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ADR-0008: Automatic validation middleware via Echo context wrapping

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Status

Accepted

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Tags

http, echo, validation, middleware, handlers

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Decision

Use an AutoValidate() Echo middleware that wraps the context and overrides Bind() to call Validate() automatically. Handlers call c.Bind(&req) once — parsing and validation both happen. No manual c.Validate() calls in handlers.

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Why

Calling c.Bind() then c.Validate() in every handler is repetitive and easy to forget. Missing validation silently allows malformed input through to business logic. A middleware wrapper intercepts Bind() at the framework level — validation is guaranteed for every bound request without touching individual handlers.

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How it works

Request → AutoValidate() middleware wraps echo.Context
         ↓
Handler calls c.Bind(&req)
         ↓
validationContext.Bind() runs:
  1. vc.Context.Bind(i)      // parse JSON into struct
  2. vc.Context.Validate(i)  // validate struct tags automatically
         ↓
Handler receives validated struct or early 400 error

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Exceptions — skip AutoValidate for

  • File uploads (multipart/form-data) — Bind semantics differ
  • Webhooks with custom body parsing
  • Routes that intentionally accept partial/unvalidated input

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Rules for agents

  • Never add c.Validate(&req) after c.Bind(&req) in handlers — the middleware handles it
  • Register AutoValidate() globally in main.go after echo.Validator is set
  • For file upload handlers, skip binding through c.Bind() and handle multipart directly
  • The middleware must be registered after e.Validator = validator.New() — middleware reads the validator from the context

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Bad pattern (do not generate)

// Manual validation in every handler — repetitive and forgettable
func (h *Handler) Create(c echo.Context) error {
    var req CreateRequest
    if err := c.Bind(&req); err != nil { return err }
    if err := c.Validate(&req); err != nil { return err } // redundant
    // ...
}

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Good pattern

// main.go — register once
e.Validator = validator.New()
e.Use(customMiddleware.AutoValidate())

// handler — c.Bind() validates automatically
func (h *Handler) Create(c echo.Context) error {
    var req CreateRequest
    if err := c.Bind(&req); err != nil { return err } // validates too
    // ...
}