Consensus

HTTP deduplication protocol with secure, verifiable payments via x402
HTTP as it should be for modern blockchains. Protect your APIs from the chaos of consensus
Built for decentralization. Runs on a Raspberry Pi

• Docs • Demo • Testnet Transactions

Overview

Blockchain consensus algorithms are powerful — but they come with baggage.

On the Internet Computer (ICP), for example, when an application subnet performs an HTTP outcall, each node in the subnet independently makes the request. These nodes run replicas, and the responses from the HTTP outcalls are compared in the consensus process. This means:

• The same HTTP request is made by every node in the subnet (typically 13 for ICP).
• Millisecond differences can lead to inconsistent responses.
• Each request originates from a different physical machine, meaning no shared IP address — breaking determinism for services that rely on caller identity.

This especially becomes a problem when your target endpoint is not idempotent.

Even if only one response is used, your service may still receive multiple requests, potentially triggering duplicate processing, double charges, or conflicting writes.

With Consensus Proxy, only 1 request is executed — no matter how many are sent. In consensus-based systems like ICP, this reduces outbound traffic by up to ~93%. It also eliminates duplicate hits that waste resources, exceed rate limits, or create billing issues.

Whether your backend is a serverless function, a rate-limited SaaS API, or a payment gateway, Consensus Proxy ensures you pay once, process once — regardless of how many nodes, retries, or consensus rounds are involved.

Consensus Proxy

Consensus Proxy solves this problem at the protocol level.

It acts as a deduplication layer that:

• Receives all node-originated HTTP outcalls
• Executes the request exactly once
• Caches and returns the same result to all callers
• Challenges the caller with x402 to ensure payment before processing

---

How it works

Without deduplication, every replica sends its own request — resulting in N-1 redundant API hits per consensus round.

With Consensus Proxy, the first request triggers an x402 payment challenge. The client retries using a wrapper (like fetch-with-payment), and upon successful verification, the proxy settles the request, makes the external call, and caches the result for reuse.

sequenceDiagram
    participant R1 as Node 1
    participant R2 as Node 2
    participant R3 as Node 3
    participant P as Proxy (x402-protected)
    participant API as External API
    participant C as Consensus

    R1->>P: HTTP outcall (idempotency: icp23072025, x-api-key: ba137)
    R2->>P: HTTP outcall (idempotency: icp23072025, x-api-key: ba137)
    R3->>P: HTTP outcall (idempotency: icp23072025, x-api-key: ba137)

    Note right of P: First request → cache MISS → x402 challenge

    P-->>R1: 402 Payment Required (x402 challenge)
    R1->>P: Retry using fetch-with-payment

    Note right of P: Payment verified → request settled

    P->>API: External API call(eg: coinGecko)
    API-->>P: Response: {"usd": 6.09}

    Note right of P: Response cached → reused for remaining requests

    P-->>R1: Cached response
    P-->>R2: Cached response
    P-->>R3: Cached response

    R1->>C: Process response → State A
    R2->>C: Process response → State A
    R3->>C: Process response → State A

    C-->>R1: Consensus reached
    C-->>R2: Consensus reached
    C-->>R3: Consensus reached

    Note right of C: All replicas receive the same response

Loading

---

Step-by-Step

1. All nodes in a subnet execute the same canister function, triggering identical HTTP outcalls.
2. Each node sends its request to the Consensus Proxy, including an idempotency key.
3. The first request is met with an x402 challenge — a payment requirement.
4. The client request is wrapped automatically to fetch the data with payment, settling the request.
5. The proxy makes the external API call and caches the result.
6. All remaining requests with the same idempotency key receive the cached response.
7. Replicas process identical responses → state converges → consensus succeeds.

Quickstart

This library has not yet been published!

1. Install

npm install consensus

2. Configure environment

Consensus proxy currently uses CDP to configure the client wallet to interact with the x-402 server. In the future we will support browser wallets.

Create a .env file:

CDP_API_KEY_ID=your_api_key_id
CDP_API_KEY_SECRET=your_api_key_secret
CDP_WALLET_SECRET=your_wallet_secret

---

3. Setup your client

npm run consensus setup

This generates:

• Your wallet
• Proxy URL
• API key
• A config file with your client information(DO NOT EXPOSE THIS FILE!!!)

---

4. Make a request in any language on any platform

curl -X POST http://localhost:3001/proxy \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: icp-price-check" \
  -d '{"target_url": "https://api.coingecko.com/api/v3/simple/price?ids=internet-computer&vs_currencies=usd"}'

Returns:

{
  "status": 200,
  "data": {
    "internet-computer": {
      "usd": 6.09
    }
  }
}

Want raw metadata, proof of payment, or debug info? Add the header X-Verbose: true to get the full payload.

{
  "status": 200,
  "statusText": "OK",
  "data": {
    "internet-computer": {
      "usd": 6.09
    }
  },
  "timestamp": 1753129159138,
  "cached": false,
  "payment_required": true,
  "billing": {
    "cost": "$0.001",
    "reason": "payment_processed",
    "idempotency_key": "icp-price-check9",
    "processing_time_ms": 3045
  },
  "meta": {
    "wallet_name": "0cc495c8c94834b3", // In practice, you should not reveal your wallet name.
    "account_address": "0x7d19e332F1b84D783bd7FeA5B6aa0b809B9A80A4",
    "idempotency_key": "icp-price-check9",
    "processing_time_ms": 3143,
    "x402_proxy_handled": true,
    "timestamp": "2025-07-21T20:19:19.142Z"
  }
}

Consensus Proxy is language agnostic and is pure HTTPS. This means you can make a request from any language on any platform. You can use Motoko, Javascript/Typescript, Rust, Python, curl to interact with the Consensus server.

License

This project is licensed under the Business Source License 1.1 (BUSL-1.1).

The Licensed Work is:

• © 2025 Canister Software Inc
• Change Date: July 23, 2029
• Change License: GNU GPL v2.0 or later

For full terms, see the LICENSE file.