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horse-middlewares

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Guide to using standard Horse middlewares (CORS, Jhonson, compression, basic-auth, logger) and pipeline registration order.

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Horse Middlewares

Core Middleware Pipeline

Middlewares intercept and process HTTP requests/responses before reaching the endpoint handlers.

Required Registration Order

The registration order of middlewares in THorse is highly critical. Middlewares must be registered before defining any routes:

begin
  // 1. Logging and Error Handling (FIRST)
  THorse.Use(HandleException);
  
  // 2. Security and Headers
  THorse.Use(CORS);
  
  // 3. Payload Compression and Formatting
  THorse.Use(OctetStream);
  THorse.Use(Jhonson); // Parse JSON body and format JSON response
  
  // 4. Register Routes (AFTER all global middlewares)
  TProductController.RegisterRoutes;
  
  THorse.Listen(9000);
end;

Middleware Scope & Execution Flow

Middlewares can be declared at three levels:

  1. Global (via THorse.Use): Runs on every request.
  2. Group-level (via THorseGroup.Use): Runs on all routes inside a specific group prefix.
  3. Route-level (Local): Runs only on that specific route (defined as an array [Middleware1, Middleware2] in the verb method).

Execution Flow:

The execution order follows the nested onion pattern:

Global Middlewares → Group Middlewares → Route-level Middlewares → Final Route Handler

Always design middlewares to call Next() to pass control, or skip it to short-circuit the request (e.g., unauthorized requests).

The Johnson Middleware (Critical)

The Jhonson middleware automatically handles JSON parsing (TJSONObject / TJSONArray) for requests and responses.

  • Ownership Transfer: When you call Res.Send<TJSONObject>(LJson) or Res.Send<TJSONArray>(LArray), the Johnson middleware takes ownership of that object and will automatically destroy it after sending.
  • Safety Rule: NEVER call .Free or FreeAndNil on a JSON object after sending it through Res.Send<T>. Doing so will cause a Double-Free memory corruption (Access Violation) when the middleware attempts to clean it up.

Global Error Handler (OnError)

Horse features a native global error handling callback (THorse.OnError). It intercepts all unhandled exceptions occurring inside any middleware or route handler.

Key Points:

  • Registration: Use THorse.OnError(MyGlobalErrorHandler) during application startup.
  • Control Exceptions: Control exceptions (EHorseCallbackInterrupted and EHorseException) are bypassed and do not trigger the global OnError callback.
  • Safety (Fail-Safe): If the registered OnError callback itself crashes, the framework handles the crash safely and returns a structured 500 Internal Server Error response with the exception detail, protecting the socket from leaking or crashing.
  • Signature: The callback is a classic procedure type THorseOnError = procedure(const ARequest: THorseRequest; const AResponse: THorseResponse; const AException: Exception).