ARCA

Demo

About

### Overview Arca is a decentralized subscription and recurring billing infrastructure engineered to bring a seamless, Stripe-like checkout experience to Web3. While the traditional digital economy thrives on frictionless recurring memberships, Web3 has historically subjected users to manual monthly renewals, volatile dual-token gas requirements, and multi-chain liquidity fragmentation. Arca eliminates these barriers by uniting **Circle’s CCTP**, the **Arc blockchain (native USDC gas settlement)**, **Circle Modular Wallets with passkeys**, and an automated **non-custodial AutoPay engine** into a cohesive recurring payments protocol. --- ### The Problem Arca Solves * **The Dual-Token Gas Dilemma:** In traditional Web3 dApps, users must acquire and manage volatile gas tokens (ETH, POL, AVAX) just to pay a $10 USDC monthly membership. If a subscriber runs out of native gas, their transaction reverts and their subscription lapses. * **Subscription Churn from Manual Renewals:** Blockchains are fundamentally push-based; contracts cannot pull funds without an active signature. Forcing users to open their wallet and manually sign transactions every 30 days leads to catastrophic subscriber drop-off. * **Fragmented Multi-Chain Liquidity:** A user's funds are often scattered across Arbitrum, Base, Optimism, or Ethereum, while the merchant’s contract lives on a specific network, forcing users through tedious, multi-step manual bridging. * **Lack of Turnkey Merchant Tooling:** Web3 builders lack production-ready tooling—such as multi-tier plans, hosted checkout links, HMAC-signed webhooks, and developer API keys for gated access. --- ### Core Innovations & Architecture * **USDC-as-Gas on Arc Testnet:** Transactions execute with sub-second finality and utilize USDC directly as the native gas token. Both merchants and subscribers operate purely in stable currency with zero native token volatility or secondary gas token requirements. * **Frictionless Cross-Chain Liquidity via Circle CCTP:** Arca integrates Circle’s official Cross-Chain Transfer Protocol. Users can fund subscriptions using USDC held on 15+ supported testnets (Base, Arbitrum, Optimism, Ethereum Sepolia, Avalanche Fuji, Polygon Amoy, etc.) via 1:1 burn-and-mint bridging with zero slippage or third-party liquidity pool risk. * **Non-Custodial AutoPay Engine:** Subscribers pre-authorize renewals through a scoped EIP-712 typed signature tied to a session key permission. When a subscription cycle expires, an autonomous off-chain relayer triggers the renewal on-chain using ERC-1271 smart account signature verification. Users get true "set-it-and-forget-it" automated billing while retaining 100% custody of their funds. * **Turnkey Merchant & Developer Platform:** * **Multi-Tier Plan Creation:** Merchants can launch custom plans with flexible billing durations, tiered pricing, and perk configurations in minutes. * **Hosted Checkout Links:** Clean, responsive checkout pages (`/pay/[planId]`) with real-time balance calculations, passkey login, and single-click checkout. * **Enterprise Webhooks:** Real-time, HMAC-SHA256-signed delivery notifications (`payment.succeeded`) with dedicated per-endpoint activity logs, response tracking, and payload inspection. * **Developer API Keys:** Cryptographically hashed secret keys for programmatic subscriber gating and backend verification. * **Real-Time Analytics:** Powered by The Graph, tracking active MRR, gross revenue, churn, and protocol fees on live dashboards. --- ### Why It Matters Arca bridges the gap between Web2 user convenience and Web3 self-sovereignty. It enables SaaS platforms, content creators, gaming studios, and DAOs to build sustainable, predictable recurring revenue streams without forcing their customers through Web3 onboarding friction.

How it's made

### 1. Core Architecture & Stack * **Smart Contracts (Solidity / Arc Testnet):** The protocol is anchored by `SubscriptionGateway.sol`, which manages plan configurations, multi-tier pricing, flexible cycle durations, protocol fee routing, and permissioned renewals. All payments and protocol fees settle directly in native USDC. * **Frontend & Full-Stack Engine:** Built with Next.js 15 (App Router), React 19, TypeScript, Tailwind CSS, and Shadcn UI, powering an intuitive merchant portal and checkout dashboard. * **On-Chain Client & Transaction Dispatch:** Powered by Viem for contract encoding, EIP-712 typed data signing, and ERC-4337 smart account UserOperations via Circle's bundler. * **Data & Indexing Layer:** * **The Graph Subgraph:** Deployed directly on Arc Testnet (`indexer/subgraph.yaml`), indexing events like `PlanCreated`, `Subscribed`, and `AutoPayExecuted` into real-time metrics (MRR, active subscriber counts, historical revenue charts). * **MongoDB:** Manages high-throughput off-chain state, including encrypted session pre-authorizations, developer API keys, hashed secrets, and webhook activity logs. --- ### 2. Partner Technologies & How They Fit Together * **Arc Blockchain (Primary Execution Layer & Native USDC Gas):** * Arc provides sub-second finality and utilizes USDC as its native gas token. * This eliminated the traditional "dual-token" onboarding barrier: users never need a secondary native gas token (like ETH or MATIC) just to pay a subscription. Every membership fee and network cost is denominated and paid strictly in USDC. * **Circle Modular Wallets & WebAuthn Passkeys:** * Integrated `@circle-fin/modular-wallets-core` to deploy ERC-4337 smart accounts secured by biometric passkeys (FaceID / TouchID / Windows Hello), completely abstracting seed phrases. * Leveraged Circle's Paymaster infrastructure so initial account deployments and token approvals are sponsored seamlessly without gas fees. * **Circle Cross-Chain Transfer Protocol (CCTP):** * Integrated Circle’s official CCTP protocol to solve multi-chain liquidity fragmentation. * If a subscriber’s USDC balance on Arc is empty, the client initiates a 1:1 burn-and-mint bridge from any of 15+ supported testnets (Base, Arbitrum, Optimism, Ethereum Sepolia, Avalanche Fuji, Polygon Amoy, etc.). * The application tracks the `DepositForBurn` event on the source chain, queries Circle’s Iris attestation service for the cryptographic signature, and executes `receiveMessage` on Arc to mint native USDC directly into the user’s account. * **The Graph:** * Custom AssemblyScript mappings transform on-chain contract events into queryable GraphQL endpoints, powering real-time merchant analytics and buyer subscription tracking. --- ### 3. Notable Engineering Breakthroughs & Solutions * **Bypassing Viem’s Gas Estimator for Circle's Arc Bundler:** Arc Testnet’s bundler strictly enforces a `maxPriorityFeePerGas >= 1 gwei`. Standard Viem fee estimation defaults to ~0.002 gwei on testnets, causing immediate bundler rejections. Furthermore, manually setting gas limits (`callGasLimit`, `verificationGasLimit`) caused the bundler to invalidate its own paymaster signature (yielding `AA23` reverts). We engineered a hybrid gas strategy: fetching gas prices from Circle's oracle (`getUserOperationGasPrice`) to enforce the 1 gwei priority floor, while leaving gas limits dynamic for the bundler’s internal estimator. * **Non-Custodial AutoPay Engine via EIP-712 & ERC-1271:** Blockchains are strictly "push-based"—smart contracts cannot spontaneously withdraw funds without a transaction trigger. To achieve true Web2-style recurring renewals, we implemented an EIP-712 structured permission scheme. Users sign a typed authorization granting a renewal allowance over a defined cycle. An off-chain relayer continuously evaluates eligible expired subscriptions, verifies the authorization on-chain via ERC-1271 smart account signature validation, and executes `subscribeWithSignature()` on the user's behalf without holding custody of user keys. * **Automated CCTP Attestation State Machine:** CCTP bridging requires waiting for finality on the source chain before Circle’s attestation service signs the message. We designed a resilient client-side state machine with exponential backoff and transaction hash recovery that bridges the tokens, captures the burn nonce, waits for attestation, and automatically triggers the destination mint and subscription checkout without forcing the user to leave the page. * **HMAC-SHA256 Webhook Delivery Pipeline:** Modeled after Stripe’s webhook security, every on-chain subscription confirmation emits an event that triggers an internal dispatch queue. The queue constructs a timestamped payload, signs it using HMAC-SHA256 with the merchant’s unique endpoint secret, records execution latencies and status codes, and displays real-time delivery logs on a dedicated webhook inspection dashboard.