Module layer 

Available on crate feature server only.

Axum middleware for enforcing x402 payments on protected routes.

This middleware validates incoming payment headers using a configured x402 facilitator, verifies the payment, executes the request, and settles valid payments after successful execution. If the handler returns an error (4xx/5xx), settlement is skipped.

Returns a 402 Payment Required response if the request lacks a valid payment.

Settlement Modes

• SettlementMode::Sequential (default): verify → execute → settle. Safer — settlement only runs after the handler succeeds.
• SettlementMode::Concurrent: verify → (settle ∥ execute) → await settle. Lower latency — overlaps settlement with handler execution.

Configuration Notes

• X402Middleware::with_price_tag sets the assets and amounts accepted for payment (static pricing).
• X402Middleware::with_dynamic_price sets a callback for dynamic pricing based on request context.
• X402Middleware::with_base_url sets the base URL for computing full resource URLs. If not set, defaults to http://localhost/ (avoid in production).
• X402LayerBuilder::with_settlement_mode selects sequential or concurrent settlement.
• X402LayerBuilder::with_description is optional but helps the payer understand what is being paid for.
• X402LayerBuilder::with_mime_type sets the MIME type of the protected resource (default: application/json).
• X402LayerBuilder::with_resource explicitly sets the full URI of the protected resource.

Structs

X402LayerBuilder

Builder for configuring the X402 middleware layer.

X402Middleware

The main X402 middleware instance for enforcing x402 payments on routes.

X402MiddlewareService

Axum service that enforces x402 payments on incoming requests.

Enums

SettlementMode

Controls when on-chain settlement executes relative to the inner service.