN event subscription heartbeats
stream-timeout	3	Timeout in seconds for sending events to clients
force-start-height	0	Force-set starting Cadence height (local/testing use only)
wallet-api-key	""	ECDSA private key for wallet APIs (local/testing use only)
filter-expiry	5m	Expiry time for idle filters
traces-gcp-bucket	""	GCP bucket name for transaction traces
traces-backfill-start-height	0	Start height for backfilling transaction traces
traces-backfill-end-height	0	End height for backfilling transaction traces
index-only	false	Run in index-only mode, allowing state queries and indexing but no transaction sending
profiler-enabled	false	Enable the pprof profiler server
profiler-host	localhost	Host for the pprof profiler
profiler-port	6060	Port for the pprof profiler

Deploying

Deploying the EVM Gateway node comes with some prerequisites as well as expectations and they are best explained in the WIP document: https://flowfoundation.notion.site/EVM-Gateway-Deployment-3c41da6710af40acbaf971e22ce0a9fd

EVM Gateway Endpoints

EVM Gateway has public RPC endpoints available for the following environments:

Name	Value
Network Name	EVM on Flow Testnet
Description	The public RPC URL for Flow Testnet
RPC Endpoint	https://testnet.evm.nodes.onflow.org
Chain ID	545
Currency Symbol	FLOW
Block Explorer	https://evm-testnet.flowscan.io

Name	Value
Network Name	EVM on Flow
Description	The public RPC URL for Flow Mainnet
RPC Endpoint	https://mainnet.evm.nodes.onflow.org
Chain ID	747
Currency Symbol	FLOW
Block Explorer	https://evm.flowscan.io

JSON-RPC API

The EVM Gateway implements APIs according to the Ethereum specification: https://ethereum.org/en/developers/docs/apis/json-rpc/#json-rpc-methods

Additional APIs

• Tracing APIs allows you to fetch execution traces
  • debug_traceTransaction
  • debug_traceBlockByNumber
  • debug_traceBlockByHash

Unsupported APIs

• Wallet APIs: we don't officially support wallet APIs (eth_accounts, eth_sign, eth_signTransaction, eth_sendTransaction) due to security concerns that come with managing the keys on production environments, however, it is possible to configure the gateway to allow these methods for local development by using a special flag --wallet-api-key.
• Proof API: we don't support obtaining proofs yet, Flow piggy-backs on the Flow consensus, and hence the Flow proofs can be used to verify and trust the EVM environment. We intend to add access to EVM proofs in the future.
• Access Lists: we don't yet support creating access lists as they don't affect the fees we charge. We might support this in the future to optimize fees, but it currently is not part of our priorities.

Debugging

Profiler

The EVM Gateway supports profiling via the pprof package. To enable profiling, add the following flags to the command line:

--profiler-enabled=true
--profiler-host=localhost
--profiler-port=6060

This will start a pprof server on the provided host and port. You can generate profiles using the following go tool commands

go tool pprof -http :2000 http://localhost:6060/debug/pprof/profile

curl --output trace.out http://localhost:6060/debug/pprof/trace
go tool trace -http :2001 trace.out

Contributing

We welcome contributions from the community! Please read our Contributing Guide for information on how to get involved.

License

EVM Gateway is released under the Apache License 2.0 license. See the LICENSE file for more details.