Middleware
ergo ships 22 middleware factories covering every stage of the Fast Fail pipeline. Each guide page documents the full options table, return value, error responses, and usage examples for both standalone composition and declarative ergo-router configuration.
Pipeline Stages
Section titled “Pipeline Stages”| Stage | Middleware | Purpose |
|---|---|---|
| Negotiation | logger | Structured request/response logging |
| Negotiation | accepts | Content negotiation (Accept, Accept-Language, etc.) |
| Negotiation | cors | Cross-origin resource sharing |
| Negotiation | cookie | Cookie parsing |
| Negotiation | url | URL and query string parsing |
| Negotiation | paginate | Pagination parameter parsing (offset + cursor) |
| Negotiation | prefer | Prefer header parsing (RFC 7240) |
| Negotiation | precondition | Conditional request enforcement |
| Negotiation | rate-limit | Per-client rate limiting |
| Authorization | authorization | Bearer / Basic / API-key auth |
| Authorization | csrf | CSRF token issue and verify |
| Validation | body | Request body parsing |
| Validation | validate | JSON Schema validation (AJV) |
| Validation | json-api-query | JSON:API query validation |
| Validation | idempotency | Idempotency-Key enforcement |
| Execution | handler | Pipeline executor |
| Execution | send | Response serialization |
Cross-Cutting
Section titled “Cross-Cutting”| Middleware | Purpose |
|---|---|
| cache-control | Cache-Control header defaults |
| compress | Response compression (gzip, br, deflate) |
| security-headers | Security response headers (CSP, HSTS, etc.) |
| timeout | Configurable request deadline (setTimeout + close listener) |
| tracing | OpenTelemetry distributed tracing |
Custom Middleware
Section titled “Custom Middleware”Need to write your own middleware? ergo’s domain accumulator-based return-value contract lets you build middleware that composes cleanly with the pipeline — feature flags, audit logging, request enrichment, or third-party integrations.
See the Custom Middleware recipe for the full contract, working examples, and anti-patterns to avoid.
Two-Layer Documentation
Section titled “Two-Layer Documentation”Each middleware has two documentation surfaces:
- Guide pages (this section) — options, examples, error tables, and RFC references written for developers building with ergo.
- API Reference — auto-generated from JSDoc with precise type signatures. Linked at the bottom of each guide page.