Using TRequest and TResponse Classes

The TRequest and TResponse classes are the foundation of HTTP communication in FCL-Web. TRequest represents incoming HTTP requests with methods, headers, parameters, and content. TResponse represents outgoing HTTP responses with status codes, headers, and content.

These classes provide comprehensive access to HTTP protocol features including custom headers, content types, query parameters, form data, and file uploads.

program RequestResponseExample;

{$mode objfpc}{$H+}

uses
  httpdefs, SysUtils, Classes;

procedure ProcessRequest(Request: TRequest; Response: TResponse);
var
  UserAgent, ContentType: String;
  Stream: TStringStream;
begin
  Writeln('=== Processing HTTP Request ===');

  // Read request information
  Writeln('Method: ', Request.Method);
  Writeln('URI: ', Request.URI);
  Writeln('Query String: ', Request.QueryString);
  Writeln('Content Length: ', Request.ContentLength);

  // Read headers
  UserAgent := Request.GetCustomHeader('User-Agent');
  if UserAgent <> '' then
    Writeln('User Agent: ', UserAgent);

  // Read query parameters
  if Request.QueryFields.Values['search'] <> '' then
    Writeln('Search query: ', Request.QueryFields.Values['search']);

  // Read POST data (if any)
  if Request.ContentLength > 0 then
  begin
    Writeln('Request content: ', Request.Content);
    ContentType := Request.ContentType;
    Writeln('Content type: ', ContentType);
  end;

  // Process based on request method
  case Request.Method of
    'GET':
      begin
        Response.Content := '{"message": "GET request processed"}';
        Response.ContentType := 'application/json';
        Response.Code := 200;
      end;
    'POST':
      begin
        // Echo back the posted data
        Response.Content := 'Received: ' + Request.Content;
        Response.ContentType := 'text/plain';
        Response.Code := 201;
      end;
    'PUT':
      begin
        Response.Content := 'Resource updated';
        Response.Code := 200;
      end;
    'DELETE':
      begin
        Response.Content := '';
        Response.Code := 204; // No Content
      end;
  else
    Response.Content := 'Method not allowed';
    Response.Code := 405;
  end;

  // Set custom response headers
  Response.SetCustomHeader('X-Powered-By', 'FreePascal-FCL-Web');
  Response.SetCustomHeader('X-Request-ID', 'req-' + IntToStr(Random(99999)));

  // Set security headers
  Response.SetCustomHeader('X-Content-Type-Options', 'nosniff');
  Response.SetCustomHeader('X-Frame-Options', 'DENY');

  Writeln('=== Response Generated ===');
  Writeln('Status Code: ', Response.Code);
  Writeln('Content Type: ', Response.ContentType);
  Writeln('Content Length: ', Length(Response.Content));
end;

procedure DemonstrateStreamContent(Response: TResponse);
var
  Stream: TStringStream;
begin
  Writeln;
  Writeln('=== Demonstrating Stream Content ===');

  Stream := TStringStream.Create('{"users": ["alice", "bob", "charlie"]}');
  try
    Response.ContentStream := Stream;
    Response.ContentType := 'application/json';
    Response.FreeContentStream := False; // We manage the stream

    Writeln('Content set via stream');
    Writeln('Stream size: ', Stream.Size, ' bytes');
  finally
    Stream.Free;
  end;
end;

var
  Request: TRequest;
  Response: TResponse;
begin
  Request := TRequest.Create;
  Response := TResponse.Create(Request);
  try
    // Simulate a GET request
    Request.Method := 'GET';
    Request.URI := '/api/users';
    Request.QueryString := 'search=john&limit=10';
    Request.QueryFields.Values['search'] := 'john';
    Request.QueryFields.Values['limit'] := '10';
    Request.SetCustomHeader('User-Agent', 'TestClient/1.0');

    ProcessRequest(Request, Response);

    // Simulate a POST request
    Writeln;
    Request.Method := 'POST';
    Request.URI := '/api/users';
    Request.Content := '{"name": "John Doe", "email": "john@example.com"}';
    Request.ContentType := 'application/json';

    ProcessRequest(Request, Response);

    // Demonstrate stream content
    DemonstrateStreamContent(Response);

  finally
    Response.Free;
    Request.Free;
  end;
end.