lang="d" on the host cell

On the wasm cell, lang="d" is a <script> inside a .svelte file. On the host cell, lang="d" is the file itself: +page.server.d, +server.d, +layout.server.d, hooks.server.d. Both are D. They compile with the same LDC 1.43. They do not share object files, they do not share DFLAGS, and they do not share imports. This page is the host file, walked against the API the previous pages named, so a method you type next to a kit route and a class you read under webserver/source/generated/ are visibly the same language.

// src/routes/admin/users/+page.server.d
import helpers;
 
class UsersPageServer
{
	void getUsers(HTTPServerRequest req, HTTPServerResponse res)
	{
		Json payload = Json.emptyObject;
		payload["users"] = Json.emptyArray;
		res.writeBody(payload.serializeToJsonString(), "application/json");
	}
 
	void postSave(HTTPServerRequest req, HTTPServerResponse res)
	{
		auto name = req.form.get("name", "");
		if (!name.length)
			enforceHTTP(false, HTTPStatus.badRequest, "name required");
		res.redirect("/admin/users");
	}
 
	void getUser(HTTPServerRequest req, HTTPServerResponse res)
	{
		auto id = req.params["id"];
		Json payload = Json.emptyObject;
		payload["id"] = id;
		res.writeJsonBody(payload);
	}
}

svelte-d prints that class dest-unique (UsersPageServer stays if it does not collide; AdminUsersPageServer if it must) into webserver/source/generated/routes/admin/users/page_server.d, lifts the imports to the module header, and hangs registerWebInterface(new UsersPageServer, kit) on app.d with kit.urlPrefix = "/__svelte-d/host/". getUsers is GET /__svelte-d/host/users. postSave is POST /__svelte-d/host/save, which is how a SvelteKit actions.save is approximated. req.params["id"] is the :id from [id].

What each identifier already is

HTTPServerRequest / HTTPServerResponse are the special parameters that skip form conversion. Json is vibe.data.Json, not libwasm JSON. enforceHTTP is vibe.http.status. req.form, req.json, req.cookies, req.params, res.setCookie, res.redirect, res.writeBody, res.writeJsonBody are the server object. import helpers; is the engine barrel that already pulled those modules plus connectDB / connectCache / kitLog.

A host function that needs Postgres is still this file:

void getUsers(HTTPServerRequest req, HTTPServerResponse res)
{
	auto db = connectDB();
	auto cmd = scoped!PGCommand(db, "select id, name from users");
	Json payload = Json.emptyObject;
	payload["users"] = Json.emptyArray;
	// … fill from rows …
	res.writeBody(payload.serializeToJsonString(), "application/json");
}

kit-admin writes "skip" when the daemon is absent. The simplified admin example in this site’s docs/examples/admin does not open a database at all. Both are vibe.0. Neither is a Node load.

hooks.server.d and layouts

hooks.server handle is router.any("*", …) registered before page routes, or @before on the web interface. handleError is HTTPServerSettings.errorPageHandler. Layout load is composed in generated D; vibe.0 has no layout primitive. +server.d verbs become router.match(HTTPMethod.GET, …) (and POST / PUT / PATCH / DELETE) or a small web-interface class.

Cookies are req.cookies / res.setCookie. Sessions are settings.sessionStore (the engine may attach RedisSessionStore). $env/static/private is host-cell only.

What must not appear

Open svelte-engine-ws/webserver as a DUB root in code-d so HTTPServerRequest, Json, and helpers.connectDB complete. That is the Getting Started IDE recommendation applied to this cell. The author-facing contract, shorter, is vibe.0 host files. This page is the same file after you know what import vibe.web.web; actually is.

The wasm cell consumes these routes with window().fetch("/__svelte-d/host/users").then(...). That fetch is libwasm. The JSON it returns is this page.