Canton Middleware

MetaMask-compatible middleware for Canton Network, enabling ERC-20 style interactions with Splice-compliant CIP-56 tokens.

Overview

This project provides:

• API Server -- Ethereum JSON-RPC facade that translates MetaMask transactions to Canton CIP-56 operations
• Relayer -- Bridges PROMPT tokens between Ethereum and Canton
• Interoperability -- Native Canton users (e.g. Canton Loop) and MetaMask users can seamlessly transfer tokens to each other
• Splice Token Standard (CIP-0056) -- All tokens implement the Splice HoldingV1, TransferFactory, and Metadata interfaces
• Splice Registry API -- External wallets discover TransferFactory contracts for explicit disclosure during transfers
• External Parties -- All users are allocated as external parties using the Interactive Submission API (no ~200 internal party limit)

Quick Start (Local Development)

# 1. Bootstrap: starts Docker, registers users, mints tokens
./scripts/testing/bootstrap-local.sh --clean

# 2. Test: runs all 8 interop + bridge test steps
go run scripts/testing/interop-demo.go

Both scripts auto-detect all dynamic configuration (domain IDs, party IDs, contract addresses) from the running Docker containers. See the Local Interop Testing Guide for full details.

Prerequisites

Tool	Version	Install
Go	1.23+	https://go.dev/dl/
Docker	Latest	https://docs.docker.com/get-docker/
Docker Compose	v2+	(included with Docker Desktop)
Foundry	Latest	curl -L https://foundry.paradigm.xyz | bash && foundryup

MetaMask Configuration

After bootstrap completes, configure MetaMask:

Setting	Value
Network Name	Canton Local
RPC URL	http://localhost:8081/eth
Chain ID	31337
Currency Symbol	ETH

Test Accounts (Anvil defaults):

User	Address	Private Key
User 1	0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266	ac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80
User 2	0x70997970C51812dc3A010C7d01b50e0d17dc79C8	59c6995e998f97a5a0044966f0945389dc9e86dae88c7a8412f4603b6b78690d

Token Addresses:

Token	Address	Type
DEMO	0xDE30000000000000000000000000000000000001	Native Canton token
PROMPT	0x5FbDB2315678afecb367f032d93F642f64180aa3	Bridged ERC-20

Service Endpoints

Service	URL
API Server (MetaMask RPC)	http://localhost:8081/eth
User Registration	http://localhost:8081/register
Splice Registry API	http://localhost:8081/registry/transfer-instruction/v1/transfer-factory
API Server Health	http://localhost:8081/health
Canton gRPC	localhost:5011
Canton HTTP	http://localhost:5013
Anvil (Ethereum)	http://localhost:8545
PostgreSQL	localhost:5432

---

Architecture

┌─────────────────┐                    ┌─────────────────┐
│    MetaMask     │                    │  Canton Loop /  │
│   (EVM Wallet)  │                    │  Native Canton  │
└────────┬────────┘                    └────────┬────────┘
         │ JSON-RPC                             │ gRPC / Registry API
         ▼                                      ▼
┌──────────────────────────────────────────────────────────┐
│                     API SERVER                            │
│  • /eth         - JSON-RPC facade (MetaMask-compatible)   │
│  • /register    - User registration (EVM + Canton native) │
│  • /registry/…  - Splice Registry API (TransferFactory)   │
│  • Custodial Canton key management (AES-256-GCM)          │
│  • Balance reconciliation with Canton                     │
└────────────────────────┬─────────────────────────────────┘
                         │
        ┌────────────────┼────────────────┐
        │                │                │
        ▼                ▼                ▼
┌─────────────┐   ┌─────────────┐   ┌─────────────┐
│  PostgreSQL │   │   Canton    │   │   Relayer   │
│  (Users/    │   │  (CIP-56    │   │  (ERC-20    │
│   Balances) │   │   Ledger)   │   │   Bridge)   │
└─────────────┘   └─────────────┘   └──────┬──────┘
                                           │
                                    ┌──────▼──────┐
                                    │  Ethereum   │
                                    │  (Anvil /   │
                                    │   Mainnet)  │
                                    └─────────────┘

How Transfers Work

All users are external parties on Canton. They hold their own signing keys and use the Interactive Submission API (prepare/sign/execute) instead of the standard CommandService.

MetaMask / cast send / Canton Loop
        │
        ▼
  /eth endpoint (JSON-RPC)  or  Interactive Submission (gRPC)
        │
        ▼
  Resolve Canton signing key from encrypted DB store
        │
        ▼
  PrepareSubmission → sign with user's key → ExecuteSubmission
        │
        ▼
  Canton Ledger: TransferFactory_Transfer (Splice-compliant CIP-56)

Tokens

Token	Type	Description
DEMO	Native Canton (CIP-56)	Minted directly on Canton via CIP56Manager, implements Splice HoldingV1
PROMPT	Bridged ERC-20	Bridged from Ethereum via the Wayfinder bridge, also uses Splice HoldingV1

Both tokens carry Splice-standard metadata (TextMap Text) with DNS-prefixed keys (e.g. splice.chainsafe.io/symbol). Metadata is propagated through all transfers via the TransferFactory.

---

Project Structure

canton-middleware/
├── cmd/
│   ├── api-server/              # API server entry point
│   └── relayer/                 # Relayer entry point
├── pkg/
│   ├── apidb/                   # API database operations (users, balances, whitelist)
│   ├── app/                     # Application wiring (api server, http server)
│   ├── auth/                    # JWT and EVM authentication
│   ├── cantonsdk/               # Canton SDK
│   │   ├── bridge/              #   ERC-20 ↔ Canton bridge operations
│   │   ├── client/              #   High-level SDK facade
│   │   ├── identity/            #   Party allocation, fingerprint mappings
│   │   ├── lapi/v2/             #   Generated Ledger API v2 protobufs
│   │   ├── ledger/              #   Low-level gRPC client (state, commands, auth)
│   │   ├── token/               #   CIP-56 token operations (mint, burn, transfer)
│   │   └── values/              #   Daml value encoding/decoding helpers
│   ├── config/                  # Configuration loading
│   ├── db/                      # Relayer database schema
│   ├── ethereum/                # Ethereum client and ABI
│   ├── ethrpc/                  # Ethereum JSON-RPC server
│   ├── keys/                    # Custodial key management (secp256k1, AES-256-GCM)
│   ├── registration/            # User registration handler
│   ├── registry/                # Splice Registry API handler
│   ├── relayer/                 # Bridge relayer logic
│   └── service/                 # Token service layer
├── contracts/
│   ├── canton-erc20/            # DAML contracts (CIP-56, Splice-compliant)
│   └── ethereum-wayfinder/      # Solidity bridge contracts
├── scripts/
│   ├── setup/                   # Bootstrap and infrastructure scripts
│   ├── testing/                 # Test and demo scripts
│   ├── bridge/                  # Bridge operation scripts
│   ├── demo/                    # Demo scripts
│   ├── remote/                  # Remote deployment scripts
│   ├── utils/                   # Diagnostic utilities
│   ├── lib/                     # Shared bash functions
│   └── archive/                 # Archived migration scripts
├── docs/                        # Documentation
├── deployments/                 # Docker, Canton, Prometheus configs
└── proto/                       # Protobuf definitions

---

Scripts

Testing (scripts/testing/)

Script	Description
bootstrap-local.sh	Full local bootstrap (Docker, users, tokens)
interop-demo.go	8-step interop + bridge test suite
demo-activity.go	Display Canton token activity (holdings, configs, events)
canton-transfer-demo.go	Demo transfers and reconciliation
register-native-user.go	Register a native Canton user
register-user.go	Register an EVM user
e2e-local.go	End-to-end local tests
test-reconcile.go	Test balance reconciliation
test-whitelist.go	Test whitelist functionality

Setup (scripts/setup/)

Script	Description
bootstrap-all.sh	Full automated setup (alternative to bootstrap-local.sh)
bootstrap-bridge.go	Bootstrap bridge contracts on Canton
bootstrap-demo.go	Mint DEMO tokens to users
docker-bootstrap.sh	Docker-specific bootstrap
setup-local.sh	Local environment setup
setup-devnet.sh	DevNet setup
build-dars.sh	Build DAML archives
generate-protos.sh	Regenerate protobuf Go code

Bridge (scripts/bridge/)

Script	Description
bridge-activity.go	Display recent bridge activity
bridge-deposit.go	Deposit ERC-20 to Canton
get-holding-cid.go	Get holding contract ID for withdrawals
initiate-withdrawal.go	Initiate Canton → Ethereum withdrawal
cleanup-withdrawals.go	Clean up processed withdrawals

Utilities (scripts/utils/)

Script	Description
check-user-holdings.go	Check user holdings on Canton
verify-canton-holdings.go	Verify/compare holdings (DB vs Canton)
list-parties.go	List known parties
list-users.go	List registered users
check-mappings.go	Check fingerprint mappings
reconcile.go	Manual balance reconciliation
reset-demo-state.go	Reset demo state
query-canton-holdings.sh	Query Canton holdings (bash)
metamask-info.sh	Show MetaMask config
mock-oauth2-server.go	Local OAuth2 mock server

---

Development

Build

go mod download
go build ./...

Lint

golangci-lint run ./...

Manual Setup

export CANTON_MASTER_KEY=$(openssl rand -base64 32)
export SKIP_CANTON_SIG_VERIFY=true

docker compose up -d

# Wait for healthy status, then bootstrap
go run scripts/setup/bootstrap-bridge.go -config config.e2e-local.yaml
go run scripts/setup/bootstrap-demo.go -config config.e2e-local.yaml

Verify Setup

curl http://localhost:8081/health
curl -X POST http://localhost:8081/registry/transfer-instruction/v1/transfer-factory
go run scripts/utils/check-user-holdings.go -config config.e2e-local.yaml

---

Configuration

Environment	Config File
Local testing	config.e2e-local.yaml
Docker	config.docker.yaml
API server (Docker)	config.api-server.docker.yaml
Local devnet	config.local-devnet.yaml
Example	config.example.yaml

Key Canton-specific fields (auto-detected by bootstrap):

Field	Description
domain_id	Canton synchronizer domain ID
relayer_party	Bridge relayer / token issuer party
instrument_admin	Party administering token instruments
instrument_id	Token instrument identifier (e.g. PROMPT)
cip56_package_id	cip56-token DAR package hash
splice_holding_package_id	Splice HoldingV1 interface DAR hash
splice_transfer_package_id	Splice TransferFactory interface DAR hash
bridge_package_id	bridge-wayfinder DAR package hash

---

Documentation

Document	Description
Local Interop Testing	Full local bootstrap and 8-step interop test guide
API Documentation	Endpoint reference (JSON-RPC, Registration, Splice Registry)
Architecture	System design and data flows
DevNet Interop Testing	DEMO token testing on ChainSafe DevNet
CIP-0086 Overview	CIP-0086 compliance
Deployment Requirements	Production deployment checklist

---

License

[License details here]