@t402/extensions

t402 Payment Protocol Extensions. This package provides optional extensions that enhance the t402 payment protocol with additional functionality like resource discovery and cataloging.

Installation

``bash
pnpm install @t402/extensions
`

Overview

Extensions are optional features that can be added to t402 payment flows. They allow servers to provide additional metadata and enable facilitators to offer enhanced services like resource discovery and cataloging.

Currently, this package includes:
- Bazaar Discovery Extension: Enables automatic cataloging and indexing of t402-enabled resources

Bazaar Discovery Extension

The Bazaar Discovery Extension enables facilitators to automatically catalog and index t402-enabled resources by following server-declared discovery instructions. This allows users to discover paid APIs and services through facilitator catalogs.

$3

1. Servers declare discovery metadata when configuring their payment endpoints
2. The HTTP method is automatically inferred from the route definition (e.g., "GET /weather")
3. Facilitators extract this metadata from payment requests
4. Users can browse and discover available paid resources through facilitator catalogs

$3

Declare endpoint discovery metadata in your payment middleware configuration. This helps facilitators understand how to call your endpoints and what they return.

> Note: The HTTP method is automatically inferred from the route key (e.g., "GET /weather" → GET method). You don't need to specify it in declareDiscoveryExtension.

#### Basic Example: GET Endpoint with Query Parameters

`typescript
import { declareDiscoveryExtension } from "@t402/extensions/bazaar";

const resources = {
"GET /weather": {
accepts: {
scheme: "exact",
price: "$0.001",
network: "eip155:84532",
payTo: "0xYourAddress"
},
extensions: {
...declareDiscoveryExtension({
input: { city: "San Francisco" },
inputSchema: {
properties: {
city: { type: "string" },
units: { type: "string", enum: ["celsius", "fahrenheit"] }
},
required: ["city"]
},
output: {
example: {
city: "San Francisco",
weather: "foggy",
temperature: 15,
humidity: 85
}
},
}),
},
},
};
`

#### Example: POST Endpoint with JSON Body

For POST, PUT, and PATCH endpoints, specify bodyType to indicate the request body format:

`typescript
import { declareDiscoveryExtension } from "@t402/extensions/bazaar";

const resources = {
"POST /api/translate": {
accepts: {
scheme: "exact",
price: "$0.01",
network: "eip155:84532",
payTo: "0xYourAddress"
},
extensions: {
...declareDiscoveryExtension({
input: {
text: "Hello, world!",
targetLanguage: "es"
},
inputSchema: {
properties: {
text: { type: "string" },
targetLanguage: { type: "string", pattern: "^[a-z]{2}$" }
},
required: ["text", "targetLanguage"]
},
bodyType: "json",
output: {
example: {
translatedText: "¡Hola, mundo!",
sourceLanguage: "en",
targetLanguage: "es"
}
},
}),
},
},
};
`

#### Example: PUT Endpoint with Form Data

`typescript
const resources = {
"PUT /api/user/profile": {
accepts: {
scheme: "exact",
price: "$0.05",
network: "eip155:84532",
payTo: "0xYourAddress"
},
extensions: {
...declareDiscoveryExtension({
input: {
name: "John Doe",
email: "john@example.com",
bio: "Software developer"
},
inputSchema: {
properties: {
name: { type: "string", minLength: 1 },
email: { type: "string", format: "email" },
bio: { type: "string", maxLength: 500 }
},
required: ["name", "email"]
},
bodyType: "form-data",
output: {
example: {
success: true,
userId: "123",
updatedAt: "2024-01-01T00:00:00Z"
}
},
}),
},
},
};
`

#### Example: DELETE Endpoint

`typescript
const resources = {
"DELETE /api/data/:id": {
accepts: {
scheme: "exact",
price: "$0.001",
network: "eip155:84532",
payTo: "0xYourAddress"
},
extensions: {
...declareDiscoveryExtension({
input: { id: "123" },
inputSchema: {
properties: {
id: { type: "string" }
},
required: ["id"]
},
output: {
example: {
success: true,
deletedId: "123"
}
},
}),
},
},
};
`

#### Using with Next.js Middleware

`typescript
import { paymentProxy, t402ResourceServer } from "@t402/next";
import { HTTPFacilitatorClient } from "@t402/core/http";
import { ExactEvmScheme } from "@t402/evm/exact/server";
import { declareDiscoveryExtension } from "@t402/extensions/bazaar";

const facilitatorClient = new HTTPFacilitatorClient({ url: "https://facilitator.t402.io" });
const resourceServer = new t402ResourceServer(facilitatorClient)
.register("eip155:84532", new ExactEvmScheme());

export const proxy = paymentProxy(
{
"/api/weather": {
accepts: {
scheme: "exact",
price: "$0.001",
network: "eip155:84532",
payTo: "0xYourAddress",
},
extensions: {
...declareDiscoveryExtension({
input: { city: "San Francisco" },
inputSchema: {
properties: { city: { type: "string" } },
required: ["city"],
},
output: {
example: { city: "San Francisco", weather: "foggy" }
},
}),
},
},
},
resourceServer,
);
`

$3

Extract discovery information from incoming payment requests to catalog resources in the Bazaar.

#### Basic Usage

`typescript
import { extractDiscoveryInfo } from "@t402/extensions/bazaar";
import type { PaymentPayload, PaymentRequirements } from "@t402/core/types";

async function handlePayment(
paymentPayload: PaymentPayload,
paymentRequirements: PaymentRequirements
) {
// Extract discovery info from the payment
const discovered = extractDiscoveryInfo(paymentPayload, paymentRequirements);

if (discovered) {
// discovered contains:
// {
// resourceUrl: "https://api.example.com/weather",
// method: "GET",
// t402Version: 2,
// discoveryInfo: {
// input: { type: "http", method: "GET", queryParams: { city: "..." } },
// output: { type: "json", example: { ... } }
// }
// }

// Catalog the resource in your Bazaar
await catalogResource({
url: discovered.resourceUrl,
method: discovered.method,
inputSchema: discovered.discoveryInfo.input,
outputExample: discovered.discoveryInfo.output?.example,
});
}
}
`

#### Validating Discovery Extensions

`typescript
import { validateDiscoveryExtension, extractDiscoveryInfo } from "@t402/extensions/bazaar";

function processPayment(paymentPayload: PaymentPayload, paymentRequirements: PaymentRequirements) {
const discovered = extractDiscoveryInfo(paymentPayload, paymentRequirements);

if (discovered && paymentPayload.extensions?.bazaar) {
// Validate the extension schema
const validation = validateDiscoveryExtension(paymentPayload.extensions.bazaar);

if (!validation.valid) {
console.warn("Invalid discovery extension:", validation.errors);
// Handle invalid extension (log, reject, etc.)
return;
}

// Extension is valid, proceed with cataloging
catalogResource(discovered);
}
}
`

#### Using with Server Extension Helper

The bazaarResourceServerExtension automatically enriches discovery extensions with HTTP method information from the request context:

`typescript
import { bazaarResourceServerExtension } from "@t402/extensions/bazaar";
import { t402ResourceServer } from "@t402/core/server";

// The extension helper automatically extracts discovery info
const resourceServer = new t402ResourceServer(facilitatorClient)
.register("eip155:84532", new ExactEvmScheme())
.useExtension(bazaarResourceServerExtension);
`

API Reference

$3

Creates a discovery extension object for resource servers.

Parameters:
- config.input (optional): Example input values (query params for GET/HEAD/DELETE, body for POST/PUT/PATCH)
- config.inputSchema (optional): JSON Schema for input validation
- config.bodyType (optional): For POST/PUT/PATCH, specify "json", "form-data", or "text" (default: "json")
- config.output (optional): Output specification
- output.example: Example output data
- output.schema: JSON Schema for output validation

> Note: The HTTP method is NOT passed to this function. It is automatically inferred from the route key (e.g., "GET /weather") or enriched by bazaarResourceServerExtension at runtime.

Returns: An object with a bazaar key containing the discovery extension.

Example:
`typescript
const extension = declareDiscoveryExtension({
input: { query: "search term" },
inputSchema: {
properties: { query: { type: "string" } },
required: ["query"]
},
output: {
example: { results: [] }
}
});
// Returns: { bazaar: { info: {...}, schema: {...} } }
`

$3

Extracts discovery information from a payment request (for facilitators).

Parameters:
- paymentPayload: The payment payload from the client
- paymentRequirements: The payment requirements from the server
- validate (optional): Whether to validate the extension (default: true)

Returns: DiscoveredResource object or null if not found.

`typescript
interface DiscoveredResource {
resourceUrl: string;
method: string;
t402Version: number;
discoveryInfo: DiscoveryInfo;
}
`

Example:
`typescript
const info = extractDiscoveryInfo(paymentPayload, paymentRequirements);
if (info) {
console.log(info.resourceUrl); // "https://api.example.com/endpoint"
console.log(info.method); // "GET"
console.log(info.discoveryInfo); // { input: {...}, output: {...} }
}
`

$3

Validates a discovery extension's info against its schema.

Parameters:
- extension: A discovery extension object

Returns: { valid: boolean, errors?: string[] }

Example:
`typescript
const result = validateDiscoveryExtension(extension);
if (!result.valid) {
console.error("Validation errors:", result.errors);
}
`

$3

Validates and extracts discovery info in one step.

Parameters:
- extension: A discovery extension object

Returns: { valid: boolean, info?: DiscoveryInfo, errors?: string[] }

Example:
`typescript
const { valid, info, errors } = validateAndExtract(extension);
if (valid && info) {
// Use info
}
`

$3

A server extension that automatically enriches discovery extensions with HTTP method information from the request context.

Usage:
`typescript
import { bazaarResourceServerExtension } from "@t402/extensions/bazaar";

const resourceServer = new t402ResourceServer(facilitatorClient)
.useExtension(bazaarResourceServerExtension);
`

$3

The extension identifier constant ("bazaar").

`typescript
import { BAZAAR } from "@t402/extensions/bazaar";
// BAZAAR === "bazaar"
`

Use Cases

$3

Problem: extractDiscoveryInfo returns null.

Solutions:
- Ensure the server has declared the extension using declareDiscoveryExtension
- Check that paymentPayload.extensions.bazaar exists
- Verify you're using t402 v2 (v1 uses a different format in outputSchema)

$3

Problem: validateDiscoveryExtension returns valid: false.

Solutions:
- Ensure inputSchema matches the structure of input
- Check that required fields are marked in inputSchema.required
- Verify JSON Schema syntax is correct

$3

Problem: Discovery info is incomplete.

Solutions:
- Ensure both input and inputSchema are provided
- For POST/PUT/PATCH, include bodyType in the config
- Check that output.example is provided if you want output documentation

$3

Problem: The HTTP method is missing from discovery info.

Solutions:
- Use bazaarResourceServerExtension which automatically injects the method
- Ensure the route key follows the format "METHOD /path" (e.g., "GET /weather")

Related Resources

- t402 Core Package - Core t402 protocol implementation
- t402 Specification - Full protocol specification

Version Support

This package supports both t402 v1 and v2:
- v2: Extensions are in PaymentPayload.extensions and PaymentRequired.extensions
- v1: Discovery info is in PaymentRequirements.outputSchema (automatically converted)

The extractDiscoveryInfo` function automatically handles both versions.