expressjs/express

lib/express.js

Entry point exposing createApplication(), which mixes the application prototype into an Express app and re-exports request, response, and Route constructors.

lib/application.js

Defines the app prototype: default configuration, settings (etag, query parser, trust proxy), lazy Router instantiation, middleware mounting via app.use, template engine registration, and req/res dispatch.

Router integration (router package)

Provides the layered routing/middleware pipeline that app.route, app.param, and app.use delegate to, configured with caseSensitive and strict options.

lib/request.js

Extends Node's http.IncomingMessage prototype with Express request helpers such as header inspection, content negotiation, and IP/trust-proxy resolution.

lib/response.js

Extends Node's http.ServerResponse prototype with helpers for sending, redirecting, setting headers/cookies, content disposition, and file downloads.

lib/view.js

Implements the View abstraction that resolves template file paths and invokes registered template engine callbacks for res.render().

lib/utils.js

Shared utilities including compileETag, compileQueryParser, compileTrust, and the supported HTTP methods list consumed by application.js.

finalhandler integration

Terminal handler invoked when no callback is supplied, producing default error/not-found responses and logging errors via the debug logger.