HTTP Router Interceptors and Middleware

Interceptors allow processing requests before and after route handling. This enables middleware functionality like authentication, logging, CORS, and request validation. Interceptors are implemented as object methods that receive the request, response, and a continuation flag.

Interceptors can run at two different times: iaBefore (before route processing) and iaAfter (after route processing). The continuation parameter allows interceptors to halt request processing if needed.

program MiddlewareRouter;

{$mode objfpc}{$H+}

uses
  httproute, httpdefs, SysUtils;

type
  TMiddlewareHelper = class
  public
    procedure LoggingInterceptor(ARequest: TRequest; AResponse: TResponse; var aContinue: Boolean);
    procedure CORSInterceptor(ARequest: TRequest; AResponse: TResponse; var aContinue: Boolean);
  end;

procedure TMiddlewareHelper.LoggingInterceptor(ARequest: TRequest;
  AResponse: TResponse; var aContinue: Boolean);
begin
  Writeln(Format('[%s] %s %s', [FormatDateTime('yyyy-mm-dd hh:nn:ss', Now),
    RouteMethodToString(THTTPRouter.StringToRouteMethod(ARequest.Method)),
    ARequest.PathInfo]));
  aContinue := True;
end;

procedure TMiddlewareHelper.CORSInterceptor(ARequest: TRequest;
  AResponse: TResponse; var aContinue: Boolean);
begin
  AResponse.SetCustomHeader('Access-Control-Allow-Origin', '*');
  AResponse.SetCustomHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE');
  aContinue := True;
end;

procedure HandleAPI(ARequest: TRequest; AResponse: TResponse);
begin
  AResponse.Content := '{"message": "API response with middleware"}';
  AResponse.ContentType := 'application/json';
end;

var
  Helper: TMiddlewareHelper;
begin
  Helper := TMiddlewareHelper.Create;
  try
    // Register interceptors (middleware)
    HTTPRouter.RegisterInterceptor('logging', @Helper.LoggingInterceptor, iaBefore);
    HTTPRouter.RegisterInterceptor('cors', @Helper.CORSInterceptor, iaAfter);

    // Register API route
    Router.RegisterRoute('/api/data', rmGet, @HandleAPI, False);

    Writeln('Middleware router with logging and CORS support');
    Writeln('GET /api/data - Returns JSON with proper headers');
  finally
    Helper.Free;
  end;
end.