Middleware

ergo ships 21 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

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	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

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

Need to write your own middleware? ergo’s 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

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.